In TCP communication, data can arrive in small, fragmented pieces rather than one clean, whole block. Buffering allows your code to accumulate these fragments until the full message is assembled, ensuring that you process the data only when it's complete. This is particularly useful for protocols or formats (like JSON or XML) where the whole message structure is needed to parse or understand the data correctly. In this context, buffering is the process of collecting small fragments of data as they arrive as separate TCPEvent objects until you have accumulated a complete message before you process it. Since TCP doesn't guarantee that your full payload will be delivered in a single packet, your application might receive several "data" events from the TCPEvent class, each containing only a part of the overall message.

New in version 20R8 is the TCP class featuring the TCPEvent object. This new TCPEvent class provides information about events occurring during the lifecycle of a TCP connection

When using the TCPEvent in a 4D callback method, your callback receives a TCPEvent with type equal to "data", and the .data property contains just part of your expected message. Instead of processing this fragment immediately which could result in incomplete data, you append it to a buffer. Once enough data is accumulated , perhaps identified by a pre-defined indicator like a known message length or message delimiters, you then process the complete message.

Sending the Message: The sendDeliveryMessage() function simulates sending the sample message over the TCP connection. In your production environment, this data might be generated dynamically or come from another part of your application.

Function sendDeliveryMessage()   var $blob : Blob   // Convert the text message into a blob for transmission   TEXT TO BLOB("Delivery address is 221B Baker Street"; $blob)   This.connection.send($blob) End function

Inside the onData callback, every incoming Blob (network packet) is converted to text and appended to receivedBuffer. Since TCP is stream-based, fragments of the complete message might arrive separately.

// Callback: onData // This method is invoked when data arrives over the network. Function onData($connection : 4D.TCPConnection; $event : 4D.TCPEvent)   // Convert the incoming blob to text (assume UTF8 without length)   var $dataChunk : Text   $dataChunk := BLOB to text($event.data; UTF8 text without length)   // Append this chunk to the buffer   This.receivedBuffer := This.receivedBuffer + $dataChunk End function

In our simple fixed-length protocol, we expect exactly 37 characters for a complete message. Use a loop in case multiple messages have been received or the data comes fragmented.