Appending content in block blob

Topics: Semantic Logging Application Block, Windows Azure Integration Pack
Nov 21, 2014 at 12:13 PM
I have created these two method in azure custom sink for semantic logging.

used azure sdk 2.0

Code for Adding content to azure block blob

private void Post(EventEntry entry, string content)
        List<string> blockIds = new List<string>();
        // Retrieve storage account from connection string.
        CloudStorageAccount storageAccount = CloudStorageAccount.Parse(ConnectionString);

        // Create the blob client.
        CloudBlobClient blobClient = storageAccount.CreateCloudBlobClient();

        // Retrieve reference to a previously created container.
        CloudBlobContainer container = blobClient.GetContainerReference(ContainerName);

        // Create the container if it doesn't already exist.

        string fileName = DateTime.Now.ToShortDateString();

        CloudBlockBlob blockBlob = container.GetBlockBlobReference(string.Format("{0}_{1}", ContainerName, fileName));

        if (!blockBlob.Exists())
            var bytesToUpload = Encoding.UTF8.GetBytes(content);

            using (var ms = new MemoryStream(bytesToUpload))

Code for appending content to azure blob

public static void AppendText(this CloudBlockBlob blob, string text)

        var bytesToUpload = Encoding.UTF8.GetBytes(text);

        List<string> blockIds = new List<string>();

        if (blob.Exists())
            blockIds.AddRange(blob.DownloadBlockList(BlockListingFilter.Committed).Select(b => b.Name));

            var newId = Convert.ToBase64String(Encoding.Default.GetBytes(blockIds.Count.ToString()));

            blob.PutBlock(newId, new MemoryStream(bytesToUpload), null);



I have created two method for writing content to azure blob and append content to same blob.

This was working fine for some time. It is some time keep giving
  • web proxy authentication issue
  • StorageClientException - The specified block list is invalid.
What is the best solution to fix this azure source code issue. kindly help.
Nov 21, 2014 at 6:20 PM
Seems like you are hitting some environmental and Azure issues. For the latter, it sounds like an issue related to the size of the blockId. See:

Randy Levy
Enterprise Library support engineer
Support How-to