Node.js

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.

Node.js

NODEJS_PRELUDE

function chilkatExample() {

    var success = false;

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

    var crypt = new chilkat.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

    var fac = new chilkat.FileAccess();
    var bd = new chilkat.BinData();
    var bdHashes = new chilkat.BinData();

    success = fac.OpenForRead("qa_data/jpg/milky-way-nasa.jpg");
    if (success == false) {
        console.log(fac.LastErrorText);
        return;
    }

    var blockSize = 4194304;
    var numBlocks = fac.GetNumBlocks(blockSize);

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

        var hashHex = crypt.HashBdENC(bd);
        console.log(i + ": " + hashHex);
        bdHashes.AppendEncoded(hashHex,"hex_lower");

        i = i+1;
    }

    fac.FileClose();

    //  Hash the concatenated SHA-256 hashes.
    var content_hash = crypt.HashBdENC(bdHashes);
    console.log("content_hash = " + content_hash);

}

chilkatExample();