No more socket trouble in PHP!

Having tried to reliably transfer large amounts of binary data over a latent network, I found out that fread()/fwrite() should never be trusted to read/write the whole block with the exact length specified, even in blocking mode, even for small block lengths.

I came up with these two functions, fully-replaceable and reliable alternatives of fread()/fwrite() in a socket context:

function fullread ($sd, $len) {
  $ret = '';
  $read = 0;

  while ($read < $len && ($buf = fread($sd, $len - $read))) {
    $read += strlen($buf);
    $ret .= $buf;
  }

  return $ret;
}


function fullwrite ($sd, $buf) {
  $total = 0;
  $len = strlen($buf);

  while ($total < $len && ($written = fwrite($sd, $buf))) {
    $total += $written;
    $buf = substr($buf, $written);
  }

  return $total;
}

The functions are "greedy", i.e. trying to read/write as much data as possible at once. If the inside call to fread()/fwrite() reads/writes less than expected, then the next iteration eats up the remainder. Very smart as only the largest possible chunks are read/written.

Only in case of a broken pipe (dropped connection during execution) the functions return less than the specified length. Otherwise it is guaranteed that upon termination

strlen(fullread($sd, $len)) == $len

and

fullwrite($sd, $buf) == strlen($buf)

Works perfectly with a socket descriptor returned from stream_socket_client(), and I hope it will do so with fsockopen() as well.

Yay! Caused me two weeks of fuss how unreliable are fread()/fwrite() to suddenly come up with this simple, smart and elegant solution.