/*
# hexnow

intially used to monitor nc output, converting it into hex to be readable

## future

maybe i should make it similar to xargs, so it will call xxd with the data read each time
that way, the utility can be extended to do anything else

something like this:
```console
$ nc -l 80 | piperead -w 16 xxd -g1 -o'{}'
```

on each call to xxd, the offset number is incremented by the number of bytes actually read. this value replaces `{}` in the command, similar to `-exec` semantics in `find`.

we can also discard the bytes and only output the accumulated number of bytes read, like this:
```console
$ nc -l 80 | piperead -w 16 echo '{}'
```

while this will output the number of bytes read each time (up to a maximum of 32):
```console
$ nc -l 80 | piperead -w 32 wc -c
```
*/

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/types.h>
#include <errno.h>

#define MAX_BYTES 16

int main() {
  unsigned char buf[MAX_BYTES];
  unsigned char asciibuf[MAX_BYTES+1];

  int flags = fcntl(STDIN_FILENO, F_GETFL);
  if (flags < 0) perror("fcntl F_GETFL");
  if (fcntl(STDIN_FILENO, F_SETFL, flags | O_NONBLOCK) < 0) perror("fcntl F_SETFL");

  unsigned bytes_printed = 0;
  fd_set fd_read, fd_save;
  FD_ZERO(&fd_save);
  FD_SET(STDIN_FILENO, &fd_save);
  fd_read = fd_save;
  while (select(STDIN_FILENO+1, &fd_read, NULL, NULL, NULL) > 0) {
    if (FD_ISSET(STDIN_FILENO, &fd_read)) {
      int len = read(STDIN_FILENO, buf, sizeof(buf));
      if (len < 0) perror("read");
      if (len == 0) break;
      printf("%08x:", bytes_printed);
      for (int i = 0; i < len; ++i) printf(" %02X", buf[i]);
      for (int i = 0; i < MAX_BYTES-len; ++i) printf("   ");
      for (int i = 0; i < len; ++i) asciibuf[i] = isprint(buf[i]) ? buf[i] : '.';
      asciibuf[len] = '\0';
      printf("  %s\n", asciibuf);
      bytes_printed += len;
      fd_read = fd_save;
    }
  }
}