neighbor: new subsystem to detect file servers on the local network

This commit adds the NeighborPlugin API which can be used to detect
nearby file servers that can be used by input plugins.  This list of
servers is exported using the new "listneighbors" command.  The idle
even "neighbor" notifies interested clients when a new neighbor is
found or an existing one is lost.

There's a lot missing currently: protocol&user documentation, and a
way to "mount" remote servers into the music database.  Obviously,
some code from the UPnP database plugin can be moved to a neighbor
plugin.

26 files changed, 1101 insertions, 2 deletions

diff --git a/Makefile.am b/Makefile.am
index 6bb3c9094..ee4116211 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -17,6 +17,7 @@ noinst_LIBRARIES = \
 	libtag.a \
 	libinput.a \
 	libfs.a \
+	libneighbor.a \
 	libdb_plugins.a \
 	libplaylist_plugins.a \
 	libdecoder_plugins.a \
@@ -30,6 +31,7 @@ src_mpd_CPPFLAGS = $(AM_CPPFLAGS) \
 	$(LIBWRAP_CFLAGS) \
 	$(SQLITE_CFLAGS)
 src_mpd_LDADD = \
+	$(NEIGHBOR_LIBS) \
 	$(DB_LIBS) \
 	$(PLAYLIST_LIBS) \
 	$(AVAHI_LIBS) \
@@ -398,6 +400,37 @@ libfs_a_SOURCES = \
 	src/fs/StandardDirectory.cxx src/fs/StandardDirectory.hxx \
 	src/fs/DirectoryReader.hxx
 
+# neighbor plugins
+
+if ENABLE_NEIGHBOR_PLUGINS
+
+src_mpd_SOURCES += \
+	src/command/NeighborCommands.cxx \
+	src/command/NeighborCommands.hxx
+
+libneighbor_a_SOURCES = \
+	src/neighbor/Registry.cxx src/neighbor/Registry.hxx \
+	src/neighbor/Glue.cxx src/neighbor/Glue.hxx \
+	src/neighbor/Info.hxx \
+	src/neighbor/Listener.hxx \
+	src/neighbor/Explorer.hxx \
+	src/neighbor/NeighborPlugin.hxx
+
+libneighbor_a_CPPFLAGS = $(AM_CPPFLAGS) \
+	$(SMBCLIENT_CFLAGS)
+
+if ENABLE_SMBCLIENT
+libneighbor_a_SOURCES += \
+	src/lib/smbclient/Init.cxx src/lib/smbclient/Init.hxx \
+	src/neighbor/plugins/SmbclientNeighborPlugin.cxx src/neighbor/plugins/SmbclientNeighborPlugin.hxx
+endif
+
+NEIGHBOR_LIBS = \
+	$(SMBCLIENT_LIBS) \
+	libneighbor.a
+
+endif
+
 # database plugins
 
 libdb_plugins_a_SOURCES = \
@@ -1199,6 +1232,10 @@ noinst_PROGRAMS = \
 	test/run_normalize \
 	test/software_volume
 
+if ENABLE_NEIGHBOR_PLUGINS
+noinst_PROGRAMS += test/run_neighbor_explorer
+endif
+
 if HAVE_AVAHI
 noinst_PROGRAMS += test/run_avahi
 endif
@@ -1278,6 +1315,23 @@ test_run_input_SOURCES = test/run_input.cxx \
 	src/IOThread.cxx \
 	src/TagSave.cxx
 
+if ENABLE_NEIGHBOR_PLUGINS
+
+test_run_neighbor_explorer_SOURCES = \
+	src/Log.cxx src/LogBackend.cxx \
+	test/run_neighbor_explorer.cxx
+test_run_neighbor_explorer_LDADD = \
+	$(GLIB_LIBS) \
+	$(NEIGHBOR_LIBS) \
+	libconf.a \
+	libevent.a \
+	libfs.a \
+	libsystem.a \
+	libthread.a \
+	libutil.a
+
+endif
+
 if ENABLE_ARCHIVE
 
 test_visit_archive_LDADD = \
diff --git a/NEWS b/NEWS
index 71ab008b3..2c22aae99 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,7 @@ ver 0.19 (not yet released)
 * protocol
   - new commands "addtagid", "cleartagid"
   - "lsinfo" and "readcomments" allowed for remote files
+  - "listneighbors" lists file servers on the local network
 * database
   - proxy: forward "idle" events
   - proxy: copy "Last-Modified" from remote directories
diff --git a/configure.ac b/configure.ac
index 1bed0727d..19ead794b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -885,6 +885,27 @@ fi
 AM_CONDITIONAL(ENABLE_MMS, test x$enable_mms = xyes)
 
 dnl ---------------------------------------------------------------------------
+dnl Neighbor Plugins
+dnl ---------------------------------------------------------------------------
+
+AC_ARG_ENABLE(neighbor-plugins,
+	AS_HELP_STRING([--enable-neighbor-plugins],
+		[enable support for neighbor discovery (default: auto)]),,
+	[enable_neighbor_plugins=auto])
+
+if test x$enable_neighbor_plugins = xauto; then
+	if test x$enable_smbclient = xyes; then
+		enable_neighbor_plugins=yes
+	fi
+fi
+
+if test x$enable_neighbor_plugins = xyes; then
+	AC_DEFINE(ENABLE_NEIGHBOR_PLUGINS, 1,
+		[Define to enable support for neighbor discovery])
+fi
+AM_CONDITIONAL(ENABLE_NEIGHBOR_PLUGINS, test x$enable_neighbor_plugins = xyes)
+
+dnl ---------------------------------------------------------------------------
 dnl Archive Plugins
 dnl ---------------------------------------------------------------------------
 
diff --git a/src/CommandLine.cxx b/src/CommandLine.cxx
index c5adc4153..19bc9d4bb 100644
--- a/src/CommandLine.cxx
+++ b/src/CommandLine.cxx
@@ -42,6 +42,11 @@
 #include "util/OptionDef.hxx"
 #include "util/OptionParser.hxx"
 
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+#include "neighbor/Registry.hxx"
+#include "neighbor/NeighborPlugin.hxx"
+#endif
+
 #ifdef ENABLE_ENCODER
 #include "encoder/EncoderList.hxx"
 #include "encoder/EncoderPlugin.hxx"
@@ -104,6 +109,13 @@ static void version(void)
 	for (auto i = database_plugins; *i != nullptr; ++i)
 		printf(" %s", (*i)->name);
 
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+	puts("\n\n"
+	     "Neighbor plugins:");
+	for (auto i = neighbor_plugins; *i != nullptr; ++i)
+		printf(" %s", (*i)->name);
+#endif
+
 	puts("\n\n"
 	     "Decoders plugins:");
 
@@ -148,7 +160,7 @@ static void version(void)
 #endif
 
 	puts("\n"
-	     "input/Input plugins:");
+	     "Input plugins:");
 	input_plugins_for_each(plugin)
 		printf(" %s", plugin->name);
 
diff --git a/src/Idle.cxx b/src/Idle.cxx
index bf08caa99..ed16bbecb 100644
--- a/src/Idle.cxx
+++ b/src/Idle.cxx
@@ -44,6 +44,7 @@ static const char *const idle_names[] = {
 	"update",
 	"subscription",
 	"message",
+	"neighbor",
 	nullptr
 };
 
diff --git a/src/Idle.hxx b/src/Idle.hxx
index a0fbad32c..7fc79d10a 100644
--- a/src/Idle.hxx
+++ b/src/Idle.hxx
@@ -59,6 +59,9 @@ static constexpr unsigned IDLE_SUBSCRIPTION = 0x200;
 /** a message on the subscribed channel was received */
 static constexpr unsigned IDLE_MESSAGE = 0x400;
 
+/** a neighbor was found or lost */
+static constexpr unsigned IDLE_NEIGHBOR = 0x800;
+
 /**
  * Adds idle flag (with bitwise "or") and queues notifications to all
  * clients.
diff --git a/src/Instance.cxx b/src/Instance.cxx
index 5b7c2de2d..16000afb3 100644
--- a/src/Instance.cxx
+++ b/src/Instance.cxx
@@ -54,3 +54,19 @@ Instance::OnDatabaseModified()
 {
 	DatabaseModified();
 }
+
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+
+void
+Instance::FoundNeighbor(gcc_unused const NeighborInfo &info)
+{
+	idle_add(IDLE_NEIGHBOR);
+}
+
+void
+Instance::LostNeighbor(gcc_unused const NeighborInfo &info)
+{
+	idle_add(IDLE_NEIGHBOR);
+}
+
+#endif
diff --git a/src/Instance.hxx b/src/Instance.hxx
index ca7bb5197..a14719839 100644
--- a/src/Instance.hxx
+++ b/src/Instance.hxx
@@ -24,10 +24,24 @@
 #include "db/DatabaseListener.hxx"
 #include "Compiler.h"
 
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+#include "neighbor/Listener.hxx"
+class NeighborGlue;
+#endif
+
 class ClientList;
 struct Partition;
 
-struct Instance final : public DatabaseListener {
+struct Instance final
+	: public DatabaseListener
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+	, public NeighborListener
+#endif
+{
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+	NeighborGlue *neighbors;
+#endif
+
 	ClientList *client_list;
 
 	Partition *partition;
@@ -53,6 +67,12 @@ struct Instance final : public DatabaseListener {
 
 private:
 	virtual void OnDatabaseModified();
+
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+	/* virtual methods from class NeighborListener */
+	virtual void FoundNeighbor(const NeighborInfo &info) override;
+	virtual void LostNeighbor(const NeighborInfo &info) override;
+#endif
 };
 
 #endif
diff --git a/src/Main.cxx b/src/Main.cxx
index fc7efd036..f790ec574 100644
--- a/src/Main.cxx
+++ b/src/Main.cxx
@@ -67,6 +67,10 @@
 #include "config/ConfigOption.hxx"
 #include "Stats.hxx"
 
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+#include "neighbor/Glue.hxx"
+#endif
+
 #ifdef ENABLE_INOTIFY
 #include "db/update/InotifyUpdate.hxx"
 #endif
@@ -394,6 +398,19 @@ int mpd_main(int argc, char *argv[])
 
 	instance = new Instance();
 
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+	instance->neighbors = new NeighborGlue();
+	if (!instance->neighbors->Init(io_thread_get(), *instance, error)) {
+		LogError(error);
+		return EXIT_FAILURE;
+	}
+
+	if (instance->neighbors->IsEmpty()) {
+		delete instance->neighbors;
+		instance->neighbors = nullptr;
+	}
+#endif
+
 	const unsigned max_clients = config_get_positive(CONF_MAX_CONN, 10);
 	instance->client_list = new ClientList(max_clients);
 
@@ -460,6 +477,12 @@ int mpd_main(int argc, char *argv[])
 
 	io_thread_start();
 
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+	if (instance->neighbors != nullptr &&
+	    !instance->neighbors->Open(error))
+		FatalError(error);
+#endif
+
 	ZeroconfInit(*main_loop);
 
 	player_create(instance->partition->pc);
@@ -523,6 +546,13 @@ int mpd_main(int argc, char *argv[])
 	listen_global_finish();
 	delete instance->client_list;
 
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+	if (instance->neighbors != nullptr) {
+		instance->neighbors->Close();
+		delete instance->neighbors;
+	}
+#endif
+
 	const clock_t start = clock();
 	DatabaseGlobalDeinit();
 	FormatDebug(main_domain,
diff --git a/src/command/AllCommands.cxx b/src/command/AllCommands.cxx
index ce753b300..750fd1219 100644
--- a/src/command/AllCommands.cxx
+++ b/src/command/AllCommands.cxx
@@ -27,6 +27,7 @@
 #include "FileCommands.hxx"
 #include "OutputCommands.hxx"
 #include "MessageCommands.hxx"
+#include "NeighborCommands.hxx"
 #include "OtherCommands.hxx"
 #include "Permission.hxx"
 #include "tag/TagType.h"
@@ -99,6 +100,9 @@ static const struct command commands[] = {
 	{ "list", PERMISSION_READ, 1, -1, handle_list },
 	{ "listall", PERMISSION_READ, 0, 1, handle_listall },
 	{ "listallinfo", PERMISSION_READ, 0, 1, handle_listallinfo },
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+	{ "listneighbors", PERMISSION_READ, 0, 0, handle_listneighbors },
+#endif
 	{ "listplaylist", PERMISSION_READ, 1, 1, handle_listplaylist },
 	{ "listplaylistinfo", PERMISSION_READ, 1, 1, handle_listplaylistinfo },
 	{ "listplaylists", PERMISSION_READ, 0, 0, handle_listplaylists },
@@ -179,6 +183,11 @@ command_available(gcc_unused const struct command *cmd)
 		return sticker_enabled();
 #endif
 
+#ifdef ENABLE_NEIGHBOR_PLUGINS
+	if (strcmp(cmd->cmd, "listneighbors") == 0)
+		return neighbor_commands_available();
+#endif
+
 	return true;
 }
 
diff --git a/src/command/NeighborCommands.cxx b/src/command/NeighborCommands.cxx
new file mode 100644
index 000000000..e68e8ef15
--- /dev/null
+++ b/src/command/NeighborCommands.cxx
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2003-2014 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.
+ */
+
+#include "config.h"
+#include "NeighborCommands.hxx"
+#include "client/Client.hxx"
+#include "Instance.hxx"
+#include "Main.hxx"
+#include "protocol/Result.hxx"
+#include "neighbor/Glue.hxx"
+#include "neighbor/Info.hxx"
+
+#include <set>
+#include <string>
+
+#include <assert.h>
+
+bool
+neighbor_commands_available()
+{
+	return instance->neighbors != nullptr;
+}
+
+CommandResult
+handle_listneighbors(Client &client,
+		     gcc_unused int argc, gcc_unused char *argv[])
+{
+	assert(instance->neighbors != nullptr);
+
+	const auto neighbors = instance->neighbors->GetList();
+	for (const auto &i : neighbors)
+		client_printf(client,
+			      "neighbor: %s\n"
+			      "name: %s\n",
+			      i.uri.c_str(),
+			      i.display_name.c_str());
+	return CommandResult::OK;
+}
diff --git a/src/command/NeighborCommands.hxx b/src/command/NeighborCommands.hxx
new file mode 100644
index 000000000..7bad946b4
--- /dev/null
+++ b/src/command/NeighborCommands.hxx
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2003-2014 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_NEIGHBOR_COMMANDS_HXX
+#define MPD_NEIGHBOR_COMMANDS_HXX
+
+#include "CommandResult.hxx"
+#include "Compiler.h"
+
+class Client;
+
+gcc_pure
+bool
+neighbor_commands_available();
+
+CommandResult
+handle_listneighbors(Client &client, int argc, char *argv[]);
+
+#endif
diff --git a/src/config/ConfigOption.hxx b/src/config/ConfigOption.hxx
index 4ee108196..506c9e9dc 100644
--- a/src/config/ConfigOption.hxx
+++ b/src/config/ConfigOption.hxx
@@ -77,6 +77,7 @@ enum ConfigOption {
 	CONF_DESPOTIFY_HIGH_BITRATE,
 	CONF_AUDIO_FILTER,
 	CONF_DATABASE,
+	CONF_NEIGHBORS,
 	CONF_MAX
 };
 
diff --git a/src/config/ConfigTemplates.cxx b/src/config/ConfigTemplates.cxx
index e9cd68b5b..8eaa22bdd 100644
--- a/src/config/ConfigTemplates.cxx
+++ b/src/config/ConfigTemplates.cxx
@@ -77,6 +77,7 @@ const ConfigTemplate config_templates[] = {
 	{ "despotify_high_bitrate", false, false },
 	{ "filter", true, true },
 	{ "database", false, true },
+	{ "neighbors", true, true },
 };
 
 static constexpr unsigned n_config_templates =
diff --git a/src/neighbor/Explorer.hxx b/src/neighbor/Explorer.hxx
new file mode 100644
index 000000000..84a54840c
--- /dev/null
+++ b/src/neighbor/Explorer.hxx
@@ -0,0 +1,71 @@
+/*
+ * Copyright (C) 2003-2014 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_NEIGHBOR_EXPLORER_HXX
+#define MPD_NEIGHBOR_EXPLORER_HXX
+
+#include <forward_list>
+
+class Error;
+class NeighborListener;
+struct NeighborInfo;
+
+/**
+ * An object that explores the neighborhood for music servers.
+ *
+ * As soon as this object is opened, it will start exploring, and
+ * notify the #NeighborListener when it found or lost something.
+ *
+ * The implementation is supposed to be non-blocking.  This can be
+ * implemented either using the #EventLoop instance that was passed to
+ * the NeighborPlugin or by moving the blocking parts in a dedicated
+ * thread.
+ */
+class NeighborExplorer {
+protected:
+	NeighborListener &listener;
+
+	explicit NeighborExplorer(NeighborListener &_listener)
+		:listener(_listener) {}
+
+public:
+	typedef std::forward_list<NeighborInfo> List;
+
+	/**
+	 * Free instance data.
+         */
+	virtual ~NeighborExplorer() {}
+
+	/**
+         * Start exploring the neighborhood.
+	 */
+	virtual bool Open(Error &error) = 0;
+
+	/**
+         * Stop exploring.
+	 */
+	virtual void Close() = 0;
+
+	/**
+	 * Obtain a list of currently known neighbors.
+	 */
+	virtual List GetList() const = 0;
+};
+
+#endif
diff --git a/src/neighbor/Glue.cxx b/src/neighbor/Glue.cxx
new file mode 100644
index 000000000..cc0780d58
--- /dev/null
+++ b/src/neighbor/Glue.cxx
@@ -0,0 +1,111 @@
+/*
+ * Copyright (C) 2003-2014 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.
+ */
+
+#include "config.h"
+#include "Glue.hxx"
+#include "Registry.hxx"
+#include "Explorer.hxx"
+#include "NeighborPlugin.hxx"
+#include "Info.hxx"
+#include "config/ConfigGlobal.hxx"
+#include "config/ConfigData.hxx"
+#include "config/ConfigError.hxx"
+#include "util/Error.hxx"
+
+NeighborGlue::Explorer::~Explorer()
+{
+	delete explorer;
+}
+
+NeighborGlue::~NeighborGlue() {}
+
+static NeighborExplorer *
+CreateNeighborExplorer(EventLoop &loop, NeighborListener &listener,
+		       const config_param &param, Error &error)
+{
+	const char *plugin_name = param.GetBlockValue("plugin");
+	if (plugin_name == nullptr) {
+		error.Set(config_domain,
+			  "Missing \"plugin\" configuration");
+		return nullptr;
+	}
+
+	const NeighborPlugin *plugin = GetNeighborPluginByName(plugin_name);
+	if (plugin == nullptr) {
+		error.Format(config_domain, "No such neighbor plugin: %s",
+			     plugin_name);
+		return nullptr;
+	}
+
+	return plugin->create(loop, listener, param, error);
+}
+
+bool
+NeighborGlue::Init(EventLoop &loop, NeighborListener &listener, Error &error)
+{
+	const config_param *param = nullptr;
+	while ((param = config_get_next_param(CONF_NEIGHBORS, param))) {
+		NeighborExplorer *explorer =
+			CreateNeighborExplorer(loop, listener, *param, error);
+		if (explorer == nullptr) {
+			error.FormatPrefix("Line %i: ", param->line);
+			return false;
+		}
+
+		explorers.emplace_front(explorer);
+	}
+
+	return true;
+}
+
+bool
+NeighborGlue::Open(Error &error)
+{
+	for (auto i = explorers.begin(), end = explorers.end();
+	     i != end; ++i) {
+		if (!i->explorer->Open(error)) {
+			/* roll back */
+			for (auto k = ++i; k != end; ++k)
+				k->explorer->Close();
+			return false;
+		}
+	}
+
+	return true;
+}
+
+void
+NeighborGlue::Close()
+{
+	for (auto i = explorers.begin(), end = explorers.end(); i != end; ++i)
+		i->explorer->Close();
+}
+
+NeighborGlue::List
+NeighborGlue::GetList() const
+{
+	List result;
+
+	for (const auto &i : explorers)
+		result.splice_after(result.before_begin(),
+				    i.explorer->GetList());
+
+	return result;
+}
+
diff --git a/src/neighbor/Glue.hxx b/src/neighbor/Glue.hxx
new file mode 100644
index 000000000..92c612d22
--- /dev/null
+++ b/src/neighbor/Glue.hxx
@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2003-2014 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_NEIGHBOR_ALL_HXX
+#define MPD_NEIGHBOR_ALL_HXX
+
+#include "check.h"
+#include "Compiler.h"
+#include "thread/Mutex.hxx"
+
+#include <forward_list>
+
+struct config_param;
+class Error;
+class EventLoop;
+class NeighborExplorer;
+class NeighborListener;
+struct NeighborInfo;
+
+/**
+ * A class that initializes and opens all configured neighbor plugins.
+ */
+class NeighborGlue {
+	struct Explorer {
+		NeighborExplorer *const explorer;
+
+		Explorer(NeighborExplorer *_explorer):explorer(_explorer) {}
+		Explorer(const Explorer &) = delete;
+		~Explorer();
+	};
+
+	Mutex mutex;
+
+	std::forward_list<Explorer> explorers;
+
+public:
+	typedef std::forward_list<NeighborInfo> List;
+
+	NeighborGlue() = default;
+	NeighborGlue(const NeighborGlue &) = delete;
+	~NeighborGlue();
+
+	bool IsEmpty() const {
+		return explorers.empty();
+	}
+
+	bool Init(EventLoop &loop, NeighborListener &listener, Error &error);
+
+	bool Open(Error &error);
+	void Close();
+
+	/**
+	 * Get the combined list of all neighbors from all active
+	 * plugins.
+	 */
+	gcc_pure
+	List GetList() const;
+};
+
+#endif
diff --git a/src/neighbor/Info.hxx b/src/neighbor/Info.hxx
new file mode 100644
index 000000000..3a34896e7
--- /dev/null
+++ b/src/neighbor/Info.hxx
@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2003-2014 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_NEIGHBOR_INFO_HXX
+#define MPD_NEIGHBOR_INFO_HXX
+
+#include <string>
+
+struct NeighborInfo {
+	std::string uri;
+	std::string display_name;
+};
+
+#endif
diff --git a/src/neighbor/Listener.hxx b/src/neighbor/Listener.hxx
new file mode 100644
index 000000000..20295f5a9
--- /dev/null
+++ b/src/neighbor/Listener.hxx
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2003-2014 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_NEIGHBOR_LISTENER_HXX
+#define MPD_NEIGHBOR_LISTENER_HXX
+
+struct NeighborInfo;
+class NeighborExplorer;
+
+/**
+ * An interface that listens on events from neighbor plugins.  The
+ * methods must be thread-safe and non-blocking.
+ */
+class NeighborListener {
+public:
+	virtual void FoundNeighbor(const NeighborInfo &info) = 0;
+	virtual void LostNeighbor(const NeighborInfo &info) = 0;
+};
+
+#endif
diff --git a/src/neighbor/NeighborPlugin.hxx b/src/neighbor/NeighborPlugin.hxx
new file mode 100644
index 000000000..0d4ebaa7b
--- /dev/null
+++ b/src/neighbor/NeighborPlugin.hxx
@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2003-2014 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_NEIGHBOR_PLUGIN_HXX
+#define MPD_NEIGHBOR_PLUGIN_HXX
+
+struct config_param;
+class Error;
+class EventLoop;
+class NeighborListener;
+class NeighborExplorer;
+
+struct NeighborPlugin {
+	const char *name;
+
+	/**
+	 * Allocates and configures a #NeighborExplorer instance.
+	 */
+	NeighborExplorer *(*create)(EventLoop &loop, NeighborListener &listener,
+				    const config_param &param,
+				    Error &error);
+};
+
+#endif
diff --git a/src/neighbor/Registry.cxx b/src/neighbor/Registry.cxx
new file mode 100644
index 000000000..fc9d05ecf
--- /dev/null
+++ b/src/neighbor/Registry.cxx
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2003-2014 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.
+ */
+
+#include "config.h"
+#include "Registry.hxx"
+#include "NeighborPlugin.hxx"
+#include "plugins/SmbclientNeighborPlugin.hxx"
+
+#include <string.h>
+
+const NeighborPlugin *const neighbor_plugins[] = {
+#ifdef ENABLE_SMBCLIENT
+	&smbclient_neighbor_plugin,
+#endif
+	nullptr
+};
+
+const NeighborPlugin *
+GetNeighborPluginByName(const char *name)
+{
+	for (auto i = neighbor_plugins; *i != nullptr; ++i)
+		if (strcmp((*i)->name, name) == 0)
+			return *i;
+
+	return nullptr;
+}
diff --git a/src/neighbor/Registry.hxx b/src/neighbor/Registry.hxx
new file mode 100644
index 000000000..0b89e537d
--- /dev/null
+++ b/src/neighbor/Registry.hxx
@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2003-2014 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_NEIGHBOR_REGISTRY_HXX
+#define MPD_NEIGHBOR_REGISTRY_HXX
+
+#include "Compiler.h"
+
+struct NeighborPlugin;
+
+/**
+ * nullptr terminated list of all neighbor plugins which were enabled at
+ * compile time.
+ */
+extern const NeighborPlugin *const neighbor_plugins[];
+
+gcc_pure
+const NeighborPlugin *
+GetNeighborPluginByName(const char *name);
+
+#endif
diff --git a/src/neighbor/plugins/SmbclientNeighborPlugin.cxx b/src/neighbor/plugins/SmbclientNeighborPlugin.cxx
new file mode 100644
index 000000000..8dc537e94
--- /dev/null
+++ b/src/neighbor/plugins/SmbclientNeighborPlugin.cxx
@@ -0,0 +1,285 @@
+/*
+ * Copyright (C) 2003-2014 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.
+ */
+
+#include "config.h"
+#include "SmbclientNeighborPlugin.hxx"
+#include "lib/smbclient/Init.hxx"
+#include "neighbor/NeighborPlugin.hxx"
+#include "neighbor/Explorer.hxx"
+#include "neighbor/Listener.hxx"
+#include "neighbor/Info.hxx"
+#include "thread/Mutex.hxx"
+#include "thread/Cond.hxx"
+#include "thread/Thread.hxx"
+#include "thread/Name.hxx"
+#include "util/Macros.hxx"
+#include "util/Domain.hxx"
+#include "util/Error.hxx"
+#include "Log.hxx"
+
+#include <libsmbclient.h>
+
+#include <list>
+#include <algorithm>
+
+static constexpr Domain smbclient_domain("smbclient");
+
+class SmbclientNeighborExplorer final : public NeighborExplorer {
+	struct Server {
+		std::string name, comment;
+
+		bool alive;
+
+		Server(std::string &&_name, std::string &&_comment)
+			:name(std::move(_name)), comment(std::move(_comment)),
+			 alive(true) {}
+		Server(const Server &) = delete;
+
+		gcc_pure
+		bool operator==(const Server &other) const {
+			return name == other.name;
+		}
+
+		gcc_pure
+		NeighborInfo Export() const {
+			return { "smb://" + name + "/", comment };
+		}
+	};
+
+	Thread thread;
+
+	mutable Mutex mutex;
+	Cond cond;
+
+	List list;
+
+	bool quit;
+
+public:
+	SmbclientNeighborExplorer(NeighborListener &_listener)
+		:NeighborExplorer(_listener) {}
+
+	/* virtual methods from class NeighborExplorer */
+	virtual bool Open(Error &error) override;
+	virtual void Close() override;
+	virtual List GetList() const override;
+
+private:
+	void Run();
+	void ThreadFunc();
+	static void ThreadFunc(void *ctx);
+};
+
+bool
+SmbclientNeighborExplorer::Open(Error &error)
+{
+	quit = false;
+	return thread.Start(ThreadFunc, this, error);
+}
+
+void
+SmbclientNeighborExplorer::Close()
+{
+	mutex.lock();
+	quit = true;
+	cond.signal();
+	mutex.unlock();
+
+	thread.Join();
+}
+
+NeighborExplorer::List
+SmbclientNeighborExplorer::GetList() const
+{
+	const ScopeLock protect(mutex);
+	/*
+	List list;
+	for (const auto &i : servers)
+		list.emplace_front(i.Export());
+	*/
+	return list;
+}
+
+static void
+ReadServer(NeighborExplorer::List &list, const smbc_dirent &e)
+{
+	const std::string name(e.name, e.namelen);
+	const std::string comment(e.comment, e.commentlen);
+
+	NeighborInfo info{
+		"smb://" + name,
+		name + " (" + comment + ")",
+	};
+
+	list.emplace_front(std::move(info));
+}
+
+static void
+ReadServers(NeighborExplorer::List &list, const char *uri);
+
+static void
+ReadWorkgroup(NeighborExplorer::List &list, const std::string &name)
+{
+	std::string uri = "smb://" + name;
+	ReadServers(list, uri.c_str());
+}
+
+static void
+ReadEntry(NeighborExplorer::List &list, const smbc_dirent &e)
+{
+	switch (e.smbc_type) {
+	case SMBC_WORKGROUP:
+		ReadWorkgroup(list, std::string(e.name, e.namelen));
+		break;
+
+	case SMBC_SERVER:
+		ReadServer(list, e);
+		break;
+	}
+}
+
+static void
+ReadServers(NeighborExplorer::List &list, int fd)
+{
+	smbc_dirent *e;
+	while ((e = smbc_readdir(fd)) != nullptr)
+		ReadEntry(list, *e);
+
+	smbc_closedir(fd);
+}
+
+static void
+ReadServers(NeighborExplorer::List &list, const char *uri)
+{
+	int fd = smbc_opendir(uri);
+	if (fd >= 0) {
+		ReadServers(list, fd);
+		smbc_closedir(fd);
+	} else
+		FormatErrno(smbclient_domain, "smbc_opendir('%s') failed",
+			    uri);
+}
+
+gcc_pure
+static NeighborExplorer::List
+DetectServers()
+{
+	NeighborExplorer::List list;
+	ReadServers(list, "smb://");
+	return list;
+}
+
+gcc_pure
+static NeighborExplorer::List::const_iterator
+FindBeforeServerByURI(NeighborExplorer::List::const_iterator prev,
+		      NeighborExplorer::List::const_iterator end,
+		      const std::string &uri)
+{
+	for (auto i = std::next(prev); i != end; prev = i, i = std::next(prev))
+		if (i->uri == uri)
+			return prev;
+
+	return end;
+}
+
+inline void
+SmbclientNeighborExplorer::Run()
+{
+	List found = DetectServers(), lost;
+
+	mutex.lock();
+
+	const auto found_before_begin = found.before_begin();
+	const auto found_end = found.end();
+
+	for (auto prev = list.before_begin(), i = std::next(prev), end = list.end();
+	     i != end; i = std::next(prev)) {
+		auto f = FindBeforeServerByURI(found_before_begin, found_end,
+					       i->uri);
+		if (f != found_end) {
+			/* still visible: remove from "found" so we
+			   don't believe it's a new one */
+			*i = std::move(*std::next(f));
+			found.erase_after(f);
+			prev = i;
+		} else {
+			/* can't see it anymore: move to "lost" */
+			lost.splice_after(lost.before_begin(), list, prev);
+		}
+	}
+
+	for (auto prev = found_before_begin, i = std::next(prev);
+	     i != found_end; prev = i, i = std::next(prev))
+		list.push_front(*i);
+
+	mutex.unlock();
+
+	for (auto &i : lost)
+		listener.LostNeighbor(i);
+
+	for (auto &i : found)
+		listener.FoundNeighbor(i);
+}
+
+inline void
+SmbclientNeighborExplorer::ThreadFunc()
+{
+	mutex.lock();
+
+	while (!quit) {
+		mutex.unlock();
+
+		Run();
+
+		mutex.lock();
+		if (quit)
+			break;
+
+		// TODO: sleep for how long?
+		cond.timed_wait(mutex, 10000);
+	}
+
+	mutex.unlock();
+}
+
+void
+SmbclientNeighborExplorer::ThreadFunc(void *ctx)
+{
+	SetThreadName("smbclient");
+
+	SmbclientNeighborExplorer &e = *(SmbclientNeighborExplorer *)ctx;
+	e.ThreadFunc();
+}
+
+static NeighborExplorer *
+smbclient_neighbor_create(gcc_unused EventLoop &loop,
+			  NeighborListener &listener,
+			  gcc_unused const config_param &param,
+			  gcc_unused Error &error)
+{
+	if (!SmbclientInit(error))
+		return nullptr;
+
+	return new SmbclientNeighborExplorer(listener);
+}
+
+const NeighborPlugin smbclient_neighbor_plugin = {
+	"smbclient",
+	smbclient_neighbor_create,
+};
diff --git a/src/neighbor/plugins/SmbclientNeighborPlugin.hxx b/src/neighbor/plugins/SmbclientNeighborPlugin.hxx
new file mode 100644
index 000000000..12ec9c0cd
--- /dev/null
+++ b/src/neighbor/plugins/SmbclientNeighborPlugin.hxx
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2003-2014 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_NEIGHBOR_SMBCLIENT_HXX
+#define MPD_NEIGHBOR_SMBCLIENT_HXX
+
+struct NeighborPlugin;
+
+extern const NeighborPlugin smbclient_neighbor_plugin;
+
+#endif
diff --git a/test/.gitignore b/test/.gitignore
new file mode 100644
index 000000000..132ce5fcf
--- /dev/null
+++ b/test/.gitignore
@@ -0,0 +1 @@
+/run_neighbor_explorer
diff --git a/test/run_neighbor_explorer.cxx b/test/run_neighbor_explorer.cxx
new file mode 100644
index 000000000..374114b11
--- /dev/null
+++ b/test/run_neighbor_explorer.cxx
@@ -0,0 +1,85 @@
+/*
+ * Copyright (C) 2003-2014 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.
+ */
+
+#include "config.h"
+#include "config/ConfigGlobal.hxx"
+#include "neighbor/Listener.hxx"
+#include "neighbor/Info.hxx"
+#include "neighbor/Glue.hxx"
+#include "fs/Path.hxx"
+#include "event/Loop.hxx"
+#include "util/Error.hxx"
+#include "Log.hxx"
+
+#include <stdio.h>
+#include <stdlib.h>
+
+class MyNeighborListener final : public NeighborListener {
+ public:
+	/* virtual methods from class NeighborListener */
+	virtual void FoundNeighbor(const NeighborInfo &info) override {
+		printf("found '%s' (%s)\n",
+		       info.display_name.c_str(), info.uri.c_str());
+	}
+
+	virtual void LostNeighbor(const NeighborInfo &info) override {
+		printf("lost '%s' (%s)\n",
+		       info.display_name.c_str(), info.uri.c_str());
+	}
+};
+
+int
+main(int argc, char **argv)
+{
+	if (argc != 2) {
+		fprintf(stderr, "Usage: run_neighbor_explorer CONFIG\n");
+		return EXIT_FAILURE;
+	}
+
+	const Path config_path = Path::FromFS(argv[1]);
+
+	/* read configuration file (mpd.conf) */
+
+	Error error;
+
+	config_global_init();
+	if (!ReadConfigFile(config_path, error)) {
+		LogError(error);
+		return EXIT_FAILURE;
+	}
+
+	/* initialize the core */
+
+	EventLoop loop((EventLoop::Default()));
+
+	/* initialize neighbor plugins */
+
+	MyNeighborListener listener;
+	NeighborGlue neighbor;
+	if (!neighbor.Init(loop, listener, error) || !neighbor.Open(error)) {
+		LogError(error);
+		return EXIT_FAILURE;
+	}
+
+	/* run */
+
+	loop.Run();
+	neighbor.Close();
+	return EXIT_SUCCESS;
+}