http Server

To share data with the outside world, we can run an http server. It will take requests from clients (e.g. web browsers) and join them with matching handlers which we can write to construct responses. Here's a simple program to serve some text:

import("http")

route := {method:str    path:str,   relgen:str}{ 
         ["",           "/",        "index_handler"]
}

index_handler := {
    method:str, path:str, 
    response:tuple{header:{k:str, seq:int, v:str}, status:int, body:str},
} begin
    response := http.response{*, body := "Hello world, wide web"}
    yield
end


main := {} begin
    res := http.serve(route:=route)
    print(res)
end

It imports the http module and then defines a route relvar to map http methods + paths to handlers. The main function is set to start the server using the http.serve relation generator. The route relvar is passed into serve() and, once started, it will compose responses from incoming requests and handlers. It will keep accepting requests and returning the composed responses to clients until it's stopped e.g. via Ctrl+C.

We have one handler here, which we've named index_handler, to work with any requests for the / path. This handler simply sets the response body to some text and then yield returns it. The text isn't a complete web-page but the client browser should still show it. Visit http://localhost:8080 in your browser and you should see:

Next we'll see how we can build more complete responses by using templates and passing parameters to them.