Creating Extensions

We'll start with the creation of a very simple extension at first, which basically does nothing more than implement a function that returns the integer it receives as parameter. Example 46-2 shows the source.

Example 46-2. A simple extension.

/* include standard header */
#include "php.h"

/* declaration of functions to be exported */
ZEND_FUNCTION(first_module);

/* compiled function list so Zend knows what's in this module */
zend_function_entry firstmod_functions[] =
{
    ZEND_FE(first_module, NULL)
    {NULL, NULL, NULL}
};

/* compiled module information */
zend_module_entry firstmod_module_entry =
{
    STANDARD_MODULE_HEADER,
    "First Module",
    firstmod_functions,
    NULL, 
    NULL, 
    NULL, 
    NULL, 
    NULL,
    NO_VERSION_YET,
    STANDARD_MODULE_PROPERTIES
};

/* implement standard "stub" routine to introduce ourselves to Zend */
#if COMPILE_DL_FIRST_MODULE
ZEND_GET_MODULE(firstmod)
#endif

/* implement function that is meant to be made available to PHP */
ZEND_FUNCTION(first_module)
{
    long parameter;

    if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "l", &parameter) == FAILURE) {
        return;
    }

    RETURN_LONG(parameter);
}

This code contains a complete PHP module. We'll explain the source code in detail shortly, but first we'd like to discuss the build process. (This will allow the impatient to experiment before we dive into API discussions.)

Note: The example source makes use of some features introduced with the Zend version used in PHP 4.1.0 and above, it won't compile with older PHP 4.0.x versions.

Compiling Modules

There are basically two ways to compile modules:

Use the provided "make" mechanism in the ext directory, which also allows building of dynamic loadable modules.
Compile the sources manually.

The first method should definitely be favored, since, as of PHP 4.0, this has been standardized into a sophisticated build process. The fact that it is so sophisticated is also its drawback, unfortunately - it's hard to understand at first. We'll provide a more detailed introduction to this later in the chapter, but first let's work with the default files.

The second method is good for those who (for some reason) don't have the full PHP source tree available, don't have access to all files, or just like to juggle with their keyboard. These cases should be extremely rare, but for the sake of completeness we'll also describe this method.

Compiling Using Make. To compile the sample sources using the standard mechanism, copy all their subdirectories to the ext directory of your PHP source tree. Then run buildconf, which will create an updated configure script containing appropriate options for the new extension. By default, all the sample sources are disabled, so you don't have to fear breaking your build process.

After you run buildconf, configure --help shows the following additional modules:

--enable-array_experiments   BOOK: Enables array experiments
  --enable-call_userland       BOOK: Enables userland module
  --enable-cross_conversion    BOOK: Enables cross-conversion module
  --enable-first_module        BOOK: Enables first module
  --enable-infoprint           BOOK: Enables infoprint module
  --enable-reference_test      BOOK: Enables reference test module
  --enable-resource_test       BOOK: Enables resource test module
  --enable-variable_creation   BOOK: Enables variable-creation module

The module shown earlier in Example 46-2 can be enabled with --enable-first_module or --enable-first_module=yes.

Compiling Manually. To compile your modules manually, you need the following commands:

Action	Command
Compiling	cc -fpic -DCOMPILE_DL=1 -I/usr/local/include -I. -I.. -I../Zend -c -o `<your_object_file>` `<your_c_file>`
Linking	cc -shared -L/usr/local/lib -rdynamic -o `<your_module_file>` `<your_object_file(s)>`

The command to compile the module simply instructs the compiler to generate position-independent code (-fpic shouldn't be omitted) and additionally defines the constant COMPILE_DL to tell the module code that it's compiled as a dynamically loadable module (the test module above checks for this; we'll discuss it shortly). After these options, it specifies a number of standard include paths that should be used as the minimal set to compile the source files.

Note: All include paths in the example are relative to the directory ext. If you're compiling from another directory, change the pathnames accordingly. Required items are the PHP directory, the Zend directory, and (if necessary), the directory in which your module resides.

The link command is also a plain vanilla command instructing linkage as a dynamic module.

You can include optimization options in the compilation command, although these have been omitted in this example (but some are included in the makefile template described in an earlier section).

Note: Compiling and linking manually as a static module into the PHP binary involves very long instructions and thus is not discussed here. (It's not very efficient to type all those commands.)