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.

1 files changed, 285 insertions, 0 deletions

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,
+};