`ob_list_handlers()` should return list of real callables

[mvorisek]

Description

repro: https://3v4l.org/vpo7M

Currently, it is impossible to backup/restore the handlers before/after tests.

[mvorisek]

For completeness, here is a code we use to backup/restore error/exception handlers:

    /**
     * @return list<callable>
     */
    private function getErrorHandlers(): array
    {
        $res = [];
        while (true) {
            $previousHandler = set_error_handler(static fn () => false);
            restore_error_handler();
            if ($previousHandler === null) {
                break;
            }
            $res[] = $previousHandler;
            restore_error_handler();
        };
        $res = array_reverse($res);
        
        foreach ($res as $handler) {
            set_error_handler($handler);
        }
        
        return $res;
    }

It works well... we want the same for ob handlers.

[nielsdos]

This would at least require a way for the engine to convert FCCs back to zvals. I'm unsure we have an easy way in the engine to do that conversion, at least I couldn't find any.

Anyway, something to think about is the following. The output buffer stack may also contain internal handlers, that cannot be exposed to the PHP script, what do we do with those? I suppose we skip them when returning an array? That would leave an inconsistency between ob_list_handlers() and the potential new function though.

[Girgias]

This would at least require a way for the engine to convert FCCs back to zvals. I'm unsure we have an easy way in the engine to do that conversion, at least I couldn't find any.

There is one :)

zend_get_callable_zval_from_fcc() in zend_API.h.

Anyway, something to think about is the following. The output buffer stack may also contain internal handlers, that cannot be exposed to the PHP script, what do we do with those? I suppose we skip them when returning an array? That would leave an inconsistency between ob_list_handlers() and the potential new function though.

I'm unfamiliar with the output handlers, but which ones would be internal ones that are set by default?

[nielsdos]

Ah I missed that function, was searching in the wrong place, thx for the pointer!

There are internal output handlers that can be activated from PHPAPI functions. They are used by extensions.
For example there's php_output_start_default (called from at least soap for example) and php_output_start_devnull. The first one is used in soap to avoid output from user code during soap response handling.

[nielsdos]

This is quite easy to implement. Here's a proof-of-concept patch. This adds a $user_callables boolean argument to the function that makes it return callables, and it will skip over internal handlers. Extra argument may not necessarily be the best API design, but this is only a PoC. In any case this would at least need discussion on the mailing list.

Patch is applicable on the master branch.

diff --git a/ext/standard/basic_functions.stub.php b/ext/standard/basic_functions.stub.php
index 8592d7c0b8..d0a148fb06 100755
--- a/ext/standard/basic_functions.stub.php
+++ b/ext/standard/basic_functions.stub.php
@@ -1537,10 +1537,10 @@ function ob_get_level(): int {}
 function ob_get_length(): int|false {}
 
 /**
- * @return array<int, string>
+ * @return array<int, string>|array<int, callable>
  * @refcount 1
  */
-function ob_list_handlers(): array {}
+function ob_list_handlers(bool $user_callables = false): array {}
 
 /**
  * @return array<int|string, int|string|array>
diff --git a/ext/standard/basic_functions_arginfo.h b/ext/standard/basic_functions_arginfo.h
index 48202e7807..036c491d00 100644
--- a/ext/standard/basic_functions_arginfo.h
+++ b/ext/standard/basic_functions_arginfo.h
@@ -1,5 +1,5 @@
 /* This is a generated file, edit the .stub.php file instead.
- * Stub hash: c9edbe45bb7a2b00b413fb3c56683bb8377a725f */
+ * Stub hash: 08f45c027f62b6cc321fa28892b7a7cb03b4caeb */
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_set_time_limit, 0, 1, _IS_BOOL, 0)
 	ZEND_ARG_TYPE_INFO(0, seconds, IS_LONG, 0)
@@ -38,6 +38,7 @@ ZEND_BEGIN_ARG_WITH_RETURN_TYPE_MASK_EX(arginfo_ob_get_length, 0, 0, MAY_BE_LONG
 ZEND_END_ARG_INFO()
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_ob_list_handlers, 0, 0, IS_ARRAY, 0)
+	ZEND_ARG_TYPE_INFO_WITH_DEFAULT_VALUE(0, user_callables, _IS_BOOL, 0, "false")
 ZEND_END_ARG_INFO()
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_ob_get_status, 0, 0, IS_ARRAY, 0)
@@ -764,7 +765,8 @@ ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_headers_sent, 0, 0, _IS_BOOL, 0)
 	ZEND_ARG_INFO_WITH_DEFAULT_VALUE(1, line, "null")
 ZEND_END_ARG_INFO()
 
-#define arginfo_headers_list arginfo_ob_list_handlers
+ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_headers_list, 0, 0, IS_ARRAY, 0)
+ZEND_END_ARG_INFO()
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_htmlspecialchars, 0, 1, IS_STRING, 0)
 	ZEND_ARG_TYPE_INFO(0, string, IS_STRING, 0)
@@ -1037,7 +1039,7 @@ ZEND_END_ARG_INFO()
 
 #define arginfo_strnatcmp arginfo_strcoll
 
-#define arginfo_localeconv arginfo_ob_list_handlers
+#define arginfo_localeconv arginfo_headers_list
 
 #define arginfo_strnatcasecmp arginfo_strcoll
 
@@ -1453,7 +1455,7 @@ ZEND_END_ARG_INFO()
 
 #define arginfo_diskfreespace arginfo_disk_total_space
 
-#define arginfo_realpath_cache_get arginfo_ob_list_handlers
+#define arginfo_realpath_cache_get arginfo_headers_list
 
 #define arginfo_realpath_cache_size arginfo_ob_get_level
 
@@ -1775,7 +1777,7 @@ ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_password_verify, 0, 2, _IS_BOOL,
 	ZEND_ARG_TYPE_INFO(0, hash, IS_STRING, 0)
 ZEND_END_ARG_INFO()
 
-#define arginfo_password_algos arginfo_ob_list_handlers
+#define arginfo_password_algos arginfo_headers_list
 
 #if defined(PHP_CAN_SUPPORT_PROC_OPEN)
 ZEND_BEGIN_ARG_INFO_EX(arginfo_proc_open, 0, 0, 3)
@@ -1981,9 +1983,9 @@ ZEND_END_ARG_INFO()
 
 #define arginfo_stream_resolve_include_path arginfo_filetype
 
-#define arginfo_stream_get_wrappers arginfo_ob_list_handlers
+#define arginfo_stream_get_wrappers arginfo_headers_list
 
-#define arginfo_stream_get_transports arginfo_ob_list_handlers
+#define arginfo_stream_get_transports arginfo_headers_list
 
 #define arginfo_stream_is_local arginfo_rewind
 
@@ -2116,7 +2118,7 @@ ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_stream_bucket_new, 0, 2, IS_OBJE
 	ZEND_ARG_TYPE_INFO(0, buffer, IS_STRING, 0)
 ZEND_END_ARG_INFO()
 
-#define arginfo_stream_get_filters arginfo_ob_list_handlers
+#define arginfo_stream_get_filters arginfo_headers_list
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_stream_filter_register, 0, 2, _IS_BOOL, 0)
 	ZEND_ARG_TYPE_INFO(0, filter_name, IS_STRING, 0)
diff --git a/main/output.c b/main/output.c
index 76d4e7709e..629b4b2161 100644
--- a/main/output.c
+++ b/main/output.c
@@ -1155,6 +1155,19 @@ static int php_output_stack_apply_list(void *h, void *z)
 }
 /* }}} */
 
+static int php_output_stack_user_callables_apply_list(void *h, void *z)
+{
+	php_output_handler *handler = *(php_output_handler **) h;
+	zval *array = (zval *) z;
+
+	if (handler->flags & PHP_OUTPUT_HANDLER_USER) {
+		zval tmp;
+		zend_get_callable_zval_from_fcc(&handler->func.user->fcc, &tmp);
+		add_next_index_zval(array, &tmp);
+	}
+	return 0;
+}
+
 /* {{{ static int php_output_stack_apply_status(void *h, void *z)
  * Status callback for the stack apply function */
 static int php_output_stack_apply_status(void *h, void *z)
@@ -1463,7 +1476,9 @@ PHP_FUNCTION(ob_get_length)
 /* {{{ List all output_buffers in an array */
 PHP_FUNCTION(ob_list_handlers)
 {
-	if (zend_parse_parameters_none() == FAILURE) {
+	bool user_callables = false;
+
+	if (zend_parse_parameters(ZEND_NUM_ARGS(), "|b", &user_callables) == FAILURE) {
 		RETURN_THROWS();
 	}
 
@@ -1473,7 +1488,11 @@ PHP_FUNCTION(ob_list_handlers)
 		return;
 	}
 
-	zend_stack_apply_with_argument(&OG(handlers), ZEND_STACK_APPLY_BOTTOMUP, php_output_stack_apply_list, return_value);
+	if (user_callables) {
+		zend_stack_apply_with_argument(&OG(handlers), ZEND_STACK_APPLY_BOTTOMUP, php_output_stack_user_callables_apply_list, return_value);
+	} else {
+		zend_stack_apply_with_argument(&OG(handlers), ZEND_STACK_APPLY_BOTTOMUP, php_output_stack_apply_list, return_value);
+	}
 }
 /* }}} */
  

[mvorisek]

The motivation of this feature request is to be able to backup/verify/restore the handlers. When non-userland handlers will not be listed, this motivation is not satisfied. I would be happy if the non-userland handlers will still be returned as some callable/Closure that is impossible to call from userland, but still possible to remove and restore using the returned array later.

[haszi]

There is also no way to restore a non-userland handler. If there was a way, internal handlers could be registered from userland code. And since internal handlers can register any internal function, one could execute just about any part of PHP core.

On the other hand, there aren't too many internal handlers shipped with PHP and all three bundled extension registered internal handlers are exposed as userland functions (ob_gzhandler in zlib, ob_iconv_handler in iconv, ob_tidyhandler in tidy).
That leaves us with four truly internal handlers:

• zlib output compression: essentially the same as ob_gzhandler
• default output handler: returns the unmodified buffer contents
• null output handler: returns true
• URL-Rewriter: this is something I'm not familiar enough with to comment on

All the above handler names are exposed by ob_list_handlers() and ob_get_status(), and their chunk_size and flags by ob_get_status() so there is at least one way to backup and restore these.

[kkmuffme]

This is impossible. You can also use private methods - in that case you will get an array but it's not callable in this context.
See php/doc-en#3421