Downloading an Azure blob in chunks using WCF - wcf

Question

I have been asked to provide a WCF service that allows a blob (potentially 1GB) to be downloaded in chunks as an offset byte[] for consumption by a Silverlight application. Essentially, the operation will have a parameter for number of bytes to offset and the max number of bytes to return, nothing complex I think.
The code I have so far is:
[OperationContract]
public byte[] Download(String url, int blobOffset, int bufferSize)
{
var blob = new CloudBlob(url);
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;
}
}
I have tested this (albeit with relatively small files < 2MB) and it does work, but my questions are:
Can someone suggest improvements to the code?
Is there a better approach given the requirement?

Answer 1

using (BlobStream blobStream = blob.OpenRead())
{
bool getSuccess = false;
int getTries = 0;
rawBytes = new byte[blobStream.Length];
blobStream.Seek(0, SeekOrigin.Begin);
int blockSize = 4194304; //Start at 4 mb per batch
int index = 0;
int documentSize = rawBytes.Length;
while (getTries <= 10 && !getSuccess)
{
try
{
int batchSize = blockSize;
while (index < documentSize)
{
if ((index + batchSize) > documentSize)
batchSize = documentSize - index;
blobStream.Read(rawBytes, index, batchSize);
index += batchSize;
}
getSuccess = true;
}
catch (Exception e)
{
if (getTries > 9)
throw e;
else
blockSize = blockSize / 2; // Reduce by half for each attempt
}
finally
{ getTries++; }
}
}

Answer 2

You could return the blob as a stream instead of a byte array. There is a code sample in a related question here: Returning Azure BLOB from WCF service as a Stream - Do we need to close it?
Note there are some restrictions on which bindings you can use when you return a stream.