note 77548 deleted from function.fread by cmb
| From: | cmb@php.net | Date: | Sun, 12 Jan 2020 08:20:48 +0000 |
| Subject: | note 77548 deleted from function.fread by cmb | ||
| References: | 1 | Groups: | php.notes |
| Request: | Send a blank email to php-notes+get-213850@lists.php.net to get a copy of this message | ||
Note Submitter: Blagovest Buyukliev
----
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:
<?php
function fullwrite ($sd, $buf) {
$total = 0;
$len = strlen($buf);
while ($total < $len && ($written = fwrite($sd, $buf))) {
$total += $written;
$buf = substr($buf, $written);
}
return $total;
}
function fullread ($sd, $len) {
$ret = '';
$read = 0;
while ($read < $len && ($buf = fread($sd, $len - $read))) {
$read += strlen($buf);
$ret .= $buf;
}
return $ret;
}
?>
The functions are "greedy", i.e. trying to read/write as much data as possible at once. If
the call to fread()/fwrite() reads/writes less than expected, then the next iteration eats up the
remainder. Very smart as only the largest possible chunks are read/written.
Only in case of a broken pipe fullread()/fullwrite() return less than the specified length.
Otherwise it is guaranteed that upon termination
strlen(fullread($sd, $len)) == $len
and
fullwrite($sd, $buf) == strlen($buf)
Works perfectly with a socket descriptor returned from stream_socket_client() or fsockopen().
Greetings from Rousse, Bulgaria.