SongUpdate: read tags from songs in an archive

Add the TagStream.cxx library, similar to TagFile.cxx, and use it to
load tags from song files inside archives.

Makefile.am

@@ -202,6 +202,7 @@ src_mpd_SOURCES = \
 	src/TagPrint.cxx src/TagPrint.hxx \
 	src/TagSave.cxx src/TagSave.hxx \
 	src/TagFile.cxx src/TagFile.hxx \
+	src/TagStream.cxx src/TagStream.hxx \
 	src/TextInputStream.cxx \
 	src/Volume.cxx src/Volume.hxx \
 	src/SongFilter.cxx src/SongFilter.hxx \

NEWS

@@ -1,6 +1,8 @@
 ver 0.19 (not yet released)
 * protocol
   - new commands "addtagid", "cleartagid"
+* archive
+  - read tags from songs in an archive
 * input
   - alsa: new input plugin
   - smbclient: new input plugin

src/SongUpdate.cxx

@@ -32,6 +32,7 @@
 #include "tag/TagId3.hxx"
 #include "tag/ApeTag.hxx"
 #include "TagFile.hxx"
+#include "TagStream.hxx"
 
 #include <assert.h>
 #include <string.h>
@@ -119,12 +120,15 @@ Song::UpdateFileInArchive()
 	if (!decoder_plugins_supports_suffix(suffix))
 		return false;
 
+	const auto path_fs = map_song_fs(*this);
+	if (path_fs.IsNull())
+		return false;
+
+	TagBuilder tag_builder;
+	if (!tag_stream_scan(path_fs.c_str(), full_tag_handler, &tag_builder))
+		return false;
+
 	delete tag;
-
-	//accept every file that has music suffix
-	//because we don't support tag reading through
-	//input streams
-	tag = new Tag();
-
+	tag = tag_builder.Commit();
 	return true;
 }

src/TagStream.cxx

@@ -0,0 +1,78 @@
+/*
+ * 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.
+ */
+
+#include "config.h"
+#include "TagStream.hxx"
+#include "util/UriUtil.hxx"
+#include "util/Error.hxx"
+#include "DecoderList.hxx"
+#include "DecoderPlugin.hxx"
+#include "InputStream.hxx"
+#include "thread/Mutex.hxx"
+#include "thread/Cond.hxx"
+
+#include <assert.h>
+
+/**
+ * Does the #DecoderPlugin support either the suffix or the MIME type?
+ */
+gcc_pure
+static bool
+CheckDecoderPlugin(const DecoderPlugin &plugin,
+		   const char *suffix, const char *mime)
+{
+	return (mime != nullptr && plugin.SupportsMimeType(mime)) ||
+		(suffix != nullptr && plugin.SupportsSuffix(suffix));
+}
+
+bool
+tag_stream_scan(InputStream &is, const tag_handler &handler, void *ctx)
+{
+	assert(is.ready);
+
+	const char *const suffix = uri_get_suffix(is.uri.c_str());
+	const char *const mime = is.mime.empty() ? nullptr : is.mime.c_str();
+
+	if (suffix == nullptr && mime == nullptr)
+		return false;
+
+	return decoder_plugins_try([suffix, mime, &is,
+				    &handler, ctx](const DecoderPlugin &plugin){
+			is.LockRewind(IgnoreError());
+
+			return CheckDecoderPlugin(plugin, suffix, mime) &&
+				plugin.ScanStream(is, handler, ctx);
+		});
+}
+
+bool
+tag_stream_scan(const char *uri, const tag_handler &handler, void *ctx)
+{
+	Mutex mutex;
+	Cond cond;
+
+	InputStream *is = InputStream::OpenReady(uri, mutex, cond,
+						 IgnoreError());
+	if (is == nullptr)
+		return false;
+
+	bool success = tag_stream_scan(*is, handler, ctx);
+	is->Close();
+	return success;
+}

src/TagStream.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_TAG_STREAM_HXX
+#define MPD_TAG_STREAM_HXX
+
+#include "check.h"
+
+struct InputStream;
+struct tag_handler;
+
+/**
+ * Scan the tags of an #InputStream.  Invokes matching decoder
+ * plugins, but does not invoke the special "APE" and "ID3" scanners.
+ *
+ * @return true if the file was recognized (even if no metadata was
+ * found)
+ */
+bool
+tag_stream_scan(InputStream &is, const tag_handler &handler, void *ctx);
+
+bool
+tag_stream_scan(const char *uri, const tag_handler &handler, void *ctx);
+
+#endif