PlaylistPlugin: add interface SongEnumerator

Replaces struct playlist_provider.

24 files changed, 200 insertions, 311 deletions

diff --git a/src/playlist/MemoryPlaylistProvider.cxx b/src/MemorySongEnumerator.cxx
index c2b6d9312..7c9d05daa 100644
--- a/src/playlist/MemoryPlaylistProvider.cxx
+++ b/src/MemorySongEnumerator.cxx
@@ -18,50 +18,13 @@
  */
 
 #include "config.h"
-#include "MemoryPlaylistProvider.hxx"
-#include "Song.hxx"
+#include "MemorySongEnumerator.hxx"
 
-static void
-memory_playlist_close(struct playlist_provider *_playlist)
-{
-	MemoryPlaylistProvider *playlist = (MemoryPlaylistProvider *)_playlist;
-
-	delete playlist;
-}
-
-static Song *
-memory_playlist_read(struct playlist_provider *_playlist)
-{
-	MemoryPlaylistProvider *playlist = (MemoryPlaylistProvider *)_playlist;
-
-	return playlist->Read();
-}
-
-static constexpr struct playlist_plugin memory_playlist_plugin = {
-	nullptr,
-
-	nullptr,
-	nullptr,
-	nullptr,
-	nullptr,
-	memory_playlist_close,
-	memory_playlist_read,
-
-	nullptr,
-	nullptr,
-	nullptr,
-};
-
-MemoryPlaylistProvider::MemoryPlaylistProvider(std::forward_list<SongPointer> &&_songs)
-	:songs(std::move(_songs)) {
-	playlist_provider_init(this, &memory_playlist_plugin);
-}
-
-inline Song *
-MemoryPlaylistProvider::Read()
+Song *
+MemorySongEnumerator::NextSong()
 {
 	if (songs.empty())
-		return NULL;
+		return nullptr;
 
 	auto result = songs.front().Steal();
 	songs.pop_front();
diff --git a/src/playlist/MemoryPlaylistProvider.hxx b/src/MemorySongEnumerator.hxx
index efbc46fe1..46086a064 100644
--- a/src/playlist/MemoryPlaylistProvider.hxx
+++ b/src/MemorySongEnumerator.hxx
@@ -20,20 +20,19 @@
 #ifndef MPD_MEMORY_PLAYLIST_PROVIDER_HXX
 #define MPD_MEMORY_PLAYLIST_PROVIDER_HXX
 
-#include "PlaylistPlugin.hxx"
+#include "SongEnumerator.hxx"
 #include "SongPointer.hxx"
 
 #include <forward_list>
 
-struct Song;
-
-class MemoryPlaylistProvider : public playlist_provider {
+class MemorySongEnumerator final : public SongEnumerator {
 	std::forward_list<SongPointer> songs;
 
 public:
-	MemoryPlaylistProvider(std::forward_list<SongPointer> &&_songs);
+	MemorySongEnumerator(std::forward_list<SongPointer> &&_songs)
+		:songs(std::move(_songs)) {}
 
-	Song *Read();
+	virtual Song *NextSong() override;
 };
 
 #endif
diff --git a/src/PlaylistAny.cxx b/src/PlaylistAny.cxx
index e84d055bd..95f65dca5 100644
--- a/src/PlaylistAny.cxx
+++ b/src/PlaylistAny.cxx
@@ -27,14 +27,13 @@
 
 #include <assert.h>
 
-static struct playlist_provider *
+static SongEnumerator *
 playlist_open_remote(const char *uri, Mutex &mutex, Cond &cond,
 		     struct input_stream **is_r)
 {
 	assert(uri_has_scheme(uri));
 
-	struct playlist_provider *playlist =
-		playlist_list_open_uri(uri, mutex, cond);
+	SongEnumerator *playlist = playlist_list_open_uri(uri, mutex, cond);
 	if (playlist != NULL) {
 		*is_r = NULL;
 		return playlist;
@@ -60,7 +59,7 @@ playlist_open_remote(const char *uri, Mutex &mutex, Cond &cond,
 	return playlist;
 }
 
-struct playlist_provider *
+SongEnumerator *
 playlist_open_any(const char *uri, Mutex &mutex, Cond &cond,
 		  struct input_stream **is_r)
 {
diff --git a/src/PlaylistAny.hxx b/src/PlaylistAny.hxx
index d69087b3f..951fa1099 100644
--- a/src/PlaylistAny.hxx
+++ b/src/PlaylistAny.hxx
@@ -23,7 +23,7 @@
 #include "thread/Mutex.hxx"
 #include "thread/Cond.hxx"
 
-struct playlist_provider;
+class SongEnumerator;
 struct input_stream;
 
 /**
@@ -35,7 +35,7 @@ struct input_stream;
  * here, which must be closed after the playlist_provider object is
  * freed
  */
-struct playlist_provider *
+SongEnumerator *
 playlist_open_any(const char *uri, Mutex &mutex, Cond &cond,
 		  struct input_stream **is_r);
 
diff --git a/src/PlaylistMapper.cxx b/src/PlaylistMapper.cxx
index 08131106d..559154a4e 100644
--- a/src/PlaylistMapper.cxx
+++ b/src/PlaylistMapper.cxx
@@ -27,13 +27,11 @@
 
 #include <assert.h>
 
-static struct playlist_provider *
+static SongEnumerator *
 playlist_open_path(const char *path_fs, Mutex &mutex, Cond &cond,
 		   struct input_stream **is_r)
 {
-	struct playlist_provider *playlist;
-
-	playlist = playlist_list_open_uri(path_fs, mutex, cond);
+	auto playlist = playlist_list_open_uri(path_fs, mutex, cond);
 	if (playlist != NULL)
 		*is_r = NULL;
 	else
@@ -45,7 +43,7 @@ playlist_open_path(const char *path_fs, Mutex &mutex, Cond &cond,
 /**
  * Load a playlist from the configured playlist directory.
  */
-static struct playlist_provider *
+static SongEnumerator *
 playlist_open_in_playlist_dir(const char *uri, Mutex &mutex, Cond &cond,
 			      struct input_stream **is_r)
 {
@@ -59,8 +57,7 @@ playlist_open_in_playlist_dir(const char *uri, Mutex &mutex, Cond &cond,
 
 	path_fs = g_build_filename(playlist_directory_fs.c_str(), uri, NULL);
 
-	struct playlist_provider *playlist =
-		playlist_open_path(path_fs, mutex, cond, is_r);
+	auto playlist = playlist_open_path(path_fs, mutex, cond, is_r);
 	g_free(path_fs);
 
 	return playlist;
@@ -69,7 +66,7 @@ playlist_open_in_playlist_dir(const char *uri, Mutex &mutex, Cond &cond,
 /**
  * Load a playlist from the configured music directory.
  */
-static struct playlist_provider *
+static SongEnumerator *
 playlist_open_in_music_dir(const char *uri, Mutex &mutex, Cond &cond,
 			   struct input_stream **is_r)
 {
@@ -82,21 +79,20 @@ playlist_open_in_music_dir(const char *uri, Mutex &mutex, Cond &cond,
 	return playlist_open_path(path.c_str(), mutex, cond, is_r);
 }
 
-struct playlist_provider *
+SongEnumerator *
 playlist_mapper_open(const char *uri, Mutex &mutex, Cond &cond,
 		     struct input_stream **is_r)
 {
-	struct playlist_provider *playlist;
-
 	if (spl_valid_name(uri)) {
-		playlist = playlist_open_in_playlist_dir(uri, mutex, cond,
-							 is_r);
+		auto playlist = playlist_open_in_playlist_dir(uri, mutex, cond,
+							      is_r);
 		if (playlist != NULL)
 			return playlist;
 	}
 
 	if (uri_safe_local(uri)) {
-		playlist = playlist_open_in_music_dir(uri, mutex, cond, is_r);
+		auto playlist = playlist_open_in_music_dir(uri, mutex, cond,
+							   is_r);
 		if (playlist != NULL)
 			return playlist;
 	}
diff --git a/src/PlaylistMapper.hxx b/src/PlaylistMapper.hxx
index abfdb5481..b966e6c39 100644
--- a/src/PlaylistMapper.hxx
+++ b/src/PlaylistMapper.hxx
@@ -23,6 +23,7 @@
 #include "thread/Mutex.hxx"
 #include "thread/Cond.hxx"
 
+class SongEnumerator;
 struct input_stream;
 
 /**
@@ -33,7 +34,7 @@ struct input_stream;
  * here, which must be closed after the playlist_provider object is
  * freed
  */
-struct playlist_provider *
+SongEnumerator *
 playlist_mapper_open(const char *uri, Mutex &mutex, Cond &cond,
 		     struct input_stream **is_r);
 
diff --git a/src/PlaylistPlugin.hxx b/src/PlaylistPlugin.hxx
index f89fd9ce0..ce380d886 100644
--- a/src/PlaylistPlugin.hxx
+++ b/src/PlaylistPlugin.hxx
@@ -26,21 +26,7 @@
 struct config_param;
 struct input_stream;
 struct Tag;
-struct Song;
-
-/**
- * An object which provides the contents of a playlist.
- */
-struct playlist_provider {
-	const struct playlist_plugin *plugin;
-};
-
-static inline void
-playlist_provider_init(struct playlist_provider *playlist,
-		       const struct playlist_plugin *plugin)
-{
-	playlist->plugin = plugin;
-}
+class SongEnumerator;
 
 struct playlist_plugin {
 	const char *name;
@@ -65,19 +51,15 @@ struct playlist_plugin {
 	 * Opens the playlist on the specified URI.  This URI has
 	 * either matched one of the schemes or one of the suffixes.
 	 */
-	struct playlist_provider *(*open_uri)(const char *uri,
-					      Mutex &mutex, Cond &cond);
+	SongEnumerator *(*open_uri)(const char *uri,
+				    Mutex &mutex, Cond &cond);
 
 	/**
 	 * Opens the playlist in the specified input stream.  It has
 	 * either matched one of the suffixes or one of the MIME
 	 * types.
 	 */
-	struct playlist_provider *(*open_stream)(struct input_stream *is);
-
-	void (*close)(struct playlist_provider *playlist);
-
-	Song *(*read)(struct playlist_provider *playlist);
+	SongEnumerator *(*open_stream)(struct input_stream *is);
 
 	const char *const*schemes;
 	const char *const*suffixes;
@@ -111,30 +93,18 @@ playlist_plugin_finish(const struct playlist_plugin *plugin)
 		plugin->finish();
 }
 
-static inline struct playlist_provider *
+static inline SongEnumerator *
 playlist_plugin_open_uri(const struct playlist_plugin *plugin, const char *uri,
 			 Mutex &mutex, Cond &cond)
 {
 	return plugin->open_uri(uri, mutex, cond);
 }
 
-static inline struct playlist_provider *
+static inline SongEnumerator *
 playlist_plugin_open_stream(const struct playlist_plugin *plugin,
 			    struct input_stream *is)
 {
 	return plugin->open_stream(is);
 }
 
-static inline void
-playlist_plugin_close(struct playlist_provider *playlist)
-{
-	playlist->plugin->close(playlist);
-}
-
-static inline Song *
-playlist_plugin_read(struct playlist_provider *playlist)
-{
-	return playlist->plugin->read(playlist);
-}
-
 #endif
diff --git a/src/PlaylistPrint.cxx b/src/PlaylistPrint.cxx
index f95061ca5..012f9600b 100644
--- a/src/PlaylistPrint.cxx
+++ b/src/PlaylistPrint.cxx
@@ -26,6 +26,7 @@
 #include "PlaylistRegistry.hxx"
 #include "PlaylistPlugin.hxx"
 #include "QueuePrint.hxx"
+#include "SongEnumerator.hxx"
 #include "SongPrint.hxx"
 #include "DatabaseGlue.hxx"
 #include "DatabasePlugin.hxx"
@@ -145,12 +146,12 @@ spl_print(Client *client, const char *name_utf8, bool detail,
 
 static void
 playlist_provider_print(Client *client, const char *uri,
-			struct playlist_provider *playlist, bool detail)
+			SongEnumerator &e, bool detail)
 {
 	Song *song;
 	char *base_uri = uri != NULL ? g_path_get_dirname(uri) : NULL;
 
-	while ((song = playlist_plugin_read(playlist)) != NULL) {
+	while ((song = e.NextSong()) != nullptr) {
 		song = playlist_check_translate_song(song, base_uri, false);
 		if (song == NULL)
 			continue;
@@ -173,13 +174,12 @@ playlist_file_print(Client *client, const char *uri, bool detail)
 	Cond cond;
 
 	struct input_stream *is;
-	struct playlist_provider *playlist =
-		playlist_open_any(uri, mutex, cond, &is);
+	SongEnumerator *playlist = playlist_open_any(uri, mutex, cond, &is);
 	if (playlist == NULL)
 		return false;
 
-	playlist_provider_print(client, uri, playlist, detail);
-	playlist_plugin_close(playlist);
+	playlist_provider_print(client, uri, *playlist, detail);
+	delete playlist;
 
 	if (is != NULL)
 		is->Close();
diff --git a/src/PlaylistQueue.cxx b/src/PlaylistQueue.cxx
index af68176fe..901ee578d 100644
--- a/src/PlaylistQueue.cxx
+++ b/src/PlaylistQueue.cxx
@@ -24,10 +24,11 @@
 #include "PlaylistSong.hxx"
 #include "Playlist.hxx"
 #include "InputStream.hxx"
+#include "SongEnumerator.hxx"
 #include "Song.hxx"
 
 enum playlist_result
-playlist_load_into_queue(const char *uri, struct playlist_provider *source,
+playlist_load_into_queue(const char *uri, SongEnumerator &e,
 			 unsigned start_index, unsigned end_index,
 			 struct playlist *dest, struct player_control *pc,
 			 bool secure)
@@ -37,7 +38,7 @@ playlist_load_into_queue(const char *uri, struct playlist_provider *source,
 	char *base_uri = uri != NULL ? g_path_get_dirname(uri) : NULL;
 
 	for (unsigned i = 0;
-	     i < end_index && (song = playlist_plugin_read(source)) != NULL;
+	     i < end_index && (song = e.NextSong()) != NULL;
 	     ++i) {
 		if (i < start_index) {
 			/* skip songs before the start index */
@@ -72,15 +73,15 @@ playlist_open_into_queue(const char *uri,
 	Cond cond;
 
 	struct input_stream *is;
-	struct playlist_provider *playlist =
-		playlist_open_any(uri, mutex, cond, &is);
+	auto playlist = playlist_open_any(uri, mutex, cond, &is);
 	if (playlist == NULL)
 		return PLAYLIST_RESULT_NO_SUCH_LIST;
 
 	enum playlist_result result =
-		playlist_load_into_queue(uri, playlist, start_index, end_index,
+		playlist_load_into_queue(uri, *playlist,
+					 start_index, end_index,
 					 dest, pc, secure);
-	playlist_plugin_close(playlist);
+	delete playlist;
 
 	if (is != NULL)
 		is->Close();
diff --git a/src/PlaylistQueue.hxx b/src/PlaylistQueue.hxx
index 5a5cc641d..71768ecb4 100644
--- a/src/PlaylistQueue.hxx
+++ b/src/PlaylistQueue.hxx
@@ -26,7 +26,7 @@
 
 #include "PlaylistError.hxx"
 
-struct playlist_provider;
+class SongEnumerator;
 struct playlist;
 struct player_control;
 
@@ -40,7 +40,7 @@ struct player_control;
  * @param end_index the index of the last song (excluding)
  */
 enum playlist_result
-playlist_load_into_queue(const char *uri, struct playlist_provider *source,
+playlist_load_into_queue(const char *uri, SongEnumerator &e,
 			 unsigned start_index, unsigned end_index,
 			 struct playlist *dest, struct player_control *pc,
 			 bool secure);
diff --git a/src/PlaylistRegistry.cxx b/src/PlaylistRegistry.cxx
index 375e51d83..88628e455 100644
--- a/src/PlaylistRegistry.cxx
+++ b/src/PlaylistRegistry.cxx
@@ -124,12 +124,12 @@ playlist_list_global_finish(void)
 		playlist_plugin_finish(plugin);
 }
 
-static struct playlist_provider *
+static SongEnumerator *
 playlist_list_open_uri_scheme(const char *uri, Mutex &mutex, Cond &cond,
 			      bool *tried)
 {
 	char *scheme;
-	struct playlist_provider *playlist = NULL;
+	SongEnumerator *playlist = nullptr;
 
 	assert(uri != NULL);
 
@@ -158,12 +158,12 @@ playlist_list_open_uri_scheme(const char *uri, Mutex &mutex, Cond &cond,
 	return playlist;
 }
 
-static struct playlist_provider *
+static SongEnumerator *
 playlist_list_open_uri_suffix(const char *uri, Mutex &mutex, Cond &cond,
 			      const bool *tried)
 {
 	const char *suffix;
-	struct playlist_provider *playlist = NULL;
+	SongEnumerator *playlist = nullptr;
 
 	assert(uri != NULL);
 
@@ -187,10 +187,9 @@ playlist_list_open_uri_suffix(const char *uri, Mutex &mutex, Cond &cond,
 	return playlist;
 }
 
-struct playlist_provider *
+SongEnumerator *
 playlist_list_open_uri(const char *uri, Mutex &mutex, Cond &cond)
 {
-	struct playlist_provider *playlist;
 	/** this array tracks which plugins have already been tried by
 	    playlist_list_open_uri_scheme() */
 	bool tried[G_N_ELEMENTS(playlist_plugins) - 1];
@@ -199,7 +198,7 @@ playlist_list_open_uri(const char *uri, Mutex &mutex, Cond &cond)
 
 	memset(tried, false, sizeof(tried));
 
-	playlist = playlist_list_open_uri_scheme(uri, mutex, cond, tried);
+	auto playlist = playlist_list_open_uri_scheme(uri, mutex, cond, tried);
 	if (playlist == NULL)
 		playlist = playlist_list_open_uri_suffix(uri, mutex, cond,
 							 tried);
@@ -207,11 +206,9 @@ playlist_list_open_uri(const char *uri, Mutex &mutex, Cond &cond)
 	return playlist;
 }
 
-static struct playlist_provider *
+static SongEnumerator *
 playlist_list_open_stream_mime2(struct input_stream *is, const char *mime)
 {
-	struct playlist_provider *playlist;
-
 	assert(is != NULL);
 	assert(mime != NULL);
 
@@ -223,7 +220,7 @@ playlist_list_open_stream_mime2(struct input_stream *is, const char *mime)
 			   fresh start */
 			is->Seek(0, SEEK_SET, IgnoreError());
 
-			playlist = playlist_plugin_open_stream(plugin, is);
+			auto playlist = playlist_plugin_open_stream(plugin, is);
 			if (playlist != NULL)
 				return playlist;
 		}
@@ -232,7 +229,7 @@ playlist_list_open_stream_mime2(struct input_stream *is, const char *mime)
 	return NULL;
 }
 
-static struct playlist_provider *
+static SongEnumerator *
 playlist_list_open_stream_mime(struct input_stream *is, const char *full_mime)
 {
 	assert(full_mime != NULL);
@@ -246,17 +243,14 @@ playlist_list_open_stream_mime(struct input_stream *is, const char *full_mime)
 
 	/* probe only the portion before the semicolon*/
 	char *mime = g_strndup(full_mime, semicolon - full_mime);
-	struct playlist_provider *playlist =
-		playlist_list_open_stream_mime2(is, mime);
+	auto playlist = playlist_list_open_stream_mime2(is, mime);
 	g_free(mime);
 	return playlist;
 }
 
-static struct playlist_provider *
+static SongEnumerator *
 playlist_list_open_stream_suffix(struct input_stream *is, const char *suffix)
 {
-	struct playlist_provider *playlist;
-
 	assert(is != NULL);
 	assert(suffix != NULL);
 
@@ -268,7 +262,7 @@ playlist_list_open_stream_suffix(struct input_stream *is, const char *suffix)
 			   fresh start */
 			is->Seek(0, SEEK_SET, IgnoreError());
 
-			playlist = playlist_plugin_open_stream(plugin, is);
+			auto playlist = playlist_plugin_open_stream(plugin, is);
 			if (playlist != NULL)
 				return playlist;
 		}
@@ -277,24 +271,23 @@ playlist_list_open_stream_suffix(struct input_stream *is, const char *suffix)
 	return NULL;
 }
 
-struct playlist_provider *
+SongEnumerator *
 playlist_list_open_stream(struct input_stream *is, const char *uri)
 {
 	const char *suffix;
-	struct playlist_provider *playlist;
 
 	is->LockWaitReady();
 
 	const char *const mime = is->GetMimeType();
 	if (mime != NULL) {
-		playlist = playlist_list_open_stream_mime(is, mime);
+		auto playlist = playlist_list_open_stream_mime(is, mime);
 		if (playlist != NULL)
 			return playlist;
 	}
 
 	suffix = uri != NULL ? uri_get_suffix(uri) : NULL;
 	if (suffix != NULL) {
-		playlist = playlist_list_open_stream_suffix(is, suffix);
+		auto playlist = playlist_list_open_stream_suffix(is, suffix);
 		if (playlist != NULL)
 			return playlist;
 	}
@@ -316,12 +309,11 @@ playlist_suffix_supported(const char *suffix)
 	return false;
 }
 
-struct playlist_provider *
+SongEnumerator *
 playlist_list_open_path(const char *path_fs, Mutex &mutex, Cond &cond,
 			struct input_stream **is_r)
 {
 	const char *suffix;
-	struct playlist_provider *playlist;
 
 	assert(path_fs != NULL);
 
@@ -340,7 +332,7 @@ playlist_list_open_path(const char *path_fs, Mutex &mutex, Cond &cond,
 
 	is->LockWaitReady();
 
-	playlist = playlist_list_open_stream_suffix(is, suffix);
+	auto playlist = playlist_list_open_stream_suffix(is, suffix);
 	if (playlist != NULL)
 		*is_r = is;
 	else
diff --git a/src/PlaylistRegistry.hxx b/src/PlaylistRegistry.hxx
index 7c34c1565..350987012 100644
--- a/src/PlaylistRegistry.hxx
+++ b/src/PlaylistRegistry.hxx
@@ -23,7 +23,7 @@
 #include "thread/Mutex.hxx"
 #include "thread/Cond.hxx"
 
-struct playlist_provider;
+class SongEnumerator;
 struct input_stream;
 
 extern const struct playlist_plugin *const playlist_plugins[];
@@ -49,7 +49,7 @@ playlist_list_global_finish(void);
 /**
  * Opens a playlist by its URI.
  */
-struct playlist_provider *
+SongEnumerator *
 playlist_list_open_uri(const char *uri, Mutex &mutex, Cond &cond);
 
 /**
@@ -59,7 +59,7 @@ playlist_list_open_uri(const char *uri, Mutex &mutex, Cond &cond);
  * @param uri optional URI which was used to open the stream; may be
  * used to select the appropriate playlist plugin
  */
-struct playlist_provider *
+SongEnumerator *
 playlist_list_open_stream(struct input_stream *is, const char *uri);
 
 /**
@@ -77,7 +77,7 @@ playlist_suffix_supported(const char *suffix);
  * which must be closed after the playlist_provider object is freed
  * @return a playlist, or NULL on error
  */
-struct playlist_provider *
+SongEnumerator *
 playlist_list_open_path(const char *path_fs, Mutex &mutex, Cond &cond,
 			struct input_stream **is_r);
 
diff --git a/src/SongEnumerator.hxx b/src/SongEnumerator.hxx
new file mode 100644
index 000000000..0e268a31a
--- /dev/null
+++ b/src/SongEnumerator.hxx
@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2003-2013 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_SONG_ENUMERATOR_HXX
+#define MPD_SONG_ENUMERATOR_HXX
+
+struct Song;
+
+/**
+ * An object which provides serial access to a number of #Song
+ * objects.  It is used to enumerate the contents of a playlist file.
+ */
+class SongEnumerator {
+public:
+	virtual ~SongEnumerator() {}
+
+	/**
+	 * Obtain the next song.  The caller is responsible for
+	 * freeing the returned #Song object.  Returns nullptr if
+	 * there are no more songs.
+	 */
+	virtual Song *NextSong() = 0;
+};
+
+#endif
diff --git a/src/playlist/AsxPlaylistPlugin.cxx b/src/playlist/AsxPlaylistPlugin.cxx
index c0fc15e07..6920ec268 100644
--- a/src/playlist/AsxPlaylistPlugin.cxx
+++ b/src/playlist/AsxPlaylistPlugin.cxx
@@ -19,7 +19,8 @@
 
 #include "config.h"
 #include "AsxPlaylistPlugin.hxx"
-#include "MemoryPlaylistProvider.hxx"
+#include "PlaylistPlugin.hxx"
+#include "MemorySongEnumerator.hxx"
 #include "InputStream.hxx"
 #include "Song.hxx"
 #include "Tag.hxx"
@@ -201,7 +202,7 @@ asx_parser_destroy(gpointer data)
  *
  */
 
-static struct playlist_provider *
+static SongEnumerator *
 asx_open_stream(struct input_stream *is)
 {
 	AsxParser parser;
@@ -249,8 +250,8 @@ asx_open_stream(struct input_stream *is)
 	}
 
 	parser.songs.reverse();
-	MemoryPlaylistProvider *playlist =
-		new MemoryPlaylistProvider(std::move(parser.songs));
+	MemorySongEnumerator *playlist =
+		new MemorySongEnumerator(std::move(parser.songs));
 
 	g_markup_parse_context_free(context);
 
@@ -274,8 +275,6 @@ const struct playlist_plugin asx_playlist_plugin = {
 	nullptr,
 	nullptr,
 	asx_open_stream,
-	nullptr,
-	nullptr,
 
 	nullptr,
 	asx_suffixes,
diff --git a/src/playlist/CuePlaylistPlugin.cxx b/src/playlist/CuePlaylistPlugin.cxx
index aa84b1c4a..1c1433a6a 100644
--- a/src/playlist/CuePlaylistPlugin.cxx
+++ b/src/playlist/CuePlaylistPlugin.cxx
@@ -20,67 +20,54 @@
 #include "config.h"
 #include "CuePlaylistPlugin.hxx"
 #include "PlaylistPlugin.hxx"
+#include "SongEnumerator.hxx"
 #include "Tag.hxx"
 #include "Song.hxx"
 #include "cue/CueParser.hxx"
 #include "TextInputStream.hxx"
 
-#include <glib.h>
 #include <assert.h>
 #include <string.h>
 
 #undef G_LOG_DOMAIN
 #define G_LOG_DOMAIN "cue"
 
-struct CuePlaylist {
-	struct playlist_provider base;
-
+class CuePlaylist final : public SongEnumerator {
 	struct input_stream *is;
 	TextInputStream tis;
 	CueParser parser;
 
+ public:
 	CuePlaylist(struct input_stream *_is)
 		:is(_is), tis(is) {
-		playlist_provider_init(&base, &cue_playlist_plugin);
 	}
 
-	~CuePlaylist() {
-	}
+	virtual Song *NextSong() override;
 };
 
-static struct playlist_provider *
+static SongEnumerator *
 cue_playlist_open_stream(struct input_stream *is)
 {
-	CuePlaylist *playlist = new CuePlaylist(is);
-	return &playlist->base;
-}
-
-static void
-cue_playlist_close(struct playlist_provider *_playlist)
-{
-	CuePlaylist *playlist = (CuePlaylist *)_playlist;
-	delete playlist;
+	return new CuePlaylist(is);
 }
 
-static Song *
-cue_playlist_read(struct playlist_provider *_playlist)
+Song *
+CuePlaylist::NextSong()
 {
-	CuePlaylist *playlist = (CuePlaylist *)_playlist;
-
-	Song *song = playlist->parser.Get();
+	Song *song = parser.Get();
 	if (song != NULL)
 		return song;
 
 	std::string line;
-	while (playlist->tis.ReadLine(line)) {
-		playlist->parser.Feed(line.c_str());
-		song = playlist->parser.Get();
+	while (tis.ReadLine(line)) {
+		parser.Feed(line.c_str());
+		song = parser.Get();
 		if (song != NULL)
 			return song;
 	}
 
-	playlist->parser.Finish();
-	return playlist->parser.Get();
+	parser.Finish();
+	return parser.Get();
 }
 
 static const char *const cue_playlist_suffixes[] = {
@@ -100,8 +87,6 @@ const struct playlist_plugin cue_playlist_plugin = {
 	nullptr,
 	nullptr,
 	cue_playlist_open_stream,
-	cue_playlist_close,
-	cue_playlist_read,
 
 	nullptr,
 	cue_playlist_suffixes,
diff --git a/src/playlist/DespotifyPlaylistPlugin.cxx b/src/playlist/DespotifyPlaylistPlugin.cxx
index 5759a10c0..3e6527ea7 100644
--- a/src/playlist/DespotifyPlaylistPlugin.cxx
+++ b/src/playlist/DespotifyPlaylistPlugin.cxx
@@ -20,7 +20,8 @@
 #include "config.h"
 #include "DespotifyPlaylistPlugin.hxx"
 #include "DespotifyUtils.hxx"
-#include "MemoryPlaylistProvider.hxx"
+#include "PlaylistPlugin.hxx"
+#include "MemorySongEnumerator.hxx"
 #include "Tag.hxx"
 #include "Song.hxx"
 
@@ -86,7 +87,7 @@ parse_playlist(struct despotify_session *session,
 	return true;
 }
 
-static struct playlist_provider *
+static SongEnumerator *
 despotify_playlist_open_uri(const char *url,
 			    gcc_unused Mutex &mutex, gcc_unused Cond &cond)
 {
@@ -122,7 +123,7 @@ despotify_playlist_open_uri(const char *url,
 		return nullptr;
 
 	songs.reverse();
-	return new MemoryPlaylistProvider(std::move(songs));
+	return new MemorySongEnumerator(std::move(songs));
 }
 
 static const char *const despotify_schemes[] = {
@@ -137,8 +138,6 @@ const struct playlist_plugin despotify_playlist_plugin = {
 	nullptr,
 	despotify_playlist_open_uri,
 	nullptr,
-	nullptr,
-	nullptr,
 
 	despotify_schemes,
 	nullptr,
diff --git a/src/playlist/EmbeddedCuePlaylistPlugin.cxx b/src/playlist/EmbeddedCuePlaylistPlugin.cxx
index 237bccdd5..8c5309ac1 100644
--- a/src/playlist/EmbeddedCuePlaylistPlugin.cxx
+++ b/src/playlist/EmbeddedCuePlaylistPlugin.cxx
@@ -26,6 +26,7 @@
 #include "config.h"
 #include "EmbeddedCuePlaylistPlugin.hxx"
 #include "PlaylistPlugin.hxx"
+#include "SongEnumerator.hxx"
 #include "Tag.hxx"
 #include "TagHandler.hxx"
 #include "tag/TagId3.hxx"
@@ -41,9 +42,8 @@
 #undef G_LOG_DOMAIN
 #define G_LOG_DOMAIN "cue"
 
-struct EmbeddedCuePlaylist {
-	struct playlist_provider base;
-
+class EmbeddedCuePlaylist final : public SongEnumerator {
+public:
 	/**
 	 * This is an override for the CUE's "FILE".  An embedded CUE
 	 * sheet must always point to the song file it is contained
@@ -63,18 +63,18 @@ struct EmbeddedCuePlaylist {
 
 	CueParser *parser;
 
+public:
 	EmbeddedCuePlaylist()
 		:filename(nullptr), cuesheet(nullptr), parser(nullptr) {
-		playlist_provider_init(&base, &embcue_playlist_plugin);
 	}
 
-	~EmbeddedCuePlaylist() {
+	virtual ~EmbeddedCuePlaylist() {
 		delete parser;
 		g_free(cuesheet);
 		g_free(filename);
 	}
 
-	Song *Read();
+	virtual Song *NextSong() override;
 };
 
 static void
@@ -93,7 +93,7 @@ static const struct tag_handler embcue_tag_handler = {
 	embcue_tag_pair,
 };
 
-static struct playlist_provider *
+static SongEnumerator *
 embcue_playlist_open_uri(const char *uri,
 			 gcc_unused Mutex &mutex,
 			 gcc_unused Cond &cond)
@@ -122,19 +122,11 @@ embcue_playlist_open_uri(const char *uri,
 	playlist->next = playlist->cuesheet;
 	playlist->parser = new CueParser();
 
-	return &playlist->base;
-}
-
-static void
-embcue_playlist_close(struct playlist_provider *_playlist)
-{
-	EmbeddedCuePlaylist *playlist = (EmbeddedCuePlaylist *)_playlist;
-
-	delete playlist;
+	return playlist;
 }
 
-inline Song *
-EmbeddedCuePlaylist::Read()
+Song *
+EmbeddedCuePlaylist::NextSong()
 {
 	Song *song = parser->Get();
 	if (song != NULL)
@@ -165,14 +157,6 @@ EmbeddedCuePlaylist::Read()
 	return song;
 }
 
-static Song *
-embcue_playlist_read(struct playlist_provider *_playlist)
-{
-	EmbeddedCuePlaylist *playlist = (EmbeddedCuePlaylist *)_playlist;
-
-	return playlist->Read();
-}
-
 static const char *const embcue_playlist_suffixes[] = {
 	/* a few codecs that are known to be supported; there are
 	   probably many more */
@@ -192,8 +176,6 @@ const struct playlist_plugin embcue_playlist_plugin = {
 	nullptr,
 	embcue_playlist_open_uri,
 	nullptr,
-	embcue_playlist_close,
-	embcue_playlist_read,
 
 	embcue_playlist_suffixes,
 	nullptr,
diff --git a/src/playlist/ExtM3uPlaylistPlugin.cxx b/src/playlist/ExtM3uPlaylistPlugin.cxx
index 440dcd432..ff3fcbd7e 100644
--- a/src/playlist/ExtM3uPlaylistPlugin.cxx
+++ b/src/playlist/ExtM3uPlaylistPlugin.cxx
@@ -20,6 +20,7 @@
 #include "config.h"
 #include "ExtM3uPlaylistPlugin.hxx"
 #include "PlaylistPlugin.hxx"
+#include "SongEnumerator.hxx"
 #include "Song.hxx"
 #include "Tag.hxx"
 #include "util/StringUtil.hxx"
@@ -30,40 +31,36 @@
 #include <string.h>
 #include <stdlib.h>
 
-struct ExtM3uPlaylist {
-	struct playlist_provider base;
-
+class ExtM3uPlaylist final : public SongEnumerator {
 	TextInputStream tis;
 
+public:
 	ExtM3uPlaylist(input_stream *is)
 		:tis(is) {
-		playlist_provider_init(&base, &extm3u_playlist_plugin);
 	}
+
+	bool CheckFirstLine() {
+		std::string line;
+		return tis.ReadLine(line) &&
+			strcmp(line.c_str(), "#EXTM3U") == 0;
+	}
+
+	virtual Song *NextSong() override;
 };
 
-static struct playlist_provider *
+static SongEnumerator *
 extm3u_open_stream(struct input_stream *is)
 {
 	ExtM3uPlaylist *playlist = new ExtM3uPlaylist(is);
 
-	std::string line;
-	if (!playlist->tis.ReadLine(line)
-	   || strcmp(line.c_str(), "#EXTM3U") != 0) {
+	if (!playlist->CheckFirstLine()) {
 		/* no EXTM3U header: fall back to the plain m3u
 		   plugin */
 		delete playlist;
 		return NULL;
 	}
 
-	return &playlist->base;
-}
-
-static void
-extm3u_close(struct playlist_provider *_playlist)
-{
-	ExtM3uPlaylist *playlist = (ExtM3uPlaylist *)_playlist;
-
-	delete playlist;
+	return playlist;
 }
 
 /**
@@ -106,17 +103,16 @@ extm3u_parse_tag(const char *line)
 	return tag;
 }
 
-static Song *
-extm3u_read(struct playlist_provider *_playlist)
+Song *
+ExtM3uPlaylist::NextSong()
 {
-	ExtM3uPlaylist *playlist = (ExtM3uPlaylist *)_playlist;
 	Tag *tag = NULL;
 	std::string line;
 	const char *line_s;
 	Song *song;
 
 	do {
-		if (!playlist->tis.ReadLine(line)) {
+		if (!tis.ReadLine(line)) {
 			delete tag;
 			return NULL;
 		}
@@ -155,8 +151,6 @@ const struct playlist_plugin extm3u_playlist_plugin = {
 	nullptr,
 	nullptr,
 	extm3u_open_stream,
-	extm3u_close,
-	extm3u_read,
 
 	nullptr,
 	extm3u_suffixes,
diff --git a/src/playlist/LastFMPlaylistPlugin.cxx b/src/playlist/LastFMPlaylistPlugin.cxx
index a727a21a4..2cc538e1e 100644
--- a/src/playlist/LastFMPlaylistPlugin.cxx
+++ b/src/playlist/LastFMPlaylistPlugin.cxx
@@ -21,6 +21,7 @@
 #include "LastFMPlaylistPlugin.hxx"
 #include "PlaylistPlugin.hxx"
 #include "PlaylistRegistry.hxx"
+#include "SongEnumerator.hxx"
 #include "ConfigData.hxx"
 #include "Song.hxx"
 #include "InputStream.hxx"
@@ -31,22 +32,24 @@
 #include <assert.h>
 #include <string.h>
 
-struct LastfmPlaylist {
-	struct playlist_provider base;
-
+class LastfmPlaylist final : public SongEnumerator {
 	struct input_stream *is;
 
-	struct playlist_provider *xspf;
+	SongEnumerator *const xspf;
 
-	LastfmPlaylist(input_stream *_is, playlist_provider *_xspf)
+public:
+	LastfmPlaylist(input_stream *_is, SongEnumerator *_xspf)
 		:is(_is), xspf(_xspf) {
-		playlist_provider_init(&base, &lastfm_playlist_plugin);
 	}
 
-	~LastfmPlaylist() {
-		playlist_plugin_close(xspf);
+	virtual ~LastfmPlaylist() {
+		delete xspf;
 		is->Close();
 	}
+
+	virtual Song *NextSong() override {
+		return xspf->NextSong();
+	}
 };
 
 static struct {
@@ -161,7 +164,7 @@ lastfm_find(const char *response, const char *name)
 	}
 }
 
-static struct playlist_provider *
+static SongEnumerator *
 lastfm_open_uri(const char *uri, Mutex &mutex, Cond &cond)
 {
 	char *p, *q, *response, *session;
@@ -256,24 +259,7 @@ lastfm_open_uri(const char *uri, Mutex &mutex, Cond &cond)
 
 	/* create the playlist object */
 
-	const auto playlist = new LastfmPlaylist(is, xspf);
-	return &playlist->base;
-}
-
-static void
-lastfm_close(struct playlist_provider *_playlist)
-{
-	LastfmPlaylist *playlist = (LastfmPlaylist *)_playlist;
-
-	delete playlist;
-}
-
-static Song *
-lastfm_read(struct playlist_provider *_playlist)
-{
-	LastfmPlaylist *playlist = (LastfmPlaylist *)_playlist;
-
-	return playlist_plugin_read(playlist->xspf);
+	return new LastfmPlaylist(is, xspf);
 }
 
 static const char *const lastfm_schemes[] = {
@@ -288,8 +274,6 @@ const struct playlist_plugin lastfm_playlist_plugin = {
 	lastfm_finish,
 	lastfm_open_uri,
 	nullptr,
-	lastfm_close,
-	lastfm_read,
 
 	lastfm_schemes,
 	nullptr,
diff --git a/src/playlist/M3uPlaylistPlugin.cxx b/src/playlist/M3uPlaylistPlugin.cxx
index d9f1e4737..8854be8d7 100644
--- a/src/playlist/M3uPlaylistPlugin.cxx
+++ b/src/playlist/M3uPlaylistPlugin.cxx
@@ -20,47 +20,37 @@
 #include "config.h"
 #include "M3uPlaylistPlugin.hxx"
 #include "PlaylistPlugin.hxx"
+#include "SongEnumerator.hxx"
 #include "Song.hxx"
 #include "TextInputStream.hxx"
 
 #include <glib.h>
 
-struct M3uPlaylist {
-	struct playlist_provider base;
-
+class M3uPlaylist final : public SongEnumerator {
 	TextInputStream tis;
 
+public:
 	M3uPlaylist(input_stream *is)
 		:tis(is) {
-		playlist_provider_init(&base, &m3u_playlist_plugin);
 	}
+
+	virtual Song *NextSong() override;
 };
 
-static struct playlist_provider *
+static SongEnumerator *
 m3u_open_stream(struct input_stream *is)
 {
-	M3uPlaylist *playlist = new M3uPlaylist(is);
-
-	return &playlist->base;
-}
-
-static void
-m3u_close(struct playlist_provider *_playlist)
-{
-	M3uPlaylist *playlist = (M3uPlaylist *)_playlist;
-
-	delete playlist;
+	return new M3uPlaylist(is);
 }
 
-static Song *
-m3u_read(struct playlist_provider *_playlist)
+Song *
+M3uPlaylist::NextSong()
 {
-	M3uPlaylist *playlist = (M3uPlaylist *)_playlist;
 	std::string line;
 	const char *line_s;
 
 	do {
-		if (!playlist->tis.ReadLine(line))
+		if (!tis.ReadLine(line))
 			return NULL;
 
 		line_s = line.c_str();
@@ -89,8 +79,6 @@ const struct playlist_plugin m3u_playlist_plugin = {
 	nullptr,
 	nullptr,
 	m3u_open_stream,
-	m3u_close,
-	m3u_read,
 
 	nullptr,
 	m3u_suffixes,
diff --git a/src/playlist/PlsPlaylistPlugin.cxx b/src/playlist/PlsPlaylistPlugin.cxx
index 4a0fde45f..946fe9c55 100644
--- a/src/playlist/PlsPlaylistPlugin.cxx
+++ b/src/playlist/PlsPlaylistPlugin.cxx
@@ -19,7 +19,8 @@
 
 #include "config.h"
 #include "PlsPlaylistPlugin.hxx"
-#include "MemoryPlaylistProvider.hxx"
+#include "PlaylistPlugin.hxx"
+#include "MemorySongEnumerator.hxx"
 #include "InputStream.hxx"
 #include "Song.hxx"
 #include "Tag.hxx"
@@ -101,7 +102,7 @@ pls_parser(GKeyFile *keyfile, std::forward_list<SongPointer> &songs)
 
 }
 
-static struct playlist_provider *
+static SongEnumerator *
 pls_open_stream(struct input_stream *is)
 {
 	GError *error = NULL;
@@ -150,7 +151,7 @@ pls_open_stream(struct input_stream *is)
 	g_key_file_free(keyfile);
 
 	songs.reverse();
-	return new MemoryPlaylistProvider(std::move(songs));
+	return new MemorySongEnumerator(std::move(songs));
 }
 
 static const char *const pls_suffixes[] = {
@@ -170,8 +171,6 @@ const struct playlist_plugin pls_playlist_plugin = {
 	nullptr,
 	nullptr,
 	pls_open_stream,
-	nullptr,
-	nullptr,
 
 	nullptr,
 	pls_suffixes,
diff --git a/src/playlist/RssPlaylistPlugin.cxx b/src/playlist/RssPlaylistPlugin.cxx
index c045b4df2..97c0d806b 100644
--- a/src/playlist/RssPlaylistPlugin.cxx
+++ b/src/playlist/RssPlaylistPlugin.cxx
@@ -19,7 +19,8 @@
 
 #include "config.h"
 #include "RssPlaylistPlugin.hxx"
-#include "MemoryPlaylistProvider.hxx"
+#include "PlaylistPlugin.hxx"
+#include "MemorySongEnumerator.hxx"
 #include "InputStream.hxx"
 #include "Song.hxx"
 #include "Tag.hxx"
@@ -198,7 +199,7 @@ rss_parser_destroy(gpointer data)
  *
  */
 
-static struct playlist_provider *
+static SongEnumerator *
 rss_open_stream(struct input_stream *is)
 {
 	RssParser parser;
@@ -246,8 +247,8 @@ rss_open_stream(struct input_stream *is)
 	}
 
 	parser.songs.reverse();
-	MemoryPlaylistProvider *playlist =
-		new MemoryPlaylistProvider(std::move(parser.songs));
+	MemorySongEnumerator *playlist =
+		new MemorySongEnumerator(std::move(parser.songs));
 
 	g_markup_parse_context_free(context);
 
@@ -272,8 +273,6 @@ const struct playlist_plugin rss_playlist_plugin = {
 	nullptr,
 	nullptr,
 	rss_open_stream,
-	nullptr,
-	nullptr,
 
 	nullptr,
 	rss_suffixes,
diff --git a/src/playlist/SoundCloudPlaylistPlugin.cxx b/src/playlist/SoundCloudPlaylistPlugin.cxx
index 5679062cf..f822382fc 100644
--- a/src/playlist/SoundCloudPlaylistPlugin.cxx
+++ b/src/playlist/SoundCloudPlaylistPlugin.cxx
@@ -19,7 +19,8 @@
 
 #include "config.h"
 #include "SoundCloudPlaylistPlugin.hxx"
-#include "MemoryPlaylistProvider.hxx"
+#include "PlaylistPlugin.hxx"
+#include "MemorySongEnumerator.hxx"
 #include "ConfigData.hxx"
 #include "InputStream.hxx"
 #include "Song.hxx"
@@ -315,7 +316,7 @@ soundcloud_parse_json(const char *url, yajl_handle hand,
  *	soundcloud://url/<url or path of soundcloud page>
  */
 
-static struct playlist_provider *
+static SongEnumerator *
 soundcloud_open_uri(const char *uri, Mutex &mutex, Cond &cond)
 {
 	char *s, *p;
@@ -389,7 +390,7 @@ soundcloud_open_uri(const char *uri, Mutex &mutex, Cond &cond)
 		return NULL;
 
 	data.songs.reverse();
-	return new MemoryPlaylistProvider(std::move(data.songs));
+	return new MemorySongEnumerator(std::move(data.songs));
 }
 
 static const char *const soundcloud_schemes[] = {
@@ -404,8 +405,6 @@ const struct playlist_plugin soundcloud_playlist_plugin = {
 	soundcloud_finish,
 	soundcloud_open_uri,
 	nullptr,
-	nullptr,
-	nullptr,
 
 	soundcloud_schemes,
 	nullptr,
diff --git a/src/playlist/XspfPlaylistPlugin.cxx b/src/playlist/XspfPlaylistPlugin.cxx
index 667f484b2..002a03f8a 100644
--- a/src/playlist/XspfPlaylistPlugin.cxx
+++ b/src/playlist/XspfPlaylistPlugin.cxx
@@ -19,7 +19,8 @@
 
 #include "config.h"
 #include "XspfPlaylistPlugin.hxx"
-#include "MemoryPlaylistProvider.hxx"
+#include "PlaylistPlugin.hxx"
+#include "MemorySongEnumerator.hxx"
 #include "InputStream.hxx"
 #include "Tag.hxx"
 #include "util/Error.hxx"
@@ -217,7 +218,7 @@ xspf_parser_destroy(gpointer data)
  *
  */
 
-static struct playlist_provider *
+static SongEnumerator *
 xspf_open_stream(struct input_stream *is)
 {
 	XspfParser parser;
@@ -265,8 +266,8 @@ xspf_open_stream(struct input_stream *is)
 	}
 
 	parser.songs.reverse();
-	MemoryPlaylistProvider *playlist =
-		new MemoryPlaylistProvider(std::move(parser.songs));
+	MemorySongEnumerator *playlist =
+		new MemorySongEnumerator(std::move(parser.songs));
 
 	g_markup_parse_context_free(context);
 
@@ -290,8 +291,6 @@ const struct playlist_plugin xspf_playlist_plugin = {
 	nullptr,
 	nullptr,
 	xspf_open_stream,
-	nullptr,
-	nullptr,
 
 	nullptr,
 	xspf_suffixes,