ext/curl: Add CURLOPT_DEBUGFUNCTION option

This adds support for `CURLOPT_DEBUGFUNCTION`[^1] Curl option to set a
custom callback that gets called with debug information during the
lifetime of a Curl request.

The callback gets called with the `CurlHandle` object, an integer
containing the type of the debug message, and a string containing the
debug message. The callback may get called multiple times with the
same message type during a request.

PHP already uses `CURLOPT_DEBUGFUNCTION` functionality to internally
to expose a Curl option named `CURLINFO_HEADER_OUT`.

However,`CURLINFO_HEADER_OUT` is not a "real" Curl option supported
by libcurl. Back in 2006, `CURLINFO_HEADER_OUT` was added[^2] as
a Curl option by using the debug-callback feature. Git history does
not run that back to show why `CURLINFO_HEADER_OUT` was added as a
Curl option, and why the other debug types (such as
`CURLINFO_HEADER_IN` were not added as Curl options, but this seems
to be a historical artifact when we added features without trying
to be close to libcurl options.

This approach has a few issues:

1. `CURLINFO_HEADER_OUT` is not an actual Curl option supported by
  upstream libcurl.

2. All of the Curl options have `CURLOPT_` prefix, and `CURLINFO_HEADER_OUT`
  is the only Curl "option" that uses the `CURLINFO` prefix. This exception
  is, however, noted[^3] in docs.

3. When `CURLINFO_HEADER_OUT` is set, the `CURLOPT_VERBOSE` is also implicitly
  set. This was reported[^4] to bugs.php.net, but the bug is marked as wontfix.

This commit adds support for `CURLOPT_DEBUGFUNCTION`. It extends the existing
`curl_debug` callback to store the header-in information if it encounters
a debug message with `CURLINFO_HEADER_OUT`. In all cases, if a callable
is set, it gets called.

`CURLOPT_DEBUGFUNCTION` intends to replace `CURLINFO_HEADER_OUT` Curl
option as a versatile alternative that can also be used to extract
other debug information such as SSL data, text information messages,
incoming headers, as well as headers sent out (which `CURLINFO_HEADER_OUT`
makes available).

The callables are allowed to throw exceptions, but the return values are
ignored.

`CURLOPT_DEBUGFUNCTION` requires `CURLOPT_VERBOSE` enabled, and setting
`CURLOPT_DEBUGFUNCTION` does _not_ implicitly enable `CURLOPT_VERBOSE`.

If the `CURLOPT_DEBUGFUNCTION` option is set, setting `CURLINFO_HEADER_OUT`
throws a `ValueError` exception. Setting `CURLOPT_DEBUGFUNCTION` _after_
enabling `CURLINFO_HEADER_OUT` is allowed. Technically, it is possible
for both functionality (calling user-provided callback _and_ storing
header-out data) is possible, setting `CURLINFO_HEADER_OUT` is not
allowed to encourage the use of `CURLOPT_DEBUGFUNCTION` function.

This commit also adds the rest of the `CURLINFO_` constants used as
the `type` integer value in `CURLOPT_DEBUGFUNCTION` callback.

---

[^1]: [cur.se - CURLOPT_DEBUGFUNCTION](https://curl.se/libcurl/c/CURLOPT_DEBUGFUNCTION.html)
[^2]: [`5f25d80`](5f25d80)
[^3]: [curl_setopt doc mentioning `CURLINFO_` prefix is intentional](https://www.php.net/manual/en/function.curl-setopt.php#:~:text=prefix%20is%20intentional)
[^4]: [bugs.php.net - `CURLOPT_VERBOSE` does not work with `CURLINFO_HEADER_OUT`](https://bugs.php.net/bug.php?id=65348)

NEWS

@@ -18,6 +18,9 @@ PHP                                                                        NEWS
   . Fixed bug GH-15693 (Unnecessary include in main.c bloats binary).
     (nielsdos)
 
+- Curl:
+  . Added CURLOPT_DEBUGFUNCTION as a Curl option. (Ayesh Karunaratne)
+
 - DOM:
   . Fixed bug GH-13988 (Storing DOMElement consume 4 times more memory in
     PHP 8.1 than in PHP 8.0). (nielsdos)

UPGRADING

@@ -298,6 +298,13 @@ PHP 8.4 UPGRADE NOTES
     to allow or abort the request.
   . Added CURLOPT_SERVER_RESPONSE_TIMEOUT, which was formerly known as
     CURLOPT_FTP_RESPONSE_TIMEOUT. Both constants hold the same value.
+  . Added CURLOPT_DEBUGFUNCTION support. This Curl option accepts a callable
+    that gets called during the request lifetime with the CurlHandle object,
+    an integer containing the debug message type, and a string containing the
+    debug message. The debug message type is one of CURLINFO_TEXT, CURLINFO_HEADER_IN,
+    CURLINFO_HEADER_OUT, CURLINFO_DATA_IN, CURLINFO_DATA_OUT, CURLINFO_SSL_DATA_OUT,
+    CURLINFO_SSL_DATA_IN constants. Once this option is set, CURLINFO_HEADER_OUT
+    must not be set because it uses the same libcurl functionality.
 
 - Date:
   . Added static methods
@@ -1017,6 +1024,13 @@ PHP 8.4 UPGRADE NOTES
   . CURL_PREREQFUNC_OK.
   . CURL_PREREQFUNC_ABORT.
   . CURLOPT_SERVER_RESPONSE_TIMEOUT.
+  . CURLOPT_DEBUGFUNCTION.
+  . CURLINFO_TEXT.
+  . CURLINFO_HEADER_IN.
+  . CURLINFO_DATA_IN.
+  . CURLINFO_DATA_OUT.
+  . CURLINFO_SSL_DATA_OUT.
+  . CURLINFO_SSL_DATA_IN.
 
 - Intl:
   . The IntlDateFormatter class exposes now the new PATTERN constant

ext/curl/curl.stub.php

@@ -486,6 +486,48 @@
  */
 const CURLOPT_XFERINFOFUNCTION = UNKNOWN;
 
+/**
+ * @var int
+ * @cvalue CURLOPT_DEBUGFUNCTION
+ */
+const CURLOPT_DEBUGFUNCTION = UNKNOWN;
+
+/**
+ * @var int
+ * @cvalue CURLINFO_TEXT
+ */
+const CURLINFO_TEXT = UNKNOWN;
+
+/**
+ * @var int
+ * @cvalue CURLINFO_HEADER_IN
+ */
+const CURLINFO_HEADER_IN = UNKNOWN;
+
+/**
+ * @var int
+ * @cvalue CURLINFO_DATA_IN
+ */
+const CURLINFO_DATA_IN = UNKNOWN;
+
+/**
+ * @var int
+ * @cvalue CURLINFO_DATA_OUT
+ */
+const CURLINFO_DATA_OUT = UNKNOWN;
+
+/**
+ * @var int
+ * @cvalue CURLINFO_SSL_DATA_OUT
+ */
+const CURLINFO_SSL_DATA_OUT = UNKNOWN;
+
+/**
+ * @var int
+ * @cvalue CURLINFO_SSL_DATA_IN
+ */
+const CURLINFO_SSL_DATA_IN = UNKNOWN;
+
 /* */
 /**
  * @var int

ext/curl/curl_private.h

@@ -68,6 +68,7 @@ typedef struct {
 	zend_fcall_info_cache progress;
 	zend_fcall_info_cache xferinfo;
 	zend_fcall_info_cache fnmatch;
+	zend_fcall_info_cache debug;
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 	zend_fcall_info_cache prereq;
 #endif

ext/curl/interface.c

@@ -504,6 +504,10 @@ static HashTable *curl_get_gc(zend_object *object, zval **table, int *n)
 		zend_get_gc_buffer_add_fcc(gc_buffer, &curl->handlers.fnmatch);
 	}
 
+	if (ZEND_FCC_INITIALIZED(curl->handlers.debug)) {
+		zend_get_gc_buffer_add_fcc(gc_buffer, &curl->handlers.debug);
+	}
+
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 	if (ZEND_FCC_INITIALIZED(curl->handlers.prereq)) {
 		zend_get_gc_buffer_add_fcc(gc_buffer, &curl->handlers.prereq);
@@ -915,18 +919,46 @@ static size_t curl_write_header(char *data, size_t size, size_t nmemb, void *ctx
 }
 /* }}} */
 
-static int curl_debug(CURL *cp, curl_infotype type, char *buf, size_t buf_len, void *ctx) /* {{{ */
+static int curl_debug(CURL *handle, curl_infotype type, char *data, size_t size, void *clientp) /* {{{ */
 {
-	php_curl *ch = (php_curl *)ctx;
+	php_curl *ch = (php_curl *)clientp;
 
-	if (type == CURLINFO_HEADER_OUT) {
-		if (ch->header.str) {
-			zend_string_release_ex(ch->header.str, 0);
-		}
-		ch->header.str = zend_string_init(buf, buf_len, 0);
-	}
+    #if PHP_CURL_DEBUG
+    	fprintf(stderr, "curl_debug() called\n");
+    	fprintf(stderr, "type = %d, data = %s\n", type, data);
+    #endif
+
+	// Implicitly store the headers for compatibility with CURLINFO_HEADER_OUT
+	// used as a Curl option. Previously, setting CURLINFO_HEADER_OUT set curl_debug
+	// as the CURLOPT_DEBUGFUNCTION and stored the debug data when type is set to
+	// CURLINFO_HEADER_OUT. For backward compatibility, we now store the headers
+	// but also call the user-callback function if available.
+    if (type == CURLINFO_HEADER_OUT) {
+    	if (ch->header.str) {
+    		zend_string_release_ex(ch->header.str, 0);
+    	}
+    	ch->header.str = zend_string_init(data, size, 0);
+    }
+
+    if (!ZEND_FCC_INITIALIZED(ch->handlers.debug)) {
+       	return 0;
+    }
 
-	return 0;
+    zval args[3];
+
+    GC_ADDREF(&ch->std);
+    ZVAL_OBJ(&args[0], &ch->std);
+    ZVAL_LONG(&args[1], type);
+    ZVAL_STRINGL(&args[2], data, size);
+
+    ch->in_callback = true;
+    zend_call_known_fcc(&ch->handlers.debug, NULL, /* param_count */ 3, args, /* named_params */ NULL);
+    ch->in_callback = false;
+
+    zval_ptr_dtor(&args[0]);
+    zval_ptr_dtor(&args[2]);
+
+    return 0;
 }
 /* }}} */
 
@@ -1096,6 +1128,7 @@ void init_curl_handle(php_curl *ch)
 	ch->handlers.progress = empty_fcall_info_cache;
 	ch->handlers.xferinfo = empty_fcall_info_cache;
 	ch->handlers.fnmatch = empty_fcall_info_cache;
+	ch->handlers.debug = empty_fcall_info_cache;
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 	ch->handlers.prereq = empty_fcall_info_cache;
 #endif
@@ -1272,6 +1305,7 @@ void _php_setup_easy_copy_handlers(php_curl *ch, php_curl *source)
 	php_curl_copy_fcc_with_option(ch, CURLOPT_PROGRESSDATA, &ch->handlers.progress, &source->handlers.progress);
 	php_curl_copy_fcc_with_option(ch, CURLOPT_XFERINFODATA, &ch->handlers.xferinfo, &source->handlers.xferinfo);
 	php_curl_copy_fcc_with_option(ch, CURLOPT_FNMATCH_DATA, &ch->handlers.fnmatch, &source->handlers.fnmatch);
+	php_curl_copy_fcc_with_option(ch, CURLOPT_DEBUGDATA, &ch->handlers.debug, &source->handlers.debug);
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 	php_curl_copy_fcc_with_option(ch, CURLOPT_PREREQDATA, &ch->handlers.prereq, &source->handlers.prereq);
 #endif
@@ -1635,6 +1669,8 @@ static zend_result _php_curl_setopt(php_curl *ch, zend_long option, zval *zvalue
 		HANDLE_CURL_OPTION_CALLABLE(ch, CURLOPT_PROGRESS, handlers.progress, curl_progress);
 		HANDLE_CURL_OPTION_CALLABLE(ch, CURLOPT_XFERINFO, handlers.xferinfo, curl_xferinfo);
 		HANDLE_CURL_OPTION_CALLABLE(ch, CURLOPT_FNMATCH_, handlers.fnmatch, curl_fnmatch);
+		HANDLE_CURL_OPTION_CALLABLE(ch, CURLOPT_DEBUG, handlers.debug, curl_debug);
+
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 		HANDLE_CURL_OPTION_CALLABLE(ch, CURLOPT_PREREQ, handlers.prereq, curl_prereqfunction);
 #endif
@@ -2225,6 +2261,11 @@ static zend_result _php_curl_setopt(php_curl *ch, zend_long option, zval *zvalue
 		}
 
 		case CURLINFO_HEADER_OUT:
+			if (ZEND_FCC_INITIALIZED(ch->handlers.debug)) {
+                zend_value_error("CURLINFO_HEADER_OUT option must not be set when the CURLOPT_DEBUGFUNCTION option is set");
+                return FAILURE;
+            }
+
 			if (zend_is_true(zvalue)) {
 				curl_easy_setopt(ch->cp, CURLOPT_DEBUGFUNCTION, curl_debug);
 				curl_easy_setopt(ch->cp, CURLOPT_DEBUGDATA, (void *)ch);
@@ -2804,6 +2845,9 @@ static void curl_free_obj(zend_object *object)
 	if (ZEND_FCC_INITIALIZED(ch->handlers.fnmatch)) {
 		zend_fcc_dtor(&ch->handlers.fnmatch);
 	}
+	if (ZEND_FCC_INITIALIZED(ch->handlers.debug)) {
+		zend_fcc_dtor(&ch->handlers.debug);
+	}
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 	if (ZEND_FCC_INITIALIZED(ch->handlers.prereq)) {
 		zend_fcc_dtor(&ch->handlers.prereq);
@@ -2887,6 +2931,10 @@ static void _php_curl_reset_handlers(php_curl *ch)
 	if (ZEND_FCC_INITIALIZED(ch->handlers.fnmatch)) {
 		zend_fcc_dtor(&ch->handlers.fnmatch);
 	}
+
+	if (ZEND_FCC_INITIALIZED(ch->handlers.debug)) {
+		zend_fcc_dtor(&ch->handlers.debug);
+	}
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 	if (ZEND_FCC_INITIALIZED(ch->handlers.prereq)) {
 		zend_fcc_dtor(&ch->handlers.prereq);

ext/curl/sync-constants.php

@@ -18,6 +18,7 @@
     'CURLOPT_PROGRESSDATA',
     'CURLOPT_XFERINFODATA',
     'CURLOPT_PREREQDATA',
+    'CURLOPT_DEBUGDATA',
 ];
 
 const IGNORED_PHP_CONSTANTS = [