Electric Imp example code that processes an incoming HTTP Request (through an HttpIn node hooked up to an InputPort) and sends a "response" (which is actually just an HTTP Post to a predefined location).

HttpRequestResponse.nut

// This is the function that actually handles the incoming HTTP Request
function SimpleRequestHandler(data) {
    server.log("Got a request with value='" + data + "'");
    return 200;
}

// handles incoming HttpIn requests, and sends "responses" to an HttpRequest node through
// an output port. The ResponsePort sends a url-encoded message where "value" is the response code.
class HttpInPortWithResponse extends InputPort {
    RequestHandler = null;  // function that will be called whenever a request comes into the input port. Should return a status code.
    ResponsePort = null;    // OutputPort that will have it's value set based on RequestHandlers response.
    
    constructor(requestHandler, portName, responsePort) {
        base.constructor(portName);         // Set the port name so it's easy to identify in the planner
        OutputPort = responsePort;
        RequestHandler = requestHandler;
    }
    
    function set(value) {
        local responseCode = RequestHandler(value); // Run the request handler
        OutputPort.set(responseCode);               // and return the result
        server.log("Responded with " + responseCode);
    }
}

local httpOutPort = OutputPort("HTTPResponse");
local httpInPort = HttpInPortWithResponse(SimpleRequestHandler, "HTTPRequest", httpOutPort);

imp.configure("Http Example", [httpInPort], [httpOutPort]);