tag_id3: parse ID3 tags in AIFF files

Added a small AIFF parser library, code copied from the RIFF parser
(big-endian integers).  Look for an "ID3" chunk, and let libid3tag
parse it.

src/aiff.c

@@ -0,0 +1,103 @@
+/*
+ * Copyright (C) 2003-2009 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include "aiff.h"
+
+#include <glib.h>
+
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+
+#undef G_LOG_DOMAIN
+#define G_LOG_DOMAIN "aiff"
+
+struct aiff_header {
+	char id[4];
+	uint32_t size;
+	char format[4];
+};
+
+struct aiff_chunk_header {
+	char id[4];
+	uint32_t size;
+};
+
+size_t
+aiff_seek_id3(FILE *file)
+{
+	int ret;
+	struct stat st;
+	struct aiff_header header;
+	struct aiff_chunk_header chunk;
+	size_t size;
+
+	/* determine the file size */
+
+	ret = fstat(fileno(file), &st);
+	if (ret < 0) {
+		g_warning("Failed to stat file descriptor: %s",
+			  strerror(errno));
+		return 0;
+	}
+
+	/* seek to the beginning and read the AIFF header */
+
+	ret = fseek(file, 0, SEEK_SET);
+	if (ret != 0) {
+		g_warning("Failed to seek: %s", g_strerror(errno));
+		return 0;
+	}
+
+	size = fread(&header, sizeof(header), 1, file);
+	if (size != 1 ||
+	    memcmp(header.id, "FORM", 4) != 0 ||
+	    GUINT32_FROM_BE(header.size) > st.st_size ||
+	    memcmp(header.format, "AIFF", 4) != 0)
+		/* not a AIFF file */
+		return 0;
+
+	while (true) {
+		/* read the chunk header */
+
+		size = fread(&chunk, sizeof(chunk), 1, file);
+		if (size != 1)
+			return 0;
+
+		size = GUINT32_FROM_BE(chunk.size);
+		if (size % 2 != 0)
+			/* pad byte */
+			++size;
+
+		if (memcmp(chunk.id, "ID3 ", 4) == 0)
+			/* found it! */
+			return size;
+
+		if ((off_t)size < 0)
+			/* integer underflow after cast to signed
+			   type */
+			return 0;
+
+		ret = fseek(file, size, SEEK_CUR);
+		if (ret != 0)
+			return 0;
+	}
+}