DetachedSong: add attribute "real_uri"

Prepare for UPnP songs that retain there database identity.

src/DecoderThread.cxx

@@ -402,7 +402,7 @@ decoder_run(DecoderControl &dc)
 
 	const std::string uri = song.IsFile()
 		? map_song_fs(song).c_str()
-		: song.GetURI();
+		: song.GetRealURI();
 
 	if (uri.empty()) {
 		dc.state = DecoderState::ERROR;

src/DetachedSong.cxx

@@ -32,13 +32,23 @@ DetachedSong::DetachedSong(const LightSong &other)
 bool
 DetachedSong::IsRemote() const
 {
-	return uri_has_scheme(uri.c_str());
+	return uri_has_scheme(GetRealURI());
 }
 
 bool
 DetachedSong::IsAbsoluteFile() const
 {
-	return PathTraitsUTF8::IsAbsolute(uri.c_str());
+	return PathTraitsUTF8::IsAbsolute(GetRealURI());
+}
+
+bool
+DetachedSong::IsInDatabase() const
+{
+	/* here, we use GetURI() and not GetRealURI() because
+	   GetRealURI() is never relative */
+
+	const char *_uri = GetURI();
+	return !uri_has_scheme(_uri) && !PathTraitsUTF8::IsAbsolute(_uri);
 }
 
 double

src/DetachedSong.hxx

@@ -47,6 +47,16 @@ class DetachedSong {
 	 */
 	std::string uri;
 
+	/**
+	 * The "real" URI, the one to be used for opening the
+	 * resource.  If this attribute is empty, then #uri shall be
+	 * used.
+	 *
+	 * This attribute is used for songs from the database which
+	 * have a relative URI.
+	 */
+	std::string real_uri;
+
 	Tag tag;
 
 	time_t mtime;
@@ -97,6 +107,29 @@ public:
 		uri = std::forward<T>(_uri);
 	}
 
+	/**
+	 * Does this object have a "real" URI different from the
+	 * displayed URI?
+	 */
+	gcc_pure
+	bool HasRealURI() const {
+		return !real_uri.empty();
+	}
+
+	/**
+	 * Returns "real" URI (#real_uri) and falls back to just
+	 * GetURI().
+	 */
+	gcc_pure
+	const char *GetRealURI() const {
+		return (HasRealURI() ? real_uri : uri).c_str();
+	}
+
+	template<typename T>
+	void SetRealURI(T &&_uri) {
+		real_uri = std::forward<T>(_uri);
+	}
+
 	/**
 	 * Returns true if both objects refer to the same physical
 	 * song.
@@ -123,9 +156,7 @@ public:
 	bool IsAbsoluteFile() const;
 
 	gcc_pure
-	bool IsInDatabase() const {
+	bool IsInDatabase() const;
-		return IsFile() && !IsAbsoluteFile();
-	}
 
 	const Tag &GetTag() const {
 		return tag;

src/Mapper.cxx

@@ -26,6 +26,7 @@
 #include "Directory.hxx"
 #include "Song.hxx"
 #include "DetachedSong.hxx"
+#include "LightSong.hxx"
 #include "fs/AllocatedPath.hxx"
 #include "fs/Traits.hxx"
 #include "fs/Charset.hxx"
@@ -220,7 +221,15 @@ map_detached_song_fs(const char *uri_utf8)
 DetachedSong
 map_song_detach(const LightSong &song)
 {
-	return DetachedSong(song);
+	DetachedSong detached(song);
+
+	if (detached.IsInDatabase()) {
+		const auto uri = song.GetURI();
+		detached.SetRealURI(PathTraitsUTF8::Build(music_dir_utf8.c_str(),
+							  uri.c_str()));
+	}
+
+	return detached;
 }
 
 AllocatedPath
@@ -235,7 +244,7 @@ AllocatedPath
 map_song_fs(const DetachedSong &song)
 {
 	if (song.IsAbsoluteFile())
-		return AllocatedPath::FromUTF8(song.GetURI());
+		return AllocatedPath::FromUTF8(song.GetRealURI());
 	else
 		return map_uri_fs(song.GetURI());
 }

src/PlaylistSave.cxx

@@ -38,7 +38,8 @@
 void
 playlist_print_song(FILE *file, const DetachedSong &song)
 {
-	if (playlist_saveAbsolutePaths && song.IsInDatabase()) {
+	if (playlist_saveAbsolutePaths &&
+	    song.IsInDatabase() && song.IsFile()) {
 		const auto path = map_song_fs(song);
 		if (!path.IsNull())
 			fprintf(file, "%s\n", path.c_str());

src/PlaylistUpdate.cxx

@@ -30,7 +30,7 @@
 static bool
 UpdatePlaylistSong(const Database &db, DetachedSong &song)
 {
-	if (!song.IsInDatabase())
+	if (!song.IsInDatabase() || !song.IsFile())
 		/* only update Songs instances that are "detached"
 		   from the Database */
 		return false;

src/SongUpdate.cxx

@@ -130,7 +130,7 @@ DetachedSong::Update()
 {
 	if (IsAbsoluteFile()) {
 		const AllocatedPath path_fs =
-			AllocatedPath::FromUTF8(uri.c_str());
+			AllocatedPath::FromUTF8(GetRealURI());
 
 		struct stat st;
 		if (!StatFile(path_fs, st) || !S_ISREG(st.st_mode))