Open file handle as returned by any stream creation function.
length
Maximum number of characters to copy from handle
into the hashing context.
Return Values
Actual number of bytes added to the hashing context from handle.
Examples
Example 1. hash_update_stream() example
<?php
$fp = tmpfile();
fwrite($fp, 'The quick brown fox jumped over the lazy dog.');
rewind($fp);
$ctx = hash_init('md5');
hash_update_stream($ctx, $fp);
echo hash_final($ctx);
?>