/* Find how deeply inside an .RPM the real data is */
/* kept, and report the offset in bytes */

/* Wouldn't it be a lot more sane if we could just untar these things? */

#ifndef _GNU_SOURCE
# define _GNU_SOURCE
#endif

#include <stdint.h>
#include <stdio.h>
#include <string.h>

#ifndef ARRAY_SIZE
# define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))
#endif
#ifndef BUFSIZ
# define BUFSIZ 8192
#endif

#define MAGIC_SIZE 3

int main(int argc, char *argv[])
{
	size_t i, read_cnt, offset, left;
	FILE *fp = stdin;
	char p[BUFSIZ];

	const char magics[][MAGIC_SIZE] = {
		{ '\037', '\213', '\010' },   /* gzip */
		{ 'B', 'Z', 'h' },            /* bzip */
	};

	if (argc != 1) {
		puts("Usage: rpmoffset < rpmfile");
		return 1;
	}
	/* fp = fopen(argv[1], "r"); */

	offset = left = 0;
	while (1) {
		read_cnt = fread(p + left, 1, sizeof(p) - left, fp);
		if (read_cnt + left < MAGIC_SIZE)
			break;

		for (i = 0; i < ARRAY_SIZE(magics); ++i) {
			char *needle = memmem(p, sizeof(p), magics[i], MAGIC_SIZE);
			if (needle) {
				printf("%zu\n", offset + (needle - p));
				return 0;
			}
		}

		offset += read_cnt;
		if (left == 0) {
			offset -= MAGIC_SIZE - 1;
			left = MAGIC_SIZE - 1;
		}
		memmove(p, p + read_cnt - MAGIC_SIZE - 1, MAGIC_SIZE - 1);
	}

	if (ferror(stdin))
		perror(argv[0]);

	return 1;
}