hash_update
(PHP 5 >= 5.1.2, PECL hash >= 1.1)
hash_update — Pump data into an active hashing context
Description
bool hash_update
( resource
$context
, string $data
)Parameters
-
context -
Hashing context returned by hash_init().
-
data -
Message to be included in the hash digest.
Return Values
Returns TRUE.
See Also
- hash_init() - Initialize an incremental hashing context
- hash_update_file() - Pump data into an active hashing context from a file
- hash_update_stream() - Pump data into an active hashing context from an open stream
- hash_final() - Finalize an incremental hash and return resulting digest
Коментарии
A simple example on incremental file hashing:
$fp = fopen($file, "r");
$ctx = hash_init('sha256');
while (!feof($fp)) {
$buffer = fgets($fp, 65536);
hash_update($ctx, $buffer);
}
$hash = hash_final($ctx, true);
fclose($fp);
While incremental hashing is quite slow, it's the easiest way to hash
- parts of large files: I.e., a 700MB avi video uses first x bytes to store metadata, so in order to hash the avi's data only, you have to fseek to data start and use incremental hashing
- streaming data if php just proxies the data
- whenever it's inadequate or impossible to store the data being hashed into memory (i.e. because of their size) or on disc.