Make plugin connection much more robust, with better errors

plugin/src/Api.lua

@@ -0,0 +1,112 @@
+local HttpService = game:GetService("HttpService")
+
+local Config = require(script.Parent.Config)
+local Promise = require(script.Parent.Promise)
+local Version = require(script.Parent.Version)
+
+local Api = {}
+Api.__index = Api
+
+Api.Error = {
+	ServerIdMismatch = "ServerIdMismatch",
+}
+
+setmetatable(Api.Error, {
+	__index = function(_, key)
+		error("Invalid API.Error name " .. key, 2)
+	end
+})
+
+--[[
+	Api.connect(Http) -> Promise<Api>
+
+	Create a new Api using the given HTTP implementation.
+
+	Attempting to invoke methods on an invalid conext will throw errors!
+]]
+function Api.connect(http)
+	local context = {
+		http = http,
+		serverId = nil,
+		currentTime = 0,
+	}
+
+	setmetatable(context, Api)
+
+	return context:_start()
+end
+
+function Api:_start()
+	return self.http:get("/")
+		:andThen(function(response)
+			response = response:json()
+
+			if response.protocolVersion ~= Config.protocolVersion then
+				local message = (
+					"Found a Rojo dev server, but it's using a different protocol version, and is incompatible." ..
+					"\nMake sure you have matching versions of both the Rojo plugin and server!" ..
+					"\n\nYour client is version %s, with protocol version %s. It expects server version %s." ..
+					"\nYour server is version %s, with protocol version %s." ..
+					"\n\nGo to https://github.com/LPGhatguy/rojo for more details."
+				):format(
+					Version.display(Config.version), Config.protocolVersion,
+					Config.expectedApiVersionString,
+					response.serverVersion, response.protocolVersion
+				)
+
+				return Promise.reject(message)
+			end
+
+			self.serverId = response.serverId
+			self.currentTime = response.currentTime
+
+			return self
+		end)
+end
+
+function Api:getInfo()
+	return self.http:get("/")
+		:andThen(function(response)
+			response = response:json()
+
+			if response.serverId ~= self.serverId then
+				return Promise.reject(Api.Error.ServerIdMismatch)
+			end
+
+			return response
+		end)
+end
+
+function Api:read(paths)
+	local body = HttpService:JSONEncode(paths)
+
+	return self.http:post("/read", body)
+		:andThen(function(response)
+			response = response:json()
+
+			if response.serverId ~= self.serverId then
+				return Promise.reject(Api.Error.ServerIdMismatch)
+			end
+
+			return response.items
+		end)
+end
+
+function Api:getChanges()
+	local url = ("/changes/%f"):format(self.currentTime)
+
+	return self.http:get(url)
+		:andThen(function(response)
+			response = response:json()
+
+			if response.serverId ~= self.serverId then
+				return Promise.reject(Api.Error.ServerIdMismatch)
+			end
+
+			self.currentTime = response.currentTime
+
+			return response.changes
+		end)
+end
+
+return Api