Gzcompat
From Computer History Wiki
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.
source code
#ifndef lint
static char sccsid[] = "@(#)gzcompat.c 5.1 (Berkeley) 1/21/99";
#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()
{
char buf[4096];
int len;
int mkgzip;
/* First read the input magic number. */
len = fread(buf, 1, 2, stdin);
if (len < 0) {
perror("stdin");
return 1;
}
if (len != 2) {
fprintf(stderr, "stdin: not in compress -s or gzip format\n");
return 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, "stdin: not in compress -s or gzip format\n");
return 1;
}
/* Now read and check the gzip header if necessary. */
if (!mkgzip) {
len = fread(&gzheader, sizeof(struct gzheader), 1, stdin);
if (len < 0) {
perror("stdin");
return 1;
}
if (len != 1) {
fprintf(stderr, "stdin: invalid gzip header\n");
return 1;
}
if (gzheader.cm != CM_DEFLATE || gzheader.flg & FRSVD) {
fprintf(stderr, "stdin: invalid gzip header\n");
return 1;
}
if (gzheader.flg & FEXTRA) {
int count;
count = getchar();
if (ferror(stdin)) {
perror("stdin");
return 1;
}
if (feof(stdin)) {
fprintf(stderr, "stdin: invalid gzip header\n");
return 1;
}
while (count) {
getchar();
if (ferror(stdin)) {
perror("stdin");
return 1;
}
if (feof(stdin)) {
fprintf(stderr, "stdin: invalid gzip header\n");
return 1;
}
count--;
}
}
if (gzheader.flg & FNAME) {
int ch;
do {
ch = getchar();
if (ferror(stdin)) {
perror("stdin");
return 1;
}
if (feof(stdin)) {
fprintf(stderr, "stdin: invalid gzip header\n");
return 1;
}
}
while (ch);
}
if (gzheader.flg & FCOMMENT) {
int ch;
do {
ch = getchar();
if (ferror(stdin)) {
perror("stdin");
return 1;
}
if (feof(stdin)) {
fprintf(stderr, "stdin: invalid gzip header\n");
return 1;
}
}
while (ch);
}
if (gzheader.flg & FHCRC) {
len = fread(buf, 1, 2, stdin);
if (len < 0) {
perror("stdin");
return 1;
}
if (len != 2) {
fprintf(stderr, "stdin: invalid gzip header\n");
return 1;
}
}
}
/* Now write the output magic number. */
if (mkgzip) {
if (fwrite(magic_gzip, 1, 2, stdout) != 2) {
perror("stdout");
return 1;
}
}
else {
if (fwrite(magic_strong, 1, 2, stdout) != 2) {
perror("stdout");
return 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");
return 1;
}
}
/* Now actually copy the data! */
for (;;) {
len = fread(buf, 1, sizeof(buf), stdin);
if (len < 0) {
perror("stdin");
return 1;
}
if (len == 0)
break;
if (fwrite(buf, 1, len, stdout) != len) {
perror("stdout");
return 1;
}
}
/* I can't believe we're done! */
return 0;
}
