How to modify the extension of PHP system function

PHP is a high-level programming language popular for its ease of learning and developing powerful web applications. In PHP, system functions are widely used, but sometimes these functions need to be extended or modified to meet specific needs. In this article, we will introduce how to modify the extension of PHP system functions.

1. Extending a function

PHP’s functions are written in C, so we can extend or Modify existing functions. The first step in extending a function is to create a custom module and load it into PHP.

The following are the steps to extend the abs function:

1.1 Create the file

First, we need to create our own library file in the PHP source code. We can name it "ext/mymod/mymod.c" and write the code into that file. In this example, we will rewrite the abs function to return the absolute value of an integer.

1.2 Define the function

Next, we need to define the function of our extension:

#include "php.h"

PHP_FUNCTION(my_abs)
{
    long arg;

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

    if (arg < 0) {
        RETURN_LONG(-arg);
    } else {
        RETURN_LONG(arg);
    }
}

1.3 Define the module

Finally, we need to define our module , enabling it to be loaded in PHP. We need to add this to the end of the extension file we created:

zend_function_entry mymod_functions[] = {
    PHP_FE(my_abs, NULL)
    PHP_FE_END
};

zend_module_entry mymod_module_entry = {
    STANDARD_MODULE_HEADER,
    "mymod",
    mymod_functions, /* Functions */
    NULL, /* MINIT */
    NULL, /* MSHUTDOWN */
    NULL, /* RINIT */
    NULL, /* RSHUTDOWN */
    NULL, /* MINFO */
    "1.0.0", /* Version */
    STANDARD_MODULE_PROPERTIES
};

#ifdef ZEND_MODULE_API_NO
# undef ZEND_MODULE_API_NO
#endif
#define ZEND_MODULE_API_NO 20151012

ZEND_GET_MODULE(mymod)

1.4 Compiling and Installing the Extension

Finally, we need to compile our extension into a shared object using the following command:

phpize
./configure --enable-mymod
make && make install

2. Modify a function

Sometimes, we need to modify the behavior of PHP built-in functions. For example, we can modify the mail function so that messages are logged to a file rather than sent to the mail server. The following is an implementation:

2.1 Rewriting functions

We can redefine PHP system functions as our own functions:

#include "php.h"
#include "ext/standard/mail.h"

int my_mail(char *to, char *subject, char *message, char *headers, char *additional_params)
{
    FILE *fp;

    fp = fopen("/tmp/mail.log", "a");
    fprintf(fp, "To: %s\nSubject: %s\nHeaders: %s\nMessage: %s\n", to, subject, headers, message);
    fclose(fp);

    return SUCCESS;
}

2.2 Modify modules

We need to modify our module to define the new function as an alternative to the PHP mail function:

zend_function_entry mymod_functions[] = {
    PHP_FE(mail, NULL)
    PHP_FE_END
};

zend_module_entry mymod_module_entry = {
    STANDARD_MODULE_HEADER,
    "mymod",
    mymod_functions, /* Functions */
    NULL, /* MINIT */
    NULL, /* MSHUTDOWN */
    NULL, /* RINIT */
    NULL, /* RSHUTDOWN */
    NULL, /* MINFO */
    "1.0.0", /* Version */
    STANDARD_MODULE_PROPERTIES
};

static int my_override_mail()
{
    zend_string *fname = zend_string_init("mail", sizeof("mail")-1, 0);
    zend_internal_function *fn = (zend_internal_function*) zend_hash_find_ptr(CG(function_table), fname);

    if (!fn || !(fn->flags & ZEND_ACC_INTERNAL_FUNCTION)) {
        return FAILURE;
    }

    fn->handler = (zend_function_handler)my_mail;

    return SUCCESS;
}

PHP_MINIT_FUNCTION(mymod)
{
    my_override_mail();

    return SUCCESS;
}

2.3 Compiling and installing the extension

Finally, we need to compile our extension using the following command For shared objects:

phpize
./configure --enable-mymod
make && make install

3. Conclusion

In this article, we discussed how to create a new PHP extension using C to extend or modify an existing There are functions. Although this involves some complex programming techniques, it allows us to better meet specific programming needs. Therefore, if you are a PHP developer, you should know how to modify the extension of PHP system functions.

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