song: replaced all song constructors

Provide separate constructors for creating a remote song, a local
song, and one for loading data from a song file.  This way, we can add
more assertions.

src/playlist.c

@@ -561,7 +561,7 @@ enum playlist_result addToPlaylist(const char *url, int *added_id)
 
 	if ((song = getSongFromDB(url))) {
 	} else if (!(isValidRemoteUtf8Url(url) &&
-		     (song = newSong(url, NULL)))) {
+		     (song = song_remote_new(url)))) {
 		return PLAYLIST_RESULT_NO_SUCH_SONG;
 	}
 
@@ -581,7 +581,7 @@ int addToStoredPlaylist(const char *url, const char *utf8file)
 	if (!isValidRemoteUtf8Url(url))
 		return ACK_ERROR_NO_EXIST;
 
-	song = newSong(url, NULL);
+	song = song_remote_new(url);
 	if (song) {
 		int ret = appendSongToStoredPlaylistByPath(utf8file, song);
 		freeJustSong(song);

src/song.c

@@ -26,7 +26,7 @@
 #include "decoder_list.h"
 #include "decoder_api.h"
 
-struct song *
+static struct song *
 song_alloc(const char *url, struct directory *parent)
 {
 	size_t urllen;
@@ -45,34 +45,45 @@ song_alloc(const char *url, struct directory *parent)
 }
 
 struct song *
-newSong(const char *url, struct directory *parentDir)
+song_remote_new(const char *url)
+{
+	return song_alloc(url, NULL);
+}
+
+struct song *
+song_file_new(const char *path, struct directory *parent)
+{
+	assert(parent != NULL);
+
+	return song_alloc(path, parent);
+}
+
+struct song *
+song_file_load(const char *path, struct directory *parent)
 {
 	struct song *song;
-	assert(*url);
+	struct decoder_plugin *plugin;
+	unsigned int next = 0;
+	char path_max_tmp[MPD_PATH_MAX], *abs_path;
 
-	if (strchr(url, '\n')) {
-		DEBUG("newSong: '%s' is not a valid uri\n", url);
+	assert(parent != NULL);
+
+	if (strchr(path, '\n')) {
+		DEBUG("newSong: '%s' is not a valid uri\n", path);
 		return NULL;
 	}
 
-	song = song_alloc(url, parentDir);
+	song = song_file_new(path, parent);
 
-	if (song_is_file(song)) {
-		struct decoder_plugin *plugin;
-		unsigned int next = 0;
-		char path_max_tmp[MPD_PATH_MAX];
-		char *abs_path = rmp2amp_r(path_max_tmp,
-		                           get_song_url(path_max_tmp, song));
+	abs_path = rmp2amp_r(path_max_tmp, get_song_url(path_max_tmp, song));
+	while (song->tag == NULL &&
+	       (plugin = isMusic(abs_path, &(song->mtime), next++))) {
+		song->tag = plugin->tag_dup(abs_path);
+	}
 
-		while (!song->tag && (plugin = isMusic(abs_path,
-						       &(song->mtime),
-						       next++))) {
-			song->tag = plugin->tag_dup(abs_path);
-		}
-		if (!song->tag || song->tag->time < 0) {
-			freeJustSong(song);
-			song = NULL;
-		}
+	if (song->tag == NULL || song->tag->time < 0) {
+		freeJustSong(song);
+		return NULL;
 	}
 
 	return song;

src/song.h

@@ -36,11 +36,21 @@ struct song {
 	char url[sizeof(int)];
 };
 
+/** allocate a new song with a remote URL */
 struct song *
-song_alloc(const char *url, struct directory *parent);
+song_remote_new(const char *url);
 
+/** allocate a new song with a local file name */
 struct song *
-newSong(const char *url, struct directory *parentDir);
+song_file_new(const char *path, struct directory *parent);
+
+/**
+ * allocate a new song structure with a local file name and attempt to
+ * load its metadata.  If all decoder plugin fail to read its meta
+ * data, NULL is returned.
+ */
+struct song *
+song_file_load(const char *path, struct directory *parent);
 
 void
 freeJustSong(struct song *);

src/song_save.c

@@ -113,8 +113,8 @@ void readSongInfoIntoList(FILE *fp, struct songvec *sv,
 			if (song)
 				insertSongIntoList(sv, song);
 
-			song = song_alloc(buffer + strlen(SONG_KEY),
-					  parentDir);
+			song = song_file_new(buffer + strlen(SONG_KEY),
+					     parentDir);
 		} else if (*buffer == 0) {
 			/* ignore empty lines (starting with '\0') */
 		} else if (song == NULL) {

src/update.c

@@ -201,7 +201,7 @@ addToDirectory(struct directory *directory, const char *name)
 		struct song *song;
 		const char *shortname = mpd_basename(name);
 
-		if (!(song = newSong(shortname, directory)))
+		if (!(song = song_file_load(shortname, directory)))
 			return -1;
 		songvec_add(&directory->songs, song);
 		LOG("added %s\n", name);