PBZX handling of Yosemite-style Payload archives

pbzx.c

//
//  main.c
//  pbzx
//
//  Created by PHPdev32 on 6/20/14.
//  Licensed under GPLv3, full text at http://www.gnu.org/licenses/gpl-3.0.txt
//

#include <stdint.h>
#include <stdio.h>
#include <string.h>
#define err(m,e) { fprintf(stderr, m"\n"); return e; }
#define fswap64(f,s) fread(&s, 8, 1, f); s = __builtin_bswap64(s)
#define BSIZE 8 * 1024

int main(int argc, const char * argv[])
{

    // insert code here...
    char buffer[BSIZE];
    fread(buffer, 4, 1, stdin);
    if (strncmp(buffer, "pbzx", 4))
        err("Not a pbzx stream", 1);
    uint64_t length = 0, flags = 0, last = 0;
    fswap64(stdin, flags);
    while (flags & 1 << 24) {
        fswap64(stdin, flags);
        fswap64(stdin, length);
        fread(buffer, 1, 6, stdin);
        if (strncmp(buffer, "\xfd""7zXZ\0", 6))
            err("Header is not <FD>7zXZ<00>", 2);
        length -= fwrite(buffer, 1, 6, stdout);
        while (length)
            length -= last = fwrite(buffer, 1, fread(buffer, 1, BSIZE < length ? BSIZE : length, stdin), stdout);
        if (strncmp(buffer + last - 2, "YZ", 2))
            err("Footer is not YZ", 3);
    }
    return 0;
}