Introduce Mix_LoadMUSType_RW()

The new function allows to override SDL_mixer's auto-detection of the
music format.  Mix_LoadMUS_RW() is now a simple wrapper for
Mix_LoadMUSType_RW().

Of course, auto-detection is still possible.  The code that does the
auto-detecting has been split into the new detect_music_type() static.
This can get rid of some code duplication in Mix_LoadMUS() as well
(though this patch does not change Mix_LoadMUS() to use this new
function.)


diff -r 3a4c352a9a00 SDL_mixer.h
--- a/SDL_mixer.h	Thu Jul 14 12:33:48 2011 -0700
+++ b/SDL_mixer.h	Mon Jul 18 14:04:02 2011 +0300
@@ -155,6 +155,9 @@
    Matt Campbell (matt@campbellhome.dhs.org) April 2000 */
 extern DECLSPEC Mix_Music * SDLCALL Mix_LoadMUS_RW(SDL_RWops *rw);
 
+/* Load a music file from an SDL_RWop object assuming a specific format */
+extern DECLSPEC Mix_Music * SDLCALL Mix_LoadMUSType_RW(SDL_RWops *rw, Mix_MusicType type);
+
 /* Load a wave file of the mixer format from a memory buffer */
 extern DECLSPEC Mix_Chunk * SDLCALL Mix_QuickLoad_WAV(Uint8 *mem);
 
diff -r 3a4c352a9a00 music.c
--- a/music.c	Thu Jul 14 12:33:48 2011 -0700
+++ b/music.c	Mon Jul 18 14:04:02 2011 +0300
@@ -1385,79 +1385,140 @@
 
 Mix_Music *Mix_LoadMUS_RW(SDL_RWops *rw)
 {
-	Uint8 magic[5];	  /*Apparently there is no way to check if the file is really a MOD,*/
-	/*		    or there are too many formats supported by MikMod or MikMod does */
-	/*		    this check by itself. If someone implements other formats (e.g. MP3) */
-	/*		    the check can be uncommented */
+	return Mix_LoadMUSType_RW(rw, MUS_NONE);
+}
+
+/* MUS_MOD can't be auto-detected. If no other format was detected, MOD is
+ * assumed and MUS_MOD will be returned, meaning that the format might not
+ * actually be MOD-based.
+ *
+ * Returns MUS_NONE in case of errors. */
+static Mix_MusicType detect_music_type(SDL_RWops *rw)
+{
+	Uint8 magic[5];
 	Uint8 moremagic[9];
+
+	int start = SDL_RWtell(rw);
+	if (SDL_RWread(rw, magic, 1, 4) != 4 || SDL_RWread(rw, moremagic, 1, 8) != 8 ) {
+		Mix_SetError("Couldn't read from RWops");
+		return MUS_NONE;
+	}
+	SDL_RWseek(rw, start, RW_SEEK_SET);
+	magic[4]='\0';
+	moremagic[8] = '\0';
+
+	/* WAVE files have the magic four bytes "RIFF"
+	   AIFF files have the magic 12 bytes "FORM" XXXX "AIFF" */
+	if (((strcmp((char *)magic, "RIFF") == 0) && (strcmp((char *)(moremagic+4), "WAVE") == 0)) ||
+		 (strcmp((char *)magic, "FORM") == 0)) {
+		return MUS_WAV;
+	}
+
+	/* Ogg Vorbis files have the magic four bytes "OggS" */
+	if (strcmp((char *)magic, "OggS") == 0) {
+		return MUS_OGG;
+	}
+
+	/* FLAC files have the magic four bytes "fLaC" */
+	if (strcmp((char *)magic, "fLaC") == 0) {
+		return MUS_FLAC;
+	}
+
+	/* MP3 files either have a 0xFF byte followed by a byte for which & 0xF0
+	 * yields 0xF0, or by the three bytes "ID3" when the file has ID3 metadata */
+	if ((magic[0] == 0xFF && (magic[1] & 0xF0) == 0xF0) || (strncmp((char *)magic, "ID3", 3) == 0)) {
+		return MUS_MP3;
+	}
+
+	/* MIDI files have the magic four bytes "MThd" */
+	if (strcmp((char *)magic, "MThd") == 0) {
+		return MUS_MID;
+	}
+
+	/* Assume MOD format.
+	 *
+	 * Apparently there is no way to check if the file is really a MOD,
+	 * or there are too many formats supported by MikMod/ModPlug, or
+	 * MikMod/ModPlug does this check by itself. */
+	return MUS_MOD;
+}
+
+Mix_Music *Mix_LoadMUSType_RW(SDL_RWops *rw, Mix_MusicType want)
+{
 	Mix_Music *music;
-	int start;
 
 	if (!rw) {
 		Mix_SetError("RWops pointer is NULL");
 		return NULL;
 	}
 
-	/* Figure out what kind of file this is */
-	start = SDL_RWtell(rw);
-	if ( SDL_RWread(rw,magic,1,4) != 4 ||
-	     SDL_RWread(rw,moremagic,1,8) != 8 ) {
-		Mix_SetError("Couldn't read from RWops");
-		return NULL;
+	/* If the caller wants auto-detection, figure out what kind of file
+	 * this is. */
+	if (want == MUS_NONE) {
+		if ((want = detect_music_type(rw)) == MUS_NONE) {
+			/* Don't call Mix_SetError() here since detect_music_type()
+			 * does that. */
+			return NULL;
+		}
 	}
-	SDL_RWseek(rw, start, RW_SEEK_SET);
-	magic[4]='\0';
-	moremagic[8] = '\0';
 
 	/* Allocate memory for the music structure */
-	music=(Mix_Music *)malloc(sizeof(Mix_Music));
-	if (music==NULL ) {
+	music = (Mix_Music *)malloc(sizeof(Mix_Music));
+	if (music == NULL ) {
 		Mix_SetError("Out of memory");
 		return(NULL);
 	}
 	music->error = 0;
 
+	switch (want) {
 #ifdef WAV_MUSIC
-	/* WAVE files have the magic four bytes "RIFF"
-	   AIFF files have the magic 12 bytes "FORM" XXXX "AIFF"
-	 */
-	if ( ((strcmp((char *)magic, "RIFF") == 0) && (strcmp((char *)(moremagic+4), "WAVE") == 0)) ||
-	     (strcmp((char *)magic, "FORM") == 0) ) {
-		music->type = MUS_WAV;
-		music->data.wave = WAVStream_LoadSong_RW(rw, (char *)magic);
-		if ( music->data.wave == NULL ) {
+	case MUS_WAV:
+		/* The WAVE loader needs the first 4 bytes of the header */
+		{
+			Uint8 magic[5];
+			int start = SDL_RWtell(rw);
+			if (SDL_RWread(rw, magic, 1, 4) != 4) {
+				Mix_SetError("Couldn't read from RWops");
+				return MUS_NONE;
+			}
+			SDL_RWseek(rw, start, RW_SEEK_SET);
+			magic[4] = '\0';
+			music->type = MUS_WAV;
+			music->data.wave = WAVStream_LoadSong_RW(rw, (char *)magic);
+		}
+		if (music->data.wave == NULL) {
 			music->error = 1;
 		}
+		break;
+#endif
 
-	} else
-#endif
 #ifdef OGG_MUSIC
-	/* Ogg Vorbis files have the magic four bytes "OggS" */
-	if ( strcmp((char *)magic, "OggS") == 0 ) {
+	case MUS_OGG:
 		music->type = MUS_OGG;
 		music->data.ogg = OGG_new_RW(rw);
-		if ( music->data.ogg == NULL ) {
+		if (music->data.ogg == NULL) {
 			music->error = 1;
 		}
-	} else
+		break;
 #endif
+
 #ifdef FLAC_MUSIC
-	/* FLAC files have the magic four bytes "fLaC" */
-	if ( strcmp((char *)magic, "fLaC") == 0 ) {
+	case MUS_FLAC:
 		music->type = MUS_FLAC;
 		music->data.flac = FLAC_new_RW(rw);
-		if ( music->data.flac == NULL ) {
+		if (music->data.flac == NULL) {
 			music->error = 1;
 		}
-	} else
+		break;
 #endif
+
 #ifdef MP3_MUSIC
-	if ( ( magic[0] == 0xFF && (magic[1] & 0xF0) == 0xF0) || ( strncmp((char *)magic, "ID3", 3) == 0 ) ) {
-		if ( Mix_Init(MIX_INIT_MP3) ) {
+	case MUS_MP3:
+		if (Mix_Init(MIX_INIT_MP3)) {
 			SMPEG_Info info;
 			music->type = MUS_MP3;
 			music->data.mp3 = smpeg.SMPEG_new_rwops(rw, &info, 0);
-			if ( !info.has_audio ) {
+			if (!info.has_audio) {
 				Mix_SetError("MPEG file does not have any audio stream.");
 				music->error = 1;
 			} else {
@@ -1466,45 +1527,44 @@
 		} else {
 			music->error = 1;
 		}
-	} else
-#endif
-#ifdef MP3_MAD_MUSIC
-	if ( ( magic[0] == 0xFF && (magic[1] & 0xF0) == 0xF0) || ( strncmp((char *)magic, "ID3", 3) == 0 ) ) {
+		break;
+#elif defined(MP3_MAD_MUSIC)
+	case MUS_MP3:
 		music->type = MUS_MP3_MAD;
 		music->data.mp3_mad = mad_openFileRW(rw, &used_mixer);
 		if (music->data.mp3_mad == 0) {
 			Mix_SetError("Could not initialize MPEG stream.");
 			music->error = 1;
 		}
-	} else
+		break;
 #endif
+
 #ifdef MID_MUSIC
-	/* MIDI files have the magic four bytes "MThd" */
-	if ( strcmp((char *)magic, "MThd") == 0 ) {
+	case MUS_MID:
 		music->type = MUS_MID;
 #ifdef USE_NATIVE_MIDI
-		if ( native_midi_ok ) {
+		if (native_midi_ok) {
 			music->data.nativemidi = native_midi_loadsong_RW(rw);
-	  		if ( music->data.nativemidi == NULL ) {
-		  		Mix_SetError("%s", native_midi_error());
-			  	music->error = 1;
+			if (music->data.nativemidi == NULL) {
+				Mix_SetError("%s", native_midi_error());
+				music->error = 1;
 			}
-			goto skip;
+			break;
 		}
 #endif
 #ifdef USE_FLUIDSYNTH_MIDI
-		if ( fluidsynth_ok ) {
+		if (fluidsynth_ok) {
 			music->data.fluidsynthmidi = fluidsynth_loadsong_RW(rw);
-			if ( music->data.fluidsynthmidi == NULL ) {
+			if (music->data.fluidsynthmidi == NULL) {
 				music->error = 1;
 			}
-			goto skip;
+			break;
 		}
 #endif
 #ifdef USE_TIMIDITY_MIDI
-		if ( timidity_ok ) {
+		if (timidity_ok) {
 			music->data.midi = Timidity_LoadSong_RW(rw);
-			if ( music->data.midi == NULL ) {
+			if (music->data.midi == NULL) {
 				Mix_SetError("%s", Timidity_Error());
 				music->error = 1;
 			}
@@ -1513,40 +1573,41 @@
 			music->error = 1;
 		}
 #endif
-	} else
+		break;
 #endif
+
 #if defined(MODPLUG_MUSIC) || defined(MOD_MUSIC)
-	if (1) {
+	case MUS_MOD:
 		music->error = 1;
 #ifdef MODPLUG_MUSIC
-		if ( music->error ) {
+		if (music->error) {
 			music->type = MUS_MODPLUG;
 			music->data.modplug = modplug_new_RW(rw);
-			if ( music->data.modplug ) {
+			if (music->data.modplug) {
 				music->error = 0;
 			}
 		}
 #endif
 #ifdef MOD_MUSIC
-		if ( music->error ) {
+		if (music->error) {
 			music->type = MUS_MOD;
 			music->data.module = MOD_new_RW(rw);
-			if ( music->data.module ) {
+			if (music->data.module) {
 				music->error = 0;
 			}
 		}
 #endif
-	} else
-#endif /* MODPLUG_MUSIC || MOD_MUSIC */
-	{
+		break;
+#endif
+
+	default:
 		Mix_SetError("Unrecognized music format");
-		music->error=1;
-	}
+		music->error = 1;
+	} /* switch (want) */
 
-skip:
 	if (music->error) {
 		free(music);
-		music=NULL;
+		music = NULL;
 	}
 	return(music);
 }