/***
 * Excerpted from "Programming Erlang, Second Edition",
 * published by The Pragmatic Bookshelf.
 * Copyrights apply to this code. It may not be used to create training material,
 * courses, books, articles, and the like. Contact us if you are in doubt.
 * We make no guarantees that this code is fit for any purpose.
 * Visit http://www.pragmaticprogrammer.com/titles/jaerlang2 for more book information.
***/
/* erl_comm.c */
#include <unistd.h>
typedef unsigned char byte;

int read_cmd(byte *buf);
int write_cmd(byte *buf, int len);
int read_exact(byte *buf, int len);
int write_exact(byte *buf, int len);

int read_cmd(byte *buf)
{
  int len;
  if (read_exact(buf, 2) != 2)
    return(-1);
  len = (buf[0] << 8) | buf[1];
  return read_exact(buf, len);
}

int write_cmd(byte *buf, int len)
{
  byte li;
  li = (len >> 8) & 0xff;
  write_exact(&li, 1);
  li = len & 0xff;
  write_exact(&li, 1);
  return write_exact(buf, len);
}

int read_exact(byte *buf, int len)
{
  int i, got=0;
  do {
    if ((i = read(0, buf+got, len-got)) <= 0)
      return(i);
    got += i;
  } while (got<len);
  return(len);
}
int write_exact(byte *buf, int len)
{
  int i, wrote = 0;
  do {
    if ((i = write(1, buf+wrote, len-wrote)) <= 0)
      return (i);
    wrote += i;
  } while (wrote<len);
  return (len);
}