UPnP database plugin

[mk: renamed source files, applied coding style, reduced bloat, using
MPD's threading library, using MPD's error reporting and logging
library and refactoring, fixed lots of bugs]

src/db/UpnpDatabasePlugin.cxx

@@ -0,0 +1,923 @@
+/*
+ * Copyright (C) 2003-2012 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 "UpnpDatabasePlugin.hxx"
+#include "upnp/Domain.hxx"
+#include "upnp/upnpplib.hxx"
+#include "upnp/Discovery.hxx"
+#include "upnp/ContentDirectoryService.hxx"
+#include "upnp/Directory.hxx"
+#include "DatabasePlugin.hxx"
+#include "DatabaseSelection.hxx"
+#include "DatabaseError.hxx"
+#include "PlaylistVector.hxx"
+#include "Directory.hxx"
+#include "Song.hxx"
+#include "ConfigData.hxx"
+#include "tag/TagBuilder.hxx"
+#include "tag/TagTable.hxx"
+#include "util/Error.hxx"
+#include "util/Domain.hxx"
+#include "Log.hxx"
+#include "SongFilter.hxx"
+
+#include <string>
+#include <vector>
+#include <map>
+#include <set>
+
+#include <assert.h>
+#include <string.h>
+
+static const char *const rootid = "0";
+
+class UpnpDatabase : public Database {
+	LibUPnP *m_lib;
+	UPnPDeviceDirectory *m_superdir;
+	Directory *m_root;
+	std::string m_upnplog;
+
+public:
+	UpnpDatabase()
+		: m_lib(0), m_superdir(0), m_root(0)
+	{}
+
+	static Database *Create(const config_param &param,
+				Error &error);
+
+	virtual bool Open(Error &error) override;
+	virtual void Close() override;
+	virtual Song *GetSong(const char *uri_utf8,
+			      Error &error) const override;
+	virtual void ReturnSong(Song *song) const;
+
+	virtual bool Visit(const DatabaseSelection &selection,
+			   VisitDirectory visit_directory,
+			   VisitSong visit_song,
+			   VisitPlaylist visit_playlist,
+			   Error &error) const override;
+
+	virtual bool VisitUniqueTags(const DatabaseSelection &selection,
+				     TagType tag_type,
+				     VisitString visit_string,
+				     Error &error) const override;
+
+	virtual bool GetStats(const DatabaseSelection &selection,
+			      DatabaseStats &stats,
+			      Error &error) const override;
+	virtual time_t GetUpdateStamp() const {return 0;}
+
+protected:
+	bool Configure(const config_param &param, Error &error);
+
+private:
+	bool reallyOpen(Error &error);
+	bool VisitServer(ContentDirectoryService* server,
+			 const std::vector<std::string> &vpath,
+			 const DatabaseSelection &selection,
+			 VisitDirectory visit_directory,
+			 VisitSong visit_song,
+			 VisitPlaylist visit_playlist,
+			 Error &error) const;
+
+	/**
+	 * Run an UPnP search according to MPD parameters, and
+	 * visit_song the results.
+	 */
+	bool SearchSongs(ContentDirectoryService* server,
+			 const char *objid,
+			 const DatabaseSelection &selection,
+			 VisitSong visit_song,
+			 Error &error) const;
+
+	bool SearchSongs(ContentDirectoryService* server,
+			 const char *objid,
+			 const DatabaseSelection &selection,
+			 UPnPDirContent& dirbuf,
+			 Error &error) const;
+
+	bool Namei(ContentDirectoryService* server,
+		   const std::vector<std::string> &vpath,
+		   std::string &oobjid, UPnPDirObject &dirent,
+		   Error &error) const;
+
+	/**
+	 * Take server and objid, return metadata.
+	 */
+	bool ReadNode(ContentDirectoryService* server,
+		      const char *objid, UPnPDirObject& dirent,
+		      Error &error) const;
+
+	/**
+	 * Get the path for an object Id. This works much like pwd,
+	 * except easier cause our inodes have a parent id. Not used
+	 * any more actually (see comments in SearchSongs).
+	 */
+	bool BuildPath(ContentDirectoryService* server,
+		       const UPnPDirObject& dirent, std::string &idpath,
+		       Error &error) const;
+};
+
+gcc_pure
+static std::vector<std::string>
+stringToTokens(const std::string &str,
+	       const char *delims = "/", bool skipinit = true)
+{
+	std::vector<std::string> tokens;
+
+	std::string::size_type startPos = 0;
+
+	// Skip initial delims, return empty if this eats all.
+	if (skipinit &&
+	    (startPos = str.find_first_not_of(delims, 0)) == std::string::npos)
+		return tokens;
+
+	while (startPos < str.size()) {
+		// Find next delimiter or end of string (end of token)
+		auto pos = str.find_first_of(delims, startPos);
+
+		// Add token to the vector and adjust start
+		if (pos == std::string::npos) {
+			tokens.push_back(str.substr(startPos));
+			break;
+		} else if (pos == startPos) {
+			// Dont' push empty tokens after first
+			if (tokens.empty())
+				tokens.push_back(std::string());
+			startPos = ++pos;
+		} else {
+			tokens.push_back(str.substr(startPos, pos - startPos));
+			startPos = ++pos;
+		}
+	}
+
+	return tokens;
+}
+
+Database *
+UpnpDatabase::Create(const config_param &param, Error &error)
+{
+	UpnpDatabase *db = new UpnpDatabase();
+	if (db && !db->Configure(param, error)) {
+		delete db;
+		db = nullptr;
+	}
+	return db;
+}
+
+bool
+UpnpDatabase::Configure(const config_param& param, Error&)
+{
+	m_upnplog = param.GetBlockValue("upnplog", "");
+	return true;
+}
+
+// Open is called before mpd daemonizes, and daemonizing messes with
+// the UpNP lib (it loses its ability to receive mcast messages
+// apparently).
+// So we delay actual opening until the first client call.
+//
+// Unfortunately the servers may take a few seconds to answer the
+// first search on the network, so we would either have to sleep for a
+// relatively long time (maybe 5S), or accept that the directory may
+// not be complete on the first client call. There is no simple
+// solution to this issue, we would need a call from mpd after daemonizing.
+bool
+UpnpDatabase::Open(Error &)
+{
+	return true;
+}
+
+bool UpnpDatabase::reallyOpen(Error &error)
+{
+	if (m_root)
+		return true;
+
+	m_lib = LibUPnP::getLibUPnP(error);
+	if (!m_lib)
+		return false;
+
+	if (!m_upnplog.empty()) {
+		m_lib->setLogFileName(m_upnplog);
+	}
+	m_superdir = UPnPDeviceDirectory::getTheDir();
+	if (!m_superdir || !m_superdir->ok()) {
+		error.Set(upnp_domain, "Discovery services startup failed");
+		return false;
+	}
+
+	m_root = Directory::NewRoot();
+	// Wait for device answers. This should be consistent with the value set
+	// in the lib (currently 2)
+	sleep(2);
+	return true;
+}
+
+void
+UpnpDatabase::Close()
+{
+	if (m_root)
+		delete m_root;
+	// TBD decide what we do with the lib and superdir objects
+}
+
+void
+UpnpDatabase::ReturnSong(Song *song) const
+{
+	assert(song != nullptr);
+
+	song->Free();
+}
+
+/**
+ * Transform titles to turn '/' into '_' to make them acceptable path
+ * elements. There is a very slight risk of collision in doing
+ * this. Twonky returns directory names (titles) like 'Artist/Album'.
+ */
+gcc_pure
+static std::string
+titleToPathElt(const std::string &in)
+{
+	std::string out;
+	for (auto it = in.begin(); it != in.end(); it++) {
+		if (*it == '/') {
+			out += '_';
+		} else {
+			out += *it;
+		}
+	}
+	return out;
+}
+
+gcc_pure
+static int
+upnpDurationToSeconds(const std::string &duration)
+{
+	const auto v = stringToTokens(duration, ":");
+	if (v.size() != 3)
+		return 0;
+	return atoi(v[0].c_str())*3600 + atoi(v[1].c_str())*60 + atoi(v[2].c_str());
+}
+
+// Upnp element to mpd tag number correspondance.
+// Don't know the upnp equivalent if any: TAG_ALBUM_ARTIST TAG_NAME
+// TAG_DATE TAG_COMPOSER TAG_PERFORMER TAG_COMMENT TAG_DISC
+static std::map<std::string, TagType> propToTag = {
+	{"upnp:artist", TAG_ARTIST},
+	{"upnp:album", TAG_ALBUM},
+	{"upnp:originalTrackNumber", TAG_TRACK},
+	{"upnp:genre", TAG_GENRE},
+	{"dc:title", TAG_TITLE},
+};
+
+// If uri is empty, we use the object's url instead. This happens
+// when the target of a Visit() is a song, which  only happens when
+// "add"ing AFAIK. Visit() calls us with a null uri so that the url
+// appropriate for fetching is used instead.
+static Song *
+upnpItemToSong(const UPnPDirObject &dirent, const char *uri)
+{
+	std::string url(uri);
+	if (url.empty())
+		dirent.getprop("url", url);
+
+	Song *s = Song::NewFile(url.c_str(), nullptr);
+
+	// I don't think that upnp returns this.
+	s->mtime = time(0);
+
+	s->start_ms = 0;
+	std::string sprop("0:0:0");
+	dirent.getprop("duration", sprop);
+	int seconds = upnpDurationToSeconds(sprop);
+	s->end_ms = seconds * 1000;
+
+	TagBuilder tag;
+	tag.SetTime(seconds);
+
+	tag.AddItem(TAG_TITLE, titleToPathElt(dirent.m_title).c_str());
+
+	for (auto &pt : propToTag)
+		if (dirent.getprop(pt.first, sprop))
+			tag.AddItem(pt.second, sprop.c_str());
+
+	s->tag = tag.CommitNew();
+	return s;
+}
+
+// Get song info by path. We can receive either the id path, or the titles
+// one
+Song *
+UpnpDatabase::GetSong(const char *uri, Error &error) const
+{
+	if (!const_cast<UpnpDatabase *>(this)->reallyOpen(error))
+		return nullptr;
+
+	if (!m_superdir || !m_superdir->ok()) {
+		error.Set(upnp_domain,
+			  "UpnpDatabase::GetSong() superdir is sick");
+		return nullptr;
+	}
+
+	Song *song = nullptr;
+	auto vpath = stringToTokens(uri, "/", true);
+	if (vpath.size() >= 2) {
+		ContentDirectoryService server;
+		if (!m_superdir->getServer(vpath[0].c_str(), server)) {
+			error.Set(upnp_domain, "server not found");
+			return nullptr;
+		}
+
+		vpath.erase(vpath.begin());
+		UPnPDirObject dirent;
+		if (vpath[0].compare(rootid)) {
+			std::string objid;
+			if (!Namei(&server, vpath, objid, dirent, error))
+				return nullptr;
+		} else {
+			if (!ReadNode(&server, vpath.back().c_str(), dirent,
+				      error))
+				return nullptr;
+		}
+		song = upnpItemToSong(dirent, "");
+	}
+	if (song == nullptr)
+		error.Format(db_domain, DB_NOT_FOUND, "No such song: %s", uri);
+
+	return song;
+}
+
+static const struct tag_table upnp_tags[] = {
+	{ "upnp:artist", TAG_ARTIST },
+	{ "upnp:album", TAG_ALBUM },
+	{ "upnp:originalTrackNumber", TAG_TRACK },
+	{ "upnp:genre", TAG_GENRE },
+	{ "dc:title", TAG_TITLE },
+
+	/* sentinel */
+	{ nullptr, TAG_NUM_OF_ITEM_TYPES }
+};
+
+/**
+ * Retrieve the value for an MPD tag from an object entry.
+ */
+static bool
+getTagValue(UPnPDirObject& dirent, TagType tag,
+	    std::string &tagvalue)
+{
+	if (tag == TAG_TITLE) {
+		if (!dirent.m_title.empty()) {
+			tagvalue = titleToPathElt(dirent.m_title);
+			return true;
+		}
+		return false;
+	}
+
+	const char *name = tag_table_lookup(upnp_tags, tag);
+	if (name == nullptr)
+		return false;
+
+	std::string propvalue;
+	dirent.getprop(name, propvalue);
+	if (propvalue.empty())
+		return false;
+	tagvalue = propvalue;
+	return true;
+}
+
+/**
+ * Double-quote a string, adding internal backslash escaping.
+ */
+static void
+dquote(std::string &out, const char *in)
+{
+	out.append(1, '"');
+
+	for (; *in != 0; ++in) {
+		switch(*in) {
+		case '\\':
+		case '"':
+			out.append(1, '\\');
+			out.append(1, *in);
+			break;
+
+		default:
+			out.append(1, *in);
+		}
+	}
+
+	out.append(1, '"');
+}
+
+// Run an UPnP search, according to MPD parameters. Return results as
+// UPnP items
+bool
+UpnpDatabase::SearchSongs(ContentDirectoryService* server,
+			  const char *objid,
+			  const DatabaseSelection &selection,
+			  UPnPDirContent &dirbuf,
+			  Error &error) const
+{
+	const SongFilter *filter = selection.filter;
+	if (selection.filter == nullptr)
+		return true;
+
+	std::set<std::string> searchcaps;
+	if (!server->getSearchCapabilities(searchcaps, error))
+		return false;
+
+	if (searchcaps.empty())
+		return true;
+
+	std::string cond;
+	for (const auto &item : filter->GetItems()) {
+		switch (auto tag = item.GetTag()) {
+		case LOCATE_TAG_ANY_TYPE:
+			{
+				if (!cond.empty()) {
+					cond += " and ";
+				}
+				cond += "(";
+				bool first(true);
+				for (const auto& cap : searchcaps) {
+					if (first)
+						first = false;
+					else
+						cond += " or ";
+					cond += cap;
+					if (item.GetFoldCase()) {
+						cond += " contains ";
+					} else {
+						cond += " = ";
+					}
+					dquote(cond, item.GetValue().c_str());
+				}
+				cond += ")";
+			}
+			break;
+
+		default:
+			/* Unhandled conditions like
+			   LOCATE_TAG_BASE_TYPE or
+			   LOCATE_TAG_FILE_TYPE won't have a
+			   corresponding upnp prop, so they will be
+			   skipped */
+			if (tag == TAG_ALBUM_ARTIST)
+				tag = TAG_ARTIST;
+
+			// TODO: support LOCATE_TAG_ANY_TYPE etc.
+			const char *name = tag_table_lookup(upnp_tags,
+							    TagType(tag));
+			if (name == nullptr)
+				continue;
+
+			if (!cond.empty()) {
+				cond += " and ";
+			}
+			cond += name;
+
+			/* FoldCase doubles up as contains/equal
+			   switch. UpNP search is supposed to be
+			   case-insensitive, but at least some servers
+			   have the same convention as mpd (e.g.:
+			   minidlna) */
+			if (item.GetFoldCase()) {
+				cond += " contains ";
+			} else {
+				cond += " = ";
+			}
+			dquote(cond, item.GetValue().c_str());
+		}
+	}
+
+	return server->search(objid, cond.c_str(), dirbuf, error);
+}
+
+static bool
+visitSong(const UPnPDirObject& meta, const char *path,
+	  const DatabaseSelection &selection,
+	  VisitSong visit_song, Error& error)
+{
+	if (!visit_song)
+		return true;
+	Song *s = upnpItemToSong(meta, path);
+	if (!selection.Match(*s))
+		return true;
+	bool success = visit_song(*s, error);
+	s->Free();
+	return success;
+}
+
+/**
+ * Build synthetic path based on object id for search results. The use
+ * of "rootid" is arbitrary, any name that is not likely to be a top
+ * directory name would fit.
+ */
+static const std::string
+songPath(const std::string &servername,
+	 const std::string &objid)
+{
+	return servername + "/" + rootid + "/" + objid;
+}
+
+bool
+UpnpDatabase::SearchSongs(ContentDirectoryService* server,
+			  const char *objid,
+			  const DatabaseSelection &selection,
+			  VisitSong visit_song,
+			  Error &error) const
+{
+	UPnPDirContent dirbuf;
+	if (!visit_song)
+		return true;
+	if (!SearchSongs(server, objid, selection, dirbuf, error))
+		return false;
+
+	for (const auto &dirent : dirbuf.m_items) {
+		// We get song ids as the result of the UPnP search. But our
+		// client expects paths (e.g. we get 1$4$3788 from minidlna,
+		// but we need to translate to /Music/All_Music/Satisfaction).
+		// We can do this in two ways:
+		//  - Rebuild a normal path using BuildPath() which is a kind of pwd
+		//  - Build a bogus path based on the song id.
+		// The first method is nice because the returned paths are pretty, but
+		// it has two big problems:
+		//  - The song paths are ambiguous: e.g. minidlna returns all search
+		//    results as being from the "All Music" directory, which can
+		//    contain several songs with the same title (but different objids)
+		//  - The performance of BuildPath() is atrocious on very big
+		//    directories, even causing timeouts in clients. And of
+		//    course, 'All Music' is very big.
+		// So we return synthetic and ugly paths based on the object id,
+		// which we later have to detect.
+		std::string path = songPath(server->getFriendlyName(),
+					    dirent.m_id);
+		//BuildPath(server, dirent, path);
+		if (!visitSong(dirent, path.c_str(), selection, visit_song,
+			       error))
+			return false;
+	}
+
+	return true;
+}
+
+bool
+UpnpDatabase::ReadNode(ContentDirectoryService *server,
+		       const char *objid, UPnPDirObject &dirent,
+		       Error &error) const
+{
+	UPnPDirContent dirbuf;
+	if (!server->getMetadata(objid, dirbuf, error))
+		return false;
+
+	if (dirbuf.m_containers.size() == 1) {
+		dirent = dirbuf.m_containers[0];
+	} else if (dirbuf.m_items.size() == 1) {
+		dirent = dirbuf.m_items[0];
+	} else {
+		error.Format(upnp_domain, "Bad resource");
+		return false;
+	}
+
+	return true;
+}
+
+bool
+UpnpDatabase::BuildPath(ContentDirectoryService *server,
+			const UPnPDirObject& idirent,
+			std::string &path,
+			Error &error) const
+{
+	const char *pid = idirent.m_id.c_str();
+	path.clear();
+	UPnPDirObject dirent;
+	while (strcmp(pid, rootid) != 0) {
+		if (!ReadNode(server, pid, dirent, error))
+			return false;
+		pid = dirent.m_pid.c_str();
+		path = titleToPathElt(dirent.m_title) + (path.empty()? "" : "/" + path);
+	}
+	path = std::string(server->getFriendlyName()) + "/" + path;
+	return true;
+}
+
+// Take server and internal title pathname and return objid and metadata.
+bool
+UpnpDatabase::Namei(ContentDirectoryService* server,
+		    const std::vector<std::string> &vpath,
+		    std::string &oobjid, UPnPDirObject &odirent,
+		    Error &error) const
+{
+	oobjid.clear();
+	std::string objid(rootid);
+
+	if (vpath.empty()) {
+		// looking for root info
+		if (!ReadNode(server, rootid, odirent, error))
+			return false;
+
+		oobjid = rootid;
+		return true;
+	}
+
+	// Walk the path elements, read each directory and try to find the next one
+	for (unsigned int i = 0; i < vpath.size(); i++) {
+		UPnPDirContent dirbuf;
+		if (!server->readDir(objid.c_str(), dirbuf, error))
+			return false;
+
+		bool found = false;
+
+		// Look for the name in the sub-container list
+		for (auto& dirent : dirbuf.m_containers) {
+			if (!vpath[i].compare(titleToPathElt(dirent.m_title.c_str()))) {
+				objid = dirent.m_id; // Next readdir target
+				found = true;
+				if (i == vpath.size() - 1) {
+					// The last element in the path was found and it's
+					// a container, we're done
+					oobjid = objid;
+					odirent = dirent;
+					return true;
+				}
+				break;
+			}
+		}
+		if (found)
+			continue;
+
+		// Path elt was not a container, look at the items list
+		for (auto& dirent : dirbuf.m_items) {
+			if (!vpath[i].compare(titleToPathElt(dirent.m_title.c_str()))) {
+				// If this is the last path elt, we found the target,
+				// else it does not exist
+				if (i == vpath.size() - 1) {
+					oobjid = objid;
+					odirent = dirent;
+					return true;
+				} else {
+					return true;
+				}
+			}
+		}
+
+		// Neither container nor item, we're done.
+		if (!found)
+			break;
+	}
+
+	return true;
+}
+
+// vpath is a parsed and writeable version of selection.uri. There is
+// really just one path parameter.
+bool
+UpnpDatabase::VisitServer(ContentDirectoryService* server,
+			  const std::vector<std::string> &vpath,
+			  const DatabaseSelection &selection,
+			  VisitDirectory visit_directory,
+			  VisitSong visit_song,
+			  VisitPlaylist visit_playlist,
+			  Error &error) const
+{
+	/* If the path begins with rootid, we know that this is a
+	   song, not a directory (because that's how we set things
+	   up). Just visit it. Note that the choice of rootid is
+	   arbitrary, any value not likely to be the name of a top
+	   directory would be ok. */
+	/* !Note: this *can't* be handled by Namei further down,
+	   because the path is not valid for traversal. Besides, it's
+	   just faster to access the target node directly */
+	if (!vpath.empty() && !vpath[0].compare(rootid)) {
+		if (visit_song) {
+			UPnPDirObject dirent;
+			if (!ReadNode(server, vpath.back().c_str(), dirent,
+				      error))
+				return false;
+
+			if (!visitSong(dirent, "", selection,
+				       visit_song, error))
+				return false;
+		}
+		return true;
+	}
+
+	// Translate the target path into an object id and the associated metadata.
+	std::string objid;
+	UPnPDirObject tdirent;
+	if (!Namei(server, vpath, objid, tdirent, error))
+		return false;
+
+	if (objid.empty())
+		// Not found, not a fatal error
+		return true;
+
+	/* If recursive is set, this is a search... No use sending it
+	   if the filter is empty. In this case, we implement limited
+	   recursion (1-deep) here, which will handle the "add dir"
+	   case. */
+	if (selection.recursive && selection.filter)
+		return SearchSongs(server, objid.c_str(), selection,
+				   visit_song, error);
+
+	if (tdirent.m_type == UPnPDirObject::item) {
+		// Target is a song. Not too sure we ever get there actually, maybe
+		// this is always catched by the special uri test above.
+		if (visit_song &&
+		    tdirent.m_iclass == UPnPDirObject::audioItem_musicTrack) {
+			return visitSong(tdirent, "", selection, visit_song,
+					 error);
+		} else if (visit_playlist &&
+			   tdirent.m_iclass == UPnPDirObject::audioItem_playlist) {
+			// Note: I've yet to see a playlist item (playlists
+			// seem to be usually handled as containers, so I'll
+			// decide what to do when I see one...
+		}
+
+		return true;
+	}
+
+	/* Target was a a container. Visit it. We could read slices
+	   and loop here, but it's not useful as mpd will only return
+	   data to the client when we're done anyway. */
+	UPnPDirContent dirbuf;
+	if (!server->readDir(objid.c_str(), dirbuf, error))
+		return false;
+
+	if (visit_directory) {
+		for (auto& dirent : dirbuf.m_containers) {
+			Directory d((selection.uri + "/" +
+				     titleToPathElt(dirent.m_title)).c_str(),
+				    m_root);
+			if (!visit_directory(d, error))
+				return false;
+		}
+	}
+
+	if (visit_song || visit_playlist) {
+		for (const auto &dirent : dirbuf.m_items) {
+			if (visit_song &&
+			    dirent.m_iclass == UPnPDirObject::audioItem_musicTrack) {
+				/* We identify songs by giving them a
+				   special path. The Id is enough to
+				   fetch them from the server
+				   anyway. */
+
+				std::string p;
+				if (!selection.recursive)
+					p = selection.uri + "/" +
+						titleToPathElt(dirent.m_title);
+
+				if (!visitSong(dirent, p.c_str(),
+					       selection, visit_song, error))
+					return false;
+			} else if (visit_playlist &&
+				   dirent.m_iclass == UPnPDirObject::audioItem_playlist) {
+				/* Note: I've yet to see a playlist
+				   item (playlists seem to be usually
+				   handled as containers, so I'll
+				   decide what to do when I see
+				   one... */
+			}
+		}
+	}
+
+	return true;
+}
+
+// Deal with the possibly multiple servers, call VisitServer if needed.
+bool
+UpnpDatabase::Visit(const DatabaseSelection &selection,
+		    VisitDirectory visit_directory,
+		    VisitSong visit_song,
+		    VisitPlaylist visit_playlist,
+		    Error &error) const
+{
+	if (!const_cast<UpnpDatabase *>(this)->reallyOpen(error))
+		return false;
+
+	std::vector<ContentDirectoryService> servers;
+	if (!m_superdir || !m_superdir->ok() ||
+	    !m_superdir->getDirServices(servers)) {
+		error.Set(upnp_domain,
+			  "UpnpDatabase::Visit() superdir is sick");
+		return false;
+	}
+
+	auto vpath = stringToTokens(selection.uri, "/", true);
+	if (vpath.empty()) {
+		if (!selection.recursive) {
+			// If the path is empty and recursive is not set, synthetize a
+			// pseudo-directory from the list of servers.
+			if (visit_directory) {
+				for (auto& server : servers) {
+					Directory d(server.getFriendlyName(), m_root);
+					if (!visit_directory(d, error))
+						return false;
+				}
+			}
+		} else {
+			// Recursive is set: visit each server
+			for (auto& server : servers) {
+				if (!VisitServer(&server, std::vector<std::string>(), selection,
+						 visit_directory, visit_song, visit_playlist, error))
+					return false;
+			}
+		}
+		return true;
+	}
+
+	// We do have a path: the first element selects the server
+	std::string servername(vpath[0]);
+	vpath.erase(vpath.begin());
+
+	ContentDirectoryService* server = 0;
+	for (auto& dir : servers) {
+		if (!servername.compare(dir.getFriendlyName())) {
+			server = &dir;
+			break;
+		}
+	}
+	if (server == 0) {
+		FormatDebug(db_domain, "UpnpDatabase::Visit: server %s not found\n",
+			    vpath[0].c_str());
+		return true;
+	}
+	return VisitServer(server, vpath, selection,
+			   visit_directory, visit_song, visit_playlist, error);
+}
+
+bool
+UpnpDatabase::VisitUniqueTags(const DatabaseSelection &selection,
+			      TagType tag,
+			      VisitString visit_string,
+			      Error &error) const
+{
+	if (!const_cast<UpnpDatabase *>(this)->reallyOpen(error))
+		return false;
+
+	if (!visit_string)
+		return true;
+
+	std::vector<ContentDirectoryService> servers;
+	if (!m_superdir || !m_superdir->ok() ||
+	    !m_superdir->getDirServices(servers)) {
+		error.Set(upnp_domain,
+			  "UpnpDatabase::Visit() superdir is sick");
+		return false;
+	}
+
+	std::set<std::string> values;
+	for (auto& server : servers) {
+		UPnPDirContent dirbuf;
+		if (!SearchSongs(&server, rootid, selection, dirbuf, error))
+			return false;
+
+		for (auto &dirent : dirbuf.m_items) {
+			std::string tagvalue;
+			if (getTagValue(dirent, tag, tagvalue))
+				values.emplace(std::move(tagvalue));
+		}
+	}
+
+	for (const auto& value : values)
+		if (!visit_string(value.c_str(), error))
+			return false;
+
+	return true;
+}
+
+bool
+UpnpDatabase::GetStats(const DatabaseSelection &,
+		       DatabaseStats &stats, Error &) const
+{
+	/* Note: this gets called before the daemonizing so we can't
+	   reallyopen this would be a problem if we had real stats */
+	stats.song_count = 0;
+	stats.total_duration = 0;
+	stats.artist_count = 0;
+	stats.album_count = 0;
+	return true;
+}
+
+const DatabasePlugin upnp_db_plugin = {
+	"upnp",
+	UpnpDatabase::Create,
+};