[privoxy.git] / doc / STANDARDS.txt

** Introduction


This set of standards is designed to make our lives easier. It is
developed with the simple goal of helping us keep the "new and
improved Junkbusters" consistent and reliable.  Thus making
maintenance easier and increasing chances of success of the
project.

And that of course comes back to us as individuals. If we can
increase our development and product efficiencies then we can
solve more of the request for changes/improvements and in general 
feel good about ourselves.  ;->


** Using Comments


* Comment, Comment, Comment

Explanation:

Comment as much as possible without commenting the obvious.  For
example do not comment "aVariable is equal to bVariable".  Instead
explain why aVariable should be equal to the bVariable.  Just
because a person can read code does not mean they will understand
why or what is being done.  A reader may spend a lot more time
figuring out what is going on when a simple comment or explanation
would have prevented the extra research.  Please help your brother
IJB'ers out!

The comments will also help justify the intent of the code.  If the
comment describes something different than what the code is doing
then maybe a programming error is occurring.

Example:

/* if page size greater than 1k ... */
if ( PageLength() > 1024 )
{
    ... "block" the page up ...
}

/* if page size is small, send it in blocks */
if ( PageLength() > 1024 )
{
    ... "block" the page up ...
}

This demonstrates 2 cases of "what not to do".  The first is a
"syntax comment".  The second is a comment that does not fit what
is actually being done.


* Use blocks for comments

Explanation:

Comments can help or they can clutter.  They help when they are
differentiated from the code they describe.  One line comments do
not offer effective separation between the comment and the code.
Block identifiers do, by surrounding the code with a clear,
definable pattern.

Example:

/*********************************************************************
 * This will stand out clearly in your code!
 *********************************************************************/
if ( thisVariable == thatVariable )
{
   DoSomethingVeryImportant();
}


/* unfortunately, this may not */
if ( thisVariable == thatVariable )
{
   DoSomethingVeryImportant();
}


if ( thisVariable == thatVariable ) /* this may not either */
{
   DoSomethingVeryImportant();
}


Exception:

If you are trying to add a small logic comment and do not wish to
"disrubt" the flow of the code, feel free to use a 1 line comment
which is NOT on the same line as the code.


* Keep Comments on their own line

Explanation:

It goes back to the question of readability.  If the comment is on
the same line as the code it will be harder to read than the
comment that is on its own line.

There are three exceptions to this rule, which should be violated
freely and often: during the definition of variables, at the end
of closing braces, when used to comment parameters.

Example:

/*********************************************************************
 * This will stand out clearly in your code,
 * But the second example won't.
 *********************************************************************/
if ( thisVariable == thatVariable )
{
   DoSomethingVeryImportant();
}

if ( thisVariable == thatVariable ) /*can you see me?*/
{
   DoSomethingVeryImportant(); /*not easily*/
}


/*********************************************************************
 * But, the encouraged exceptions:
 *********************************************************************/
int urls_read     = 0;     /* # of urls read + rejected */
int urls_rejected = 0;     /* # of urls rejected */

if ( 1 == X )
{
   DoSomethingVeryImportant();
}


short DoSomethingVeryImportant(
   short firstParam,   /* represents something */
   short nextParam     /* represents something else */ )
{
...code here...

}   /* -END- DoSomethingVeryImportant */


* Comment each logical step

Explanation:

Logical steps should be commented to help others follow the
intent of the written code and comments will make the code more
readable.

If you have 25 lines of code without a comment, you should
probably go back into it to see where you forgot to put one.

Most "for", "while", "do", etc... loops _probably_ need a
comment.  After all, these are usually major logic containers.


* Comment All Functions Thoroughly

Explanation:

A reader of the code should be able to look at the comments just
prior to the beginning of a function and discern the reason for
its existence and the consequences of using it.  The reader
should not have to read through the code to determine if a given
function is safe for a desired use.  The proper information
thoroughly presented at the introduction of a function not only
saves time for subsequent maintenance or debugging, it more
importantly aids in code reuse by allowing a user to determine
the safety and applicability of any function for the problem at
hand.  As a result of such benefits, all functions should contain
the information presented in the addendum section of this
document.


* Comment at the end of braces if the content is more than one screen length

Explanation:

Each closing brace should be followed on the same line by a
comment that describes the origination of the brace if the
original brace is off of the screen, or otherwise far away from
the closing brace.  This will simplify the debugging, maintenance,
and readability of the code.

As a suggestion , use the following flags to make the comment and
its brace more readable:

use following a closing brace:
   } /* -END- if() or while () or etc... */

Example:

if ( 1 == X )
{
   DoSomethingVeryImportant();
   ...some long list of commands...
} /* -END- if x is 1 */

or:

if ( 1 == X )
{
   DoSomethingVeryImportant();
   ...some long list of commands...
} /* -END- if ( 1 == X ) */


** Naming Conventions


* Variable Names

Explanation:

Capitalize the first letter of each word in a variable name
except the first word.

Example:

int msIis5Hack = 0;


Instead of:

int ms_iis5_hack = 0;

Note: This is not an "enforcable" issue since too much of IJB uses
the underscore (_) to seperate words.

Status: developer-descrition.  This item is at developer
discrection and is currently open to debate by the IJB developer
team.  Too much of IJB violates this proposed standard.


* Function Names

Explanation:

Capitalize the first letter of each word in a function name.

Example:

int loadAclFile(struct client_state *csp)

Instead of:

int load_aclfile(struct client_state *csp)

Status: developer-descrition.  This item is at developer
discrection and is currently open to debate by the IJB developer
team.  Too much of IJB violates this proposed standard.

Note: on the 2 above "standards" ... if enough of the current
developer team agrees, I can use XEmacs to apply a few regular
expressions to make the current tree comply with these 2 points.
Otherwise I will remove them from this document.  Afterall, there
is no need to add to the "multiple personallity" syndrome that IJB
now has.


* Header file prototypes

Explanation:

Use a descriptive parameter name in the function prototype in
header files.  Use the same parameter name in the header file
that you use in the c file.

Example:

(.h) extern int load_aclfile(struct client_state *csp);
(.c) int load_aclfile(struct client_state *csp)

Instead of:
(.h) extern int load_aclfile(struct client_state *);   or
(.h) extern int load_aclfile();


18.  Ennumerations, and #defines

Explanation:

Use all capital letters, with underscores between words.

Example:

(enumeration) : enum Boolean { FALSE, TRUE };
(#define) : #define DEFAULT_SIZE 100;

Note: We should have a standard naming scheme for Symbols that
toggle a feature in the precompiler, and the constants used by that
feature. I'd propose that the toggles should be just one word, with
a common prefix, and that any depandant constants should be
prefixed by that word.

The prefix could be WITH_, HAVE_, ENABLE_, FEATURE_ etc.

Status: I see some this in the code currently!  Anybody "figured"
out a standard way to do this?

Example:

#define ENABLE_FORCE 1

#ifdef ENABLE_FORCE
#define FORCE_PREFIX blah
#endif /* def ENABLE_FORCE */


* Constants

Explanation:

Spell common words out entirely (do not remove vowels).

Use only widely-known domain acronyms and abbreviations.
Capitalize all letters of an acronym.

Use underscore (_) to separate adjacent acronyms and
abbreviations.  Never terminate a name with an underscore.

Example:

#define USE_IMAGE_LIST 1

Instead of:

#define _USE_IMAGE_LIST 1   or
#define USE_IMAGE_LIST_ 1   or
#define use_image_list  1   or
#define UseImageList    1


** Using Space


* Put braces on a line by themselves.

Explanation:

The brace needs to be on a line all by itself, not at the end of
the statement.  Curly braces should line up with the construct
that they're associated with.  This practice makes it easier to
identify the opening and closing braces for a block.

Example:

if ( this == that )
{
   ...
}

Instead of:

if ( this == that ) {
...
}

or

if ( this == that ) { ...  }

Note: In the special case that the if-statement is inside a loop,
and it is trivial, i.e. it tests for a condidtion that is obvious
from the purpose of the block, one-liners as above may optically
preserve the loop structure and make it easier to read.

Status: developer-descrition.

Example exception:

while (more lines are read)
{
   /* Please document what is/is not a comment line here */
   if (it's a comment) continue;

   do_something(line);
}


* ALL control statements should have a block

Explanation:

Using braces to make a block will make your code more readable
and less prone to error.  All control statements should have a
block defined.

Example:

if ( this == that )
{
   DoSomething();
}

Instead of:

if ( this == that )
   DoSomething();

or

if ( this == that ) DoSomething();

Note: see the exception above.


* Do not belabor/blow-up boolean expressions

Example:

structure->flag = (condition);

Instead of:

if (condition)
{
   structure->flag = 1;
}
else
{
   structure->flag = 0;
}

Note: The former is readable and consice.  The later is wordy and
inefficient.  Please assume that any new developer has at least a
"good" knowledge of C/C++.  (Hope I do not offend by that last
comment ... 8-)


* Use white space freely because it is free

Explanation:

Make it readable.  The notable exception to using white space
freely is listed in the next guideline.

Example:

int firstValue   = 0;
int someValue    = 0;
int anotherValue = 0;
int thisVariable = 0;

if ( thisVariable == thatVariable )

firstValue = oldValue + ( ( someValue - anotherValue ) - whatever )


* Don't use white space around structure operators

Explanation:

- structure pointer operator ( "->" ) 
- member operator ( "." )
- functions and parentheses

It is a general coding practice to put pointers, references, and
function parentheses next to names.  With spaces, the connection
between the object and variable/function name is not as clear.

Example:

aStruct->aMember;
aStruct.aMember;
FunctionName();

Instead of:
aStruct -> aMember;
aStruct .  aMember;
FunctionName ();


* Make the last brace of a function stand out

Example:

int function1( ... )
{
   ...code...
   return( retCode );

}   /* -END- function1 */


int function2( ... )
{
}   /* -END- function2 */


Instead of:

int function1( ... )
{
   ...code...
   return( retCode );
}
int function2( ... )
{
}

NOTE: Use 1 blank line before the closing brace and 2 lines
afterwards.  This makes the end of function standout to the most
casual viewer.  Although function comments help seperate
functions, this is still a good coding practice.  In fact, I
follow these rules when using blocks in "for", "while", "do"
loops, and long if {} statements too.  After all whitespace is
free!

Status: developer-descrition on the number of blank lines.
Enforced is the end of function comments.


* Use 3 character indentions

Explanation:

If some use 8 character TABs and some use 3 character TABs, the
code can look *very* ragged.  So use 3 character indentions only.
If you like to use TABs, pass your code through a filter such as
"expand -t3" before checking in your code.

Example:

static const char * const url_code_map[256] =
{
   NULL, ...
};


int function1( ... )
{
   if ( 1 )
   {
      return( ALWAYS_TRUE );
   }
   else
   {
      return( HOW_DID_YOU_GET_HERE );
   }

   return( NEVER_GETS_HERE );

}


** Initializing


* Initialize all variables

Explanation:

Do not assume that the variables declared will not be used until
after they have been assigned a value somewhere else in the
code.  Remove the chance of accidentally using an unassigned
variable.

Example:

short anShort = 0;
float aFloat  = 0;
struct *ptr = NULL;

NOTE: It is much easier to debug a SIGSEGV if the message says
you are trying to access memory address 00000000 and not
129FA012; or arrayPtr[20] causes a SIGSEV vs. arrayPtr[0].

Status: developer-descrition if and only if the variable is
assigned a value "shortly after" declaration.


** Functions


* Name functions that return a boolean as a question.

Explanation:

Value should be phrased as a question that would logically be
answered as a true or false statement

Example:

ShouldWeBlockThis();
ContainsAnImage();
IsWebPageBlank();


* Always specify a return type for a function.

Explanation:

The default return for a function is an int.  To avoid ambiguity,
create a return for a function when the return has a purpose, and
create a void return type if the function does not need to return
anything.


* Minimize function calls when iterating by using variables

Explanation:

It is easy to write the following code, and a clear argument can
be made that the code is easy to understand:

Example:

for ( size_t curr = 0; curr < PageLength(); curr ++ )
{
   ....
}

Unfortunately, this makes a function call for each and every
iteration.  This increases the overhead in the program, because
the compiler has to look up the function each time, call it, and
return a value.  Depending on what occurs in the PageLength()
call, it might even be creating and destroying structures with
each iteration, even though in each case it is comparing "curr"
to the same value, over and over.  Remember too - even a call to
PageLength() is a function call, with the same overhead.

Instead of using a function call during the iterations, assign
the value to a variable, and evaluate using the variable.

Example:

size_t len = PageLength();

for ( size_t curr = 0; curr < len; curr ++ )
{
   ....
}

Exceptions: if the value of PageLength() *may* change or could
*potentially* change, then you must code the function call in the
for/while loop.


* Pass and Return by Const Reference

Explanation:

This allows a developer to define a const pointer and call your
function.  If your function does not have the const keyword, we
may not be able to use your function.  Consider strcmp, if it
were defined as:
   extern int strcmp( char *s1, char *s2 );

I could then not use it to compare argv's in main:
   int main( int argc, const char *argv[] )
   {
     strcmp( argv[0], "junkbusters" );
   }

Both these pointers are *const*!  If the c runtime library
maintainers do it, we should too.


* Pass and Return by Value

Explanation:

Most structures cannot fit onto a normal stack entry (i.e. they
are not 4 bytes or less).  Aka, a function declaration like:
   int load_aclfile(struct client_state csp)

would not work.  So, to be consistent, we should declare all
prototypes with "pass by value":
   int load_aclfile(struct client_state *csp)


* Use #include <fileName> and #include "fileName" for locals

Explanation:

Your include statements should contain the file name without a
path.  The path should be listed in the Makefile, using -I as
processor directive to search the indicated paths.  An exception
to this would be for some proprietary software that utilizes a
partial path to distinguish their header files from system or
other header files.

Example:

#include <iostream.h>     /* This is not a local include */
#include "config.h"       /* This IS a local include */

Exception:

/* This is not a local include, but requires a path element. */
#include <sys/fileName.h>


* Provide multiple inclusion protection

Explanation:

Prevents compiler and linker errors resulting from redefinition of
items.

Wrap each header file with the following syntax to prevent multiple
inclusions of the file.  Of course, replace FILENAME_UPPERCASE with
your file name, with "." Changed to "_", and make it uppercase.

Example (from project.h):

#ifndef _PROJECT_H
#define _PROJECT_H

...

#endif /* ndef _PROJECT_H */


* Where Possible, Use Forward Struct Declaration Instead of Includes

Explanation:

Useful in headers that include pointers to other struct's.
Modifications to excess header files may cause needless compiles.

Example:

/*********************************************************************
 * We're avoiding an include statement here!
 *********************************************************************/
struct file_list;
file_list *xyz;

NOTE: If you declare "file_list xyz;" (without the pointer), then
including the proper header file is necessary.  If you only want to
prototype a pointer, however, the header file is unneccessary.  Use
with discrection.


** General Coding Practices


* Provide a default case for all switch statements

Explanation:

What you think is guaranteed is never really guaranteed.  The
value that you don't think you need to check is the one that
someday will be passed.  So, to protect yourself from the unknown,
always have a default step in a switch statement.

Example:

switch( hash_string( cmd ) )
{
   case hash_actions_file :
      ... code ...
      break;

   case hash_confdir :
      ... code ...
      break;

   default :
      log_error( ... );
      ... more code ...
      continue; / break; / exit(1); / etc ...
} /* end switch( hash_string(cmd) ) */

NOTE: If you already have a default condition, you are obviously
exempt from this point.  Of note, most of the WIN32 code calls
`DefWindowProc' after the switch statement.  This API call
*should* be included in a default statement.

Another NOTE: This is not so much a readability issue as a robust
programming issue.  The "anomly code goes here" may be no more
than a print to the STDERR stream (as in load_config).  Or it may 
really be an ABEND condition.  Programmer discretion is advised.


* Try to avoid falling through cases in a switch statement.

Explanation:

In general, you will want to have a 'break' statement within each
'case' of a switch statement.  This allows for the code to be more
readable and understandable, and furthermore can prevent unwanted
surprises if someone else later gets creative and moves the code
around.

The language allows you to plan the fall through from one case
statement to another simply by omitting the break statement within
the case statement.  This feature does have benefits, but should
only be used in rare cases.  In general, use a break statement for
each case statement.

If you choose to allow fall through, you should comment both the
fact of the fall through and reason why you felt it was
necessary.


* Use 'long' or 'short' Instead of 'int'

Explanation:

On 32-bit platforms, int usually has the range of long.  On 16-bit
platforms, int has the range of short.

Status: open-to-debate.  In the case of most FSF projects
(including X/GNU-Emacs), there are typedefs to int4, int8, int16,
(or equivalence ... I forget the exact typedefs now).  Should we
add these to IJB now that we have a "configure" script?


* Declare each variable and struct on its own line.

Explanation:

It can be tempting to declare a series of variables all on one
line.  Don't.

Example:

long a = 0;
long b = 0;
long c = 0;

Instead of:

long a, b, c;

Reasons:
- there is more room for comments on the individual variables
- easier to add new variables without messing up the original ones
- when searching on a variable to find its type, there is less
  clutter to "visually" eliminate

Exceptions: when you want to declare a bunch of loop variables or
other trivial variables; feel free to declare them on 1 line.  You
should, although, provide a good comment on their functions.

Status: developer-descrition.


* Use malloc/zalloc sparingly

Explanation:

Create a local stuct (on the stack) if the variable will live
and die within the context of one function call.

Only "malloc" a struct (on the heap) if the variable's life will
extend beyond the context of one function call.

Example:

If a function creates a struct and stores a pointer to it in a
list, then it should definately be allocated via `malloc'.


* The Programmer Who Uses 'malloc' is Responsible for Ensuring 'free'

Explanation:

If you have to "malloc" an instance, you are responsible for
insuring that the instance is `free'd, even if the deallocation
event falls within some other programmer's code.  You are also
responsible for ensuring that deletion is timely (i.e. not too
soon, not too late).  This is known as "low-coupling" and is a
"good thing (tm)".  You may need to offer a free/unload/destuctor
type function to accomodate this.

Example:

static void unload_re_filterfile(void *f) { ... }
int load_re_filterfile(struct client_state *csp) { ... }

Exceptions:

The developer cannot be expected to provide `free'ing functions for 
C run-time library functions ... such as `strdup'.

Status: developer-descrition.  The "main" use of this standard is
for allocating and freeing data structures (complex or nested).


* Add loaders to the `file_list' structure and in order

Explanation:

I have ordered all of the "blocker" file code to be in alpha
order.  It is easier to add/read new blockers when you expect a
certain order.

NOTE: It may appear that the alpha order is broken in places by
POPUP tests coming before PCRS tests.  But since POPUPs can also
be referred to as KILLPOPUPs, it is clear that it should come
first.


* "Uncertain" new code and/or changes to exitinst code, use FIXME

Explanation:

If you have enough confidence in new code or confidence in your
changes, but are not *quite* sure of the reprocussions, add this:

/* FIXME: this code has a logic error on platform XYZ,
 * attempthing to fix
 */
#ifdef PLATFORM
   ...changed code here...
#endif

or:

/* FIXME: I think the original author really meant this... */
   ...changed code here...

or:

/* FIXME: new code that *may* break something else... */
   ...new code here...

NOTE: If you make it clear that this may or may not be a "good
thing (tm)", it will be easier to identify and include in the
project (or conversly exclude from the project).


** Addendum: Template for files and function comment blocks:


Example for file comments:

const char FILENAME_rcs[] = "$Id: $";
/*********************************************************************
 *
 * File        :  $Source: $
 *
 * Purpose     :  (Fill me in with a good description!)
 *
 * Copyright   :  Written by and Copyright (C) 2001 the SourceForge
 *                IJBSWA team.  http://ijbswa.sourceforge.net
 *
 *                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.
 *
 * Revisions   :
 *    $Log: $
 *
 *********************************************************************/


#include "config.h"

...necessary include files for us to do our work...

const char FILENAME_h_rcs[] = FILENAME_H_VERSION;


NOTE: This declares the rcs variables that should be added to the 
"show-proxy-args" page.  If this is a brand new creation by you,
you are free to change the "Copyright" section to represent the
rights you wish to maintain.

NOTE: The formfeed character that is present right after the
comment flower box is handy for (X|GNU)Emacs users to skip the
verbige and get to the heart of the code (via `forward-page' and
`backward-page').  Please include it if you can.


Example for file header comments:

#ifndef _FILENAME_H
#define _FILENAME_H
#define FILENAME_H_VERSION "$Id: $"
/*********************************************************************
 *
 * File        :  $Source: $
 *
 * Purpose     :  (Fill me in with a good description!)
 *
 * Copyright   :  Written by and Copyright (C) 2001 the SourceForge
 *                IJBSWA team.  http://ijbswa.sourceforge.net
 *
 *                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.
 *
 * Revisions   :
 *    $Log: $
 *
 *********************************************************************/
\f

#include "project.h"

#ifdef __cplusplus
extern "C" {
#endif

... function headers here ...


/* Revision control strings from this header and associated .c file */
extern const char FILENAME_rcs[];
extern const char FILENAME_h_rcs[];


#ifdef __cplusplus
} /* extern "C" */
#endif

#endif /* ndef _FILENAME_H */

/*
  Local Variables:
  tab-width: 3
  end:
*/


Example for function comments:

/*********************************************************************
 *
 * Function    :  FUNCTION_NAME
 *
 * Description :  (Fill me in with a good description!)
 *
 * Parameters  :
 *          1  :  param1 = pointer to an important thing
 *          2  :  x      = pointer to something else
 *
 * Returns     :  0 => Ok, everything else is an error.
 *
 *********************************************************************/
int FUNCTION_NAME( void *param1, const char *x )
{
...
   return( 0 );

}


NOTE: If we all follow this practice, we should be able to parse
our code to create a "self-documenting" web page.


** Local variables for this standards file


* Hopefully this will be in outline-mode soon.


/*
  Local Variables:
  tab-width: 3
  fill-column: 67
  mode: auto-fill
  end:
*/