SongLoader: new class that merges duplicate code

There was quite a lot of duplicate code for loading DetachedSong
objects, with different semantics for "securely" loading local files.

src/playlist/PlaylistQueue.cxx

@@ -32,7 +32,7 @@ PlaylistResult
 playlist_load_into_queue(const char *uri, SongEnumerator &e,
 			 unsigned start_index, unsigned end_index,
 			 playlist &dest, PlayerControl &pc,
-			 bool secure)
+			 const SongLoader &loader)
 {
 	const std::string base_uri = uri != nullptr
 		? PathTraitsUTF8::GetParent(uri)
@@ -49,7 +49,7 @@ playlist_load_into_queue(const char *uri, SongEnumerator &e,
 		}
 
 		if (!playlist_check_translate_song(*song, base_uri.c_str(),
-						   secure)) {
+						   loader)) {
 			delete song;
 			continue;
 		}
@@ -67,7 +67,7 @@ PlaylistResult
 playlist_open_into_queue(const char *uri,
 			 unsigned start_index, unsigned end_index,
 			 playlist &dest, PlayerControl &pc,
-			 bool secure)
+			 const SongLoader &loader)
 {
 	Mutex mutex;
 	Cond cond;
@@ -80,7 +80,7 @@ playlist_open_into_queue(const char *uri,
 	PlaylistResult result =
 		playlist_load_into_queue(uri, *playlist,
 					 start_index, end_index,
-					 dest, pc, secure);
+					 dest, pc, loader);
 	delete playlist;
 
 	if (is != nullptr)

src/playlist/PlaylistQueue.hxx

@@ -26,6 +26,7 @@
 
 #include "PlaylistError.hxx"
 
+class SongLoader;
 class SongEnumerator;
 struct playlist;
 struct PlayerControl;
@@ -43,7 +44,7 @@ PlaylistResult
 playlist_load_into_queue(const char *uri, SongEnumerator &e,
 			 unsigned start_index, unsigned end_index,
 			 playlist &dest, PlayerControl &pc,
-			 bool secure);
+			 const SongLoader &loader);
 
 /**
  * Opens a playlist with a playlist plugin and append to the specified
@@ -53,7 +54,7 @@ PlaylistResult
 playlist_open_into_queue(const char *uri,
 			 unsigned start_index, unsigned end_index,
 			 playlist &dest, PlayerControl &pc,
-			 bool secure);
+			 const SongLoader &loader);
 
 #endif
 

src/playlist/PlaylistSong.cxx

@@ -20,8 +20,7 @@
 #include "config.h"
 #include "PlaylistSong.hxx"
 #include "Mapper.hxx"
-#include "db/DatabaseSong.hxx"
-#include "ls.hxx"
+#include "SongLoader.hxx"
 #include "tag/Tag.hxx"
 #include "tag/TagBuilder.hxx"
 #include "fs/AllocatedPath.hxx"
@@ -65,44 +64,22 @@ apply_song_metadata(DetachedSong &dest, const DetachedSong &src)
 }
 
 static bool
-playlist_check_load_song(DetachedSong &song)
+playlist_check_load_song(DetachedSong &song, const SongLoader &loader)
 {
-	const char *const uri = song.GetURI();
-
-	if (uri_has_scheme(uri)) {
-		return true;
-	} else if (PathTraitsUTF8::IsAbsolute(uri)) {
-		DetachedSong tmp(uri);
-		if (!tmp.Update())
-			return false;
-
-		apply_song_metadata(song, tmp);
-		return true;
-	} else {
-#ifdef ENABLE_DATABASE
-		DetachedSong *tmp = DatabaseDetachSong(uri, IgnoreError());
-		if (tmp == nullptr)
-			return false;
-
-		apply_song_metadata(song, *tmp);
-		delete tmp;
-		return true;
-#else
+	DetachedSong *tmp = loader.LoadSong(song.GetURI(), IgnoreError());
+	if (tmp == nullptr)
 		return false;
-#endif
-	}
+
+	song.SetURI(tmp->GetURI());
+	apply_song_metadata(song, *tmp);
+	delete tmp;
+	return true;
 }
 
 bool
 playlist_check_translate_song(DetachedSong &song, const char *base_uri,
-			      bool secure)
+			      const SongLoader &loader)
 {
-	const char *const uri = song.GetURI();
-
-	if (uri_has_scheme(uri))
-		/* valid remote song? */
-		return uri_supported_scheme(uri);
-
 	if (base_uri != nullptr && strcmp(base_uri, ".") == 0)
 		/* PathTraitsUTF8::GetParent() returns "." when there
 		   is no directory name in the given path; clear that
@@ -110,26 +87,10 @@ playlist_check_translate_song(DetachedSong &song, const char *base_uri,
 		   functions */
 		base_uri = nullptr;
 
-	if (PathTraitsUTF8::IsAbsolute(uri)) {
-		/* XXX fs_charset vs utf8? */
-		const char *suffix = map_to_relative_path(uri);
-		assert(suffix != nullptr);
-
-		if (suffix != uri)
-			song.SetURI(std::string(suffix));
-		else if (!secure)
-			/* local files must be relative to the music
-			   directory when "secure" is enabled */
-			return false;
-
-		base_uri = nullptr;
-	}
-
-	if (base_uri != nullptr) {
+	const char *uri = song.GetURI();
+	if (base_uri != nullptr && !uri_has_scheme(uri) &&
+	    !PathTraitsUTF8::IsAbsolute(uri))
 		song.SetURI(PathTraitsUTF8::Build(base_uri, uri));
-		/* repeat the above checks */
-		return playlist_check_translate_song(song, nullptr, secure);
-	}
 
-	return playlist_check_load_song(song);
+	return playlist_check_load_song(song, loader);
 }

src/playlist/PlaylistSong.hxx

@@ -20,18 +20,17 @@
 #ifndef MPD_PLAYLIST_SONG_HXX
 #define MPD_PLAYLIST_SONG_HXX
 
+class SongLoader;
 class DetachedSong;
 
 /**
  * Verifies the song, returns false if it is unsafe.  Translate the
  * song to a song within the database, if it is a local file.
  *
- * @param secure if true, then local files are only allowed if they
- * are relative to base_uri
  * @return true on success, false if the song should not be used
  */
 bool
 playlist_check_translate_song(DetachedSong &song, const char *base_uri,
-			      bool secure);
+			      const SongLoader &loader);
 
 #endif

src/playlist/Print.cxx

@@ -25,6 +25,7 @@
 #include "SongPrint.hxx"
 #include "input/InputStream.hxx"
 #include "DetachedSong.hxx"
+#include "SongLoader.hxx"
 #include "fs/Traits.hxx"
 #include "thread/Cond.hxx"
 
@@ -36,10 +37,12 @@ playlist_provider_print(Client &client, const char *uri,
 		? PathTraitsUTF8::GetParent(uri)
 		: std::string(".");
 
+	const SongLoader loader(client);
+
 	DetachedSong *song;
 	while ((song = e.NextSong()) != nullptr) {
 		if (playlist_check_translate_song(*song, base_uri.c_str(),
-						  false)) {
+						  loader)) {
 			if (detail)
 				song_print_info(client, *song);
 			else