(Lianja) Azure Service Bus - Peek-Lock Message (Non-Destructive Read)

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Shows how to atomically retrieve and lock a message from a queue or subscription for processing. The message is guaranteed not to be delivered to other receivers (on the same queue or subscription only) during the lock duration specified in the queue/subscription description.

For more information, see https://docs.microsoft.com/en-us/rest/api/servicebus/peek-lock-message-non-destructive-read

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// Note: Requires Chilkat v9.5.0.65 or greater.

// This requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// Make the initial connection.
// A single REST object, once connected, can be used for many Azure Service Bus REST API calls.
// The auto-reconnect indicates that if the already-established HTTPS connection is closed,
// then it will be automatically re-established as needed.
loRest = createobject("CkRest")
llBAutoReconnect = .T.
llSuccess = loRest.Connect("<yournamespace>.servicebus.windows.net",443,.T.,llBAutoReconnect)
if (llSuccess <> .T.) then
    ? loRest.LastErrorText
    release loRest
    return
endif

// ----------------------------------------------------------------------------------------------
// The code above this comment could be placed inside a function/subroutine within the application
// because the connection does not need to be made for every request.  Once the connection is made
// the app may send many requests..
// ----------------------------------------------------------------------------------------------

// Let's load a previously computed SAS token and use it.
// See Azure Shared Access Signature for an example to genenerate an Azure SAS token.
loSbToken = createobject("CkStringBuilder")
loSbToken.LoadFile("qa_data/tokens/serviceBusSas.txt","utf-8")

// Tell the REST object to use the Azure Shared Access Signature for authorization.
loSbToken.Prepend("SharedAccessSignature ")
loRest.AddHeader("Authorization",loSbToken.GetAsString())

// ----------------------------------------------------------------------------------------------

// Peek-lock a message from the subscription "feedings" in the topic "gilaMonster"
lcTopicName = "gilaMonster"
lcSubscriptionName = "feedings"

// Build the path..
loSbPath = createobject("CkStringBuilder")
loSbPath.Append("/")
loSbPath.Append(lcTopicName)
loSbPath.Append("/subscriptions/")
loSbPath.Append(lcSubscriptionName)
loSbPath.Append("/messages/head")

// If peek-locking from a queue, the path would be built like this:
loSbQueuePath = createobject("CkStringBuilder")
loSbQueuePath.Append("/")
loSbQueuePath.Append("queueName")
loSbQueuePath.Append("/messages/head")
// This example will use the sbPath..

// Add a timeout parameter.
loRest.AddQueryParam("timeout","20")

// Use the POST HTTP verb to peek-lock the message.
// Note that the only difference between the destructive Read-and-Delete and the non-destructive Peek-Lock
// is that the HTTP verb.  (POST is for peek-lock, DELETE is fore read-and-delete.)
loSbResponseBody = createobject("CkStringBuilder")
llSuccess = loRest.FullRequestNoBodySb("POST",loSbPath.GetAsString(),loSbResponseBody)
if (llSuccess <> .T.) then
    ? loRest.LastErrorText
    release loRest
    release loSbToken
    release loSbPath
    release loSbQueuePath
    release loSbResponseBody
    return
endif

? "Response Status Code = " + str(loRest.ResponseStatusCode)

// Check for a success response.
// CAREFUL: This returns a 201 response instead of a 200 response.  In general, either 200 or 201 should always indicate success.
if (loRest.ResponseStatusCode <> 201) then
    ? loRest.LastRequestStartLine
    ? loRest.LastRequestHeader
    ? loSbResponseBody.GetAsString()
    ? "Failed."
    release loRest
    release loSbToken
    release loSbPath
    release loSbQueuePath
    release loSbResponseBody
    return
endif

// The content of the message is returned in the HTTP response body.
// The HTTP response headers contains extra information.  For example:
loJsonBrokerProps = createobject("CkJsonObject")
loJsonBrokerProps.Load(loRest.ResponseHdrByName("BrokerProperties"))
loJsonBrokerProps.EmitCompact = .F.
? loJsonBrokerProps.Emit()

// An example of the BrokerProperties JSON that is returned:

// 	{
// 	  "DeliveryCount": 2,
// 	  "EnqueuedSequenceNumber": 3000003,
// 	  "EnqueuedTimeUtc": "Wed, 07 Dec 2016 17:42:48 GMT",
// 	  "Label": "M2",
// 	  "LockToken": "0a13ee8a-be32-4458-89e0-5e1401caa6a0",
// 	  "LockedUntilUtc": "Wed, 07 Dec 2016 18:13:12 GMT",
// 	  "MessageId": "7bea513a6ddb49089e07bfbee26d85bd",
// 	  "SequenceNumber": 3,
// 	  "State": "Active",
// 	  "TimeToLive": 922337203685.47754
// 	}

// Also the "Location" response header contains the URI of the locked message.
// This can be used to ulock or delete the message.
? "Location: " + loRest.ResponseHdrByName("Location")

// An example of the Location URI:
// https://chilkat.servicebus.windows.net/gilamonster/subscriptions/feedings/messages/3/0a13ee8a-be32-4458-89e0-5e1401caa6a0

// If successful, the message is the contents of the response body.
lcMessage = loSbResponseBody.GetAsString()
? "Received message: " + lcMessage

? "Success."


release loRest
release loSbToken
release loSbPath
release loSbQueuePath
release loSbResponseBody
release loJsonBrokerProps