Gzcompat

gzcompat is a utility to convert from Sokolov compression into gzip. The primary use is to convert the Quasijarus install files into gzip, so that they can easily be decompressed. This is for the 4.3 BSD Quasijarus Operating System.

source code

#ifndef lint
static char sccsid[] = "@(#)gzcompat.c	5.2 (Berkeley) 12/21/00";
#endif

/* gzcompat converts between compress -s and gzip formats. */

#include <stdio.h>

char magic_strong[2] = {037, 0241};
char magic_gzip[2]   = {037, 0213};

struct gzheader {
	unsigned char cm;
	unsigned char flg;
	unsigned char mtime[4];
	unsigned char xfl;
	unsigned char os;
} gzheader;

#define CM_DEFLATE 0x08

#define FTEXT    0x01
#define FHCRC    0x02
#define FEXTRA   0x04
#define FNAME    0x08
#define FCOMMENT 0x10
#define FRSVD    0xE0

#define OS_UNIX 0x03

int main(argc, argv)
	char **argv;
{
	FILE *infile;
	char *inname;
	char buf[4096];
	int len;
	int mkgzip;

	if (argc == 1) {
		infile = stdin;
		inname = "stdin";
	} else if (argc == 2) {
		inname = argv[1];
		infile = fopen(inname, "r");
		if (infile == NULL) {
			perror(inname);
			exit(1);
		}
	} else {
		fprintf(stderr, "usage: %s [infile]\n", argv[0]);
		exit(1);
	}

	/* First read the input magic number. */
	len = fread(buf, 1, 2, infile);
	if (len < 0) {
		perror(inname);
		exit(1);
	}
	if (len != 2) {
		fprintf(stderr, "%s: not in compress -s or gzip format\n",
			inname);
		exit(1);
	}
	if (buf[0] == magic_strong[0] && buf[1] == magic_strong[1])
		mkgzip = 1;
	else if (buf[0] == magic_gzip[0] && buf[1] == magic_gzip[1])
		mkgzip = 0;
	else {
		fprintf(stderr, "%s: not in compress -s or gzip format\n",
			inname);
		exit(1);
	}

	/* Now read and check the gzip header if necessary. */
	if (!mkgzip) {
		len = fread(&gzheader, sizeof(struct gzheader), 1, infile);
		if (len < 0) {
			perror(inname);
			exit(1);
		}
		if (len != 1) {
			fprintf(stderr, "%s: invalid gzip header\n", inname);
			exit(1);
		}
		if (gzheader.cm != CM_DEFLATE || gzheader.flg & FRSVD) {
			fprintf(stderr, "%s: invalid gzip header\n", inname);
			exit(1);
		}
		if (gzheader.flg & FEXTRA) {
			int count;

			count = getc(infile);
			if (ferror(infile)) {
				perror(inname);
				exit(1);
			}
			if (feof(infile)) {
				fprintf(stderr, "%s: invalid gzip header\n",
					inname);
				exit(1);
			}
			while (count) {
				getc(infile);
				if (ferror(infile)) {
					perror(inname);
					exit(1);
				}
				if (feof(infile)) {
					fprintf(stderr, "%s: invalid gzip header\n", inname);
					exit(1);
				}
				count--;
			}
		}
		if (gzheader.flg & FNAME) {
			int ch;

			do {
				ch = getc(infile);
				if (ferror(infile)) {
					perror(inname);
					exit(1);
				}
				if (feof(infile)) {
					fprintf(stderr, "%s: invalid gzip header\n", inname);
					exit(1);
				}
			}
			while (ch);
		}
		if (gzheader.flg & FCOMMENT) {
			int ch;

			do {
				ch = getc(infile);
				if (ferror(infile)) {
					perror(inname);
					exit(1);
				}
				if (feof(infile)) {
					fprintf(stderr, "%s: invalid gzip header\n", inname);
					exit(1);
				}
			}
			while (ch);
		}
		if (gzheader.flg & FHCRC) {
			len = fread(buf, 1, 2, infile);
			if (len < 0) {
				perror(inname);
				exit(1);
			}
			if (len != 2) {
				fprintf(stderr, "%s: invalid gzip header\n",
					inname);
				exit(1);
			}
		}
	}

	/* Now write the output magic number. */
	if (mkgzip) {
		if (fwrite(magic_gzip, 1, 2, stdout) != 2) {
			perror("stdout");
			exit(1);
		}
	}
	else {
		if (fwrite(magic_strong, 1, 2, stdout) != 2) {
			perror("stdout");
			exit(1);
		}
	}

	/* Now write the gzip header if necessary. */
	if (mkgzip) {
		gzheader.cm = CM_DEFLATE;
		gzheader.flg = 0;
		gzheader.mtime[0] = 0;
		gzheader.mtime[1] = 0;
		gzheader.mtime[2] = 0;
		gzheader.mtime[3] = 0;
		gzheader.xfl = 0;
		gzheader.os = OS_UNIX;
		if (fwrite(&gzheader, sizeof(struct gzheader), 1, stdout) != 1) {
			perror("stdout");
			exit(1);
		}
	}

	/* Now actually copy the data! */
	for (;;) {
		len = fread(buf, 1, sizeof(buf), infile);
		if (len < 0) {
			perror(inname);
			exit(1);
		}
		if (len == 0)
			break;
		if (fwrite(buf, 1, len, stdout) != len) {
			perror("stdout");
			exit(1);
		}
	}

	/* I can't believe we're done! */
	if (argc == 2)
		fclose(infile);
	return(0);
}