feat: realtime:ping(cb) + drop default ports from URLs (#20)

realtime:ping(callback) times a session.heartbeat round-trip and
reports (rtt_ms, err). Lets games surface live RTT in HUDs without
poking the private _send_with_callback. send_heartbeat (fire-and-
forget) is unchanged.

client.lua's URL builders drop the explicit port when it matches the
scheme default. Defold's extension-websocket fails to connect to
wss://host:443/path even though the URL is technically valid; tested
against barrow.fly.dev.

Reviewed by asobi-qa-lua (quick): GREEN, 0 issues introduced.

Author: Taure

asobi/client.lua

@@ -18,19 +18,31 @@ local dm = require("asobi.api.dm")
 
 local M = {}
 
+-- Drop the explicit port when it matches the scheme default. Some WS
+-- clients (notably Defold's extension-websocket) fail to connect to
+-- wss://host:443/path even though the URL is technically valid.
+local function authority(host, port, default_port)
+	if port == default_port then
+		return host
+	end
+	return host .. ":" .. tostring(port)
+end
+
 function M.create(host, port, use_ssl)
 	port = port or 8084
 	use_ssl = use_ssl or false
 
 	local scheme = use_ssl and "https" or "http"
 	local ws_scheme = use_ssl and "wss" or "ws"
+	local http_default = use_ssl and 443 or 80
+	local ws_default = use_ssl and 443 or 80
 
 	local client = {
 		host = host,
 		port = port,
 		use_ssl = use_ssl,
-		base_url = scheme .. "://" .. host .. ":" .. tostring(port),
-		ws_url = ws_scheme .. "://" .. host .. ":" .. tostring(port) .. "/ws",
+		base_url = scheme .. "://" .. authority(host, port, http_default),
+		ws_url = ws_scheme .. "://" .. authority(host, port, ws_default) .. "/ws",
 		session_token = nil,
 		player_id = nil,
 	}

asobi/realtime.lua

@@ -145,6 +145,31 @@ function M:send_heartbeat()
 	self:_send_fire_and_forget("session.heartbeat", {})
 end
 
+-- Round-trip a session.heartbeat and report the elapsed time. The server
+-- echoes the heartbeat with the same cid, so this is the cheapest way for
+-- a game to surface live RTT (e.g. in a HUD).
+function M:ping(callback)
+	if not self.connection then
+		if callback then
+			callback(nil, "not connected")
+		end
+		return
+	end
+	local t0 = socket.gettime()
+	self:_send_with_callback("session.heartbeat", {}, function(_payload, err)
+		if err then
+			if callback then
+				callback(nil, err)
+			end
+			return
+		end
+		local rtt_ms = math.floor((socket.gettime() - t0) * 1000 + 0.5)
+		if callback then
+			callback(rtt_ms, nil)
+		end
+	end)
+end
+
 function M:list_worlds(opts, callback)
 	local payload = {}
 	if type(opts) == "string" then