#! /usr/bin/tcc -run
/* -*-c-*- */

/* Some of the scripts in the `flaccrip' suite want to chop streams of PCM
 * data about.  Once upon a time, they used dd(1) for this, but dd does
 * entirely the wrong thing on short reads, and short reads happen quite
 * regularly on pipes.
 *
 * The requirements on this program are that it copy exactly the first N
 * bytes from stdin to stdout, without reading anything else from stdin or
 * writing anything else to stdout.  (That's why it doesn't use stdio to do
 * the copying: stdio buffering will read too much from stdin, which will
 * cause stream corruption later.)
 *
 * As a special bonus, it's quite paranoid about error checking, and does way
 * more work on dealing with short reads and writes than is necessary for
 * working on pipes.  It will fail miserably if either stdin or stdout is
 * non-blocking.
 */

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

#include <sys/types.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
  unsigned long n;
  size_t nn, nleft;
  ssize_t sz;
  char buf[40960], *p;

  if (argc != 2) {
    fprintf(stderr, "Usage: %s LENGTH\n", argv[0]);
    exit(1);
  }
  n = strtoul(argv[1], 0, 0);

  while (n) {
    nn = nleft = n > sizeof(buf) ? sizeof(buf) : n;
    p = buf;
    while (nleft) {
      sz = read(STDIN_FILENO, p, nleft);
      if (sz < 0) {
	if (errno == EINTR)
	  continue;
	fprintf(stderr, "%s: read error: %s", argv[0], strerror(errno));
	exit(1);
      } else if (!sz) {
	fprintf(stderr, "%s: unexpected eof", argv[0]);
	exit(1);
      }
      nleft -= sz; p += sz;
    }

    nleft = nn;
    p = buf;
    while (nleft) {
      sz = write(STDOUT_FILENO, p, nleft);
      if (sz < 0) {
	if (errno == EINTR)
	  continue;
	fprintf(stderr, "%s: write error: %s", argv[0], strerror(errno));
	exit(1);
      } else if (!sz) {
	fprintf(stderr, "%s: empty write", argv[0]);
	exit(1);
      }
      nleft -= sz; p += sz;
    }

    n -= nn;
  }
  return (0);
}