A method for communication includes coupling a client device to communicate with a host computer over a serial link. Responsively to a call from a client application running on the client device, the client device submits a request over the serial link to the host computer to open a proxy connection for communication between the client application and a server application. Responsively to the request, the host computer creates a socket for communication with the server application, so as to establish the proxy connection via the socket. The host computer and client device convey data between the server application and the client application over the serial link using the proxy connection.