Network Connections

The data sent over TCP and similar streaming connections are handled via Connection and ConnectionObserver objects. A Connection object represents the network towards which data is sent or received, a ConnectionObserver represents the application side handling sent or received data. For example, the C++ wrapper for Lightweight IP provides a class ConnectionLwIP which derives from Connection; the HttpClientImpl class derives from ConnectionObserver, since HttpClientImpl interprets received data, parses HTTP headers, and forwards body data.

The lifetime of a Connection/ConnectionObserver pair is under control of the network stack, since the network stacks knows when a connection is alive and when it is terminated. The Connection object therefore derives from SharedOwnedObserver, which holds a SharedPtr to its SharedOwningSubject, which is the ConnectionObserver. When a connection is closed, the Connection object is destructed, and thereby releases its control over its ConnectionObserver, which typically results in the ConnectionObserver being destructed.

The methods on Connection and ConnectionObserver for sending and receiving data are geared towards asynchronous behaviour and as little copying as possible. By having fully asynchronous behaviour, the need for threads and/or blocking waits is completely avoided, and one application can easily handle multiple connections, in parallel with SPI transfers, UART communication, etc. without the need for locks or wasting MCU time on busy waits. When DataReceived() is called on the ConnectionObserver by the Connection, data to be received is of non-zero length.