Perl Requires Chilkat v9.5.0.79+

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. Chilkat2 Perl

use strict;
use warnings;
use Chilkat2;

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

my $crypt = Chilkat2::Crypt2->new;

# 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

my $fac = Chilkat2::FileAccess->new;
my $bd = Chilkat2::BinData->new;
my $bdHashes = Chilkat2::BinData->new;

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

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

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

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

    $i = $i + 1;
}

$fac->FileClose();

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