fix(mpd): regularly timeout the event listener to prevent timeout

The MPD server has a connection_timeout that defaults to 60. If no data
is transferred in this timespan, the connection is closed. If the
connection is closed while the event listener is listening for events,
it will block forever. By timing out the event listening and
re-connecting regularly, we prevent this issue. An option "timeout" has
been added for users that have a lower server connection_timeout than
default. Fixes #277

include/modules/mpd.hpp

@@ -48,6 +48,8 @@ class MPD : public ALabel {
   const char*    server_;
   const unsigned port_;
 
+  unsigned timeout_;
+
   // We need a mutex here because we can trigger updates from multiple thread:
   // the event based updates, the periodic updates needed for the elapsed time,
   // and the click play/pause feature

src/modules/mpd.cpp

@@ -7,17 +7,29 @@ waybar::modules::MPD::MPD(const std::string& id, const Json::Value& config)
     : ALabel(config, "{album} - {artist} - {title}", 5),
       module_name_(id.empty() ? "mpd" : "mpd#" + id),
       server_(nullptr),
-      port_(config["port"].asUInt()),
+      port_(config_["port"].isUInt() ? config["port"].asUInt() : 0),
+      timeout_(config_["timeout"].isUInt() ? config_["timeout"].asUInt() * 1'000 : 30'000),
       connection_(nullptr, &mpd_connection_free),
       alternate_connection_(nullptr, &mpd_connection_free),
       status_(nullptr, &mpd_status_free),
       song_(nullptr, &mpd_song_free) {
+  if (!config_["port"].isNull() && !config_["port"].isUInt()) {
+    std::cerr << module_name_ << ": `port` configuration should be an unsigned int" << std::endl;
+  }
+
+  if (!config_["timeout"].isNull() && !config_["timeout"].isUInt()) {
+    std::cerr << module_name_ << ": `timeout` configuration should be an unsigned int" << std::endl;
+  }
+
   label_.set_name("mpd");
   if (!id.empty()) {
     label_.get_style_context()->add_class(id);
   }
 
   if (!config["server"].isNull()) {
+    if (!config_["server"].isString()) {
+      std::cerr << module_name_ << "`server` configuration should be a string" << std::endl;
+    }
     server_ = config["server"].asCString();
   }
 
@@ -50,18 +62,18 @@ auto waybar::modules::MPD::update() -> void {
 std::thread waybar::modules::MPD::event_listener() {
   return std::thread([this] {
     while (true) {
+      try {
         if (connection_ == nullptr) {
           // Retry periodically if no connection
-        try {
           update();
-        } catch (const std::exception& e) {
-          std::cerr << module_name_ + ": " + e.what() << std::endl;
-        }
           std::this_thread::sleep_for(interval_);
         } else {
           waitForEvent();
           dp.emit();
         }
+      } catch (const std::exception& e) {
+        std::cerr << module_name_ + ": " + e.what() << std::endl;
+      }
     }
   });
 }
@@ -76,12 +88,12 @@ std::thread waybar::modules::MPD::periodic_updater() {
 }
 
 std::string waybar::modules::MPD::getTag(mpd_tag_type type, unsigned idx) {
-  std::string result = config_["unknown-tag"].isString() ? config_["unknown-tag"].asString() : "N/A";
+  std::string result =
+      config_["unknown-tag"].isString() ? config_["unknown-tag"].asString() : "N/A";
   const char* tag = mpd_song_get_tag(song_.get(), type, idx);
 
   // mpd_song_get_tag can return NULL, so make sure it's valid before setting
-  if (tag)
+  if (tag) result = tag;
-    result = tag;
 
   return result;
 }
@@ -89,8 +101,9 @@ std::string waybar::modules::MPD::getTag(mpd_tag_type type, unsigned idx) {
 void waybar::modules::MPD::setLabel() {
   if (connection_ == nullptr) {
     label_.get_style_context()->add_class("disconnected");
-    // In the case connection closed while MPD is stopped
     label_.get_style_context()->remove_class("stopped");
+    label_.get_style_context()->remove_class("playing");
+    label_.get_style_context()->remove_class("paused");
 
     auto format = config_["format-disconnected"].isString()
                       ? config_["format-disconnected"].asString()
@@ -231,10 +244,11 @@ void waybar::modules::MPD::tryConnect() {
     return;
   }
 
-  connection_ = unique_connection(mpd_connection_new(server_, port_, 5'000), &mpd_connection_free);
+  connection_ =
+      unique_connection(mpd_connection_new(server_, port_, timeout_), &mpd_connection_free);
 
   alternate_connection_ =
-      unique_connection(mpd_connection_new(server_, port_, 5'000), &mpd_connection_free);
+      unique_connection(mpd_connection_new(server_, port_, timeout_), &mpd_connection_free);
 
   if (connection_ == nullptr || alternate_connection_ == nullptr) {
     std::cerr << module_name_ << ": Failed to connect to MPD" << std::endl;
@@ -250,19 +264,22 @@ void waybar::modules::MPD::tryConnect() {
     connection_.reset();
     alternate_connection_.reset();
   }
+
+  std::cerr << module_name_ << ": Connected to MPD" << std::endl;
 }
 
 void waybar::modules::MPD::checkErrors(mpd_connection* conn) {
   switch (mpd_connection_get_error(conn)) {
     case MPD_ERROR_SUCCESS:
+      mpd_connection_clear_error(conn);
       return;
+    case MPD_ERROR_TIMEOUT:
     case MPD_ERROR_CLOSED:
-      std::cerr << module_name_ << ": Connection to MPD closed" << std::endl;
       mpd_connection_clear_error(conn);
       connection_.reset();
       alternate_connection_.reset();
       state_ = MPD_STATE_UNKNOWN;
-      return;
+      throw std::runtime_error("Connection to MPD closed");
     default:
       auto error_message = mpd_connection_get_error_message(conn);
       mpd_connection_clear_error(conn);
@@ -285,8 +302,19 @@ void waybar::modules::MPD::waitForEvent() {
   auto conn = alternate_connection_.get();
   // Wait for a player (play/pause), option (random, shuffle, etc.), or playlist
   // change
-  mpd_run_idle_mask(conn,
+  if (!mpd_send_idle_mask(
-                    static_cast<mpd_idle>(MPD_IDLE_PLAYER | MPD_IDLE_OPTIONS | MPD_IDLE_PLAYLIST));
+          conn, static_cast<mpd_idle>(MPD_IDLE_PLAYER | MPD_IDLE_OPTIONS | MPD_IDLE_PLAYLIST))) {
+    checkErrors(conn);
+    return;
+  }
+  // alternate_idle_ = true;
+
+  // See issue #277:
+  // https://github.com/Alexays/Waybar/issues/277
+  mpd_recv_idle(conn, /* disable_timeout = */ false);
+  checkErrors(conn);
+  mpd_response_finish(conn);
+
   checkErrors(conn);
 }