Dart

AWS S3 File Streaming Upload

See more Amazon S3 (new) Examples

Demonstrates how to do a streaming upload from a file to the AWS S3 storage service. The AWS authorization presents some difficulties when the REST request body is to be streamed from a file (or from some other source). The issue is that the SHA-256 hash of the file data must be calculated. There are only two possible ways to do this: (1) stream the file into memory in its entirety and calculate the SHA-256 hash prior to uploading, or (2) pre-calculate the SHA-256 in a streaming fashion, and then provide it to the AWS authentication object.

If the application does NOT pre-compute the SHA-256, then Chilkat (internally) is forced to stream into memory, calculate the SHA-256, and then upload from the in-memory copy of the file.

Dart

import 'package:chilkat/chilkat.dart';

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

  // This first part is optional.  AWS authentication requires
  // the SHA-256 hash of the request body (i.e. the contents of the file
  // to be uploaded).  We can choose to pre-calculate the SHA-256 in a streaming fashion
  // and then provide it to the authenticator object.  This way, if the file is
  // extremely large, it never needs to completely reside in memory.
  final crypt = CkCrypt2();
  crypt.encodingMode = 'hex';
  crypt.hashAlgorithm = 'sha-256';
  final fileToUploadPath = 'qa_data/xml/hamlet.xml';
  final hashStr = crypt.hashFileENC(fileToUploadPath);

  final rest = CkRest();

  // Connect to the Amazon AWS REST server.
  final bTls = true;
  final port = 443;
  final bAutoReconnect = true;
  rest.connect('s3.amazonaws.com', port, bTls, bAutoReconnect);

  // ----------------------------------------------------------------------------
  // Important: For buckets created in regions outside us-east-1,
  // there are three important changes that need to be made.
  // See Working with S3 Buckets in Non-us-east-1 Regions for the details.
  // ----------------------------------------------------------------------------

  // Provide AWS credentials for the REST call.
  final authAws = CkAuthAws();
  authAws.accessKey = 'AWS_ACCESS_KEY';
  authAws.secretKey = 'AWS_SECRET_KEY';
  authAws.serviceName = 's3';
  // Provide the pre-computed SHA-256 here:
  authAws.precomputedSha256 = hashStr;

  rest.setAuthAws(authAws);

  // Set the bucket name via the HOST header.
  // In this case, the bucket name is "chilkat100".
  rest.host = 'chilkat100.s3.amazonaws.com';

  final fileStream = CkStream();
  fileStream.sourceFile = fileToUploadPath;

  // Upload to the S3 Storage service.
  // If the application provided the SHA-256 hash of the file contents (as shown above)
  // then file is streamed and never has to completely reside in memory.
  // If the application did NOT provide the SHA-256, then Chilkat will (internally) 
  // load the entire file into memory, calculate the SHA-256, and then upload.
  final String responseStr;
  try {
    responseStr = rest.fullRequestStream('PUT', '/hamlet.xml', fileStream);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // When successful, the S3 Storage service will respond with a 200 response code,
  // with an XML body.  
  if (rest.responseStatusCode == 200) {
    print(responseStr);
    print('File uploaded.');
  } else {
    // Examine the request/response to see what happened.
    print('response status code = ${rest.responseStatusCode}');
    print('response status text = ${rest.responseStatusText}');
    print('response header: ${rest.responseHeader}');
    print('response body: $responseStr');
    print('---');
    print('LastRequestStartLine: ${rest.lastRequestStartLine}');
    print('LastRequestHeader: ${rest.lastRequestHeader}');
  }
}