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hash_update

(PHP 5 >= 5.1.2, PECL hash >= 1.1)

hash_updatePump data into an active hashing context

Descrição

bool hash_update ( resource $context , string $data )

Parâmetros

context

Hashing context returned by hash_init().

data

Message to be included in the hash digest.

Valor Retornado

Returns TRUE.

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Dainichi
8 years ago
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.
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