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We would like to establish one or more WebSocket connections on top of an existing WebSocket channel between a device and a bridge. For instance, this could be useful in the scenario where a remote user, who has access to the bridge, wishes to open a remote terminal exposed by the device on a specific port and make it accessible through a WebSocket connection. The implementation of this functionality is described as follows:
edgehog-device-runtime-forwarder/src/messages.rshas been extended to reflect the changes in theproto.rsfile, which contains theProtobufdefinition of the data exchanged between the device and the bridge. Since this extension introduces the WebSocket message type, nowmessages.rscontains the necessary structs andimplblocks responsible for handling such messages.edgehog-device-runtime-forwarder/src/connections_manager.rsalso handles the sending and receiving of WebSocket messages on an already established WebSocket connection between the device and the bridge (refer to thehandle_ws()method). To establish a WebSocket connection, the bridge first sends a triplet of HTTP messages, with the third being an HTTPupgraderequest to the WebSocket protocol. Once this request is received, the device creates an internal WebSocket connection usingTTYD, a tool used for sharing a remote terminal over a WebSocket interface. To simplify the connections' collection stored within theConnectionsManagerstruct, both the HTTP and WebSocket connections are stored in the same collection (avoiding the problem of managing two separate collections for each type of connection). To this extent, the WebSocket connection is given the same ID as the corresponding HTTP upgrade request.edgehog-device-runtime-forwarder/src/connection.rshas been split into submodules, containing now two builder traits:TransportBuilderandTransport. These traits (declared inmod.rs) define thebuild()andnext()methods, respectively, which are necessary to construct and handle each connection. Specifically, two builders that implement theTransportBuildertrait have been defined to create an HTTP and a WebSocket connection, respectively implemented in theconnection/http.rsandconnection/websocket.rs. These builders are used when spawning the Tokio task responsible for handling a singleConnection. TheConnectionis now a struct that is generic on a type that implements theTransporttrait. This is why theHttpandWebSocketstructs both implement this trait. TheHttpstruct sends an HTTP request and waits for a response, while theWebSocketstruct continuously sends and receives data to/from TTYD.