Add API endpoint for extensions (#7576)

* Add API endpoint for extensions
Useful for https://github.com/FreshRSS/FreshRSS/issues/7572

* Support PATH_INFO
Now also support being invoked like `/api/misc.php/Extension%20Name/`

* More  documentation

2 files changed, 76 insertions, 6 deletions

diff --git a/p/api/index.php b/p/api/index.php
index 66c9e465c..fd9828080 100644
--- a/p/api/index.php
+++ b/p/api/index.php
@@ -28,9 +28,7 @@ echo json_encode([
 <h2>Google Reader compatible API</h2>
 <dl>
 <dt>Your API address:</dt>
-<dd><?php
-echo Minz_Url::display('/api/greader.php', 'html', true);
-?></dd>
+<dd><?= Minz_Url::display('/api/greader.php', 'html', true) ?></dd>
 <dt>Google Reader API configuration test:</dt>
 <dd id="greaderOutput">?</dd>
 </dl>
@@ -38,12 +36,16 @@ echo Minz_Url::display('/api/greader.php', 'html', true);
 <h2>Fever compatible API</h2>
 <dl>
 <dt>Your API address:</dt>
-<dd><?php
-echo Minz_Url::display('/api/fever.php', 'html', true);
-?></dd>
+<dd><?= Minz_Url::display('/api/fever.php', 'html', true) ?></dd>
 <dt>Fever API configuration test:</dt>
 <dd id="feverOutput">?</dd>
 </dl>
 
+<h2>API for extensions</h2>
+<dl>
+<dt>Your API address:</dt>
+<dd><?= Minz_Url::display('/api/misc.php/Extension%20name/', 'html', true) ?></dd>
+</dl>
+
 </body>
 </html>
diff --git a/p/api/misc.php b/p/api/misc.php
new file mode 100644
index 000000000..7724caa7a
--- /dev/null
+++ b/p/api/misc.php
@@ -0,0 +1,68 @@
+<?php
+declare(strict_types=1);
+/**
+ * API entry point for FreshRSS extensions on
+ * `/api/misc.php/Extension%20name/` or `/api/misc.php?ext=Extension%20name`
+ */
+
+require(__DIR__ . '/../../constants.php');
+require(LIB_PATH . '/lib_rss.php');	//Includes class autoloader
+
+function badRequest(): never {
+	header('HTTP/1.1 400 Bad Request');
+	header('Content-Type: text/plain; charset=UTF-8');
+	die('Bad Request!');
+}
+
+function serviceUnavailable(): never {
+	header('HTTP/1.1 503 Service Unavailable');
+	header('Content-Type: text/plain; charset=UTF-8');
+	die('Service Unavailable!');
+}
+
+$extensionName = is_string($_GET['ext'] ?? null) ? $_GET['ext'] : '';
+
+if ($extensionName === '') {
+	$pathInfo = '';
+	if (empty($_SERVER['PATH_INFO']) || !is_string($_SERVER['PATH_INFO'] ?? null)) {
+		if (!empty($_SERVER['ORIG_PATH_INFO']) && is_string($_SERVER['ORIG_PATH_INFO'])) {
+			// Compatibility https://php.net/reserved.variables.server
+			$pathInfo = $_SERVER['ORIG_PATH_INFO'];
+		}
+	} else {
+		$pathInfo = $_SERVER['PATH_INFO'];
+	}
+	$pathInfo = rawurldecode($pathInfo);
+	$pathInfo = preg_replace('%^(/api)?(/misc\.php)?%', '', $pathInfo);	//Discard common errors
+	if ($pathInfo !== '' && is_string($pathInfo)) {
+		$pathInfos = explode('/', $pathInfo, limit: 3);
+		if (count($pathInfos) > 1) {
+			$extensionName = $pathInfos[1];
+		}
+	}
+}
+
+if ($extensionName === '') {
+	badRequest();
+}
+
+Minz_Session::init('FreshRSS', volatile: true);
+
+FreshRSS_Context::initSystem();
+if (
+	!FreshRSS_Context::hasSystemConf() ||
+	!FreshRSS_Context::systemConf()->api_enabled ||
+	empty(FreshRSS_Context::systemConf()->extensions_enabled[$extensionName])
+) {
+	serviceUnavailable();
+}
+
+// Only enable the extension that is being called
+FreshRSS_Context::systemConf()->extensions_enabled = [$extensionName => true];
+Minz_ExtensionManager::init();
+
+Minz_Translate::init();
+
+if (!Minz_ExtensionManager::callHookUnique('api_misc')) {
+	serviceUnavailable();
+}