(Android™) Dropbox Content Hash

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.

For more information, see https://www.dropbox.com/developers/reference/content-hash

Chilkat Android™ Downloads Android™ Java Libraries Android C/C++ Libraries

// Important: Don't forget to include the call to System.loadLibrary
// as shown at the bottom of this code sample.
package com.test;

import android.app.Activity;
import com.chilkatsoft.*;

import android.widget.TextView;
import android.os.Bundle;

public class SimpleActivity extends Activity {

  private static final String TAG = "Chilkat";

  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

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

    CkCrypt2 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

    CkFileAccess fac = new CkFileAccess();
    CkBinData bd = new CkBinData();
    CkBinData bdHashes = new CkBinData();

    boolean success = fac.OpenForRead("qa_data/jpg/milky-way-nasa.jpg");
    if (success == false) {
        Log.i(TAG, fac.lastErrorText());
        return;
        }

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

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

        String hashHex = crypt.hashBdENC(bd);
        Log.i(TAG, String.valueOf(i) + ": " + hashHex);
        bdHashes.AppendEncoded(hashHex,"hex_lower");

        i = i + 1;
        }

    fac.FileClose();

    // Hash the concatenated SHA-256 hashes.
    String content_hash = crypt.hashBdENC(bdHashes);
    Log.i(TAG, "content_hash = " + content_hash);

  }

  static {
      System.loadLibrary("chilkat");

      // Note: If the incorrect library name is passed to System.loadLibrary,
      // then you will see the following error message at application startup:
      //"The application <your-application-name> has stopped unexpectedly. Please try again."
  }
}