Simulating require_once within an extension View as Markdown

I suspect you could implement the desired functionality
using http://php.net/manual/en/function.stream-wrapper-register.php

although I can't find any info on whether include/require
actually work with registered stream wrappers .. maybe one of the
devs could confirm/deny whether this is possible.

which would allow you to do something like this (assuming it is possible to do):

require_once 'momcr://foo/script.php';

Mo McRoberts wrote:

Hi list,

Apologies if I'm sending this to the wrong list; I couldn't see another
which was more appropriate on the PHP Mailing Lists page.

I'm developing a PHP extension for which part of the functionality can
be described in a nutshell as:

• at request start-up time, build a map of identifiers to path-names, read
  from a configuration file;

• whilst a user script is being processed, a function provided by the
  extension can be called to add, remove or modify items in the mapping;

• a user script can call a function, passing it an identifier in the map,
  and the extension should simulate require_once being called with the
  corresponding pathname (with some transformation applied).

For example, if the configuration file specified that 'foo' mapped to
/www/common/foo, calling the above function with a parameter of 'foo'
might simulate require_once('/www/common/foo/script.php') (where the
transformation applied in this case is appending 'script.php' to the given
pathname). A prototype implementation written in PHP itself works well enough,
but obviously there are scoping issues with such an implementation (i.e.,
any scripts included are included within the scope of the function, not the
caller) which I want to avoid through the use of an extension.

Obviously, much of this is pretty trivial and straightforward. My problem is
the actual simulation of require_once itself. As it's a language intrinsic,
there's no simply-exposed API for performing the same action. Digging through
the PHP sources, I've come across zend_execute_scripts(), which seems to
fit the bill, although there's no documentation and very few examples of it
being used outside of the PHP engine itself.

From skimming as many bits of the PHP sources that actually use
zend_execute_scripts() that I could find, the code I've come up
with isn't hugely dissimilar to this:

static int
do_required(const char *filename TSRMLS_DC)
{
int r;
zend_file_handle zh;

if(SUCCESS != (r = zend_stream_open(filename, &zh TSRMLS_CC)))
{
return r;
}
if(NULL == zh.opened_path)
{
zh.opened_path = estrdup(filename);
}
if(zend_hash_add_empty_element(&EG(included_files),
zh.opened_path, strlen(zh.opened_path) + 1) == SUCCESS)
{
r = zend_execute_scripts(ZEND_REQUIRE_ONCE TSRMLS_CC, NULL, 1, &zh);
}
zend_stream_close(TSRMLS_CC);
return r;
}

Simple enough, right? Wrong.

I'm hoping at this point that somebody who knows the Zend internals pretty
well will immediately spot which things I'm not initialising, saving/restoring,
or happen to be double-freeing at this point, because I'm at a loss. My
symptoms are this:

• If calls to this function are nested, and an inner call results in
  zend_stream_open() failing, I get faults in zend_get_executed_lineno(),
  suggesting corruption somewhere.

• If I save, reset and restore return_value_ptr_ptr, active_op_array,
  opline_ptr before doing anything, things seem better, but the Warning
  message reported when the file can't be opened gives the error location
  as [no active file] on line 0, which is less than ideal.

• If I only save/reset/restore around the call to zend_get_executed_lineno()
  itself, things seem to work until I get as far as installing the extension
  for my Apache 2.2 module build of PHP: at which point, as soon as there's
  some nesting things start to go bad (errors reported or not). Removing the
  final zend_stream_close() call stops Apache from dying, but I strongly
  suspect that I'm just masking the problem rather than fixing it.

So, my questions are: what am I doing wrong, and is there a better way to
accomplish the same thing? I considered evaluating a script instead of
trying to simulate require_once itself, but that seemed incredibly kludgy.

Any help appreciated.

Thanks,

Mo.

Sorry, I can't help with your C extension but I can give you a solution I implemented in PHP
for the same needs. I did using two mechanisms :

- A stream wrapper to allow require_once to reference a virtual path. Not required if you 

require 'real' files. In PHK, I need it because I implement a virtual file system.

- A 'tunneling' function like yours, used through an eval(). I agree it is not very 

elegant but, unfortunately, there is no 'uplevel' feature in PHP (could be an interesting
addition, along with a who_called_me()). This function generally returns a
'require_once <stream-wrapped path>' string, but as we eval()uate the result, it can return
any code, even a 'throw Exception', to be thrown from the calling scope.

If you want to see more about this example, download the PHK_Creator building kit from
http://www.tekwire.net/joomla/download/phk, and search for the 'web_tunnel' function in
file PHK.php.

Regards

François

-----Original Message-----
From: Mo McRoberts [mailto:mo@nevali.net]
Sent: Saturday, February 24, 2007 4:18 AM
To: internals@lists.php.net
Subject: [PHP-DEV] Simulating require_once within an extension

Hi list,

Apologies if I'm sending this to the wrong list; I couldn't
see another which was more appropriate on the PHP Mailing Lists page.

I'm developing a PHP extension for which part of the
functionality can be described in a nutshell as:

• at request start-up time, build a map of identifiers to
  path-names, read
  from a configuration file;

• whilst a user script is being processed, a function provided by the
  extension can be called to add, remove or modify items in
  the mapping;

• a user script can call a function, passing it an identifier
  in the map,
  and the extension should simulate require_once being called with the
  corresponding pathname (with some transformation applied).

For example, if the configuration file specified that 'foo'
mapped to /www/common/foo, calling the above function with a
parameter of 'foo' might simulate
require_once('/www/common/foo/script.php') (where the
transformation applied in this case is appending 'script.php'
to the given pathname). A prototype implementation written in
PHP itself works well enough, but obviously there are scoping
issues with such an implementation (i.e., any scripts
included are included within the scope of the function, not the
caller) which I want to avoid through the use of an extension.

Obviously, much of this is pretty trivial and
straightforward. My problem is the actual simulation of
require_once itself. As it's a language intrinsic, there's no
simply-exposed API for performing the same action. Digging
through the PHP sources, I've come across
zend_execute_scripts(), which seems to fit the bill, although
there's no documentation and very few examples of it being
used outside of the PHP engine itself.

From skimming as many bits of the PHP sources that actually use
zend_execute_scripts() that I could find, the code I've come
up with isn't hugely dissimilar to this:

static int
do_required(const char *filename TSRMLS_DC)
{
int r;
zend_file_handle zh;

if(SUCCESS != (r = zend_stream_open(filename, &zh TSRMLS_CC)))
{
return r;
}
if(NULL == zh.opened_path)
{
zh.opened_path = estrdup(filename);
}
if(zend_hash_add_empty_element(&EG(included_files),
zh.opened_path, strlen(zh.opened_path) + 1) == SUCCESS)
{
r = zend_execute_scripts(ZEND_REQUIRE_ONCE
TSRMLS_CC, NULL, 1, &zh);
}
zend_stream_close(TSRMLS_CC);
return r;
}

Simple enough, right? Wrong.

I'm hoping at this point that somebody who knows the Zend
internals pretty well will immediately spot which things I'm
not initialising, saving/restoring, or happen to be
double-freeing at this point, because I'm at a loss. My
symptoms are this:

• If calls to this function are nested, and an inner call results in
  zend_stream_open() failing, I get faults in
  zend_get_executed_lineno(),
  suggesting corruption somewhere.

• If I save, reset and restore return_value_ptr_ptr, active_op_array,
  opline_ptr before doing anything, things seem better, but
  the Warning
  message reported when the file can't be opened gives the
  error location
  as [no active file] on line 0, which is less than ideal.

• If I only save/reset/restore around the call to
  zend_get_executed_lineno()
  itself, things seem to work until I get as far as
  installing the extension
  for my Apache 2.2 module build of PHP: at which point, as
  soon as there's
  some nesting things start to go bad (errors reported or
  not). Removing the
  final zend_stream_close() call stops Apache from dying, but
  I strongly
  suspect that I'm just masking the problem rather than fixing it.

So, my questions are: what am I doing wrong, and is there a
better way to accomplish the same thing? I considered
evaluating a script instead of trying to simulate
require_once itself, but that seemed incredibly kludgy.

Any help appreciated.

Thanks,

Mo.