InputPlugin: allow init() to soft-fail

Add enum InputResult which is a tri-state.  Input plugins may now fail
and just become unavailable.

src/input/Init.cxx

@@ -25,6 +25,7 @@
 #include "config/ConfigGlobal.hxx"
 #include "config/ConfigOption.hxx"
 #include "config/ConfigData.hxx"
+#include "Log.hxx"
 
 #include <assert.h>
 #include <string.h>
@@ -49,12 +50,29 @@ input_stream_global_init(Error &error)
 			/* the plugin is disabled in mpd.conf */
 			continue;
 
-		if (plugin->init == nullptr || plugin->init(*param, error))
+		InputPlugin::InitResult result = plugin->init != nullptr
+			? plugin->init(*param, error)
+			: InputPlugin::InitResult::SUCCESS;
+
+		switch (result) {
+		case InputPlugin::InitResult::SUCCESS:
 			input_plugins_enabled[i] = true;
-		else {
+			break;
+
+		case InputPlugin::InitResult::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

@@ -26,12 +26,41 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#ifdef WIN32
+#include <windows.h>
+/* damn you, windows.h! */
+#ifdef ERROR
+#undef ERROR
+#endif
+#endif
+
 struct config_param;
 struct InputStream;
 class Error;
 struct Tag;
 
 struct InputPlugin {
+	enum class InitResult {
+		/**
+		 * A fatal error has occurred (e.g. misconfiguration).
+		 * The #Error has been set.
+		 */
+		ERROR,
+
+		/**
+		 * The plugin was initialized successfully and is
+		 * 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,
+	};
+
 	typedef int64_t offset_type;
 
 	const char *name;
@@ -42,7 +71,7 @@ struct InputPlugin {
 	 * @return true on success, false if the plugin should be
 	 * disabled
 	 */
-	bool (*init)(const config_param &param, Error &error);
+	InitResult (*init)(const config_param &param, Error &error);
 
 	/**
 	 * Global deinitialization.  Called once before MPD shuts

src/input/plugins/CdioParanoiaInputPlugin.cxx

@@ -87,7 +87,7 @@ static constexpr Domain cdio_domain("cdio");
 
 static bool default_reverse_endian;
 
-static bool
+static InputPlugin::InitResult
 input_cdio_init(const config_param &param, Error &error)
 {
 	const char *value = param.GetBlockValue("default_byte_order");
@@ -100,11 +100,11 @@ input_cdio_init(const config_param &param, Error &error)
 			error.Format(config_domain, 0,
 				     "Unrecognized 'default_byte_order' setting: %s",
 				     value);
-			return false;
+			return InputPlugin::InitResult::ERROR;
 		}
 	}
 
-	return true;
+	return InputPlugin::InitResult::SUCCESS;
 }
 
 static void

src/input/plugins/CurlInputPlugin.cxx

@@ -595,7 +595,7 @@ CurlMulti::OnTimeout()
  *
  */
 
-static bool
+static InputPlugin::InitResult
 input_curl_init(const config_param &param, Error &error)
 {
 	CURLcode code = curl_global_init(CURL_GLOBAL_ALL);
@@ -603,7 +603,7 @@ input_curl_init(const config_param &param, Error &error)
 		error.Format(curl_domain, code,
 			     "curl_global_init() failed: %s",
 			     curl_easy_strerror(code));
-		return false;
+		return InputPlugin::InitResult::UNAVAILABLE;
 	}
 
 	const auto version_info = curl_version_info(CURLVERSION_FIRST);
@@ -634,12 +634,14 @@ input_curl_init(const config_param &param, Error &error)
 
 	CURLM *multi = curl_multi_init();
 	if (multi == nullptr) {
+		curl_slist_free_all(http_200_aliases);
+		curl_global_cleanup();
 		error.Set(curl_domain, 0, "curl_multi_init() failed");
-		return false;
+		return InputPlugin::InitResult::UNAVAILABLE;
 	}
 
 	curl_multi = new CurlMulti(io_thread_get(), multi);
-	return true;
+	return InputPlugin::InitResult::SUCCESS;
 }
 
 static void

src/input/plugins/FfmpegInputPlugin.cxx

@@ -69,7 +69,7 @@ input_ffmpeg_supported(void)
 	return avio_enum_protocols(&opaque, 0) != nullptr;
 }
 
-static bool
+static InputPlugin::InitResult
 input_ffmpeg_init(gcc_unused const config_param &param,
 		  Error &error)
 {
@@ -78,10 +78,10 @@ input_ffmpeg_init(gcc_unused const config_param &param,
 	/* disable this plugin if there's no registered protocol */
 	if (!input_ffmpeg_supported()) {
 		error.Set(ffmpeg_domain, "No protocol");
-		return false;
+		return InputPlugin::InitResult::UNAVAILABLE;
 	}
 
-	return true;
+	return InputPlugin::InitResult::SUCCESS;
 }
 
 static InputStream *

src/input/plugins/SmbclientInputPlugin.cxx

@@ -91,17 +91,17 @@ public:
  *
  */
 
-static bool
+static InputPlugin::InitResult
 input_smbclient_init(gcc_unused const config_param &param, Error &error)
 {
 	if (!SmbclientInit(error))
-		return false;
+		return InputPlugin::InitResult::UNAVAILABLE;
 
 	// TODO: create one global SMBCCTX here?
 
 	// TODO: evaluate config_param, call smbc_setOption*()
 
-	return true;
+	return InputPlugin::InitResult::SUCCESS;
 }
 
 static InputStream *