decoder_plugin: added method stream_tag()

This is like tag_dup(), but works with an input_stream object instead
of a file path.

src/decoder/sidplay_plugin.cxx

@@ -411,6 +411,7 @@ const struct decoder_plugin sidplay_decoder_plugin = {
 	NULL, /* stream_decode() */
 	sidplay_file_decode,
 	sidplay_tag_dup,
+	NULL, /* stream_tag() */
 	sidplay_container_scan,
 	sidplay_suffixes,
 	NULL, /* mime_types */

src/decoder_plugin.h

@@ -76,6 +76,13 @@ struct decoder_plugin {
 	 */
 	struct tag *(*tag_dup)(const char *path_fs);
 
+	/**
+	 * Read the tags of a stream.
+	 *
+	 * @return NULL if the operation has failed
+	 */
+	struct tag *(*stream_tag)(struct input_stream *is);
+
 	/**
 	 * @brief Return a "virtual" filename for subtracks in
 	 * container formats like flac
@@ -147,7 +154,21 @@ static inline struct tag *
 decoder_plugin_tag_dup(const struct decoder_plugin *plugin,
 		       const char *path_fs)
 {
-	return plugin->tag_dup(path_fs);
+	return plugin->tag_dup != NULL
+		? plugin->tag_dup(path_fs)
+		: NULL;
+}
+
+/**
+ * Read the tag of a stream.
+ */
+static inline struct tag *
+decoder_plugin_stream_tag(const struct decoder_plugin *plugin,
+			  struct input_stream *is)
+{
+	return plugin->stream_tag != NULL
+		? plugin->stream_tag(is)
+		: NULL;
 }
 
 /**

src/song_update.c

@@ -27,12 +27,14 @@
 #include "tag_ape.h"
 #include "tag_id3.h"
 #include "tag.h"
+#include "input_stream.h"
 
 #include <glib.h>
 
 #include <assert.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <stdio.h>
 
 struct song *
 song_file_load(const char *path, struct directory *parent)
@@ -99,6 +101,7 @@ song_file_update(struct song *song)
 	char *path_fs;
 	const struct decoder_plugin *plugin;
 	struct stat st;
+	struct input_stream is = { .plugin = NULL };
 
 	assert(song_is_file(song));
 
@@ -129,13 +132,36 @@ song_file_update(struct song *song)
 	song->mtime = st.st_mtime;
 
 	do {
+		/* load file tag */
 		song->tag = decoder_plugin_tag_dup(plugin, path_fs);
 		if (song->tag != NULL)
 			break;
 
+		/* fall back to stream tag */
+		if (plugin->stream_tag != NULL) {
+			/* open the input_stream (if not already
+			   open) */
+			if (is.plugin == NULL &&
+			    !input_stream_open(&is, path_fs, NULL))
+				is.plugin = NULL;
+
+			/* now try the stream_tag() method */
+			if (is.plugin != NULL) {
+				song->tag = decoder_plugin_stream_tag(plugin,
+								      &is);
+				if (song->tag != NULL)
+					break;
+
+				input_stream_seek(&is, 0, SEEK_SET, NULL);
+			}
+		}
+
 		plugin = decoder_plugin_from_suffix(suffix, plugin);
 	} while (plugin != NULL);
 
+	if (is.plugin != NULL)
+		input_stream_close(&is);
+
 	if (song->tag != NULL && tag_is_empty(song->tag))
 		song->tag = tag_fallback(path_fs, song->tag);
 

test/read_tags.c

@@ -169,6 +169,20 @@ int main(int argc, char **argv)
 	}
 
 	tag = decoder_plugin_tag_dup(plugin, path);
+	if (tag == NULL && plugin->stream_tag != NULL) {
+		struct input_stream is;
+
+		if (!input_stream_open(&is, path, &error)) {
+			g_printerr("Failed to open %s: %s\n",
+				   path, error->message);
+			g_error_free(error);
+			return 1;
+		}
+
+		tag = decoder_plugin_stream_tag(plugin, &is);
+		input_stream_close(&is);
+	}
+
 	decoder_plugin_deinit_all();
 	input_stream_global_finish();
 	if (tag == NULL) {