input_plugin: added methods init(), finish()

Instead of hard-coding the plugin global initialization in
input_stream_global_init(), make it walk the plugin list and
initialize all plugins.

src/input/curl_input_plugin.c

@@ -91,17 +91,23 @@ struct input_curl {
 /** libcurl should accept "ICY 200 OK" */
 static struct curl_slist *http_200_aliases;
 
-void input_curl_global_init(void)
+static bool
+input_curl_init(void)
 {
 	CURLcode code = curl_global_init(CURL_GLOBAL_ALL);
-	if (code != CURLE_OK)
+	if (code != CURLE_OK) {
 		g_warning("curl_global_init() failed: %s\n",
 			  curl_easy_strerror(code));
+		return false;
+	}
 
 	http_200_aliases = curl_slist_append(http_200_aliases, "ICY 200 OK");
+
+	return true;
 }
 
-void input_curl_global_finish(void)
+static void
+input_curl_finish(void)
 {
 	curl_slist_free_all(http_200_aliases);
 
@@ -948,6 +954,9 @@ input_curl_open(struct input_stream *is, const char *url)
 }
 
 const struct input_plugin input_plugin_curl = {
+	.init = input_curl_init,
+	.finish = input_curl_finish,
+
 	.open = input_curl_open,
 	.close = input_curl_close,
 	.tag = input_curl_tag,

src/input/curl_input_plugin.h

@@ -21,8 +21,4 @@
 
 extern const struct input_plugin input_plugin_curl;
 
-void input_curl_global_init(void);
-
-void input_curl_global_finish(void);
-
 #endif

src/input_plugin.h

@@ -28,6 +28,20 @@
 struct input_stream;
 
 struct input_plugin {
+	/**
+	 * Global initialization.  This method is called when MPD starts.
+	 *
+	 * @return true on success, false if the plugin should be
+	 * disabled
+	 */
+	bool (*init)(void);
+
+	/**
+	 * Global deinitialization.  Called once before MPD shuts
+	 * down (only if init() has returned true).
+	 */
+	void (*finish)(void);
+
 	bool (*open)(struct input_stream *is, const char *url);
 	void (*close)(struct input_stream *is);
 

src/input_stream.c

@@ -49,21 +49,24 @@ static const struct input_plugin *const input_plugins[] = {
 #endif
 };
 
+static bool input_plugins_enabled[G_N_ELEMENTS(input_plugins)];
+
 static const unsigned num_input_plugins =
 	sizeof(input_plugins) / sizeof(input_plugins[0]);
 
 void input_stream_global_init(void)
 {
-#ifdef HAVE_CURL
-	input_curl_global_init();
-#endif
+	for (unsigned i = 0; i < num_input_plugins; ++i)
+		if (input_plugins[i]->init == NULL || input_plugins[i]->init())
+			input_plugins_enabled[i] = true;
 }
 
 void input_stream_global_finish(void)
 {
-#ifdef HAVE_CURL
-	input_curl_global_finish();
-#endif
+	for (unsigned i = 0; i < num_input_plugins; ++i)
+		if (input_plugins_enabled[i] &&
+		    input_plugins[i]->finish != NULL)
+			input_plugins[i]->finish();
 }
 
 bool