Use a PHP file pointer resource in C extension

Question

I started developing my own little extension for PHP. But I'm struggling now with the resource types.

Basically I like to use a file pointer passed as parameter to my own function. So let's say the following PHP code is the end result:

<?php

$fp = fopen('file.txt', 'w');

my_ext_function($fp);

Now I like to play around with this file pointer in C back in my extension:

PHP_FUNCTION(my_ext_function)
{
        zval *res;
        php_stream *stream;

        char ch;

        if (zend_parse_parameters(ZEND_NUM_ARGS(), "r", &res) == FAILURE) {
                RETURN_FALSE;
        }

        PHP_STREAM_TO_ZVAL(stream, res); // Not sure about that

        // Do some crazy stuff here like it would be a native file pointer from C
        while( ( ch = fgetc(res) ) != EOF )
            php_printf("%c", res);

        RETURN_TRUE;
}

My extension function is based on the fread function of PHP itself.

So how can I achieve this? Basically the question is: how can cast the php_stream pointer to a FILE pointer?

BACKTRACE

#0  0x000000010081b330 in zend_parse_va_args (num_args=1, type_spec=0x7fff5fbfec88 "@9\321\002\001", va=0x7fff5fbfec10, flags=0, tsrm_ls=0x102cdef07) at Zend/zend_API.c:790
#1  0x000000010081bc67 in zend_parse_parameters (num_args=1, tsrm_ls=0x102cdef07, type_spec=0x7fff5fbfec88 "@9\321\002\001") at Zend/zend_API.c:924
#2  0x0000000102cdeb2a in zif_my_ext_function (ht=1, return_value=0x102cd2d38, return_value_ptr=0x102c9e168, this_ptr=0x0, return_value_used=0, tsrm_ls=0x102d13940) at hello.c:65
#3  0x00000001008cacd5 in zend_do_fcall_common_helper_SPEC (execute_data=0x102c9e1c0, tsrm_ls=0x102d13940) at Zend/zend_vm_execute.h:558
#4  0x0000000100882252 in ZEND_DO_FCALL_SPEC_CONST_HANDLER (execute_data=0x102c9e1c0, tsrm_ls=0x102d13940) at Zend/zend_vm_execute.h:2595
#5  0x0000000100869f28 in execute_ex (execute_data=0x102c9e1c0, tsrm_ls=0x102d13940) at Zend/zend_vm_execute.h:363
#6  0x000000010086a060 in zend_execute (op_array=0x102cd39f0, tsrm_ls=0x102d13940) at Zend/zend_vm_execute.h:388
#7  0x00000001007fde27 in zend_eval_stringl (str=0x102d138a0 "$fp = fopen(\"test.txt\", \"r\"); my_ext_function($fp);", str_len=41, retval_ptr=0x0,
    string_name=0x100dbd1d6 "Command line code", tsrm_ls=0x102d13940) at Zend/zend_execute_API.c:1077
#8  0x00000001007fe627 in zend_eval_stringl_ex (str=0x102d138a0 "$fp = fopen(\"test.txt\", \"r\"); my_ext_function($fp);", str_len=41, retval_ptr=0x0,
    string_name=0x100dbd1d6 "Command line code", handle_exceptions=1, tsrm_ls=0x102d13940) at Zend/zend_execute_API.c:1124
#9  0x00000001007fe6ff in zend_eval_string_ex (str=0x102d138a0 "$fp = fopen(\"test.txt\", \"r\"); my_ext_function($fp);", retval_ptr=0x0, string_name=0x100dbd1d6 "Command line code",
    handle_exceptions=1, tsrm_ls=0x102d13940) at Zend/zend_execute_API.c:1135
#10 0x00000001008f96ab in do_cli (argc=3, argv=0x102d13840, tsrm_ls=0x102d13940) at sapi/cli/php_cli.c:1034
#11 0x00000001008f8172 in main (argc=3, argv=0x102d13840) at sapi/cli/php_cli.c:1378

Answer 1

The PHP_STREAM_TO_ZVAL can't be used directly because it's declared inside the implementation of ext/standard/file.c; you need to use this instead:

php_stream_from_zval(stream, &res);

You can cast the stream to what you need using php_stream_cast():

{
    FILE *f;

    if (FAILURE == php_stream_cast(stream, PHP_STREAM_AS_STDIO, (void**)&f, REPORT_ERRORS))   {
        RETURN_FALSE;
    }
    /* do what you want with f */
}