initial commit

oggextract.c

@@ -0,0 +1,174 @@
+/*
+ * Author: Adrian Keet
+ * Last modified: October 21, 2012
+ *
+ * This code is in the public domain. Go ahead and use it for whatever you
+ * want. I don't care. :)
+ */
+
+#include <stdio.h>
+#include <malloc.h>
+#include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+
+int usage()
+{
+	fprintf(stderr, "Usage: oggextract <filename> [<filename> ...]");
+	return 255;
+}
+
+int findpattern(unsigned char *data, int datalen, int start)
+{
+	int i;
+
+	for (i = start; i < datalen - 4; i++)
+		if (*(int *)(data + i) == 0x5367674f) /* "OggS" */
+			return i;
+	return -1;
+}
+
+int ogg_ispage(unsigned char *data)
+{
+	/* capture pattern */
+	if (*(int *)data != 0x5367674f) /* "OggS" */
+		return 0;
+
+	/* stream structure version */
+	if (data[4] != 0x00)
+		return 0;
+
+	/* header type flag */
+	if ((data[5] & ~7) != 0x00)
+		return 0;
+
+	/* I think we can reasonably assume it is a real page now */
+	return 1;
+}
+
+unsigned int ogg_getlength(unsigned char *data)
+{
+	unsigned char nsegs;
+	unsigned char *segs;
+	int i;
+	int length;
+
+	nsegs = data[26];
+	segs = data + 27;
+	length = 27 + nsegs;
+
+	for (i = 0; i < nsegs; i++)
+		length += segs[i];
+	return length;
+}
+
+int ogg_isinitial(unsigned char *data)
+{
+	return data[5] & 2;
+}
+
+int ogg_isfinal(unsigned char *data)
+{
+	return data[5] & 4;
+}
+
+int extract(char *filename)
+{
+	int fd;
+	struct stat statdata;
+	int filesize;
+	unsigned char *filedata, *oggdata;
+
+	int pos = 0;
+
+	int pagelen;
+	int outfd = -1;
+	char *outfilename;
+
+	int numfiles = 0;
+
+	printf("Extracting %s...\n", filename);
+	if (stat(filename, &statdata) < 0)
+	{
+		perror("stat");
+		return 1;
+	}
+	if (statdata.st_mode & S_IFDIR)
+	{
+		fprintf(stderr, "error: Is a directory\n", filename);
+		return 1;
+	}
+	filesize = statdata.st_size;
+
+	/* FIXME: prone to race conditions */
+
+	fd = open(filename, O_RDONLY);
+	if (fd < 0)
+	{
+		perror("open");
+		return 1;
+	}
+
+	filedata = mmap(0, filesize, PROT_READ, MAP_PRIVATE, fd, 0);
+
+	outfilename = malloc(strlen(filename) + 16);
+
+	while (1)
+	{
+		pos = findpattern(filedata, filesize, pos);
+		if (pos < 0)
+			break;
+
+		oggdata = filedata + pos;
+		if (ogg_ispage(oggdata))
+		{
+			pagelen = ogg_getlength(oggdata);
+
+			if (outfd < 0 && ogg_isinitial(oggdata))
+			{
+				sprintf(outfilename, "%s_%08x.ogg", filename, pos);
+				outfd = creat(outfilename, -1);
+				numfiles++;
+			}
+			if (outfd >= 0)
+			{
+				write(outfd, oggdata, pagelen);
+				if (ogg_isfinal(oggdata))
+				{
+					close(outfd);
+					outfd = -1;
+				}
+			}
+		}
+
+		pos += pagelen;
+	}
+
+	if (outfd != -1 && ogg_isfinal(oggdata))
+		close(outfd);
+	free(outfilename);
+	munmap(filedata, filesize);
+	close(fd);
+
+	printf("%d file(s) written.\n", numfiles);
+
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+	int i;
+	int failures;
+
+	if (argc < 2)
+		return usage();
+
+	failures = 0;
+	for (i = 1; i < argc; i++)
+		failures += extract(argv[i]);
+	if (failures > 0)
+		fprintf(stderr, "Errors processing %d file(s).\n", failures);
+}