Windows Azure Storage : Message Operations (part 1) - Put Message

Table 2 lists some of the important characteristics of the message operations.

The <account name> is the storage account name in the cloud, and the <devstorageaccount> is the development storage account. The <queue name> is the name of the queue in which messages are stored. The following sections discuss some of the operations from Table 5-9 in detail. Even though the operations are different, the programming concepts behind them are similar. To keep the book at a conceptual level, I discuss just the Put Message and Get Messages operations. By studying these two operations in detail, you can understand the programming concepts behind all the message operations. The Windows Azure Storage Operations application included with this chapter's source code contains implementations of most of the message operations.

1. Put Message

The Put Message operation en-queues (puts) a message at the end of the queue. The URI of a Put Message operation is of the format account name>.queue.core.windows.net/<queue name>/messages. You can send a message with size up to 8KB. To send larger files, you can save the message as a blob and send the URI of the blob to the queue. The body of the message while sending can be text or binary, but it should support inclusion in an XML body with UTF-8 encoding. This is because a message received from the queue is always returned in Base64-encoded format within an XML response body. You see this in the Get Messages operation. The URI for the Put Message operation supports an additional optional parameter, listed in Table 3.

The Put Message REST request looks like Listing 1.

Example 1. Put Message REST Request

POST /myfirstazurequeue/messages?messagettl=120&timeout=30 HTTP/1.1
x-ms-date: Thu, 18 Jun 2009 05:52:00 GMT
Authorization: SharedKey proazurestorage:Ahv5yhR9xOrHiMTnq3fBcaBKL8KeUFQ3r
Host: proazurestorage.queue.core.windows.net
Content-Length: 84
Expect: 100-continue

<QueueMessage>
<MessageText>bXlmaXJzdGF6dXJlbWVzc2FnZQ==</MessageText>
</QueueMessage>

In Listing 1, a string message "myfirstazuremessage" is sent to the queue named myfirstazurequeue. The time-to-live seconds for the message is 120, which means if the message isn't received or deleted by an application within 120 seconds in the queue, the message will be marked for deletion and won't be visible to any applications. The request body consists of the message content wrapped in the <QueueMessage> element. Note that the content of the message within the <MessageText /> element is in Base64-encoded format. Listing 2 shows the response from the Queue service.

Example 2. Put Message REST Response

HTTP/1.1 201 Created
Server: Queue Service Version 1.0 Microsoft-HTTPAPI/2.0
x-ms-request-id: e724cc82-3d21-4253-9317-3b3964374be7
Date: Thu, 18 Jun 2009 05:53:32 GMT
Content-Length: 0

As shown in Listing 2, the Queue service responds with an HTTP/1.1 201 Created status code for a successful Put Message operation. Figure 1 shows the working of the Put Message operation in the Windows Azure Storage Operations application.

Figure 1. Put Message in Windows Azure Storage Operations.exe

As illustrated in Figure 1, you can send a text message using the Windows Azure Storage Operations application. The steps for sending a message to a queue are as follows:

The WindowsAzureStorage.cs file in the Windows Azure Storage Operations project consists of a PutMessage() method, as shown in Listing 3.

Example 3. PutMessage() Method in WindowsAzureStorage.cs

private void PutMessage()
        {
            string messageBody = string.Empty;
            if (txtMessageBody.Text.Length > 0)
            {
                messageBody = txtMessageBody.Text;

            }
            else
            {
                messageBody = String.Format
("Message from Windows Azure Storage Operations",
System.Guid.NewGuid().ToString("N"));
            }
            int ttlsecs = 300;
            if(txtTimeTolive.Text.Length > 0)
            {
                ttlsecs = int.Parse(txtTimeTolive.Text);
            }
            if (StorageHelper.PutMessage(txtQueueName.Text, new
 Microsoft.Samples.ServiceHosting.StorageClient.Message(messageBody), ttlsecs))
            {
                statusLabel.Text = String.Format
("Message {0} sent successfully to queue {1}", messageBody, txtQueueName.Text);

            }
        }

					  

As shown in Listing 3, the PutMessage() method calls the PutMessage() operation on the WindowsAzureStorageHelper (StorageHelper object). The message body and the time-to-live values are parsed appropriately from the server controls and passed as parameters to the method. If you don't enter a message in the Message Body text box, the application automatically creates a default message for you. Figure 2 shows the sequence of Put Message operation from the application to the Queue service as it passes through various assemblies and objects.

Figure 2. Put Message sequence diagram

As shown in Figure 2, the Windows Azure Storage Operations application calls the PutMessage() method on the WindowsStorageHelper object in the ProAzureCommonLib.dll. The WindowsStorageHelper object calls the GetQueue() method on the QueueStorage object to get an instance of the MessageQueue object. The WindowsStorageHelper object then calls the PutMessage() method on the MessageQueue object. The PutMessage() method of the MessageQueue object creates the REST message request and sends it synchronously to the Queue service. It uses the System.Net.HttpWebRequest to send the REST message over HTTP. Upon the success of the operation, the Queue service returns an HTTP status code: HTTP/1.1 201 Created. The PutMessage() method translates the HTTP code into true for success and false for failure. The Boolean value is passed all the way to the Windows Azure Storage Operations application as a return parameter of the PutMessage() method.