PHP

Dropbox Content Hash

See more Dropbox Examples

Demonstrates how to compute the Dropbox content_hash of a file. (This is the "content_hash" found in the Dropbox FileMetadata object.

Note: This example requires Chilkat v9.5.0.79 or greater because it uses the fac.ReadBlockBd method.

Chilkat2 PHP

<?php

use Chilkat2\BinData;
use Chilkat2\Crypt2;
use Chilkat2\FileAccess;

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

$crypt = new Crypt2();

// To calculate the content_hash of a file:
// Split the file into blocks of 4 MB (4,194,304 or 4 * 1024 * 1024 bytes). The last block (if any) may be smaller than 4 MB.
// Compute the hash of each block using SHA-256.
// Concatenate the hash of all blocks in the binary format to form a single binary string.
// Compute the hash of the concatenated string using SHA-256. Output the resulting hash in hexadecimal format.

$crypt->HashAlgorithm = 'sha256';
$crypt->EncodingMode = 'hex_lower';

// We're going to calculate the content_hash for the Milky Way JPG image linked here:  https://www.dropbox.com/developers/reference/content-hash

$fac = new FileAccess();
$bd = new BinData();
$bdHashes = new BinData();

try {
    $fac->OpenForRead('qa_data/jpg/milky-way-nasa.jpg');
} catch (\Chilkat2\Exception $e) {
    echo $e->getMessage(), "\n";
    exit;
}

$blockSize = 4194304;
$numBlocks = $fac->GetNumBlocks($blockSize);

$i = 0;
while ($i < $numBlocks) {
    // Read the next 4MB block into bd.
    $bd->Clear();
    $fac->ReadBlockBd($i, $blockSize, $bd);

    $hashHex = $crypt->HashBdENC($bd);
    echo $i, ': ', $hashHex, "\n";
    $bdHashes->AppendEncoded($hashHex, 'hex_lower');

    $i = $i + 1;
}

$fac->FileClose();

// Hash the concatenated SHA-256 hashes.
$content_hash = $crypt->HashBdENC($bdHashes);
echo 'content_hash = ', $content_hash, "\n";