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CONTRIBUTING.md

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Contributing clixon code

The clixon project welcomes contributions from the community.

Licensing

A contribution must follow the CLIXON licensing with the dual licensing: either Apache License, Version 2.0 or GNU General Public License Version 3.

Note especially, the contribution license agreement (CLA) is described in the CLA section of the Apache License, Version 2.0.

C style

Clixon uses 4-char space indentation.

Function declarations

Functions in C code are written as follows:

static int
myfn(int           par1,
     my_structure *par2)
{
    int           retval = -1;
    my_structure *ms;

    ms = NULL;

Notes:

  1. The return type of the function and all qualifers on first line (static int)
  2. Function name and first parameter on second line, thereafter each parameter on own line
  3. Each parameter indented to match the "longest" (my_structure)
  4. Pointer declarations written: type *p, not: type* p.
  5. All local variables in a function declared at top of function, not inline with C-statements.
  6. Local variables can be initialized with scalars or constants, not eg malloc or functions with return values that need to be checked for errors
  7. There is a single empty line between local variable declarations and the first function statement.

Function signatures are declared in include files or in forward declaration using "one-line" syntax, unless very long:

static int myfn(int par1, my_structure *par2);

Errors

Errors are typically declared as follows:

    if (myfn(0) < 0){
       clicon_err(OE_UNIX, EINVAL, "myfn");
       goto done;
    }

All function returns that have return values must be checked

Default return values form a function are:

  • 0 OK
  • -1 Fatal Error

In some cases, Clixon uses three-value returns as follows:

  • 1 OK
  • 0 Invalid
  • -1 Fatal error

Return values

Clixon uses goto:s only to get a single point of exit functions as follows:

{
    int retval = -1;

    ...
    retval = 0;
  done:
    return retval
}

Notes:

  1. Use only a single return statement in a function
  2. Do not use of goto:s in other ways

Comments

Use /* */. Use // only for temporal comments.

Do not use "======", ">>>>>" or "<<<<<<" in comments since git merge conflict uses that.

Format ints

Use:

  • %zu for size_t
  • PRIu64 for uint64
  • %p for pointers

Include files

Avoid include statements in .h files, place them in .c files whenever possible.

The reason is to avoid deep include chains where file dependencies are difficult to analyze and understand. If include statements are only placed in .c files, there is only a single level of include file dependencies.

The drawback is that the same include file may need to be repeated in many .c files.

Structs

Struct fields should have a prefix to distinguish them from other struct fields. The prefix should use an abbreviation of the struct name.

Example:

  struct my_struct{
    int   ms_foo;
    char *ms_string[42];
  }

where ms_ is the prefix and is an abbreviation of my_struct.

Global variables

Try to avoid global variables.

If you absolutely need a global variable, try to contain it as static within a single C-file, ie do not declare it extern and use it elsewhere.

Also, always prepend a global variable with _, underscore.

Testing

For a new feature, it is important to write (or extend) a clixon test, including some functionality tests and preferably some negative tests. Tests are then run automatically as regression on commit by github actions.

These tests are also the basis for more extensive CI tests run by the project which include: