input/Plugin: remove InitResult::UNAVAILABLE, throw PluginUnavailable instead

Makefile.am

@@ -166,6 +166,7 @@ libmpd_a_SOURCES = \
 	src/queue/PlaylistTag.cxx \
 	src/queue/PlaylistState.cxx src/queue/PlaylistState.hxx \
 	src/queue/Listener.hxx \
+	src/PluginUnavailable.hxx \
 	src/ReplayGainConfig.cxx src/ReplayGainConfig.hxx \
 	src/ReplayGainInfo.cxx src/ReplayGainInfo.hxx \
 	src/DetachedSong.cxx src/DetachedSong.hxx \

src/PluginUnavailable.hxx

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2003-2016 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_PLUGIN_UNAVAILABLE_HXX
+#define MPD_PLUGIN_UNAVAILABLE_HXX
+
+#include <stdexcept>
+
+/**
+ * An exception class which is used by plugin initializers to indicate
+ * that this plugin is unavailable.  It will be disabled, and MPD can
+ * continue initialization.
+ */
+class PluginUnavailable final : public std::runtime_error {
+public:
+	explicit PluginUnavailable(const char *msg)
+		:std::runtime_error(msg) {}
+};
+
+#endif

src/input/Init.cxx

@@ -26,6 +26,7 @@
 #include "config/ConfigOption.hxx"
 #include "config/Block.hxx"
 #include "Log.hxx"
+#include "PluginUnavailable.hxx"
 #include "util/RuntimeError.hxx"
 
 #include <stdexcept>
@@ -59,6 +60,11 @@ input_stream_global_init(Error &error)
 			result = plugin->init != nullptr
 				? plugin->init(*block, error)
 				: InputPlugin::InitResult::SUCCESS;
+		} catch (const PluginUnavailable &e) {
+			FormatError(e,
+				    "Input plugin '%s' is unavailable",
+				    plugin->name);
+			continue;
 		} catch (const std::runtime_error &e) {
 			std::throw_with_nested(FormatRuntimeError("Failed to initialize input plugin '%s'",
 								  plugin->name));
@@ -73,16 +79,6 @@ input_stream_global_init(Error &error)
 			error.FormatPrefix("Failed to initialize input plugin '%s': ",
 					   plugin->name);
 			return false;
-
-		case InputPlugin::InitResult::UNAVAILABLE:
-			if (error.IsDefined()) {
-				FormatError(error,
-					    "Input plugin '%s' is unavailable",
-					    plugin->name);
-				error.Clear();
-			}
-
-			break;
 		}
 	}
 

src/input/InputPlugin.hxx

@@ -52,13 +52,6 @@ struct InputPlugin {
 		 * ready to be used.
 		 */
 		SUCCESS,
-
-		/**
-		 * The plugin is not available and shall be disabled.
-		 * The #Error may be set describing the situation (to
-		 * be logged).
-		 */
-		UNAVAILABLE,
 	};
 
 	const char *name;
@@ -66,8 +59,8 @@ struct InputPlugin {
 	/**
 	 * Global initialization.  This method is called when MPD starts.
 	 *
-	 * @return true on success, false if the plugin should be
-	 * disabled
+	 * Throws #PluginUnavailable if the plugin is not available
+	 * and shall be disabled.
 	 */
 	InitResult (*init)(const ConfigBlock &block, Error &error);
 

src/input/plugins/CurlInputPlugin.cxx

@@ -35,6 +35,7 @@
 #include "util/Error.hxx"
 #include "util/Domain.hxx"
 #include "Log.hxx"
+#include "PluginUnavailable.hxx"
 
 #include <assert.h>
 #include <string.h>
@@ -533,15 +534,11 @@ CurlMulti::OnTimeout()
  */
 
 static InputPlugin::InitResult
-input_curl_init(const ConfigBlock &block, Error &error)
+input_curl_init(const ConfigBlock &block, gcc_unused Error &error)
 {
 	CURLcode code = curl_global_init(CURL_GLOBAL_ALL);
-	if (code != CURLE_OK) {
-		error.Format(curl_domain, code,
-			     "curl_global_init() failed: %s",
-			     curl_easy_strerror(code));
-		return InputPlugin::InitResult::UNAVAILABLE;
-	}
+	if (code != CURLE_OK)
+		throw PluginUnavailable(curl_easy_strerror(code));
 
 	const auto version_info = curl_version_info(CURLVERSION_FIRST);
 	if (version_info != nullptr) {
@@ -576,8 +573,7 @@ input_curl_init(const ConfigBlock &block, Error &error)
 	if (multi == nullptr) {
 		curl_slist_free_all(http_200_aliases);
 		curl_global_cleanup();
-		error.Set(curl_domain, 0, "curl_multi_init() failed");
-		return InputPlugin::InitResult::UNAVAILABLE;
+		throw PluginUnavailable("curl_multi_init() failed");
 	}
 
 	curl_multi = new CurlMulti(io_thread_get(), multi);

src/input/plugins/FfmpegInputPlugin.cxx

@@ -27,6 +27,7 @@
 #include "lib/ffmpeg/Error.hxx"
 #include "../InputStream.hxx"
 #include "../InputPlugin.hxx"
+#include "PluginUnavailable.hxx"
 #include "util/StringCompare.hxx"
 #include "util/Error.hxx"
 
@@ -73,15 +74,13 @@ input_ffmpeg_supported(void)
 
 static InputPlugin::InitResult
 input_ffmpeg_init(gcc_unused const ConfigBlock &block,
-		  Error &error)
+		  gcc_unused Error &error)
 {
 	FfmpegInit();
 
 	/* disable this plugin if there's no registered protocol */
-	if (!input_ffmpeg_supported()) {
-		error.Set(ffmpeg_domain, "No protocol");
-		return InputPlugin::InitResult::UNAVAILABLE;
-	}
+	if (!input_ffmpeg_supported())
+		throw PluginUnavailable("No protocol");
 
 	return InputPlugin::InitResult::SUCCESS;
 }

src/input/plugins/SmbclientInputPlugin.cxx

@@ -23,6 +23,7 @@
 #include "lib/smbclient/Mutex.hxx"
 #include "../InputStream.hxx"
 #include "../InputPlugin.hxx"
+#include "PluginUnavailable.hxx"
 #include "util/StringCompare.hxx"
 #include "util/Error.hxx"
 
@@ -73,7 +74,8 @@ input_smbclient_init(gcc_unused const ConfigBlock &block, gcc_unused Error &erro
 	try {
 		SmbclientInit();
 	} catch (const std::runtime_error &e) {
-		return InputPlugin::InitResult::UNAVAILABLE;
+		// TODO: use std::throw_with_nested()?
+		throw PluginUnavailable(e.what());
 	}
 
 	// TODO: create one global SMBCCTX here?