Question

All, I am trying to find a way to chunk read blob from windows azure .now I had some problem with it , the total size of chunk read is not equal to the total size of the blob. My test blob size is 154805720 bytes, and every chunk reading size is 10*1024*1024. I found the last buffer of chunk read is not the supposed size 8005080 bytes .It is always 4M.
BTW, I have downloaded this blob to local by cloudbrerry storage explorer. it is same size with the original file I uploaded before. so ,I am sure the blob original size is ok ,that means 154805720 bytes.
Here is my code .please help review it .

        private static CloudBlobClient CreateBlobClient(StorageAccount account)
        {
            CloudBlobClient blobClient = null;
            CloudStorageAccount oStorageAccount = CreateStorageAccount(account);
            blobClient = oStorageAccount.CreateCloudBlobClient();
            blobClient.Timeout = new TimeSpan(2, 0, 0);
            blobClient.WriteBlockSizeInBytes = 4 * 1024 * 1024;
            blobClient.RetryPolicy = RetryPolicies.Retry(20, TimeSpan.Zero);

            return blobClient;
        }



        public static byte[] DownloadChunkFromBlob(StorageAccount account, string sContainerName, String sBlobName, int blobOffset, int bufferSize)
        {
            CloudBlobClient blobClient = CreateBlobClient(account);

            CloudBlobContainer container = blobClient.GetContainerReference(sContainerName);
            bool b = container.CreateIfNotExist();
            CloudBlob blob = container.GetBlobReference(sBlobName);

            using (var blobStream = blob.OpenRead())
            {
                var buffer = new byte[bufferSize];
                blobStream.Seek(blobOffset, SeekOrigin.Begin);
                int numBytesRead = blobStream.Read(buffer, 0, bufferSize);

                if (numBytesRead != bufferSize)
                {
                    var trimmedBuffer = new byte[numBytesRead];
                    Array.Copy(buffer, trimmedBuffer, numBytesRead);
                    return trimmedBuffer;
                }
                return buffer;
            }
        }

Answer 1

The answer is OpenRead() can only read up to 4 MB in a single go. When I set the chunk read size is 4MB . Everything is Fine.