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.
hash_update
(PHP 5 >= 5.1.2, PHP 7, PHP 8, PECL hash >= 1.1)
hash_update — 向活跃的哈希运算上下文中填充数据
说明
返回值
返回 true。
参见
- hash_init() - 初始化增量散列运算上下文
- hash_update_file() - 从文件向活跃的散列运算上下文中填充数据
- hash_update_stream() - 从打开的流向活跃的散列运算上下文中填充数据
- hash_final() - 结束增量散列且返回摘要结果
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User Contributed Notes 1 note
Dainichi ¶
18 years ago
