writeonce/docs/examples/writeonce-framework/http/serve.wo

-- http/serve.wo — response serialization + the blocking keep-alive serve
-- loop. The dispatch seam is the Dispatcher interface (the router's App
-- satisfies it, Task 3); it is wrapped in `try`, so a trapping handler
-- answers 500 and the loop lives — a bad request must never kill the
-- server. Every accept path closes its fd; `env.stopping()` is honored
-- between connections and between keep-alive requests (a SIGTERM landing
-- in a blocking call already unwinds cleanly — the runtime's stop story).
use net
use env

pub interface Dispatcher {
  fn dispatch(mut req: Req) -> Resp
}

fn status_text(code: Int) -> Text {
  switch code {
    case 200: return "OK";
    case 201: return "Created";
    case 302: return "Found";
    case 400: return "Bad Request";
    case 401: return "Unauthorized";
    case 404: return "Not Found";
    case 405: return "Method Not Allowed";
    case 409: return "Conflict";
    case 500: return "Internal Server Error";
    default:  return "Status";
  }
}

-- head_only: HEAD answers — full status line + headers (Content-Length of
-- the body a GET would have sent) with the body itself suppressed.
pub fn serialize(resp: Resp, keep: Bool, head_only: Bool) -> Text {
  let head = "HTTP/1.1 ${resp.status} ${status_text(resp.status)}\r\n";
  for k, v in resp.headers {
    head = head .. "${k}: ${v}\r\n";
  }
  if keep {
    head = head .. "Connection: keep-alive\r\n";
  } else {
    head = head .. "Connection: close\r\n";
  }
  head = head .. "Content-Length: ${len(resp.body)}\r\n\r\n";
  if head_only { return head; }
  return head .. resp.body;
}

pub fn serve(host: Text, port: Int, d: Dispatcher) -> Int {
  let srv = net.listen(host, port);
  print("listening on ${host}:${port}");
  while true {
    if env.stopping() { net.close(srv); return 0; }
    let c = net.accept(srv);
    let carry = "";
    let alive = true;
    while alive {
      if env.stopping() { alive = false; continue; }
      let p = try parse_request(c, carry) catch (e) nil;   -- an IO trap = gone
      if p == nil { alive = false; continue; }
      if p.closed { alive = false; continue; }
      if p.ok == false {
        try net.write(c, serialize(bad_request("malformed request"), false, false)) catch (e) {}
        alive = false;
        continue;
      }
      let r = p.req;
      if r == nil { alive = false; continue; }
      carry = p.rest;
      -- HEAD is GET with the body suppressed: route and dispatch as GET,
      -- serialize with head_only so Content-Length still names the body a
      -- GET would have carried (RFC 9110 §9.3.2).
      let is_head = r.method == "HEAD";
      if is_head { r.method = "GET"; }
      -- Connection policy for a single-threaded server: serve PIPELINED
      -- requests on one connection (bytes already buffered), but close when
      -- the client would idle — a parked keep-alive connection would block
      -- `accept` and starve every other client. A proxy in front simply
      -- reconnects; this is the honest shape until shards/fibers (8/11).
      let keep = len(carry) > 0;
      let conn = r.headers["connection"];
      if conn != nil {
        if to_lower(conn) == "close" { keep = false; }
      }
      let resp = try d.dispatch(r) catch (e) server_error();
      try net.write(c, serialize(resp, keep, is_head)) catch (e) { alive = false; }
      if keep == false { alive = false; }
    }
    net.close(c);
  }
}