Add SOCKS5 username/password support
[privoxy.git] / gateway.c
index 3049530..03e56ee 100644 (file)
--- a/gateway.c
+++ b/gateway.c
@@ -1,4 +1,3 @@
-const char gateway_rcs[] = "$Id: gateway.c,v 1.63 2009/10/01 16:07:33 fabiankeil Exp $";
 /*********************************************************************
  *
  * File        :  $Source: /cvsroot/ijbswa/current/gateway.c,v $
@@ -7,7 +6,7 @@ const char gateway_rcs[] = "$Id: gateway.c,v 1.63 2009/10/01 16:07:33 fabiankeil
  *                using a "forwarder" (i.e. HTTP proxy and/or a SOCKS4
  *                or SOCKS5 proxy).
  *
- * Copyright   :  Written by and Copyright (C) 2001-2009 the
+ * Copyright   :  Written by and Copyright (C) 2001-2017 the
  *                Privoxy team. http://www.privoxy.org/
  *
  *                Based on the Internet Junkbuster originally written
@@ -66,9 +65,12 @@ const char gateway_rcs[] = "$Id: gateway.c,v 1.63 2009/10/01 16:07:33 fabiankeil
 #include "jbsockets.h"
 #include "gateway.h"
 #include "miscutil.h"
+#include "list.h"
+#include "parsers.h"
+
 #ifdef FEATURE_CONNECTION_KEEP_ALIVE
 #ifdef HAVE_POLL
-#ifdef __GLIBC__ 
+#ifdef __GLIBC__
 #include <sys/poll.h>
 #else
 #include <poll.h>
@@ -76,8 +78,6 @@ const char gateway_rcs[] = "$Id: gateway.c,v 1.63 2009/10/01 16:07:33 fabiankeil
 #endif /* HAVE_POLL */
 #endif /* def FEATURE_CONNECTION_KEEP_ALIVE */
 
-const char gateway_h_rcs[] = GATEWAY_H_VERSION;
-
 static jb_socket socks4_connect(const struct forward_spec * fwd,
                                 const char * target_host,
                                 int target_port,
@@ -88,21 +88,24 @@ static jb_socket socks5_connect(const struct forward_spec *fwd,
                                 int target_port,
                                 struct client_state *csp);
 
+enum {
+   SOCKS4_REQUEST_GRANTED        =  90,
+   SOCKS4_REQUEST_REJECT         =  91,
+   SOCKS4_REQUEST_IDENT_FAILED   =  92,
+   SOCKS4_REQUEST_IDENT_CONFLICT =  93
+};
 
-#define SOCKS_REQUEST_GRANTED          90
-#define SOCKS_REQUEST_REJECT           91
-#define SOCKS_REQUEST_IDENT_FAILED     92
-#define SOCKS_REQUEST_IDENT_CONFLICT   93
-
-#define SOCKS5_REQUEST_GRANTED             0
-#define SOCKS5_REQUEST_FAILED              1
-#define SOCKS5_REQUEST_DENIED              2
-#define SOCKS5_REQUEST_NETWORK_UNREACHABLE 3
-#define SOCKS5_REQUEST_HOST_UNREACHABLE    4
-#define SOCKS5_REQUEST_CONNECTION_REFUSED  5
-#define SOCKS5_REQUEST_TTL_EXPIRED         6
-#define SOCKS5_REQUEST_PROTOCOL_ERROR      7
-#define SOCKS5_REQUEST_BAD_ADDRESS_TYPE    8
+enum {
+   SOCKS5_REQUEST_GRANTED             = 0,
+   SOCKS5_REQUEST_FAILED              = 1,
+   SOCKS5_REQUEST_DENIED              = 2,
+   SOCKS5_REQUEST_NETWORK_UNREACHABLE = 3,
+   SOCKS5_REQUEST_HOST_UNREACHABLE    = 4,
+   SOCKS5_REQUEST_CONNECTION_REFUSED  = 5,
+   SOCKS5_REQUEST_TTL_EXPIRED         = 6,
+   SOCKS5_REQUEST_PROTOCOL_ERROR      = 7,
+   SOCKS5_REQUEST_BAD_ADDRESS_TYPE    = 8
+};
 
 /* structure of a socks client operation */
 struct socks_op {
@@ -128,7 +131,6 @@ static const char socks_userid[] = "anonymous";
 #ifdef FEATURE_CONNECTION_SHARING
 
 #define MAX_REUSABLE_CONNECTIONS 100
-static unsigned int keep_alive_timeout = DEFAULT_KEEP_ALIVE_TIMEOUT;
 
 static struct reusable_connection reusable_connection[MAX_REUSABLE_CONNECTIONS];
 static int mark_connection_unused(const struct reusable_connection *connection);
@@ -209,7 +211,7 @@ void remember_connection(const struct reusable_connection *connection)
    if (!free_slot_found)
    {
       log_error(LOG_LEVEL_CONNECT,
-        "No free slots found to remembering socket for %s:%d. Last slot %d.",
+        "No free slots found to remember socket for %s:%d. Last slot %d.",
         connection->host, connection->port, slot);
       privoxy_mutex_unlock(&connection_reuse_mutex);
       close_socket(connection->sfd);
@@ -217,18 +219,15 @@ void remember_connection(const struct reusable_connection *connection)
    }
 
    assert(NULL != connection->host);
-   reusable_connection[slot].host = strdup(connection->host);
-   if (NULL == reusable_connection[slot].host)
-   {
-      log_error(LOG_LEVEL_FATAL, "Out of memory saving socket.");
-   }
+   reusable_connection[slot].host = strdup_or_die(connection->host);
    reusable_connection[slot].sfd = connection->sfd;
    reusable_connection[slot].port = connection->port;
    reusable_connection[slot].in_use = 0;
    reusable_connection[slot].timestamp = connection->timestamp;
-   reusable_connection->request_sent = connection->request_sent;
-   reusable_connection->response_received = connection->response_received;
+   reusable_connection[slot].request_sent = connection->request_sent;
+   reusable_connection[slot].response_received = connection->response_received;
    reusable_connection[slot].keep_alive_timeout = connection->keep_alive_timeout;
+   reusable_connection[slot].requests_sent_total = connection->requests_sent_total;
 
    assert(reusable_connection[slot].gateway_host == NULL);
    assert(reusable_connection[slot].gateway_port == 0);
@@ -239,11 +238,7 @@ void remember_connection(const struct reusable_connection *connection)
    reusable_connection[slot].forwarder_type = connection->forwarder_type;
    if (NULL != connection->gateway_host)
    {
-      reusable_connection[slot].gateway_host = strdup(connection->gateway_host);
-      if (NULL == reusable_connection[slot].gateway_host)
-      {
-         log_error(LOG_LEVEL_FATAL, "Out of memory saving gateway_host.");
-      }
+      reusable_connection[slot].gateway_host = strdup_or_die(connection->gateway_host);
    }
    else
    {
@@ -253,11 +248,7 @@ void remember_connection(const struct reusable_connection *connection)
 
    if (NULL != connection->forward_host)
    {
-      reusable_connection[slot].forward_host = strdup(connection->forward_host);
-      if (NULL == reusable_connection[slot].forward_host)
-      {
-         log_error(LOG_LEVEL_FATAL, "Out of memory saving forward_host.");
-      }
+      reusable_connection[slot].forward_host = strdup_or_die(connection->forward_host);
    }
    else
    {
@@ -270,7 +261,6 @@ void remember_connection(const struct reusable_connection *connection)
 #endif /* def FEATURE_CONNECTION_SHARING */
 
 
-#ifdef FEATURE_CONNECTION_KEEP_ALIVE
 /*********************************************************************
  *
  * Function    :  mark_connection_closed
@@ -293,13 +283,13 @@ void mark_connection_closed(struct reusable_connection *closed_connection)
    closed_connection->request_sent = 0;
    closed_connection->response_received = 0;
    closed_connection->keep_alive_timeout = 0;
+   closed_connection->requests_sent_total = 0;
    closed_connection->forwarder_type = SOCKS_NONE;
    freez(closed_connection->gateway_host);
    closed_connection->gateway_port = 0;
    freez(closed_connection->forward_host);
    closed_connection->forward_port = 0;
 }
-#endif /* def FEATURE_CONNECTION_KEEP_ALIVE */
 
 
 #ifdef FEATURE_CONNECTION_SHARING
@@ -335,16 +325,12 @@ void forget_connection(jb_socket sfd)
             sfd, reusable_connection[slot].host,
             reusable_connection[slot].port, slot);
          mark_connection_closed(&reusable_connection[slot]);
-         privoxy_mutex_unlock(&connection_reuse_mutex);
-
-         return;
+         break;
       }
    }
 
-   log_error(LOG_LEVEL_CONNECT,
-      "Socket %d already forgotten or never remembered.", sfd);
-
    privoxy_mutex_unlock(&connection_reuse_mutex);
+
 }
 #endif /* def FEATURE_CONNECTION_SHARING */
 
@@ -383,7 +369,9 @@ int connection_destination_matches(const struct reusable_connection *connection,
          && strcmpic(connection->gateway_host, fwd->gateway_host))
        && (connection->gateway_host != fwd->gateway_host))
    {
-      log_error(LOG_LEVEL_CONNECT, "Gateway mismatch.");
+      log_error(LOG_LEVEL_CONNECT,
+         "Gateway mismatch. Previous gateway: %s. Current gateway: %s",
+         connection->gateway_host, fwd->gateway_host);
       return FALSE;
    }
 
@@ -392,7 +380,9 @@ int connection_destination_matches(const struct reusable_connection *connection,
          && strcmpic(connection->forward_host, fwd->forward_host))
       && (connection->forward_host != fwd->forward_host))
    {
-      log_error(LOG_LEVEL_CONNECT, "Forwarding proxy mismatch.");
+      log_error(LOG_LEVEL_CONNECT,
+         "Forwarding proxy mismatch. Previous proxy: %s. Current proxy: %s",
+         connection->forward_host, fwd->forward_host);
       return FALSE;
    }
 
@@ -444,7 +434,7 @@ int close_unusable_connections(void)
             close_socket(reusable_connection[slot].sfd);
             mark_connection_closed(&reusable_connection[slot]);
          }
-         else if (!socket_is_still_usable(reusable_connection[slot].sfd))
+         else if (!socket_is_still_alive(reusable_connection[slot].sfd))
          {
             log_error(LOG_LEVEL_CONNECT,
                "The connection to %s:%d in slot %d is no longer usable. "
@@ -503,13 +493,14 @@ static jb_socket get_reusable_connection(const struct http_request *http,
             reusable_connection[slot].in_use = TRUE;
             sfd = reusable_connection[slot].sfd;
             log_error(LOG_LEVEL_CONNECT,
-               "Found reusable socket %d for %s:%d in slot %d. "
-               "Timestamp made %d seconds ago. Timeout: %d. Latency: %d.",
+               "Found reusable socket %d for %s:%d in slot %d. Timestamp made %d "
+               "seconds ago. Timeout: %d. Latency: %d. Requests served: %d",
                sfd, reusable_connection[slot].host, reusable_connection[slot].port,
                slot, time(NULL) - reusable_connection[slot].timestamp,
                reusable_connection[slot].keep_alive_timeout,
                (int)(reusable_connection[slot].response_received -
-               reusable_connection[slot].request_sent));
+               reusable_connection[slot].request_sent),
+               reusable_connection[slot].requests_sent_total);
             break;
          }
       }
@@ -565,25 +556,6 @@ static int mark_connection_unused(const struct reusable_connection *connection)
    return socket_found;
 
 }
-
-
-/*********************************************************************
- *
- * Function    :  set_keep_alive_timeout
- *
- * Description :  Sets the timeout after which open
- *                connections will no longer be reused.
- *
- * Parameters  :
- *          1  :  timeout = The timeout in seconds.
- *
- * Returns     :  void
- *
- *********************************************************************/
-void set_keep_alive_timeout(unsigned int timeout)
-{
-   keep_alive_timeout = timeout;
-}
 #endif /* def FEATURE_CONNECTION_SHARING */
 
 
@@ -640,6 +612,7 @@ jb_socket forwarded_connect(const struct forward_spec * fwd,
    switch (fwd->type)
    {
       case SOCKS_NONE:
+      case FORWARD_WEBSERVER:
          sfd = connect_to(dest_host, dest_port, csp);
          break;
       case SOCKS_4:
@@ -647,12 +620,13 @@ jb_socket forwarded_connect(const struct forward_spec * fwd,
          sfd = socks4_connect(fwd, dest_host, dest_port, csp);
          break;
       case SOCKS_5:
+      case SOCKS_5T:
          sfd = socks5_connect(fwd, dest_host, dest_port, csp);
          break;
       default:
          /* Should never get here */
          log_error(LOG_LEVEL_FATAL,
-            "SOCKS4 impossible internal error - bad SOCKS type.");
+            "Internal error in forwarded_connect(). Bad proxy type: %d", fwd->type);
    }
 
    if (JB_INVALID_SOCKET != sfd)
@@ -667,6 +641,51 @@ jb_socket forwarded_connect(const struct forward_spec * fwd,
 }
 
 
+#ifdef FUZZ
+/*********************************************************************
+ *
+ * Function    :  socks_fuzz
+ *
+ * Description :  Wrapper around socks[45]_connect() used for fuzzing.
+ *
+ * Parameters  :
+ *          1  :  csp = Current client state (buffers, headers, etc...)
+ *
+ * Returns     :  JB_ERR_OK or JB_ERR_PARSE
+ *
+ *********************************************************************/
+extern jb_err socks_fuzz(struct client_state *csp)
+{
+   jb_socket socket;
+   static struct forward_spec fwd;
+   char target_host[] = "fuzz.example.org";
+   int target_port = 12345;
+
+   fwd.gateway_host = strdup_or_die("fuzz.example.org");
+   fwd.gateway_port = 12345;
+
+   fwd.type = SOCKS_4A;
+   socket = socks4_connect(&fwd, target_host, target_port, csp);
+
+   if (JB_INVALID_SOCKET != socket)
+   {
+      fwd.type = SOCKS_5;
+      socket = socks5_connect(&fwd, target_host, target_port, csp);
+   }
+
+   if (JB_INVALID_SOCKET == socket)
+   {
+      log_error(LOG_LEVEL_ERROR, "%s", csp->error_message);
+      return JB_ERR_PARSE;
+   }
+
+   log_error(LOG_LEVEL_INFO, "Input looks like an acceptable socks response");
+
+   return JB_ERR_OK;
+
+}
+#endif
+
 /*********************************************************************
  *
  * Function    :  socks4_connect
@@ -721,7 +740,7 @@ static jb_socket socks4_connect(const struct forward_spec * fwd,
    if (err)
    {
       log_error(LOG_LEVEL_CONNECT, "socks4_connect: %s", errstr);
-      csp->error_message = strdup(errstr); 
+      csp->error_message = strdup(errstr);
       errno = EINVAL;
       return(JB_INVALID_SOCKET);
    }
@@ -790,24 +809,23 @@ static jb_socket socks4_connect(const struct forward_spec * fwd,
 
    c->vn          = 4;
    c->cd          = 1;
-   c->dstport[0]  = (unsigned char)((target_port       >> 8  ) & 0xff);
-   c->dstport[1]  = (unsigned char)((target_port             ) & 0xff);
-   c->dstip[0]    = (unsigned char)((web_server_addr   >> 24 ) & 0xff);
-   c->dstip[1]    = (unsigned char)((web_server_addr   >> 16 ) & 0xff);
-   c->dstip[2]    = (unsigned char)((web_server_addr   >>  8 ) & 0xff);
-   c->dstip[3]    = (unsigned char)((web_server_addr         ) & 0xff);
-
+   c->dstport[0]  = (unsigned char)((target_port       >> 8 ) & 0xff);
+   c->dstport[1]  = (unsigned char)((target_port            ) & 0xff);
+   c->dstip[0]    = (unsigned char)((web_server_addr   >> 24) & 0xff);
+   c->dstip[1]    = (unsigned char)((web_server_addr   >> 16) & 0xff);
+   c->dstip[2]    = (unsigned char)((web_server_addr   >>  8) & 0xff);
+   c->dstip[3]    = (unsigned char)((web_server_addr        ) & 0xff);
+
+#ifdef FUZZ
+   sfd = 0;
+#else
    /* pass the request to the socks server */
    sfd = connect_to(fwd->gateway_host, fwd->gateway_port, csp);
 
    if (sfd == JB_INVALID_SOCKET)
    {
-      /*
-       * XXX: connect_to should fill in the exact reason.
-       * Most likely resolving the IP of the forwarder failed.
-       */
-      errstr = "connect_to failed: see logfile for details";
-      err = 1;
+      /* The error an its reason have already been logged by connect_to()  */
+      return(JB_INVALID_SOCKET);
    }
    else if (write_socket(sfd, (char *)c, csiz))
    {
@@ -816,7 +834,23 @@ static jb_socket socks4_connect(const struct forward_spec * fwd,
       err = 1;
       close_socket(sfd);
    }
-   else if (read_socket(sfd, buf, sizeof(buf)) != sizeof(*s))
+   else if (!data_is_available(sfd, csp->config->socket_timeout))
+   {
+      if (socket_is_still_alive(sfd))
+      {
+         errstr = "SOCKS4 negotiation timed out";
+      }
+      else
+      {
+         errstr = "SOCKS4 negotiation got aborted by the server";
+      }
+      log_error(LOG_LEVEL_CONNECT, "socks4_connect: %s", errstr);
+      err = 1;
+      close_socket(sfd);
+   }
+   else
+#endif
+       if (read_socket(sfd, buf, sizeof(buf)) != sizeof(*s))
    {
       errstr = "SOCKS4 negotiation read failed.";
       log_error(LOG_LEVEL_CONNECT, "socks4_connect: %s", errstr);
@@ -826,24 +860,24 @@ static jb_socket socks4_connect(const struct forward_spec * fwd,
 
    if (err)
    {
-      csp->error_message = strdup(errstr);      
+      csp->error_message = strdup(errstr);
       return(JB_INVALID_SOCKET);
    }
 
    switch (s->cd)
    {
-      case SOCKS_REQUEST_GRANTED:
+      case SOCKS4_REQUEST_GRANTED:
          return(sfd);
-      case SOCKS_REQUEST_REJECT:
+      case SOCKS4_REQUEST_REJECT:
          errstr = "SOCKS request rejected or failed.";
          errno = EINVAL;
          break;
-      case SOCKS_REQUEST_IDENT_FAILED:
+      case SOCKS4_REQUEST_IDENT_FAILED:
          errstr = "SOCKS request rejected because "
             "SOCKS server cannot connect to identd on the client.";
          errno = EACCES;
          break;
-      case SOCKS_REQUEST_IDENT_CONFLICT:
+      case SOCKS4_REQUEST_IDENT_CONFLICT:
          errstr = "SOCKS request rejected because "
             "the client program and identd report "
             "different user-ids.";
@@ -888,7 +922,7 @@ static const char *translate_socks5_error(int socks_error)
       case SOCKS5_REQUEST_NETWORK_UNREACHABLE:
          return "SOCKS5 network unreachable";
       case SOCKS5_REQUEST_HOST_UNREACHABLE:
-         return "SOCKS5 host unreachable";
+         return "SOCKS5 destination host unreachable";
       case SOCKS5_REQUEST_CONNECTION_REFUSED:
          return "SOCKS5 connection refused";
       case SOCKS5_REQUEST_TTL_EXPIRED:
@@ -904,6 +938,7 @@ static const char *translate_socks5_error(int socks_error)
    }
 }
 
+
 /*********************************************************************
  *
  * Function    :  socks5_connect
@@ -928,9 +963,12 @@ static jb_socket socks5_connect(const struct forward_spec *fwd,
                                 int target_port,
                                 struct client_state *csp)
 {
+#define SIZE_SOCKS5_REPLY_IPV4 10
+#define SIZE_SOCKS5_REPLY_IPV6 22
+#define SOCKS5_REPLY_DIFFERENCE (SIZE_SOCKS5_REPLY_IPV6 - SIZE_SOCKS5_REPLY_IPV4)
    int err = 0;
    char cbuf[300];
-   char sbuf[30];
+   char sbuf[SIZE_SOCKS5_REPLY_IPV6];
    size_t client_pos = 0;
    int server_size = 0;
    size_t hostlen = 0;
@@ -962,7 +1000,7 @@ static jb_socket socks5_connect(const struct forward_spec *fwd,
       err = 1;
    }
 
-   if (fwd->type != SOCKS_5)
+   if ((fwd->type != SOCKS_5) && (fwd->type != SOCKS_5T))
    {
       /* Should never get here */
       log_error(LOG_LEVEL_FATAL,
@@ -979,6 +1017,10 @@ static jb_socket socks5_connect(const struct forward_spec *fwd,
       return(JB_INVALID_SOCKET);
    }
 
+#ifdef FUZZ
+   sfd = 0;
+   if (!err && read_socket(sfd, sbuf, 2) != 2)
+#else
    /* pass the request to the socks server */
    sfd = connect_to(fwd->gateway_host, fwd->gateway_port, csp);
 
@@ -986,13 +1028,24 @@ static jb_socket socks5_connect(const struct forward_spec *fwd,
    {
       errstr = "socks5 server unreachable";
       log_error(LOG_LEVEL_CONNECT, "socks5_connect: %s", errstr);
+      /* Free the generic error message provided by connect_to() */
+      freez(csp->error_message);
       csp->error_message = strdup(errstr);
       return(JB_INVALID_SOCKET);
    }
 
    client_pos = 0;
    cbuf[client_pos++] = '\x05'; /* Version */
-   cbuf[client_pos++] = '\x01'; /* One authentication method supported */
+
+   if (fwd->auth_username && fwd->auth_password)
+   {
+      cbuf[client_pos++] = '\x02'; /* Two authentication methods supported */
+      cbuf[client_pos++] = '\x02'; /* Username/password */
+   }
+   else
+   {
+      cbuf[client_pos++] = '\x01'; /* One authentication method supported */
+   }
    cbuf[client_pos++] = '\x00'; /* The no authentication authentication method */
 
    if (write_socket(sfd, cbuf, client_pos))
@@ -1003,8 +1056,21 @@ static jb_socket socks5_connect(const struct forward_spec *fwd,
       close_socket(sfd);
       return(JB_INVALID_SOCKET);
    }
+   if (!data_is_available(sfd, csp->config->socket_timeout))
+   {
+      if (socket_is_still_alive(sfd))
+      {
+         errstr = "SOCKS5 negotiation timed out";
+      }
+      else
+      {
+         errstr = "SOCKS5 negotiation got aborted by the server";
+      }
+      err = 1;
+   }
 
-   if (read_socket(sfd, sbuf, sizeof(sbuf)) != 2)
+   if (!err && read_socket(sfd, sbuf, sizeof(sbuf)) != 2)
+#endif
    {
       errstr = "SOCKS5 negotiation read failed";
       err = 1;
@@ -1022,7 +1088,51 @@ static jb_socket socks5_connect(const struct forward_spec *fwd,
       err = 1;
    }
 
-   if (!err && (sbuf[1] != '\x00'))
+   if (!err && (sbuf[1] == '\x02'))
+   {
+      /* check cbuf overflow */
+      size_t auth_len = strlen(fwd->auth_username) + strlen(fwd->auth_password) + 3;
+      if (auth_len > sizeof(cbuf))
+      {
+         errstr = "SOCKS5 username and/or password too long";
+         err = 1;
+      }
+
+      if (!err)
+      {
+         client_pos = 0;
+         cbuf[client_pos++] = '\x01'; /* Version */
+         cbuf[client_pos++] = (char)strlen(fwd->auth_username);
+
+         memcpy(cbuf + client_pos, fwd->auth_username, strlen(fwd->auth_username));
+         client_pos += strlen(fwd->auth_username);
+         cbuf[client_pos++] = (char)strlen(fwd->auth_password);
+         memcpy(cbuf + client_pos, fwd->auth_password, strlen(fwd->auth_password));
+         client_pos += strlen(fwd->auth_password);
+
+         if (write_socket(sfd, cbuf, client_pos))
+         {
+            errstr = "SOCKS5 negotiation auth write failed";
+            csp->error_message = strdup(errstr);
+            log_error(LOG_LEVEL_CONNECT, "%s", errstr);
+            close_socket(sfd);
+            return(JB_INVALID_SOCKET);
+         }
+
+         if (read_socket(sfd, sbuf, sizeof(sbuf)) != 2)
+         {
+            errstr = "SOCKS5 negotiation auth read failed";
+            err = 1;
+         }
+      }
+
+      if (!err && (sbuf[1] != '\x00'))
+      {
+         errstr = "SOCKS5 authentication failed";
+         err = 1;
+      }
+   }
+   else if (!err && (sbuf[1] != '\x00'))
    {
       errstr = "SOCKS5 negotiation protocol error";
       err = 1;
@@ -1051,9 +1161,10 @@ static jb_socket socks5_connect(const struct forward_spec *fwd,
    cbuf[client_pos++] = (char)((target_port >> 8) & 0xff);
    cbuf[client_pos++] = (char)((target_port     ) & 0xff);
 
+#ifndef FUZZ
    if (write_socket(sfd, cbuf, client_pos))
    {
-      errstr = "SOCKS5 negotiation read failed";
+      errstr = "SOCKS5 negotiation write failed";
       csp->error_message = strdup(errstr);
       log_error(LOG_LEVEL_CONNECT, "%s", errstr);
       close_socket(sfd);
@@ -1061,39 +1172,102 @@ static jb_socket socks5_connect(const struct forward_spec *fwd,
       return(JB_INVALID_SOCKET);
    }
 
-   server_size = read_socket(sfd, sbuf, sizeof(sbuf));
-   if (server_size < 3)
+   /*
+    * Optimistically send the HTTP request with the initial
+    * SOCKS request if the user enabled the use of Tor extensions,
+    * the CONNECT method isn't being used (in which case the client
+    * doesn't send data until it gets our 200 response) and the
+    * client request has actually been completely read already.
+    */
+   if ((fwd->type == SOCKS_5T) && (csp->http->ssl == 0)
+      && (csp->flags & CSP_FLAG_CLIENT_REQUEST_COMPLETELY_READ))
    {
-      errstr = "SOCKS5 negotiation read failed";
-      err = 1;
-   }
-   else if (server_size > 20)
-   {
-      /* This is somewhat unexpected but doesn't realy matter. */
-      log_error(LOG_LEVEL_CONNECT, "socks5_connect: read %d bytes "
-         "from socks server. Would have accepted up to %d.",
-         server_size, sizeof(sbuf));
-   }
+      char *client_headers = list_to_text(csp->headers);
+      size_t header_length;
 
-   if (!err && (sbuf[0] != '\x05'))
-   {
-      errstr = "SOCKS5 negotiation protocol version error";
-      err = 1;
+      if (client_headers == NULL)
+      {
+         log_error(LOG_LEVEL_FATAL, "Out of memory rebuilding client headers");
+      }
+      list_remove_all(csp->headers);
+      header_length= strlen(client_headers);
+
+      log_error(LOG_LEVEL_CONNECT,
+         "Optimistically sending %d bytes of client headers intended for %s",
+         header_length, csp->http->hostport);
+
+      if (write_socket(sfd, client_headers, header_length))
+      {
+         log_error(LOG_LEVEL_CONNECT,
+            "optimistically writing header to: %s failed: %E", csp->http->hostport);
+         freez(client_headers);
+         return(JB_INVALID_SOCKET);
+      }
+      freez(client_headers);
+      if (csp->expected_client_content_length != 0)
+      {
+         unsigned long long buffered_request_bytes =
+            (unsigned long long)(csp->client_iob->eod - csp->client_iob->cur);
+         log_error(LOG_LEVEL_CONNECT,
+            "Optimistically sending %llu bytes of client body. Expected %llu",
+            csp->expected_client_content_length, buffered_request_bytes);
+         assert(csp->expected_client_content_length == buffered_request_bytes);
+         if (write_socket(sfd, csp->client_iob->cur, buffered_request_bytes))
+         {
+            log_error(LOG_LEVEL_CONNECT,
+               "optimistically writing %llu bytes of client body to: %s failed: %E",
+               buffered_request_bytes, csp->http->hostport);
+            return(JB_INVALID_SOCKET);
+         }
+         clear_iob(csp->client_iob);
+      }
    }
+#endif
 
-   if (!err && (sbuf[2] != '\x00'))
+   server_size = read_socket(sfd, sbuf, SIZE_SOCKS5_REPLY_IPV4);
+   if (server_size != SIZE_SOCKS5_REPLY_IPV4)
    {
-      errstr = "SOCKS5 negotiation protocol error";
-      err = 1;
+      errstr = "SOCKS5 negotiation read failed";
    }
-
-   if (!err)
+   else
    {
-      if (sbuf[1] == SOCKS5_REQUEST_GRANTED)
+      if (sbuf[0] != '\x05')
       {
-         return(sfd);
+         errstr = "SOCKS5 negotiation protocol version error";
+      }
+      else if (sbuf[2] != '\x00')
+      {
+         errstr = "SOCKS5 negotiation protocol error";
+      }
+      else if (sbuf[1] != SOCKS5_REQUEST_GRANTED)
+      {
+         errstr = translate_socks5_error(sbuf[1]);
+      }
+      else
+      {
+         if (sbuf[3] == '\x04')
+         {
+            /*
+             * The address field contains an IPv6 address
+             * which means we didn't get the whole reply
+             * yet. Read and discard the rest of it to make
+             * sure it isn't treated as HTTP data later on.
+             */
+            server_size = read_socket(sfd, sbuf, SOCKS5_REPLY_DIFFERENCE);
+            if (server_size != SOCKS5_REPLY_DIFFERENCE)
+            {
+               errstr = "SOCKS5 negotiation read failed (IPv6 address)";
+            }
+         }
+         else if (sbuf[3] != '\x01')
+         {
+             errstr = "SOCKS5 reply contains unsupported address type";
+         }
+         if (errstr == NULL)
+         {
+            return(sfd);
+         }
       }
-      errstr = translate_socks5_error(sbuf[1]);
    }
 
    assert(errstr != NULL);