PHP Extension

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.

PHP Extension

<?php

include("chilkat.php");

$success = false;

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

$crypt = new CkCrypt2();

// 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->put_HashAlgorithm('sha256');
$crypt->put_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 CkFileAccess();
$bd = new CkBinData();
$bdHashes = new CkBinData();

$success = $fac->OpenForRead('qa_data/jpg/milky-way-nasa.jpg');
if ($success == false) {
    print $fac->lastErrorText() . "\n";
    exit;
}

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

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

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

    $i = $i + 1;
}

$fac->FileClose();

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

?>