Commands | AMQP1 Receiver Links

In the AMQP 1.0.0 protocol, a Receiver Link is a communication channel established between an AMQP client and an AMQP server for the purpose of receiving messages. It operates within the context of an AMQP session, which represents a logical channel for communication between the client and server.

 

Create Receiver Link

To Create a new Receiver Link, call the method CreateReceiverLink which contains the following parameters:

 

• Session: the session name where the sender link will be attached.
• Name: (optional) the name of the sender link, if is not set, a random name will be assigned automatically.
• Source: (optional) the source can be configured to indicate the location of the node on the remote host that is supposed to act as the sender. In some situations, specifying this address may not be required. In such cases, simply providing an empty string as the value for the parameters will be enough.
• ReadMode: (amqp1srmAuto by default) Receiver links can function in one of two modes for receiving messages:

  • amqp1srmAuto: Automatic Mode, in this mode the receiver actively works to ensure that messages are received promptly as soon as they become available. It automatically listens for and receives messages without any explicit instruction each time a new message arrives.

  • amqp1srmManual: Fetch-Based Mode, in this mode, the receiver will only retrieve or fetch a new message when it is specifically told to do so. Unlike the automatic mode, the receiver will not actively listen for new messages but will instead wait for manual instructions to fetch the next message.

• RcvSettleMode: (amqp1rsmFirst by default) Receiver Links operate within one of these modes:

  • amqp1rsmFirst: When messages arrive, they will be processed and confirmed right away. If the message hasn't already been confirmed by the time it was sent, the sender will be informed that the message has been received.

  • amqp1rsmSecond: Messages that arrive will only be confirmed after the sender has confirmed them first. Additionally, the sender will receive a notification when a message has been received, provided the message wasn't already confirmed when it was sent.

 

 

When the Receiver Link has been created successfully, the event OnAMQPLinkOpen will be fired.

 

oAMQP1.CreateReceiverLink('MySession', 'MyReceiverLink');
procedure procedure TfrmClientAMQP1.AMQP1AMQPLinkOpen(Sender: TObject; const aSession: TsgcAMQP1Session; const aLink: TsgcAMQP1Link; const aAttach: TsgcAMQP1FrameAttach);
begin
  ShowMessage('#link-open: ' + aLink.Name);
end;

 

Await Create Receiver Link

 

By default, the CreateReceiverLink method is Asynchronous, so after calling the method, the code continue. If you want to wait till the CreateReceiverLink method is completed and the confirmation sent by the server is received, set the property Await to True in the Options parameter.

 

procedure CreateReceiverLink(const aSession, aReceiver: string);
var
  oOptions: TsgcAMQP1MethodOptions_CreateReceiverLink;
begin
  oOptions := TsgcAMQP1MethodOptions_CreateReceiverLink.Create;
  Try
    oOptions.Await := True;
    AMQP1.CreateReceiverLink(aSession, aReceiver, '', oOptions);
  Finally
    oOptions.Free;
  End;
end;

 

Sync Messages

When the Receiver Link works in Manual ReadMode, call the method GetMessage to get new messages. This method is synchronous, which means that waits till a timeout is exceeded (by default 10 seconds). When the method is called, the component increases the credit in one unit and waits till a new message arrives or the timeout has been exceeded. If no message arrives, the credit is set to zero again.

 

The method GetMessage has the following parameters:

 

• Session: name of the session that contains the link.
• Link: name of the receiver link.
• Timeout: (by default 1000 = 10 seconds) the max time the function will wait to get a new message.

 

Close Receiver Link

To Close an existing Receiver Link, call the method CloseLink which contains the following parameters:

 

• Session: name of the session that contains the link.
• Link: name of the receiver link.
• Error: (optional) here you can set the reason why the link is closed.

 

When the Receiver Link has been closed successfully, the event OnAMQPLinkClose will be fired.

oAMQP1.CloseLink('MySession', 'MyReceiverLink');
procedure OnAMQPLinkCloseEvent(Sender: TObject; const aSession: TsgcAMQP1Session; const aLink: TsgcAMQP1Link; const aDetach: TsgcAMQP1FrameDetach);
begin
  ShowMessage('#link-close: ' + aLink.Name);
end;

 

Await Close Receiver Link

 

By default, the CloseLink method is Asynchronous, so after calling the method, the code continue. If you want to wait till the CloseLink method is completed and the confirmation sent by the server is received, set the property Await to True in the Options parameter.

 

procedure CloseReceiverLink(const aSession, aReceiverLink: string);
var
  oOptions: TsgcAMQP1MethodOptions_CloseLink;
begin
  oOptions := TsgcAMQP1MethodOptions_CloseLink.Create;
  Try
    oOptions.Await := True;
    AMQP1.CloseLink(aSession, aReceiverLink, oOptions);
  Finally
    oOptions.Free;
  End;
end;