input: pass config_param to input_plugin.init()

Allow input plugins to configure with an "input" block in mpd.conf.
Also allow the user to disable a plugin completely.

src/input_stream.c

@@ -18,6 +18,7 @@
 
 #include "input_plugin.h"
 #include "config.h"
+#include "conf.h"
 
 #include "input/file_input_plugin.h"
 
@@ -35,6 +36,7 @@
 
 #include <glib.h>
 #include <assert.h>
+#include <string.h>
 
 static const struct input_plugin *const input_plugins[] = {
 	&input_plugin_file,
@@ -54,11 +56,45 @@ static bool input_plugins_enabled[G_N_ELEMENTS(input_plugins)];
 static const unsigned num_input_plugins =
 	sizeof(input_plugins) / sizeof(input_plugins[0]);
 
+/**
+ * Find the "input" configuration block for the specified plugin.
+ *
+ * @param plugin_name the name of the input plugin
+ * @return the configuration block, or NULL if none was configured
+ */
+static const struct config_param *
+input_plugin_config(const char *plugin_name)
+{
+	const struct config_param *param = NULL;
+
+	while ((param = config_get_next_param(CONF_INPUT, param)) != NULL) {
+		const char *name =
+			config_get_block_string(param, "plugin", NULL);
+		if (name == NULL)
+			g_error("input configuration without 'plugin' name in line %d",
+				param->line);
+
+		if (strcmp(name, plugin_name) == 0)
+			return param;
+	}
+
+	return NULL;
+}
+
 void input_stream_global_init(void)
 {
-	for (unsigned i = 0; i < num_input_plugins; ++i)
-		if (input_plugins[i]->init == NULL || input_plugins[i]->init())
+	for (unsigned i = 0; i < num_input_plugins; ++i) {
+		const struct input_plugin *plugin = input_plugins[i];
+		const struct config_param *param =
+			input_plugin_config(plugin->name);
+
+		if (!config_get_block_bool(param, "enabled", true))
+			/* the plugin is disabled in mpd.conf */
+			continue;
+
+		if (plugin->init == NULL || plugin->init(param))
 			input_plugins_enabled[i] = true;
+	}
 }
 
 void input_stream_global_finish(void)
@@ -82,10 +118,8 @@ input_stream_open(struct input_stream *is, const char *url)
 	for (unsigned i = 0; i < num_input_plugins; ++i) {
 		const struct input_plugin *plugin = input_plugins[i];
 
-		if (plugin->open(is, url)) {
+		if (input_plugins_enabled[i] && plugin->open(is, url)) {
 			assert(is->plugin != NULL);
-			assert(is->plugin->open == NULL ||
-			       is->plugin == plugin);
 			assert(is->plugin->close != NULL);
 			assert(is->plugin->read != NULL);
 			assert(is->plugin->eof != NULL);