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In PHP, hash_update_stream and hash_file() are both functions used to generate hash values, but they differ in their usage, which may lead to inconsistencies in the hash values they generate under certain circumstances. This article will analyze these two functions and discuss their consistency in generating hash values.
hash_update_stream is used to incrementally update a hash value through a stream. When using this function, a resource stream (such as a file stream) must be provided, and multiple calls to hash_update_stream are made to update the hash calculation. This method is generally suitable for scenarios where data is read in chunks.
<?php
$hash = hash_init('sha256'); // Initialize the hash algorithm to sha256
$fp = fopen('sample.txt', 'rb'); // Open the file stream
<p>// Update the hash value via the stream<br>
while (!feof($fp)) {<br>
$data = fread($fp, 4096); // Read file content in chunks<br>
hash_update_stream($hash, $data); // Update the hash value<br data-is-only-node="">
}</p>
<p>fclose($fp);</p>
<p>// Get the final hash value<br>
echo hash_final($hash);<br>
?><br>
In contrast to hash_update_stream, hash_file() is a simpler function that directly computes the hash value of a file without needing to read the data in chunks. It automatically handles the file reading and generates the hash value internally.
<?php
// Calculate the hash value of the file directly using hash_file
$hash_value = hash_file('sha256', 'sample.txt');
echo $hash_value;
?>
hash_update_stream and hash_file() can both be used to generate hash values of files, but their calculation methods differ slightly, which may lead to differences in the resulting hash values. Although, theoretically, both functions should yield the same result, the hash_update_stream function updates the hash value incrementally and relies on the way the file stream is read, whereas hash_file() directly computes the hash value of the entire file. In some cases, factors such as the size of the buffer used for stream reading and the order in which the file is read may affect the generated hash value.
However, in standard usage scenarios, where the file has not changed and there are no other interfering factors, the hash values generated by hash_update_stream and hash_file() should be the same. This is because both functions use the same hash algorithm, and the data used in the hash computation is exactly the same.
hash_update_stream is a method for incrementally updating hash values, suitable for large files or streaming data scenarios.
hash_file() is a convenient method for calculating the hash value of a file, ideal for directly computing the hash of a file.
Theoretically, under standard conditions, the hash values generated by hash_update_stream and hash_file() should be consistent, but different reading methods may affect the results.
In practical development, if the goal is simply to compute a file’s hash value, using hash_file() is the simplest and most efficient option. If you need to read data incrementally and update the hash value, then hash_update_stream would be the better choice.
