Fix the locking of gmtime()

[privoxy.git] / parsers.c

/*********************************************************************
 *
 * File        :  $Source: /cvsroot/ijbswa/current/parsers.c,v $
 *
 * Purpose     :  Declares functions to parse/crunch headers and pages.
 *
 * Copyright   :  Written by and Copyright (C) 2001-2020 the
 *                Privoxy team. https://www.privoxy.org/
 *
 *                Based on the Internet Junkbuster originally written
 *                by and Copyright (C) 1997 Anonymous Coders and
 *                Junkbusters Corporation.  http://www.junkbusters.com
 *
 *                This program is free software; you can redistribute it
 *                and/or modify it under the terms of the GNU General
 *                Public License as published by the Free Software
 *                Foundation; either version 2 of the License, or (at
 *                your option) any later version.
 *
 *                This program is distributed in the hope that it will
 *                be useful, but WITHOUT ANY WARRANTY; without even the
 *                implied warranty of MERCHANTABILITY or FITNESS FOR A
 *                PARTICULAR PURPOSE.  See the GNU General Public
 *                License for more details.
 *
 *                The GNU General Public License should be included with
 *                this file.  If not, you can view it at
 *                http://www.gnu.org/copyleft/gpl.html
 *                or write to the Free Software Foundation, Inc., 59
 *                Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 *********************************************************************/


#include "config.h"

#ifndef _WIN32
#include <stdio.h>
#include <sys/types.h>
#endif

#include <stdlib.h>
#include <ctype.h>
#include <assert.h>
#include <string.h>

#ifdef __GLIBC__
/*
 * Convince GNU's libc to provide a strptime prototype.
 */
#define __USE_XOPEN
#endif /*__GLIBC__ */
#include <time.h>

#ifdef FEATURE_ZLIB
#include <zlib.h>

#define GZIP_IDENTIFIER_1       0x1f
#define GZIP_IDENTIFIER_2       0x8b

#define GZIP_FLAG_CHECKSUM      0x02
#define GZIP_FLAG_EXTRA_FIELDS  0x04
#define GZIP_FLAG_FILE_NAME     0x08
#define GZIP_FLAG_COMMENT       0x10
#define GZIP_FLAG_RESERVED_BITS 0xe0
#endif

#if !defined(_WIN32) && !defined(__OS2__)
#include <unistd.h>
#endif

#include "project.h"

#ifdef FEATURE_PTHREAD
#include "jcc.h"
/* jcc.h is for mutex semapores only */
#endif /* def FEATURE_PTHREAD */
#include "list.h"
#include "parsers.h"
#include "ssplit.h"
#include "errlog.h"
#include "jbsockets.h"
#include "miscutil.h"
#include "list.h"
#include "actions.h"
#include "filters.h"

#ifndef HAVE_STRPTIME
#include "strptime.h"
#endif

static char *get_header_line(struct iob *iob);
static jb_err scan_headers(struct client_state *csp);
static jb_err header_tagger(struct client_state *csp, char *header);
static jb_err parse_header_time(const char *header_time, time_t *result);
static jb_err parse_time_header(const char *header, time_t *result);

static jb_err crumble                   (struct client_state *csp, char **header);
static jb_err filter_header             (struct client_state *csp, char **header);
static jb_err client_connection         (struct client_state *csp, char **header);
static jb_err client_referrer           (struct client_state *csp, char **header);
static jb_err client_uagent             (struct client_state *csp, char **header);
static jb_err client_ua                 (struct client_state *csp, char **header);
static jb_err client_from               (struct client_state *csp, char **header);
static jb_err client_send_cookie        (struct client_state *csp, char **header);
static jb_err client_x_forwarded        (struct client_state *csp, char **header);
static jb_err client_accept_encoding    (struct client_state *csp, char **header);
static jb_err client_te                 (struct client_state *csp, char **header);
static jb_err client_max_forwards       (struct client_state *csp, char **header);
static jb_err client_host               (struct client_state *csp, char **header);
static jb_err client_if_modified_since  (struct client_state *csp, char **header);
static jb_err client_accept_language    (struct client_state *csp, char **header);
static jb_err client_if_none_match      (struct client_state *csp, char **header);
static jb_err crunch_client_header      (struct client_state *csp, char **header);
static jb_err client_x_filter           (struct client_state *csp, char **header);
static jb_err client_range              (struct client_state *csp, char **header);
static jb_err client_expect             (struct client_state *csp, char **header);
static jb_err server_set_cookie         (struct client_state *csp, char **header);
static jb_err server_connection         (struct client_state *csp, char **header);
static jb_err server_content_type       (struct client_state *csp, char **header);
static jb_err server_adjust_content_length(struct client_state *csp, char **header);
static jb_err server_content_md5        (struct client_state *csp, char **header);
static jb_err server_content_encoding   (struct client_state *csp, char **header);
static jb_err server_transfer_coding    (struct client_state *csp, char **header);
static jb_err server_http               (struct client_state *csp, char **header);
static jb_err crunch_server_header      (struct client_state *csp, char **header);
static jb_err server_last_modified      (struct client_state *csp, char **header);
static jb_err server_content_disposition(struct client_state *csp, char **header);
#ifdef FEATURE_ZLIB
static jb_err server_adjust_content_encoding(struct client_state *csp, char **header);
#endif

#ifdef FEATURE_CONNECTION_KEEP_ALIVE
static jb_err server_save_content_length(struct client_state *csp, char **header);
static jb_err server_keep_alive(struct client_state *csp, char **header);
static jb_err server_proxy_connection(struct client_state *csp, char **header);
static jb_err client_keep_alive(struct client_state *csp, char **header);
static jb_err client_save_content_length(struct client_state *csp, char **header);
static jb_err client_proxy_connection(struct client_state *csp, char **header);
#endif /* def FEATURE_CONNECTION_KEEP_ALIVE */

static jb_err client_host_adder       (struct client_state *csp);
static jb_err client_xtra_adder       (struct client_state *csp);
static jb_err client_x_forwarded_for_adder(struct client_state *csp);
static jb_err client_connection_header_adder(struct client_state *csp);
static jb_err server_connection_adder(struct client_state *csp);
#ifdef FEATURE_CONNECTION_KEEP_ALIVE
static jb_err server_proxy_connection_adder(struct client_state *csp);
#endif /* def FEATURE_CONNECTION_KEEP_ALIVE */
static jb_err proxy_authentication(struct client_state *csp, char **header);

static jb_err create_forged_referrer(char **header, const char *hostport);
static jb_err create_fake_referrer(char **header, const char *fake_referrer);
static jb_err handle_conditional_hide_referrer_parameter(char **header,
   const char *host, const int parameter_conditional_block);
static void create_content_length_header(unsigned long long content_length,
                                         char *header, size_t buffer_length);

/*
 * List of functions to run on a list of headers.
 */
struct parsers
{
   /** The header prefix to match */
   const char *str;

   /** The length of the prefix to match */
   const size_t len;

   /** The function to apply to this line */
   const parser_func_ptr parser;
};

static const struct parsers client_patterns[] = {
   { "referer:",                  8,   client_referrer },
   { "user-agent:",              11,   client_uagent },
   { "ua-",                       3,   client_ua },
   { "from:",                     5,   client_from },
   { "cookie:",                   7,   client_send_cookie },
   { "x-forwarded-for:",         16,   client_x_forwarded },
   { "Accept-Encoding:",         16,   client_accept_encoding },
   { "TE:",                       3,   client_te },
   { "Host:",                     5,   client_host },
   { "if-modified-since:",       18,   client_if_modified_since },
#ifdef FEATURE_CONNECTION_KEEP_ALIVE
   { "Keep-Alive:",              11,   client_keep_alive },
   { "Content-Length:",          15,   client_save_content_length },
   { "Proxy-Connection:",        17,   client_proxy_connection },
#else
   { "Keep-Alive:",              11,   crumble },
   { "Proxy-Connection:",        17,   crumble },
#endif
   { "connection:",              11,   client_connection },
   { "max-forwards:",            13,   client_max_forwards },
   { "Accept-Language:",         16,   client_accept_language },
   { "if-none-match:",           14,   client_if_none_match },
   { "Range:",                    6,   client_range },
   { "Request-Range:",           14,   client_range },
   { "If-Range:",                 9,   client_range },
   { "X-Filter:",                 9,   client_x_filter },
   { "Proxy-Authorization:",     20,   proxy_authentication },
#if 0
   { "Transfer-Encoding:",       18,   client_transfer_encoding },
#endif
   { "Expect:",                   7,   client_expect },
   { "*",                         0,   crunch_client_header },
   { "*",                         0,   filter_header },
   { NULL,                        0,   NULL }
};

static const struct parsers server_patterns[] = {
   { "HTTP/",                     5, server_http },
   { "set-cookie:",              11, server_set_cookie },
   { "connection:",              11, server_connection },
   { "Content-Type:",            13, server_content_type },
   { "Content-MD5:",             12, server_content_md5 },
   { "Content-Encoding:",        17, server_content_encoding },
#ifdef FEATURE_CONNECTION_KEEP_ALIVE
   { "Content-Length:",          15, server_save_content_length },
   { "Keep-Alive:",              11, server_keep_alive },
   { "Proxy-Connection:",        17, server_proxy_connection },
#else
   { "Keep-Alive:",              11, crumble },
#endif /* def FEATURE_CONNECTION_KEEP_ALIVE */
   { "Transfer-Encoding:",       18, server_transfer_coding },
   { "content-disposition:",     20, server_content_disposition },
   { "Last-Modified:",           14, server_last_modified },
   { "Proxy-Authenticate:",      19, proxy_authentication },
   { "*",                         0, crunch_server_header },
   { "*",                         0, filter_header },
   { NULL,                        0, NULL }
};

static const add_header_func_ptr add_client_headers[] = {
   client_host_adder,
   client_x_forwarded_for_adder,
   client_xtra_adder,
   client_connection_header_adder,
   NULL
};

static const add_header_func_ptr add_server_headers[] = {
   server_connection_adder,
#ifdef FEATURE_CONNECTION_KEEP_ALIVE
   server_proxy_connection_adder,
#endif /* def FEATURE_CONNECTION_KEEP_ALIVE */
   NULL
};

/*********************************************************************
 *
 * Function    :  flush_iob
 *
 * Description :  Write any pending "buffered" content.
 *
 * Parameters  :
 *          1  :  fd = file descriptor of the socket to read
 *          2  :  iob = The I/O buffer to flush, usually csp->iob.
 *          3  :  delay = Number of milliseconds to delay the writes
 *
 * Returns     :  On success, the number of bytes written are returned (zero
 *                indicates nothing was written).  On error, -1 is returned,
 *                and errno is set appropriately.  If count is zero and the
 *                file descriptor refers to a regular file, 0 will be
 *                returned without causing any other effect.  For a special
 *                file, the results are not portable.
 *
 *********************************************************************/
long flush_iob(jb_socket fd, struct iob *iob, unsigned int delay)
{
   long len = iob->eod - iob->cur;

   if (len <= 0)
   {
      return(0);
   }

   if (write_socket_delayed(fd, iob->cur, (size_t)len, delay))
   {
      return(-1);
   }
   iob->eod = iob->cur = iob->buf;
   return(len);

}


/*********************************************************************
 *
 * Function    :  add_to_iob
 *
 * Description :  Add content to the buffer, expanding the
 *                buffer if necessary.
 *
 * Parameters  :
 *          1  :  iob = Destination buffer.
 *          2  :  buffer_limit = Limit to which the destination may grow
 *          3  :  src = holds the content to be added
 *          4  :  n = number of bytes to be added
 *
 * Returns     :  JB_ERR_OK on success, JB_ERR_MEMORY if out-of-memory
 *                or buffer limit reached.
 *
 *********************************************************************/
jb_err add_to_iob(struct iob *iob, const size_t buffer_limit, char *src, long n)
{
   size_t used, offset, need;
   char *p;

   if (n <= 0) return JB_ERR_OK;

   used   = (size_t)(iob->eod - iob->buf);
   offset = (size_t)(iob->cur - iob->buf);
   need   = used + (size_t)n + 1;

   /*
    * If the buffer can't hold the new data, extend it first.
    * Use the next power of two if possible, else use the actual need.
    */
   if (need > buffer_limit)
   {
      log_error(LOG_LEVEL_INFO,
         "Buffer limit reached while extending the buffer (iob). Needed: %d. Limit: %d",
         need, buffer_limit);
      return JB_ERR_MEMORY;
   }

   if (need > iob->size)
   {
      size_t want = iob->size ? iob->size : 512;

      while (want <= need)
      {
         want *= 2;
      }

      if (want <= buffer_limit && NULL != (p = (char *)realloc(iob->buf, want)))
      {
         iob->size = want;
      }
      else if (NULL != (p = (char *)realloc(iob->buf, need)))
      {
         iob->size = need;
      }
      else
      {
         log_error(LOG_LEVEL_ERROR, "Extending the buffer (iob) failed: %E");
         return JB_ERR_MEMORY;
      }

      /* Update the iob pointers */
      iob->cur = p + offset;
      iob->eod = p + used;
      iob->buf = p;
   }

   /* copy the new data into the iob buffer */
   memcpy(iob->eod, src, (size_t)n);

   /* point to the end of the data */
   iob->eod += n;

   /* null terminate == cheap insurance */
   *iob->eod = '\0';

   return JB_ERR_OK;

}


/*********************************************************************
 *
 * Function    :  clear_iob
 *
 * Description :  Frees the memory allocated for an I/O buffer and
 *                resets the structure.
 *
 * Parameters  :
 *          1  :  iob = I/O buffer to clear.
 *
 * Returns     :  JB_ERR_OK on success, JB_ERR_MEMORY if out-of-memory
 *                or buffer limit reached.
 *
 *********************************************************************/
void clear_iob(struct iob *iob)
{
   free(iob->buf);
   memset(iob, '\0', sizeof(*iob));
}


#ifdef FEATURE_ZLIB
/*********************************************************************
 *
 * Function    :  decompress_iob
 *
 * Description :  Decompress buffered page, expanding the
 *                buffer as necessary.  csp->iob->cur
 *                should point to the the beginning of the
 *                compressed data block.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *
 * Returns     :  JB_ERR_OK on success,
 *                JB_ERR_MEMORY if out-of-memory limit reached, and
 *                JB_ERR_COMPRESS if error decompressing buffer.
 *
 *********************************************************************/
jb_err decompress_iob(struct client_state *csp)
{
   char  *buf;       /* new, uncompressed buffer */
   char  *cur;       /* Current iob position (to keep the original
                      * iob->cur unmodified if we return early) */
   size_t bufsize;   /* allocated size of the new buffer */
   size_t old_size;  /* Content size before decompression */
   size_t skip_size; /* Number of bytes at the beginning of the iob
                        that we should NOT decompress. */
   int status;       /* return status of the inflate() call */
   z_stream zstr;    /* used by calls to zlib */

#ifdef FUZZ
   assert(csp->iob->cur - csp->iob->buf >= 0);
   assert(csp->iob->eod - csp->iob->cur >= 0);
#else
   assert(csp->iob->cur - csp->iob->buf > 0);
   assert(csp->iob->eod - csp->iob->cur > 0);
#endif

   bufsize = csp->iob->size;
   skip_size = (size_t)(csp->iob->cur - csp->iob->buf);
   old_size = (size_t)(csp->iob->eod - csp->iob->cur);

   cur = csp->iob->cur;

   if (bufsize < (size_t)10)
   {
      /*
       * This is to protect the parsing of gzipped data,
       * but it should(?) be valid for deflated data also.
       */
      log_error(LOG_LEVEL_ERROR,
         "Insufficient data to start decompression. Bytes in buffer: %d",
         csp->iob->eod - csp->iob->cur);
      return JB_ERR_COMPRESS;
   }

   if (csp->content_type & CT_GZIP)
   {
      /*
       * Our task is slightly complicated by the facts that data
       * compressed by gzip does not include a zlib header, and
       * that there is no easily accessible interface in zlib to
       * handle a gzip header. We strip off the gzip header by
       * hand, and later inform zlib not to expect a header.
       */

      /*
       * Strip off the gzip header. Please see RFC 1952 for more
       * explanation of the appropriate fields.
       */
      if (((*cur++ & 0xff) != GZIP_IDENTIFIER_1)
       || ((*cur++ & 0xff) != GZIP_IDENTIFIER_2)
       || (*cur++ != Z_DEFLATED))
      {
         log_error(LOG_LEVEL_ERROR, "Invalid gzip header when decompressing");
         return JB_ERR_COMPRESS;
      }
      else
      {
         int flags = *cur++;
         if (flags & GZIP_FLAG_RESERVED_BITS)
         {
            /* The gzip header has reserved bits set; bail out. */
            log_error(LOG_LEVEL_ERROR, "Invalid gzip header flags when decompressing");
            return JB_ERR_COMPRESS;
         }

         /*
          * Skip mtime (4 bytes), extra flags (1 byte)
          * and OS type (1 byte).
          */
         cur += 6;

         /* Skip extra fields if necessary. */
         if (flags & GZIP_FLAG_EXTRA_FIELDS)
         {
            /*
             * Skip a given number of bytes, specified
             * as a 16-bit little-endian value.
             *
             * XXX: this code is untested and should probably be removed.
             */
            int skip_bytes;
            skip_bytes = *cur++;
            skip_bytes += *cur++ << 8;

            /*
             * The number of bytes to skip should be positive
             * and we'd like to stay in the buffer.
             */
            if ((skip_bytes < 0) || (skip_bytes >= (csp->iob->eod - cur)))
            {
               log_error(LOG_LEVEL_ERROR,
                  "Unreasonable amount of bytes to skip (%d). Stopping decompression",
                  skip_bytes);
               return JB_ERR_COMPRESS;
            }
            log_error(LOG_LEVEL_INFO,
               "Skipping %d bytes for gzip compression. Does this sound right?",
               skip_bytes);
            cur += skip_bytes;
         }

         /* Skip the filename if necessary. */
         if (flags & GZIP_FLAG_FILE_NAME)
         {
            /* A null-terminated string is supposed to follow. */
            while (*cur++ && (cur < csp->iob->eod));
         }

         /* Skip the comment if necessary. */
         if (flags & GZIP_FLAG_COMMENT)
         {
            /* A null-terminated string is supposed to follow. */
            while (*cur++ && (cur < csp->iob->eod));
         }

         /* Skip the CRC if necessary. */
         if (flags & GZIP_FLAG_CHECKSUM)
         {
            cur += 2;
         }

         if (cur >= csp->iob->eod)
         {
            /*
             * If the current position pointer reached or passed
             * the buffer end, we were obviously tricked to skip
             * too much.
             */
            log_error(LOG_LEVEL_ERROR,
               "Malformed gzip header detected. Aborting decompression.");
            return JB_ERR_COMPRESS;
         }
      }
   }
   else if (csp->content_type & CT_DEFLATE)
   {
      /*
       * In theory (that is, according to RFC 1950), deflate-compressed
       * data should begin with a two-byte zlib header and have an
       * adler32 checksum at the end. It seems that in practice only
       * the raw compressed data is sent. Note that this means that
       * we are not RFC 1950-compliant here, but the advantage is that
       * this actually works. :)
       *
       * We add a dummy null byte to tell zlib where the data ends,
       * and later inform it not to expect a header.
       *
       * Fortunately, add_to_iob() has thoughtfully null-terminated
       * the buffer; we can just increment the end pointer to include
       * the dummy byte.
       */
      csp->iob->eod++;
   }
   else
   {
      log_error(LOG_LEVEL_ERROR,
         "Unable to determine compression format for decompression");
      return JB_ERR_COMPRESS;
   }

   /* Set up the fields required by zlib. */
   zstr.next_in  = (Bytef *)cur;
   zstr.avail_in = (unsigned int)(csp->iob->eod - cur);
   zstr.zalloc   = Z_NULL;
   zstr.zfree    = Z_NULL;
   zstr.opaque   = Z_NULL;

   /*
    * Passing -MAX_WBITS to inflateInit2 tells the library
    * that there is no zlib header.
    */
   if (inflateInit2(&zstr, -MAX_WBITS) != Z_OK)
   {
      log_error(LOG_LEVEL_ERROR, "Error initializing decompression");
      return JB_ERR_COMPRESS;
   }

   /*
    * Next, we allocate new storage for the inflated data.
    * We don't modify the existing iob yet, so in case there
    * is error in decompression we can recover gracefully.
    */
   buf = zalloc(bufsize);
   if (NULL == buf)
   {
      log_error(LOG_LEVEL_ERROR, "Out of memory decompressing iob");
      return JB_ERR_MEMORY;
   }

   assert(bufsize >= skip_size);
   memcpy(buf, csp->iob->buf, skip_size);
   zstr.avail_out = (uInt)(bufsize - skip_size);
   zstr.next_out  = (Bytef *)buf + skip_size;

   /* Try to decompress the whole stream in one shot. */
   while (Z_BUF_ERROR == (status = inflate(&zstr, Z_FINISH)))
   {
      /* We need to allocate more memory for the output buffer. */

      char *tmpbuf;                /* used for realloc'ing the buffer */
      size_t oldbufsize = bufsize; /* keep track of the old bufsize */

      if (0 == zstr.avail_in)
      {
         /*
          * If zlib wants more data then there's a problem, because
          * the complete compressed file should have been buffered.
          */
         log_error(LOG_LEVEL_ERROR,
            "Unexpected end of compressed iob. Using what we got so far.");
         break;
      }

      /*
       * If we reached the buffer limit and still didn't have enough
       * memory, just give up. Due to the ceiling enforced by the next
       * if block we could actually check for equality here, but as it
       * can be easily mistaken for a bug we don't.
       */
      if (bufsize >= csp->config->buffer_limit)
      {
         log_error(LOG_LEVEL_ERROR, "Buffer limit reached while decompressing iob");
         freez(buf);
         return JB_ERR_MEMORY;
      }

      /* Try doubling the buffer size each time. */
      bufsize *= 2;

      /* Don't exceed the buffer limit. */
      if (bufsize > csp->config->buffer_limit)
      {
         bufsize = csp->config->buffer_limit;
      }

      /* Try to allocate the new buffer. */
      tmpbuf = realloc(buf, bufsize);
      if (NULL == tmpbuf)
      {
         log_error(LOG_LEVEL_ERROR, "Out of memory decompressing iob");
         freez(buf);
         return JB_ERR_MEMORY;
      }
      else
      {
         char *oldnext_out = (char *)zstr.next_out;

         /*
          * Update the fields for inflate() to use the new
          * buffer, which may be in a location different from
          * the old one.
          */
         zstr.avail_out += (uInt)(bufsize - oldbufsize);
         zstr.next_out   = (Bytef *)tmpbuf + bufsize - zstr.avail_out;

         /*
          * Compare with an uglier method of calculating these values
          * that doesn't require the extra oldbufsize variable.
          */
         assert(zstr.avail_out == tmpbuf + bufsize - (char *)zstr.next_out);
         assert((char *)zstr.next_out == tmpbuf + ((char *)oldnext_out - buf));

         buf = tmpbuf;
      }
   }

   if (Z_STREAM_ERROR == inflateEnd(&zstr))
   {
      log_error(LOG_LEVEL_ERROR,
         "Inconsistent stream state after decompression: %s", zstr.msg);
      /*
       * XXX: Intentionally no return.
       *
       * According to zlib.h, Z_STREAM_ERROR is returned
       * "if the stream state was inconsistent".
       *
       * I assume in this case inflate()'s status
       * would also be something different than Z_STREAM_END
       * so this check should be redundant, but lets see.
       */
   }

   if ((status != Z_STREAM_END) && (0 != zstr.avail_in))
   {
      /*
       * We failed to decompress the stream and it's
       * not simply because of missing data.
       */
      log_error(LOG_LEVEL_ERROR,
         "Unexpected error while decompressing to the buffer (iob): %s",
         zstr.msg);
      return JB_ERR_COMPRESS;
   }

   /*
    * Finally, we can actually update the iob, since the
    * decompression was successful. First, free the old
    * buffer.
    */
   freez(csp->iob->buf);

   /* Now, update the iob to use the new buffer. */
   csp->iob->buf  = buf;
   csp->iob->cur  = csp->iob->buf + skip_size;
   csp->iob->eod  = (char *)zstr.next_out;
   csp->iob->size = bufsize;

   /*
    * Make sure the new uncompressed iob obeys some minimal
    * consistency conditions.
    */
   if ((csp->iob->buf <=  csp->iob->cur)
    && (csp->iob->cur <= csp->iob->eod)
    && (csp->iob->eod <= csp->iob->buf + csp->iob->size))
   {
      const size_t new_size = (size_t)(csp->iob->eod - csp->iob->cur);
      if (new_size > (size_t)0)
      {
         log_error(LOG_LEVEL_RE_FILTER,
            "Decompression successful. Old size: %d, new size: %d.",
            old_size, new_size);
      }
      else
      {
         /* zlib thinks this is OK, so lets do the same. */
         log_error(LOG_LEVEL_INFO, "Decompression didn't result in any content.");
      }
   }
   else
   {
      /* It seems that zlib did something weird. */
      log_error(LOG_LEVEL_ERROR,
         "Unexpected error decompressing the buffer (iob): %d==%d, %d>%d, %d<%d",
         csp->iob->cur, csp->iob->buf + skip_size, csp->iob->eod, csp->iob->buf,
         csp->iob->eod, csp->iob->buf + csp->iob->size);
      return JB_ERR_COMPRESS;
   }

   return JB_ERR_OK;

}
#endif /* defined(FEATURE_ZLIB) */


/*********************************************************************
 *
 * Function    :  normalize_lws
 *
 * Description :  Reduces unquoted linear whitespace in headers to
 *                a single space in accordance with RFC 7230 3.2.4.
 *                This simplifies parsing and filtering later on.
 *
 * Parameters  :
 *          1  :  header = A header with linear whitespace to reduce.
 *
 * Returns     :  N/A
 *
 *********************************************************************/
static void normalize_lws(char *header)
{
   char *p = header;

   while (*p != '\0')
   {
      if (privoxy_isspace(*p) && privoxy_isspace(*(p+1)))
      {
         char *q = p+1;

         while (privoxy_isspace(*q))
         {
            q++;
         }
         log_error(LOG_LEVEL_HEADER, "Reducing whitespace in '%s'", header);
         string_move(p+1, q);
      }

      if (*p == '\t')
      {
         log_error(LOG_LEVEL_HEADER,
            "Converting tab to space in '%s'", header);
         *p = ' ';
      }
      else if (*p == '"')
      {
         char *end_of_token = strstr(p+1, "\"");

         if (NULL != end_of_token)
         {
            /* Don't mess with quoted text. */
            p = end_of_token;
         }
         else
         {
            log_error(LOG_LEVEL_HEADER,
               "Ignoring single quote in '%s'", header);
         }
      }
      p++;
   }

   p = strchr(header, ':');
   if ((p != NULL) && (p != header) && privoxy_isspace(*(p-1)))
   {
      /*
       * There's still space before the colon.
       * We don't want it.
       */
      string_move(p-1, p);
   }
}


/*********************************************************************
 *
 * Function    :  get_header
 *
 * Description :  This (odd) routine will parse the csp->iob
 *                to get the next complete header.
 *
 * Parameters  :
 *          1  :  iob = The I/O buffer to parse, usually csp->iob.
 *
 * Returns     :  Any one of the following:
 *
 * 1) a pointer to a dynamically allocated string that contains a header line
 * 2) NULL  indicating that the end of the header was reached
 * 3) ""    indicating that the end of the iob was reached before finding
 *          a complete header line.
 *
 *********************************************************************/
char *get_header(struct iob *iob)
{
   char *header;

   header = get_header_line(iob);

   if ((header == NULL) || (*header == '\0'))
   {
      /*
       * No complete header read yet, tell the client.
       */
      return header;
   }

   while ((iob->cur[0] == ' ') || (iob->cur[0] == '\t'))
   {
      /*
       * Header spans multiple lines, append the next one.
       */
      char *continued_header;

      continued_header = get_header_line(iob);
      if ((continued_header == NULL) || (*continued_header == '\0'))
      {
         /*
          * No complete header read yet, return what we got.
          * XXX: Should "unread" header instead.
          */
         log_error(LOG_LEVEL_INFO,
            "Failed to read a multi-line header properly: '%s'",
            header);
         break;
      }

      if (JB_ERR_OK != string_join(&header, continued_header))
      {
         log_error(LOG_LEVEL_FATAL,
            "Out of memory while appending multiple headers.");
      }
      else
      {
         /* XXX: remove before next stable release. */
         log_error(LOG_LEVEL_HEADER,
            "Merged multiple header lines to: '%s'",
            header);
      }
   }

   normalize_lws(header);

   return header;

}


/*********************************************************************
 *
 * Function    :  get_header_line
 *
 * Description :  This (odd) routine will parse the csp->iob
 *                to get the next header line.
 *
 * Parameters  :
 *          1  :  iob = The I/O buffer to parse, usually csp->iob.
 *
 * Returns     :  Any one of the following:
 *
 * 1) a pointer to a dynamically allocated string that contains a header line
 * 2) NULL  indicating that the end of the header was reached
 * 3) ""    indicating that the end of the iob was reached before finding
 *          a complete header line.
 *
 *********************************************************************/
static char *get_header_line(struct iob *iob)
{
   char *p, *q, *ret;

   if ((iob->cur == NULL)
      || ((p = strchr(iob->cur, '\n')) == NULL))
   {
      return(""); /* couldn't find a complete header */
   }

   *p = '\0';

   ret = strdup(iob->cur);
   if (ret == NULL)
   {
      /* FIXME No way to handle error properly */
      log_error(LOG_LEVEL_FATAL, "Out of memory in get_header_line()");
   }
   assert(ret != NULL);

   iob->cur = p+1;

   if ((q = strchr(ret, '\r')) != NULL) *q = '\0';

   /* is this a blank line (i.e. the end of the header) ? */
   if (*ret == '\0')
   {
      freez(ret);
      return NULL;
   }

   return ret;

}


/*********************************************************************
 *
 * Function    :  get_header_value
 *
 * Description :  Get the value of a given header from a chained list
 *                of header lines or return NULL if no such header is
 *                present in the list.
 *
 * Parameters  :
 *          1  :  header_list = pointer to list
 *          2  :  header_name = string with name of header to look for.
 *                              Trailing colon required, capitalization
 *                              doesn't matter.
 *
 * Returns     :  NULL if not found, else value of header
 *
 *********************************************************************/
char *get_header_value(const struct list *header_list, const char *header_name)
{
   struct list_entry *cur_entry;
   char *ret = NULL;
   size_t length = 0;

   assert(header_list);
   assert(header_name);
   length = strlen(header_name);

   for (cur_entry = header_list->first; cur_entry ; cur_entry = cur_entry->next)
   {
      if (cur_entry->str)
      {
         if (!strncmpic(cur_entry->str, header_name, length))
         {
            /*
             * Found: return pointer to start of value
             */
            ret = cur_entry->str + length;
            while (*ret && privoxy_isspace(*ret)) ret++;
            return ret;
         }
      }
   }

   /*
    * Not found
    */
   return NULL;

}


/*********************************************************************
 *
 * Function    :  scan_headers
 *
 * Description :  Scans headers, applies tags and updates action bits.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *
 * Returns     :  JB_ERR_OK
 *
 *********************************************************************/
static jb_err scan_headers(struct client_state *csp)
{
   struct list_entry *h; /* Header */
   jb_err err = JB_ERR_OK;

   for (h = csp->headers->first; (err == JB_ERR_OK) && (h != NULL) ; h = h->next)
   {
      /* Header crunch()ed in previous run? -> ignore */
      if (h->str == NULL) continue;
      log_error(LOG_LEVEL_HEADER, "scan: %s", h->str);
      err = header_tagger(csp, h->str);
   }

   return err;
}


/*********************************************************************
 *
 * Function    :  enforce_header_order
 *
 * Description :  Enforces a given header order.
 *
 * Parameters  :
 *          1  :  headers         = List of headers to order.
 *          2  :  ordered_headers = List of ordered header names.
 *
 * Returns     :  N/A
 *
 *********************************************************************/
static void enforce_header_order(struct list *headers, const struct list *ordered_headers)
{
   struct list_entry *sorted_header;
   struct list new_headers[1];
   struct list_entry *header;

   init_list(new_headers);

   /* The request line is always the first "header" */

   assert(NULL != headers->first->str);
   enlist(new_headers, headers->first->str);
   freez(headers->first->str)

   /* Enlist the specified headers in the given order */

   for (sorted_header = ordered_headers->first; sorted_header != NULL;
        sorted_header = sorted_header->next)
   {
      const size_t sorted_header_length = strlen(sorted_header->str);
      for (header = headers->first; header != NULL; header = header->next)
      {
         /* Header enlisted in previous run? -> ignore */
         if (header->str == NULL) continue;

         if (0 == strncmpic(sorted_header->str, header->str, sorted_header_length)
            && (header->str[sorted_header_length] == ':'))
         {
            log_error(LOG_LEVEL_HEADER, "Enlisting sorted header %s", header->str);
            if (JB_ERR_OK != enlist(new_headers, header->str))
            {
               log_error(LOG_LEVEL_HEADER, "Failed to enlist %s", header->str);
            }
            freez(header->str);
         }
      }
   }

   /* Enlist the rest of the headers behind the ordered ones */
   for (header = headers->first; header != NULL; header = header->next)
   {
      /* Header enlisted in previous run? -> ignore */
      if (header->str == NULL) continue;

      log_error(LOG_LEVEL_HEADER,
         "Enlisting left-over header %s", header->str);
      if (JB_ERR_OK != enlist(new_headers, header->str))
      {
         log_error(LOG_LEVEL_HEADER, "Failed to enlist %s", header->str);
      }
      freez(header->str);
   }

   list_remove_all(headers);
   list_duplicate(headers, new_headers);
   list_remove_all(new_headers);

   return;
}


/*********************************************************************
 *
 * Function    :  sed
 *
 * Description :  add, delete or modify lines in the HTTP header streams.
 *                On entry, it receives a linked list of headers space
 *                that was allocated dynamically (both the list nodes
 *                and the header contents).
 *
 *                As a side effect it frees the space used by the original
 *                header lines.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  filter_server_headers = Boolean to switch between
 *                                        server and header filtering.
 *
 * Returns     :  JB_ERR_OK in case off success, or
 *                JB_ERR_MEMORY on some out-of-memory errors, or
 *                JB_ERR_PARSE in case of fatal parse errors.
 *
 *********************************************************************/
jb_err sed(struct client_state *csp, int filter_server_headers)
{
   /* XXX: use more descriptive names. */
   struct list_entry *p;
   const struct parsers *v;
   const add_header_func_ptr *f;
   jb_err err = JB_ERR_OK;

   scan_headers(csp);

   if (filter_server_headers)
   {
      v = server_patterns;
      f = add_server_headers;
      check_negative_tag_patterns(csp, PATTERN_SPEC_NO_RESPONSE_TAG_PATTERN);
   }
   else
   {
      v = client_patterns;
      f = add_client_headers;
      check_negative_tag_patterns(csp, PATTERN_SPEC_NO_REQUEST_TAG_PATTERN);
   }

   while (v->str != NULL)
   {
      for (p = csp->headers->first; p != NULL; p = p->next)
      {
         /* Header crunch()ed in previous run? -> ignore */
         if (p->str == NULL) continue;

         /* Does the current parser handle this header? */
         if ((strncmpic(p->str, v->str, v->len) == 0) ||
             (v->len == CHECK_EVERY_HEADER_REMAINING))
         {
            err = v->parser(csp, &(p->str));
            if (err != JB_ERR_OK)
            {
               return err;
            }
         }
      }
      v++;
   }

   /* place additional headers on the csp->headers list */
   while ((err == JB_ERR_OK) && (*f))
   {
      err = (*f)(csp);
      f++;
   }

   if (!filter_server_headers && !list_is_empty(csp->config->ordered_client_headers))
   {
      enforce_header_order(csp->headers, csp->config->ordered_client_headers);
   }

   return err;
}


#ifdef FEATURE_HTTPS_INSPECTION
/*********************************************************************
 *
 * Function    :  sed_https
 *
 * Description :  add, delete or modify lines in the HTTPS client
 *                header streams. Wrapper around sed().
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *
 * Returns     :  JB_ERR_OK in case off success, or
 *                JB_ERR_MEMORY on some out-of-memory errors, or
 *                JB_ERR_PARSE in case of fatal parse errors.
 *
 *********************************************************************/
jb_err sed_https(struct client_state *csp)
{
   jb_err err;
   struct list headers;

   /*
    * Temporarily replace csp->headers with csp->https_headers
    * to trick sed() into filtering the https headers.
    */
   headers.first = csp->headers->first;
   headers.last  = csp->headers->last;
   csp->headers->first = csp->https_headers->first;
   csp->headers->last  = csp->https_headers->last;

   /*
    * Start with fresh tags. Already existing tags may
    * be set again. This is necessary to overrule
    * URL-based patterns.
    */
   destroy_list(csp->tags);

   /*
    * We want client header filters and taggers
    * so temporarily remove the flag.
    */
   csp->flags &= ~CSP_FLAG_CLIENT_HEADER_PARSING_DONE;
   err = sed(csp, FILTER_CLIENT_HEADERS);
   csp->flags |= CSP_FLAG_CLIENT_HEADER_PARSING_DONE;

   /*
    * Update the last header which may have changed
    * due to header additions,
    */
   csp->https_headers->last = csp->headers->last;

   csp->headers->first = headers.first;
   csp->headers->last  = headers.last;

   return err;
}
#endif /* def FEATURE_HTTPS_INSPECTION */


/*********************************************************************
 *
 * Function    :  update_server_headers
 *
 * Description :  Updates server headers after the body has been modified.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *
 * Returns     :  JB_ERR_OK in case off success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
jb_err update_server_headers(struct client_state *csp)
{
   jb_err err = JB_ERR_OK;

   static const struct parsers server_patterns_light[] = {
      { "Content-Length:",    15, server_adjust_content_length },
      { "Transfer-Encoding:", 18, server_transfer_coding },
#ifdef FEATURE_ZLIB
      { "Content-Encoding:",  17, server_adjust_content_encoding },
#endif /* def FEATURE_ZLIB */
      { NULL,                  0, NULL }
   };

   if (strncmpic(csp->http->cmd, "HEAD", 4))
   {
      const struct parsers *v;
      struct list_entry *p;

      for (v = server_patterns_light; (err == JB_ERR_OK) && (v->str != NULL); v++)
      {
         for (p = csp->headers->first; (err == JB_ERR_OK) && (p != NULL); p = p->next)
         {
            /* Header crunch()ed in previous run? -> ignore */
            if (p->str == NULL) continue;

            /* Does the current parser handle this header? */
            if (strncmpic(p->str, v->str, v->len) == 0)
            {
               err = v->parser(csp, (char **)&(p->str));
            }
         }
      }
   }

#ifdef FEATURE_CONNECTION_KEEP_ALIVE
   if ((JB_ERR_OK == err)
    && (csp->flags & CSP_FLAG_MODIFIED)
    && (csp->flags & CSP_FLAG_CLIENT_CONNECTION_KEEP_ALIVE)
    && !(csp->flags & CSP_FLAG_SERVER_CONTENT_LENGTH_SET))
   {
      char header[50];

      create_content_length_header(csp->content_length, header, sizeof(header));
      err = enlist(csp->headers, header);
      if (JB_ERR_OK == err)
      {
         log_error(LOG_LEVEL_HEADER,
            "Content modified with no Content-Length header set. "
            "Created: %s.", header);
         csp->flags |= CSP_FLAG_SERVER_CONTENT_LENGTH_SET;
      }
   }
#endif /* def FEATURE_CONNECTION_KEEP_ALIVE */

#ifdef FEATURE_COMPRESSION
   if ((JB_ERR_OK == err)
      && (csp->flags & CSP_FLAG_BUFFERED_CONTENT_DEFLATED))
   {
      err = enlist_unique_header(csp->headers, "Content-Encoding", "deflate");
      if (JB_ERR_OK == err)
      {
         log_error(LOG_LEVEL_HEADER, "Added header: Content-Encoding: deflate");
      }
   }
#endif

   return err;
}


/*********************************************************************
 *
 * Function    :  header_tagger
 *
 * Description :  Executes all text substitutions from applying
 *                tag actions and saves the result as tag.
 *
 *                XXX: Shares enough code with filter_header() and
 *                pcrs_filter_response() to warrant some helper functions.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = Header that is used as tagger input
 *
 * Returns     :  JB_ERR_OK on success and always succeeds
 *
 *********************************************************************/
static jb_err header_tagger(struct client_state *csp, char *header)
{
   enum filter_type wanted_filter_type;
   int multi_action_index;
   pcrs_job *job;

   struct re_filterfile_spec *b;
   struct list_entry *tag_name;

   const size_t header_length = strlen(header);

   if (csp->flags & CSP_FLAG_CLIENT_HEADER_PARSING_DONE)
   {
      wanted_filter_type = FT_SERVER_HEADER_TAGGER;
      multi_action_index = ACTION_MULTI_SERVER_HEADER_TAGGER;
   }
   else
   {
      wanted_filter_type = FT_CLIENT_HEADER_TAGGER;
      multi_action_index = ACTION_MULTI_CLIENT_HEADER_TAGGER;
   }

   if (list_is_empty(csp->action->multi[multi_action_index])
      || filters_available(csp) == FALSE)
   {
      /* Return early if no taggers apply or if none are available. */
      return JB_ERR_OK;
   }

   /* Execute all applying taggers */
   for (tag_name = csp->action->multi[multi_action_index]->first;
        NULL != tag_name; tag_name = tag_name->next)
   {
      char *modified_tag = NULL;
      char *tag = header;
      size_t size = header_length;
      pcrs_job *joblist;

      b = get_filter(csp, tag_name->str, wanted_filter_type);
      if (b == NULL)
      {
         continue;
      }

      joblist = b->joblist;

      if (b->dynamic) joblist = compile_dynamic_pcrs_job_list(csp, b);

      if (NULL == joblist)
      {
         log_error(LOG_LEVEL_RE_FILTER,
            "Tagger %s has empty joblist. Nothing to do.", b->name);
         continue;
      }

      /* execute their pcrs_joblist on the header. */
      for (job = joblist; NULL != job; job = job->next)
      {
         const int hits = pcrs_execute(job, tag, size, &modified_tag, &size);

         if (0 < hits)
         {
            /* Success, continue with the modified version. */
            if (tag != header)
            {
               freez(tag);
            }
            tag = modified_tag;
         }
         else
         {
            /* Tagger doesn't match */
            if (0 > hits)
            {
               /* Regex failure, log it but continue anyway. */
               assert(NULL != header);
               log_error(LOG_LEVEL_ERROR,
                  "Problems with tagger \'%s\' and header \'%s\': %s",
                  b->name, *header, pcrs_strerror(hits));
            }
            freez(modified_tag);
         }
      }

      if (b->dynamic) pcrs_free_joblist(joblist);

      /* If this tagger matched */
      if (tag != header)
      {
         if (0 == size)
         {
            /*
             * There is no technical limitation which makes
             * it impossible to use empty tags, but I assume
             * no one would do it intentionally.
             */
            freez(tag);
            log_error(LOG_LEVEL_INFO,
               "Tagger \'%s\' created an empty tag. Ignored.", b->name);
            continue;
         }

         if (!list_contains_item(csp->tags, tag))
         {
            if (JB_ERR_OK != enlist(csp->tags, tag))
            {
               log_error(LOG_LEVEL_ERROR,
                  "Insufficient memory to add tag \'%s\', "
                  "based on tagger \'%s\' and header \'%s\'",
                  tag, b->name, *header);
            }
            else
            {
               char *action_message;
               /*
                * update the action bits right away, to make
                * tagging based on tags set by earlier taggers
                * of the same kind possible.
                */
               if (update_action_bits_for_tag(csp, tag))
               {
                  action_message = "Action bits updated accordingly.";
               }
               else
               {
                  action_message = "No action bits update necessary.";
               }

               log_error(LOG_LEVEL_HEADER,
                  "Tagger \'%s\' added tag \'%s\'. %s",
                  b->name, tag, action_message);
            }
         }
         else
         {
            /* XXX: Is this log-worthy? */
            log_error(LOG_LEVEL_HEADER,
               "Tagger \'%s\' didn't add tag \'%s\'. Tag already present",
               b->name, tag);
         }
         freez(tag);
      }
   }

   return JB_ERR_OK;
}

/* here begins the family of parser functions that reformat header lines */

/*********************************************************************
 *
 * Function    :  filter_header
 *
 * Description :  Executes all text substitutions from all applying
 *                +(server|client)-header-filter actions on the header.
 *                Most of the code was copied from pcrs_filter_response,
 *                including the rather short variable names
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success and always succeeds
 *
 *********************************************************************/
static jb_err filter_header(struct client_state *csp, char **header)
{
   int hits=0;
   int matches;
   size_t size = strlen(*header);

   char *newheader = NULL;
   pcrs_job *job;

   struct re_filterfile_spec *b;
   struct list_entry *filtername;

   enum filter_type wanted_filter_type;
   int multi_action_index;

   if (csp->flags & CSP_FLAG_NO_FILTERING)
   {
      return JB_ERR_OK;
   }

   if (csp->flags & CSP_FLAG_CLIENT_HEADER_PARSING_DONE)
   {
      wanted_filter_type = FT_SERVER_HEADER_FILTER;
      multi_action_index = ACTION_MULTI_SERVER_HEADER_FILTER;
   }
   else
   {
      wanted_filter_type = FT_CLIENT_HEADER_FILTER;
      multi_action_index = ACTION_MULTI_CLIENT_HEADER_FILTER;
   }

   if (list_is_empty(csp->action->multi[multi_action_index])
      || filters_available(csp) == FALSE)
   {
      /* Return early if no filters apply or if none are available. */
      return JB_ERR_OK;
   }

   /* Execute all applying header filters */
   for (filtername = csp->action->multi[multi_action_index]->first;
        filtername != NULL; filtername = filtername->next)
   {
      int current_hits = 0;
      pcrs_job *joblist;

      b = get_filter(csp, filtername->str, wanted_filter_type);
      if (b == NULL)
      {
         continue;
      }

      joblist = b->joblist;

      if (b->dynamic) joblist = compile_dynamic_pcrs_job_list(csp, b);

      if (NULL == joblist)
      {
         log_error(LOG_LEVEL_RE_FILTER, "Filter %s has empty joblist. Nothing to do.", b->name);
         continue;
      }

      log_error(LOG_LEVEL_RE_FILTER, "filtering \'%s\' (size %d) with \'%s\' ...",
         *header, size, b->name);

      /* Apply all jobs from the joblist */
      for (job = joblist; NULL != job; job = job->next)
      {
         matches = pcrs_execute(job, *header, size, &newheader, &size);
         if (0 < matches)
         {
            current_hits += matches;
            log_error(LOG_LEVEL_HEADER, "Transforming \"%s\" to \"%s\"", *header, newheader);
            freez(*header);
            *header = newheader;
         }
         else if (0 == matches)
         {
            /* Filter doesn't change header */
            freez(newheader);
         }
         else
         {
            /* RegEx failure */
            log_error(LOG_LEVEL_ERROR, "Filtering \'%s\' with \'%s\' didn't work out: %s",
               *header, b->name, pcrs_strerror(matches));
            if (newheader != NULL)
            {
               log_error(LOG_LEVEL_ERROR, "Freeing what's left: %s", newheader);
               freez(newheader);
            }
         }
      }

      if (b->dynamic) pcrs_free_joblist(joblist);

      log_error(LOG_LEVEL_RE_FILTER, "... produced %d hits (new size %d).", current_hits, size);
      hits += current_hits;
   }

   /*
    * Additionally checking for hits is important because if
    * the continue hack is triggered, server headers can
    * arrive empty to separate multiple heads from each other.
    */
   if ((0 == size) && hits)
   {
      log_error(LOG_LEVEL_HEADER, "Removing empty header %s", *header);
      freez(*header);
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  server_connection
 *
 * Description :  Makes sure a proper "Connection:" header is
 *                set and signals connection_header_adder to
 *                do nothing.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success.
 *
 *********************************************************************/
static jb_err server_connection(struct client_state *csp, char **header)
{
   if (!strcmpic(*header, "Connection: keep-alive")
#ifdef FEATURE_CONNECTION_KEEP_ALIVE
    && !(csp->flags & CSP_FLAG_SERVER_SOCKET_TAINTED)
#endif
     )
   {
#ifdef FEATURE_CONNECTION_KEEP_ALIVE
      if ((csp->config->feature_flags & RUNTIME_FEATURE_CONNECTION_KEEP_ALIVE))
      {
         csp->flags |= CSP_FLAG_SERVER_CONNECTION_KEEP_ALIVE;
      }

      if ((csp->flags & CSP_FLAG_CLIENT_CONNECTION_KEEP_ALIVE))
      {
         log_error(LOG_LEVEL_HEADER,
            "Keeping the server header '%s' around.", *header);
      }
      else
#endif /* FEATURE_CONNECTION_KEEP_ALIVE */
      {
         char *old_header = *header;

         *header = strdup_or_die("Connection: close");
         log_error(LOG_LEVEL_HEADER, "Replaced: \'%s\' with \'%s\'", old_header, *header);
         freez(old_header);
      }
   }

   /* Signal server_connection_adder() to return early. */
   csp->flags |= CSP_FLAG_SERVER_CONNECTION_HEADER_SET;

   return JB_ERR_OK;
}


#ifdef FEATURE_CONNECTION_KEEP_ALIVE
/*********************************************************************
 *
 * Function    :  server_keep_alive
 *
 * Description :  Stores the server's keep alive timeout.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK.
 *
 *********************************************************************/
static jb_err server_keep_alive(struct client_state *csp, char **header)
{
   unsigned int keep_alive_timeout;
   const char *timeout_position = strstr(*header, "timeout=");

   if ((NULL == timeout_position)
    || (1 != sscanf(timeout_position, "timeout=%u", &keep_alive_timeout)))
   {
      log_error(LOG_LEVEL_ERROR, "Couldn't parse: %s", *header);
   }
   else
   {
      if (keep_alive_timeout < csp->server_connection.keep_alive_timeout)
      {
         log_error(LOG_LEVEL_HEADER,
            "Reducing keep-alive timeout from %u to %u.",
            csp->server_connection.keep_alive_timeout, keep_alive_timeout);
         csp->server_connection.keep_alive_timeout = keep_alive_timeout;
      }
      else
      {
         /* XXX: Is this log worthy? */
         log_error(LOG_LEVEL_HEADER,
            "Server keep-alive timeout is %u. Sticking with %u.",
            keep_alive_timeout, csp->server_connection.keep_alive_timeout);
      }
      csp->flags |= CSP_FLAG_SERVER_KEEP_ALIVE_TIMEOUT_SET;
   }

   freez(*header);

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  server_proxy_connection
 *
 * Description :  Figures out whether or not we should add a
 *                Proxy-Connection header.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK.
 *
 *********************************************************************/
static jb_err server_proxy_connection(struct client_state *csp, char **header)
{
   csp->flags |= CSP_FLAG_SERVER_PROXY_CONNECTION_HEADER_SET;
   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  proxy_authentication
 *
 * Description :  Removes headers that are relevant for proxy
 *                authentication unless forwarding them has
 *                been explicitly requested.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK.
 *
 *********************************************************************/
static jb_err proxy_authentication(struct client_state *csp, char **header)
{
   if ((csp->config->feature_flags &
      RUNTIME_FEATURE_FORWARD_PROXY_AUTHENTICATION_HEADERS) == 0) {
      log_error(LOG_LEVEL_HEADER,
         "Forwarding proxy authentication headers is disabled. Crunching: %s", *header);
      freez(*header);
   }
   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_keep_alive
 *
 * Description :  Stores the client's keep alive timeout.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK.
 *
 *********************************************************************/
static jb_err client_keep_alive(struct client_state *csp, char **header)
{
   unsigned int keep_alive_timeout;
   char *timeout_position;

   if (!(csp->config->feature_flags & RUNTIME_FEATURE_CONNECTION_KEEP_ALIVE))
   {
      log_error(LOG_LEVEL_HEADER,
         "keep-alive support is disabled. Crunching: %s.", *header);
      freez(*header);
      return JB_ERR_OK;
   }

   /* Check for parameter-less format "Keep-Alive: 100" */
   timeout_position = strstr(*header, ": ");
   if ((NULL == timeout_position)
    || (1 != sscanf(timeout_position, ": %u", &keep_alive_timeout)))
   {
      /* Assume parameter format "Keep-Alive: timeout=100" */
      timeout_position = strstr(*header, "timeout=");
      if ((NULL == timeout_position)
         || (1 != sscanf(timeout_position, "timeout=%u", &keep_alive_timeout)))
      {
         log_error(LOG_LEVEL_HEADER,
            "Couldn't parse: '%s'. Using default timeout %u",
            *header, csp->config->keep_alive_timeout);
         freez(*header);

         return JB_ERR_OK;
      }
   }

   if (keep_alive_timeout < csp->config->keep_alive_timeout)
   {
      log_error(LOG_LEVEL_HEADER,
         "Reducing keep-alive timeout from %u to %u.",
         csp->config->keep_alive_timeout, keep_alive_timeout);
      csp->server_connection.keep_alive_timeout = keep_alive_timeout;
   }
   else
   {
      /* XXX: Is this log worthy? */
      log_error(LOG_LEVEL_HEADER,
         "Client keep-alive timeout is %u. Sticking with %u.",
         keep_alive_timeout, csp->config->keep_alive_timeout);
      freez(*header);
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  get_content_length
 *
 * Description :  Gets the content length specified in a
 *                Content-Length header.
 *
 * Parameters  :
 *          1  :  header_value = The Content-Length header value.
 *          2  :  length = Storage to return the value.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_PARSE if no value is recognized.
 *
 *********************************************************************/
static jb_err get_content_length(const char *header_value, unsigned long long *length)
{
#ifdef _WIN32
#if SIZEOF_LONG_LONG < 8
#error sizeof(unsigned long long) too small
#endif
   if (1 != sscanf(header_value, "%I64u", length))
#else
   if (1 != sscanf(header_value, "%llu", length))
#endif
   {
      return JB_ERR_PARSE;
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_save_content_length
 *
 * Description :  Save the Content-Length sent by the client.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_save_content_length(struct client_state *csp, char **header)
{
   unsigned long long content_length = 0;
   const char *header_value;

   assert(*(*header+14) == ':');

   header_value = *header + 15;
   if (JB_ERR_OK != get_content_length(header_value, &content_length))
   {
      log_error(LOG_LEVEL_ERROR, "Crunching invalid header: %s", *header);
      freez(*header);
   }
   else
   {
      csp->expected_client_content_length = content_length;
   }

   return JB_ERR_OK;
}
#endif /* def FEATURE_CONNECTION_KEEP_ALIVE */



/*********************************************************************
 *
 * Function    :  client_connection
 *
 * Description :  Makes sure a proper "Connection:" header is
 *                set and signals connection_header_adder
 *                to do nothing.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success.
 *
 *********************************************************************/
static jb_err client_connection(struct client_state *csp, char **header)
{
   static const char connection_close[] = "Connection: close";

   if (!strcmpic(*header, connection_close))
   {
#ifdef FEATURE_CONNECTION_KEEP_ALIVE
      if ((csp->config->feature_flags & RUNTIME_FEATURE_CONNECTION_SHARING)
        && !(csp->flags & CSP_FLAG_SERVER_SOCKET_TAINTED))
      {
          if (!strcmpic(csp->http->version, "HTTP/1.1"))
          {
             log_error(LOG_LEVEL_HEADER,
                "Removing \'%s\' to imply keep-alive.", *header);
             freez(*header);
             /*
              * While we imply keep-alive to the server,
              * we have to remember that the client didn't.
              */
             csp->flags &= ~CSP_FLAG_CLIENT_CONNECTION_KEEP_ALIVE;
          }
          else
          {
             char *old_header = *header;

             *header = strdup_or_die("Connection: keep-alive");
             log_error(LOG_LEVEL_HEADER,
                "Replaced: \'%s\' with \'%s\'", old_header, *header);
             freez(old_header);
          }
      }
      else
      {
         log_error(LOG_LEVEL_HEADER,
            "Keeping the client header '%s' around. "
            "The connection will not be kept alive.",
            *header);
         csp->flags &= ~CSP_FLAG_CLIENT_CONNECTION_KEEP_ALIVE;
      }
   }
   else if ((csp->config->feature_flags & RUNTIME_FEATURE_CONNECTION_KEEP_ALIVE)
        && !(csp->flags & CSP_FLAG_SERVER_SOCKET_TAINTED))
   {
      log_error(LOG_LEVEL_HEADER,
         "Keeping the client header '%s' around. "
         "The server connection will be kept alive if possible.",
         *header);
      csp->flags |= CSP_FLAG_CLIENT_CONNECTION_KEEP_ALIVE;
#endif  /* def FEATURE_CONNECTION_KEEP_ALIVE */
   }
   else
   {
      char *old_header = *header;

      *header = strdup_or_die(connection_close);
      log_error(LOG_LEVEL_HEADER,
         "Replaced: \'%s\' with \'%s\'", old_header, *header);
      freez(old_header);
   }

   /* Signal client_connection_header_adder() to return early. */
   csp->flags |= CSP_FLAG_CLIENT_CONNECTION_HEADER_SET;

   return JB_ERR_OK;
}


#ifdef FEATURE_CONNECTION_KEEP_ALIVE
/*********************************************************************
 *
 * Function    :  client_proxy_connection
 *
 * Description :  Sets the CLIENT_CONNECTION_KEEP_ALIVE flag when
 *                appropriate and removes the Proxy-Connection
 *                header.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK
 *
 *********************************************************************/
static jb_err client_proxy_connection(struct client_state *csp, char **header)
{
   if (0 == (csp->flags & CSP_FLAG_CLIENT_CONNECTION_KEEP_ALIVE)
      && (csp->http->ssl == 0)
      && (NULL == strstr(*header, "close")))
   {
      log_error(LOG_LEVEL_HEADER,
         "The client connection can be kept alive due to: %s", *header);
      csp->flags |= CSP_FLAG_CLIENT_CONNECTION_KEEP_ALIVE;
   }
   crumble(csp, header);

   return JB_ERR_OK;
}
#endif  /* def FEATURE_CONNECTION_KEEP_ALIVE */


/*********************************************************************
 *
 * Function    :  client_transfer_encoding
 *
 * Description :  Raise the CSP_FLAG_CHUNKED_CLIENT_BODY flag if
 *                the request body is "chunked"
 *
 *                XXX: Currently not called through sed() as we
 *                     need the flag earlier on. Should be fixed.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *
 *********************************************************************/
jb_err client_transfer_encoding(struct client_state *csp, char **header)
{
   if (strstr(*header, "chunked"))
   {
      csp->flags |= CSP_FLAG_CHUNKED_CLIENT_BODY;
      log_error(LOG_LEVEL_HEADER, "Expecting chunked client body");
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_expect
 *
 * Description :  Raise the CSP_FLAG_UNSUPPORTED_CLIENT_EXPECTATION
 *                if the Expect header value is unsupported.
 *
 *                Rejecting unsupported expectations is a RFC 7231 5.1.1
 *                MAY and a RFC 2616 (obsolete) MUST.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *
 *********************************************************************/
jb_err client_expect(struct client_state *csp, char **header)
{
   if (0 != strcmpic(*header, "Expect: 100-continue"))
   {
      csp->flags |= CSP_FLAG_UNSUPPORTED_CLIENT_EXPECTATION;
      log_error(LOG_LEVEL_HEADER,
         "Unsupported client expectaction: %s", *header);
   }

   return JB_ERR_OK;

}


/*********************************************************************
 *
 * Function    :  crumble
 *
 * Description :  This is called if a header matches a pattern to "crunch"
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err crumble(struct client_state *csp, char **header)
{
   (void)csp;
   log_error(LOG_LEVEL_HEADER, "crumble crunched: %s!", *header);
   freez(*header);
   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  crunch_server_header
 *
 * Description :  Crunch server header if it matches a string supplied by the
 *                user. Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success and always succeeds
 *
 *********************************************************************/
static jb_err crunch_server_header(struct client_state *csp, char **header)
{
   const char *crunch_pattern;

   /* Do we feel like crunching? */
   if ((csp->action->flags & ACTION_CRUNCH_SERVER_HEADER))
   {
      crunch_pattern = csp->action->string[ACTION_STRING_SERVER_HEADER];

      /* Is the current header the lucky one? */
      if (strstr(*header, crunch_pattern))
      {
         log_error(LOG_LEVEL_HEADER, "Crunching server header: %s (contains: %s)", *header, crunch_pattern);
         freez(*header);
      }
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  server_content_type
 *
 * Description :  Set the content-type for filterable types (text/.*,
 *                .*xml.*, .*script.* and image/gif) unless filtering has been
 *                forbidden (CT_TABOO) while parsing earlier headers.
 *                NOTE: Since text/plain is commonly used by web servers
 *                      for files whose correct type is unknown, we don't
 *                      set CT_TEXT for it.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err server_content_type(struct client_state *csp, char **header)
{
   /* Remove header if it isn't the first Content-Type header */
   if ((csp->content_type & CT_DECLARED))
   {
      if (content_filters_enabled(csp->action))
      {
         /*
          * Making sure the client interprets the content the same way
          * Privoxy did is only relevant if Privoxy modified it.
          *
          * Checking for this is "hard" as it's not yet known when
          * this function is called, thus go shopping and and just
          * check if Privoxy could filter it.
          *
          * The main thing is that we don't mess with the headers
          * unless the user signalled that it's acceptable.
          */
         log_error(LOG_LEVEL_HEADER,
            "Multiple Content-Type headers detected. "
            "Removing and ignoring: %s",
            *header);
         freez(*header);
      }
      return JB_ERR_OK;
   }

   /*
    * Signal that the Content-Type has been set.
    */
   csp->content_type |= CT_DECLARED;

   if (!(csp->content_type & CT_TABOO))
   {
      /*
       * XXX: The assumption that text/plain is a sign of
       * binary data seems to be somewhat unreasonable nowadays
       * and should be dropped after 3.0.8 is out.
       */
      if ((strstr(*header, "text/") && !strstr(*header, "plain"))
        || strstr(*header, "xml")
        || strstr(*header, "script"))
      {
         csp->content_type |= CT_TEXT;
      }
      else if (strstr(*header, "image/gif"))
      {
         csp->content_type |= CT_GIF;
      }
   }

   /*
    * Are we messing with the content type?
    */
   if (csp->action->flags & ACTION_CONTENT_TYPE_OVERWRITE)
   {
      /*
       * Make sure the user doesn't accidentally
       * change the content type of binary documents.
       */
      if ((csp->content_type & CT_TEXT) || (csp->action->flags & ACTION_FORCE_TEXT_MODE))
      {
         jb_err err;
         freez(*header);
         *header = strdup_or_die("Content-Type: ");

         err = string_append(header, csp->action->string[ACTION_STRING_CONTENT_TYPE]);
         if (JB_ERR_OK != err)
         {
            log_error(LOG_LEVEL_HEADER, "Insufficient memory to replace Content-Type!");
            return JB_ERR_MEMORY;
         }
         log_error(LOG_LEVEL_HEADER, "Modified: %s!", *header);
      }
      else
      {
         log_error(LOG_LEVEL_HEADER, "%s not replaced. "
            "It doesn't look like a content type that should be filtered. "
            "Enable force-text-mode if you know what you're doing.", *header);
      }
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  server_transfer_coding
 *
 * Description :  - Prohibit filtering (CT_TABOO) if transfer coding compresses
 *                - Raise the CSP_FLAG_CHUNKED flag if coding is "chunked"
 *                - Remove header if body was chunked but has been
 *                  de-chunked for filtering.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err server_transfer_coding(struct client_state *csp, char **header)
{
   /*
    * Turn off pcrs and gif filtering if body compressed
    */
   if (strstr(*header, "gzip") || strstr(*header, "compress") || strstr(*header, "deflate"))
   {
#ifdef FEATURE_ZLIB
      /*
       * XXX: Added to test if we could use CT_GZIP and CT_DEFLATE here.
       */
      log_error(LOG_LEVEL_INFO, "Marking content type for %s as CT_TABOO because of %s.",
         csp->http->cmd, *header);
#endif /* def FEATURE_ZLIB */
      csp->content_type = CT_TABOO;
   }

   /*
    * Raise flag if body chunked
    */
   if (strstr(*header, "chunked"))
   {
      csp->flags |= CSP_FLAG_CHUNKED;

      /*
       * If the body was modified, it has been de-chunked first
       * and the header must be removed.
       *
       * FIXME: If there is more than one transfer encoding,
       * only the "chunked" part should be removed here.
       */
      if (csp->flags & CSP_FLAG_MODIFIED)
      {
         log_error(LOG_LEVEL_HEADER, "Removing: %s", *header);
         freez(*header);
      }
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  server_content_encoding
 *
 * Description :  Used to check if the content is compressed, and if
 *                FEATURE_ZLIB is disabled, filtering is disabled as
 *                well.
 *
 *                If FEATURE_ZLIB is enabled and the compression type
 *                supported, the content is marked for decompression.
 *
 *                XXX: Doesn't properly deal with multiple or with
 *                     unsupported but unknown encodings.
 *                     Is case-sensitive but shouldn't be.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err server_content_encoding(struct client_state *csp, char **header)
{
#ifdef FEATURE_ZLIB
   if (strstr(*header, "sdch"))
   {
      /*
       * Shared Dictionary Compression over HTTP isn't supported,
       * filtering it anyway is pretty much guaranteed to mess up
       * the encoding.
       */
      csp->content_type |= CT_TABOO;

      /*
       * Log a warning if the user expects the content to be filtered.
       */
      if (content_filters_enabled(csp->action))
      {
         log_error(LOG_LEVEL_INFO,
            "SDCH-compressed content detected, content filtering disabled. "
            "Consider suppressing SDCH offers made by the client.");
      }
   }
   else if (strstr(*header, "gzip"))
   {
      /* Mark for gzip decompression */
      csp->content_type |= CT_GZIP;
   }
   else if (strstr(*header, "deflate"))
   {
      /* Mark for zlib decompression */
      csp->content_type |= CT_DEFLATE;
   }
   else if (strstr(*header, "compress"))
   {
      /*
       * We can't decompress this; therefore we can't filter
       * it either.
       */
      csp->content_type |= CT_TABOO;
   }
#else /* !defined(FEATURE_ZLIB) */
   /*
    * XXX: Using a black list here isn't the right approach.
    *
    *      In case of SDCH, building with zlib support isn't
    *      going to help.
    */
   if (strstr(*header, "gzip") ||
       strstr(*header, "compress") ||
       strstr(*header, "deflate") ||
       strstr(*header, "sdch"))
   {
      /*
       * Body is compressed, turn off pcrs and gif filtering.
       */
      csp->content_type |= CT_TABOO;

      /*
       * Log a warning if the user expects the content to be filtered.
       */
      if (content_filters_enabled(csp->action))
      {
         log_error(LOG_LEVEL_INFO,
            "Compressed content detected, content filtering disabled. "
            "Consider recompiling Privoxy with zlib support or "
            "enable the prevent-compression action.");
      }
   }
#endif /* defined(FEATURE_ZLIB) */

   return JB_ERR_OK;

}


#ifdef FEATURE_ZLIB
/*********************************************************************
 *
 * Function    :  server_adjust_content_encoding
 *
 * Description :  Remove the Content-Encoding header if the
 *                decompression was successful and the content
 *                has been modified.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err server_adjust_content_encoding(struct client_state *csp, char **header)
{
   if ((csp->flags & CSP_FLAG_MODIFIED)
    && (csp->content_type & (CT_GZIP | CT_DEFLATE)))
   {
      /*
       * We successfully decompressed the content,
       * and have to clean the header now, so the
       * client no longer expects compressed data.
       *
       * XXX: There is a difference between cleaning
       * and removing it completely.
       */
      log_error(LOG_LEVEL_HEADER, "Crunching: %s", *header);
      freez(*header);
   }

   return JB_ERR_OK;

}
#endif /* defined(FEATURE_ZLIB) */


/*********************************************************************
 *
 * Function    :  server_adjust_content_length
 *
 * Description :  Adjust Content-Length header if we modified
 *                the body.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err server_adjust_content_length(struct client_state *csp, char **header)
{
   /* Regenerate header if the content was modified. */
   if (csp->flags & CSP_FLAG_MODIFIED)
   {
      const size_t header_length = 50;
      freez(*header);
      *header = malloc(header_length);
      if (*header == NULL)
      {
         return JB_ERR_MEMORY;
      }
      create_content_length_header(csp->content_length, *header, header_length);
      log_error(LOG_LEVEL_HEADER,
         "Adjusted Content-Length to %llu", csp->content_length);
   }

   return JB_ERR_OK;
}


#ifdef FEATURE_CONNECTION_KEEP_ALIVE
/*********************************************************************
 *
 * Function    :  server_save_content_length
 *
 * Description :  Save the Content-Length sent by the server.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err server_save_content_length(struct client_state *csp, char **header)
{
   unsigned long long content_length = 0;
   const char *header_value;

   assert(*(*header+14) == ':');

   header_value = *header + 15;
   if (JB_ERR_OK != get_content_length(header_value, &content_length))
   {
      log_error(LOG_LEVEL_ERROR, "Crunching invalid header: %s", *header);
      freez(*header);
   }
   else
   {
      csp->expected_content_length = content_length;
      csp->flags |= CSP_FLAG_SERVER_CONTENT_LENGTH_SET;
      csp->flags |= CSP_FLAG_CONTENT_LENGTH_SET;
   }

   return JB_ERR_OK;
}
#endif /* def FEATURE_CONNECTION_KEEP_ALIVE */


/*********************************************************************
 *
 * Function    :  server_content_md5
 *
 * Description :  Crumble any Content-MD5 headers if the document was
 *                modified. FIXME: Should we re-compute instead?
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err server_content_md5(struct client_state *csp, char **header)
{
   if (csp->flags & CSP_FLAG_MODIFIED)
   {
      log_error(LOG_LEVEL_HEADER, "Crunching Content-MD5");
      freez(*header);
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  server_content_disposition
 *
 * Description :  If enabled, blocks or modifies the "Content-Disposition" header.
 *                Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err server_content_disposition(struct client_state *csp, char **header)
{
   const char *newval;

   /*
    * Are we messing with the Content-Disposition header?
    */
   if ((csp->action->flags & ACTION_HIDE_CONTENT_DISPOSITION) == 0)
   {
      /* Me tinks not */
      return JB_ERR_OK;
   }

   newval = csp->action->string[ACTION_STRING_CONTENT_DISPOSITION];

   if ((newval == NULL) || (0 == strcmpic(newval, "block")))
   {
      /*
       * Blocking content-disposition header
       */
      log_error(LOG_LEVEL_HEADER, "Crunching %s!", *header);
      freez(*header);
      return JB_ERR_OK;
   }
   else
   {
      /*
       * Replacing Content-Disposition header
       */
      freez(*header);
      *header = strdup("Content-Disposition: ");
      string_append(header, newval);

      if (*header != NULL)
      {
         log_error(LOG_LEVEL_HEADER,
            "Content-Disposition header crunched and replaced with: %s", *header);
      }
   }
   return (*header == NULL) ? JB_ERR_MEMORY : JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  server_last_modified
 *
 * Description :  Changes Last-Modified header to the actual date
 *                to help hide-if-modified-since.
 *                Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err server_last_modified(struct client_state *csp, char **header)
{
   const char *newval;
   time_t last_modified;
   char newheader[50];

   /*
    * Are we messing with the Last-Modified header?
    */
   if ((csp->action->flags & ACTION_OVERWRITE_LAST_MODIFIED) == 0)
   {
      /*Nope*/
      return JB_ERR_OK;
   }

   newval = csp->action->string[ACTION_STRING_LAST_MODIFIED];

   if (0 == strcmpic(newval, "block"))
   {
      /*
       * Blocking Last-Modified header. Useless but why not.
       */
      log_error(LOG_LEVEL_HEADER, "Crunching %s!", *header);
      freez(*header);
      return JB_ERR_OK;
   }
   else if (0 == strcmpic(newval, "reset-to-request-time"))
   {
      /*
       * Setting Last-Modified Header to now.
       */
      char buf[30];
      get_http_time(0, buf, sizeof(buf));
      freez(*header);
      *header = strdup("Last-Modified: ");
      string_append(header, buf);

      if (*header == NULL)
      {
         log_error(LOG_LEVEL_HEADER, "Insufficient memory. Last-Modified header got lost, boohoo.");
      }
      else
      {
         log_error(LOG_LEVEL_HEADER, "Reset to present time: %s", *header);
      }
   }
   else if (0 == strcmpic(newval, "randomize"))
   {
      log_error(LOG_LEVEL_HEADER, "Randomizing: %s", *header);

      if (JB_ERR_OK != parse_time_header(*header, &last_modified))
      {
         log_error(LOG_LEVEL_HEADER,
            "Couldn't parse time in %s (crunching!)", *header);
         freez(*header);
      }
      else
      {
         time_t now;
         struct tm *timeptr = NULL;
         long int rtime;
#ifdef HAVE_GMTIME_R
         struct tm gmt;
#endif
         now = time(NULL);
         rtime = (long int)difftime(now, last_modified);
         if (rtime)
         {
            long int days, hours, minutes, seconds;
            const int negative_delta = (rtime < 0);

            if (negative_delta)
            {
               rtime *= -1;
               log_error(LOG_LEVEL_HEADER, "Server time in the future.");
            }
            rtime = pick_from_range(rtime);
            if (negative_delta)
            {
               rtime *= -1;
            }
            last_modified += rtime;
#ifdef HAVE_GMTIME_R
            timeptr = gmtime_r(&last_modified, &gmt);
#elif defined(MUTEX_LOCKS_AVAILABLE)
            privoxy_mutex_lock(&gmtime_mutex);
            timeptr = gmtime(&last_modified);
#else
            timeptr = gmtime(&last_modified);
#endif
            if ((NULL == timeptr) || !strftime(newheader,
                  sizeof(newheader), "%a, %d %b %Y %H:%M:%S GMT", timeptr))
            {
#if !defined(HAVE_GMTIME_R) && defined(MUTEX_LOCKS_AVAILABLE)
               privoxy_mutex_unlock(&gmtime_mutex);
#endif
               log_error(LOG_LEVEL_ERROR,
                  "Randomizing '%s' failed. Crunching the header without replacement.",
                  *header);
               freez(*header);
               return JB_ERR_OK;
            }
#if !defined(HAVE_GMTIME_R) && defined(MUTEX_LOCKS_AVAILABLE)
            privoxy_mutex_unlock(&gmtime_mutex);
#endif
            freez(*header);
            *header = strdup("Last-Modified: ");
            string_append(header, newheader);

            if (*header == NULL)
            {
               log_error(LOG_LEVEL_ERROR, "Insufficient memory, header crunched without replacement.");
               return JB_ERR_MEMORY;
            }

            days    = rtime / (3600 * 24);
            hours   = rtime / 3600 % 24;
            minutes = rtime / 60 % 60;
            seconds = rtime % 60;

            log_error(LOG_LEVEL_HEADER,
               "Randomized:  %s (added %d da%s %d hou%s %d minut%s %d second%s",
               *header, days, (days == 1) ? "y" : "ys", hours, (hours == 1) ? "r" : "rs",
               minutes, (minutes == 1) ? "e" : "es", seconds, (seconds == 1) ? ")" : "s)");
         }
         else
         {
            log_error(LOG_LEVEL_HEADER, "Randomized ... or not. No time difference to work with.");
         }
      }
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_accept_encoding
 *
 * Description :  Rewrite the client's Accept-Encoding header so that
 *                if doesn't allow compression, if the action applies.
 *                Note: For HTTP/1.0 the absence of the header is enough.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_accept_encoding(struct client_state *csp, char **header)
{
#ifdef FEATURE_COMPRESSION
   if ((csp->config->feature_flags & RUNTIME_FEATURE_COMPRESSION)
      && strstr(*header, "deflate"))
   {
      csp->flags |= CSP_FLAG_CLIENT_SUPPORTS_DEFLATE;
   }
#endif
   if ((csp->action->flags & ACTION_NO_COMPRESSION) != 0)
   {
      log_error(LOG_LEVEL_HEADER, "Suppressed offer to compress content");
      freez(*header);
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_te
 *
 * Description :  Rewrite the client's TE header so that
 *                if doesn't allow compression, if the action applies.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_te(struct client_state *csp, char **header)
{
   if ((csp->action->flags & ACTION_NO_COMPRESSION) != 0)
   {
      freez(*header);
      log_error(LOG_LEVEL_HEADER, "Suppressed offer to compress transfer");
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_referrer
 *
 * Description :  Handle the "referer" config setting properly.
 *                Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_referrer(struct client_state *csp, char **header)
{
   const char *parameter;
   /* booleans for parameters we have to check multiple times */
   int parameter_conditional_block;
   int parameter_conditional_forge;

#ifdef FEATURE_FORCE_LOAD
   /*
    * Since the referrer can include the prefix even
    * if the request itself is non-forced, we must
    * clean it unconditionally.
    *
    * XXX: strclean is too broad
    */
   strclean(*header, FORCE_PREFIX);
#endif /* def FEATURE_FORCE_LOAD */

   if ((csp->action->flags & ACTION_HIDE_REFERER) == 0)
   {
      /* Nothing left to do */
      return JB_ERR_OK;
   }

   parameter = csp->action->string[ACTION_STRING_REFERER];
   assert(parameter != NULL);
   parameter_conditional_block = (0 == strcmpic(parameter, "conditional-block"));
   parameter_conditional_forge = (0 == strcmpic(parameter, "conditional-forge"));

   if (!parameter_conditional_block && !parameter_conditional_forge)
   {
      /*
       * As conditional-block and conditional-forge are the only
       * parameters that rely on the original referrer, we can
       * remove it now for all the others.
       */
      freez(*header);
   }

   if (0 == strcmpic(parameter, "block"))
   {
      log_error(LOG_LEVEL_HEADER, "Referer crunched!");
      return JB_ERR_OK;
   }
   else if (parameter_conditional_block || parameter_conditional_forge)
   {
      return handle_conditional_hide_referrer_parameter(header,
         csp->http->hostport, parameter_conditional_block);
   }
   else if (0 == strcmpic(parameter, "forge"))
   {
      return create_forged_referrer(header, csp->http->hostport);
   }
   else
   {
      /* interpret parameter as user-supplied referer to fake */
      return create_fake_referrer(header, parameter);
   }
}


/*********************************************************************
 *
 * Function    :  client_accept_language
 *
 * Description :  Handle the "Accept-Language" config setting properly.
 *                Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_accept_language(struct client_state *csp, char **header)
{
   const char *newval;

   /*
    * Are we messing with the Accept-Language?
    */
   if ((csp->action->flags & ACTION_HIDE_ACCEPT_LANGUAGE) == 0)
   {
      /*I don't think so*/
      return JB_ERR_OK;
   }

   newval = csp->action->string[ACTION_STRING_LANGUAGE];

   if ((newval == NULL) || (0 == strcmpic(newval, "block")))
   {
      /*
       * Blocking Accept-Language header
       */
      log_error(LOG_LEVEL_HEADER, "Crunching Accept-Language!");
      freez(*header);
      return JB_ERR_OK;
   }
   else
   {
      /*
       * Replacing Accept-Language header
       */
      freez(*header);
      *header = strdup("Accept-Language: ");
      string_append(header, newval);

      if (*header == NULL)
      {
         log_error(LOG_LEVEL_ERROR,
            "Insufficient memory. Accept-Language header crunched without replacement.");
      }
      else
      {
         log_error(LOG_LEVEL_HEADER,
            "Accept-Language header crunched and replaced with: %s", *header);
      }
   }
   return (*header == NULL) ? JB_ERR_MEMORY : JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  crunch_client_header
 *
 * Description :  Crunch client header if it matches a string supplied by the
 *                user. Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success and always succeeds
 *
 *********************************************************************/
static jb_err crunch_client_header(struct client_state *csp, char **header)
{
   const char *crunch_pattern;

   /* Do we feel like crunching? */
   if ((csp->action->flags & ACTION_CRUNCH_CLIENT_HEADER))
   {
      crunch_pattern = csp->action->string[ACTION_STRING_CLIENT_HEADER];

      /* Is the current header the lucky one? */
      if (strstr(*header, crunch_pattern))
      {
         log_error(LOG_LEVEL_HEADER, "Crunching client header: %s (contains: %s)", *header, crunch_pattern);
         freez(*header);
      }
   }
   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_uagent
 *
 * Description :  Handle the "user-agent" config setting properly
 *                and remember its original value to enable browser
 *                bug workarounds. Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_uagent(struct client_state *csp, char **header)
{
   const char *newval;

   if ((csp->action->flags & ACTION_HIDE_USER_AGENT) == 0)
   {
      return JB_ERR_OK;
   }

   newval = csp->action->string[ACTION_STRING_USER_AGENT];
   if (newval == NULL)
   {
      return JB_ERR_OK;
   }

   freez(*header);
   *header = strdup("User-Agent: ");
   string_append(header, newval);

   log_error(LOG_LEVEL_HEADER, "Modified: %s", *header);

   return (*header == NULL) ? JB_ERR_MEMORY : JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_ua
 *
 * Description :  Handle "ua-" headers properly.  Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_ua(struct client_state *csp, char **header)
{
   if ((csp->action->flags & ACTION_HIDE_USER_AGENT) != 0)
   {
      log_error(LOG_LEVEL_HEADER, "crunched User-Agent!");
      freez(*header);
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_from
 *
 * Description :  Handle the "from" config setting properly.
 *                Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_from(struct client_state *csp, char **header)
{
   const char *newval;

   if ((csp->action->flags & ACTION_HIDE_FROM) == 0)
   {
      return JB_ERR_OK;
   }

   freez(*header);

   newval = csp->action->string[ACTION_STRING_FROM];

   /*
    * Are we blocking the e-mail address?
    */
   if ((newval == NULL) || (0 == strcmpic(newval, "block")))
   {
      log_error(LOG_LEVEL_HEADER, "crunched From!");
      return JB_ERR_OK;
   }

   log_error(LOG_LEVEL_HEADER, " modified");

   *header = strdup("From: ");
   string_append(header, newval);

   return (*header == NULL) ? JB_ERR_MEMORY : JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_send_cookie
 *
 * Description :  Crunches the "cookie" header if necessary.
 *                Called from `sed'.
 *
 *                XXX: Stupid name, doesn't send squat.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_send_cookie(struct client_state *csp, char **header)
{
   if (csp->action->flags & ACTION_CRUNCH_OUTGOING_COOKIES)
   {
      log_error(LOG_LEVEL_HEADER, "Crunched outgoing cookie: %s", *header);
      freez(*header);
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_x_forwarded
 *
 * Description :  Handle the "x-forwarded-for" config setting properly,
 *                also used in the add_client_headers list.  Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
jb_err client_x_forwarded(struct client_state *csp, char **header)
{
   if (0 != (csp->action->flags & ACTION_CHANGE_X_FORWARDED_FOR))
   {
      const char *parameter = csp->action->string[ACTION_STRING_CHANGE_X_FORWARDED_FOR];

      if (0 == strcmpic(parameter, "block"))
      {
         freez(*header);
         log_error(LOG_LEVEL_HEADER, "crunched x-forwarded-for!");
      }
      else if (0 == strcmpic(parameter, "add"))
      {
         string_append(header, ", ");
         string_append(header, csp->ip_addr_str);

         if (*header == NULL)
         {
            return JB_ERR_MEMORY;
         }
         log_error(LOG_LEVEL_HEADER,
            "Appended client IP address to %s", *header);
         csp->flags |= CSP_FLAG_X_FORWARDED_FOR_APPENDED;
      }
      else
      {
         log_error(LOG_LEVEL_FATAL,
            "Invalid change-x-forwarded-for parameter: '%s'", parameter);
      }
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_max_forwards
 *
 * Description :  If the HTTP method is OPTIONS or TRACE, subtract one
 *                from the value of the Max-Forwards header field.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_max_forwards(struct client_state *csp, char **header)
{
   int max_forwards;

   if ((0 == strcmpic(csp->http->gpc, "trace")) ||
       (0 == strcmpic(csp->http->gpc, "options")))
   {
      assert(*(*header+12) == ':');
      if (1 == sscanf(*header+12, ": %d", &max_forwards))
      {
         if (max_forwards > 0)
         {
            snprintf(*header, strlen(*header)+1, "Max-Forwards: %d", --max_forwards);
            log_error(LOG_LEVEL_HEADER,
               "Max-Forwards value for %s request reduced to %d.",
               csp->http->gpc, max_forwards);
         }
         else if (max_forwards < 0)
         {
            log_error(LOG_LEVEL_ERROR, "Crunching invalid header: %s", *header);
            freez(*header);
         }
      }
      else
      {
         log_error(LOG_LEVEL_ERROR, "Crunching invalid header: %s", *header);
         freez(*header);
      }
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_host
 *
 * Description :  If the request URI did not contain host and
 *                port information, parse and evaluate the Host
 *                header field.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_host(struct client_state *csp, char **header)
{
   char *p, *q;

   if (strlen(*header) < 7)
   {
      log_error(LOG_LEVEL_HEADER, "Removing empty Host header");
      freez(*header);
      return JB_ERR_OK;
   }

   if (!csp->http->hostport || (*csp->http->hostport == '*') ||
       *csp->http->hostport == ' ' || *csp->http->hostport == '\0')
   {

      p = strdup_or_die((*header)+6);
      chomp(p);
      q = strdup_or_die(p);

      freez(csp->http->hostport);
      csp->http->hostport = p;
      freez(csp->http->host);
      csp->http->host = q;
      q = strchr(csp->http->host, ':');
      if (q != NULL)
      {
         /* Terminate hostname and evaluate port string */
         *q++ = '\0';
         csp->http->port = atoi(q);
      }
      else
      {
         csp->http->port = csp->http->ssl ? 443 : 80;
      }

      log_error(LOG_LEVEL_HEADER, "New host and port from Host field: %s = %s:%d",
                csp->http->hostport, csp->http->host, csp->http->port);
   }

   /* Signal client_host_adder() to return right away */
   csp->flags |= CSP_FLAG_HOST_HEADER_IS_SET;

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_if_modified_since
 *
 * Description :  Remove or modify the If-Modified-Since header.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_if_modified_since(struct client_state *csp, char **header)
{
   char newheader[50];
#ifdef HAVE_GMTIME_R
   struct tm gmt;
#endif
   struct tm *timeptr = NULL;
   time_t tm = 0;
   const char *newval;
   char * endptr;

   if (0 == strcmpic(*header, "If-Modified-Since: Wed, 08 Jun 1955 12:00:00 GMT"))
   {
      /*
       * The client got an error message because of a temporary problem,
       * the problem is gone and the client now tries to revalidate our
       * error message on the real server. The revalidation would always
       * end with the transmission of the whole document and there is
       * no need to expose the bogus If-Modified-Since header.
       */
      log_error(LOG_LEVEL_HEADER, "Crunching useless If-Modified-Since header.");
      freez(*header);
   }
   else if (csp->action->flags & ACTION_HIDE_IF_MODIFIED_SINCE)
   {
      newval = csp->action->string[ACTION_STRING_IF_MODIFIED_SINCE];

      if ((0 == strcmpic(newval, "block")))
      {
         log_error(LOG_LEVEL_HEADER, "Crunching %s", *header);
         freez(*header);
      }
      else /* add random value */
      {
         if (JB_ERR_OK != parse_time_header(*header, &tm))
         {
            log_error(LOG_LEVEL_HEADER,
               "Couldn't parse time in %s (crunching!)", *header);
            freez(*header);
         }
         else
         {
            long int hours, minutes, seconds;
            long int rtime = strtol(newval, &endptr, 0);
            const int negative_range = (rtime < 0);

            if (rtime)
            {
               log_error(LOG_LEVEL_HEADER, "Randomizing: %s (random range: %d minut%s)",
                  *header, rtime, (rtime == 1 || rtime == -1) ? "e": "es");
               if (negative_range)
               {
                  rtime *= -1;
               }
               rtime *= 60;
               rtime = pick_from_range(rtime);
            }
            else
            {
               log_error(LOG_LEVEL_ERROR, "Random range is 0. Assuming time transformation test.",
                  *header);
            }
            tm += rtime * (negative_range ? -1 : 1);
#ifdef HAVE_GMTIME_R
            timeptr = gmtime_r(&tm, &gmt);
#elif defined(MUTEX_LOCKS_AVAILABLE)
            privoxy_mutex_lock(&gmtime_mutex);
            timeptr = gmtime(&tm);
#else
            timeptr = gmtime(&tm);
#endif
            if ((NULL == timeptr) || !strftime(newheader,
                  sizeof(newheader), "%a, %d %b %Y %H:%M:%S GMT", timeptr))
            {
#if !defined(HAVE_GMTIME_R) && defined(MUTEX_LOCKS_AVAILABLE)
               privoxy_mutex_unlock(&gmtime_mutex);
#endif
               log_error(LOG_LEVEL_ERROR,
                  "Randomizing '%s' failed. Crunching the header without replacement.",
                  *header);
               freez(*header);
               return JB_ERR_OK;
            }
#if !defined(HAVE_GMTIME_R) && defined(MUTEX_LOCKS_AVAILABLE)
            privoxy_mutex_unlock(&gmtime_mutex);
#endif
            freez(*header);
            *header = strdup("If-Modified-Since: ");
            string_append(header, newheader);

            if (*header == NULL)
            {
               log_error(LOG_LEVEL_HEADER, "Insufficient memory, header crunched without replacement.");
               return JB_ERR_MEMORY;
            }

            hours   = rtime / 3600;
            minutes = rtime / 60 % 60;
            seconds = rtime % 60;

            log_error(LOG_LEVEL_HEADER,
               "Randomized:  %s (%s %d hou%s %d minut%s %d second%s",
               *header, (negative_range) ? "subtracted" : "added", hours,
               (hours == 1) ? "r" : "rs", minutes, (minutes == 1) ? "e" : "es",
               seconds, (seconds == 1) ? ")" : "s)");
         }
      }
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_if_none_match
 *
 * Description :  Remove the If-None-Match header.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_if_none_match(struct client_state *csp, char **header)
{
   if (csp->action->flags & ACTION_CRUNCH_IF_NONE_MATCH)
   {
      log_error(LOG_LEVEL_HEADER, "Crunching %s", *header);
      freez(*header);
   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_x_filter
 *
 * Description :  Disables filtering if the client set "X-Filter: No".
 *                Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK on success
 *
 *********************************************************************/
jb_err client_x_filter(struct client_state *csp, char **header)
{
   if (0 == strcmpic(*header, "X-Filter: No"))
   {
      if (!(csp->config->feature_flags & RUNTIME_FEATURE_HTTP_TOGGLE))
      {
         log_error(LOG_LEVEL_INFO, "Ignored the client's request to fetch without filtering.");
      }
      else
      {
         if (csp->action->flags & ACTION_FORCE_TEXT_MODE)
         {
            log_error(LOG_LEVEL_HEADER,
               "force-text-mode overruled the client's request to fetch without filtering!");
         }
         else
         {
            csp->content_type = CT_TABOO; /* XXX: This hack shouldn't be necessary */
            csp->flags |= CSP_FLAG_NO_FILTERING;
            log_error(LOG_LEVEL_HEADER, "Accepted the client's request to fetch without filtering.");
         }
         log_error(LOG_LEVEL_HEADER, "Crunching %s", *header);
         freez(*header);
      }
   }
   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_range
 *
 * Description :  Removes Range, Request-Range and If-Range headers if
 *                content filtering is enabled and the range doesn't
 *                start at byte 0.
 *
 *                If the client's version of the document has been
 *                altered by Privoxy, the server could interpret the
 *                range differently than the client intended in which
 *                case the user could end up with corrupted content.
 *
 *                If the range starts at byte 0 this isn't an issue
 *                so the header can pass. Partial requests like this
 *                are used to render preview images for videos without
 *                downloading the whole video.
 *
 *                While HTTP doesn't require that range requests are
 *                honoured and the client could simply abort the download
 *                after receiving a sufficient amount of data, various
 *                clients don't handle complete responses to range
 *                requests gracefully and emit misleading error messages
 *                instead.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *          2  :  header = On input, pointer to header to modify.
 *                On output, pointer to the modified header, or NULL
 *                to remove the header.  This function frees the
 *                original string if necessary.
 *
 * Returns     :  JB_ERR_OK
 *
 *********************************************************************/
static jb_err client_range(struct client_state *csp, char **header)
{
   if (content_filters_enabled(csp->action)
      && (0 != strncmpic(strstr(*header, ":"), ": bytes=0-", 10)))
   {
      log_error(LOG_LEVEL_HEADER, "Content filtering is enabled."
         " Crunching: \'%s\' to prevent range-mismatch problems.", *header);
      freez(*header);
   }

   return JB_ERR_OK;
}

/* the following functions add headers directly to the header list */

/*********************************************************************
 *
 * Function    :  client_host_adder
 *
 * Description :  Adds the Host: header field if it is missing.
 *                Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_host_adder(struct client_state *csp)
{
   char *p;
   jb_err err;

   if (csp->flags & CSP_FLAG_HOST_HEADER_IS_SET)
   {
      /* Header already set by the client, nothing to do. */
      return JB_ERR_OK;
   }

   if (!csp->http->hostport || !*(csp->http->hostport))
   {
      log_error(LOG_LEVEL_ERROR, "Destination host unknown.");
      return JB_ERR_PARSE;
   }

   /*
    * remove 'user:pass@' from 'proto://user:pass@host'
    */
   if ((p = strchr( csp->http->hostport, '@')) != NULL)
   {
      p++;
   }
   else
   {
      p = csp->http->hostport;
   }

   /* XXX: Just add it, we already made sure that it will be unique */
   log_error(LOG_LEVEL_HEADER, "addh-unique: Host: %s", p);
   err = enlist_unique_header(csp->headers, "Host", p);
   return err;

}


/*********************************************************************
 *
 * Function    :  client_xtra_adder
 *
 * Description :  Used in the add_client_headers list.  Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_xtra_adder(struct client_state *csp)
{
   struct list_entry *lst;
   jb_err err;

   for (lst = csp->action->multi[ACTION_MULTI_ADD_HEADER]->first;
        lst ; lst = lst->next)
   {
      log_error(LOG_LEVEL_HEADER, "addh: %s", lst->str);
      err = enlist(csp->headers, lst->str);
      if (err)
      {
         return err;
      }

   }

   return JB_ERR_OK;
}


/*********************************************************************
 *
 * Function    :  client_x_forwarded_for_adder
 *
 * Description :  Used in the add_client_headers list.  Called from `sed'.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *
 * Returns     :  JB_ERR_OK on success, or
 *                JB_ERR_MEMORY on out-of-memory error.
 *
 *********************************************************************/
static jb_err client_x_forwarded_for_adder(struct client_state *csp)
{
   char *header = NULL;
   jb_err err;

   if (!((csp->action->flags & ACTION_CHANGE_X_FORWARDED_FOR)
         && (0 == strcmpic(csp->action->string[ACTION_STRING_CHANGE_X_FORWARDED_FOR], "add")))
      || (csp->flags & CSP_FLAG_X_FORWARDED_FOR_APPENDED))
   {
      /*
       * If we aren't adding X-Forwarded-For headers,
       * or we already appended an existing X-Forwarded-For
       * header, there's nothing left to do here.
       */
      return JB_ERR_OK;
   }