initMultipartUpload method
start multipart upload
Implementation
HttpRequest initMultipartUpload(String bucketName, String fileKey) {
final url = "https://${bucketName}.${this.endpoint}/${fileKey}?uploads";
final headers = <String, String>{'content-type': "application/xml"};
HttpRequest req = HttpRequest(url, 'POST', <String, dynamic>{}, headers);
this._auth!.signRequest(req, bucketName, fileKey);
return req;
}