/* Extracts a tar archive from a tape in SIMH format */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>

int main(int argc, char **argv)
{
	int f1, f2, n, recbytes, rootlen;
	int err = 0;
	char tapefile[512], tarfile[512];
	char buf[512], *p;

	if (argc < 2) {
		fprintf(stderr, "usage: extar <tapefile> [<tarfile>]\n");
		exit(0);
	}

	strcpy(tapefile, argv[1]);
	if (argc > 2)
		strcpy(tarfile, argv[2]);
	else {
		p = strchr(tapefile, '.');
		if (! p)
			rootlen = strlen(tapefile);
		else
			rootlen = p - tapefile;
		memset(tarfile, 0, 512);
		strncpy(tarfile, tapefile, rootlen);
		strcat(tarfile, ".tar");
	}

	if ((f1 = open(tapefile, O_RDONLY)) == -1) {
		perror("open");
		exit(1);
	}
	if ((f2 = open(tarfile, O_CREAT | O_WRONLY)) == -1) {
		perror("open");
		exit(1);
	}
	fchmod(f2, 0666);

	while (1) {
		if ((n = read(f1, &recbytes, 4)) == 0)
			break;
		if (n == -1) {
			perror("read");
			err++;
			break;
		}
		if (n != sizeof(recbytes)) {
			fprintf(stderr, "Error: read too few bytes\n");
			err++;
			break;
		}
		if ((n = read(f1, buf, recbytes)) == -1) {
			perror("read");
			err++;
			break;
		}
		if ((n != 0) && (n != sizeof(buf))) {
			fprintf(stderr, "Error: read too few bytes\n");
			err++;
			break;
		}
		if ((n = read(f1, &recbytes, 4)) == -1) {
			perror("read");
			err++;
			break;
		}
		if (n != sizeof(recbytes)) {
			fprintf(stderr, "Error: read too few bytes\n");
			err++;
			break;
		}
		if ((write(f2, buf, recbytes)) == -1) {
			perror("write");
			err++;
			break;
		}
	}

	close(f1);
	close(f2);
	if (err) {
		unlink(tarfile);
		exit(1);
	}
	exit(0);
}
.