It doesn't have to be REST: WebSockets in Go

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It doesn’t have to be REST WebSockets in Go

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@konradreiche

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HTTP 0.9 HTTP 1.0 HTTP 1.1 HTTP/2 GraphQL WebSocket 1991 1996 1999 2000 2005 2008 2013 2015 2016 2018 REST React High React Adoption Towards Real-Time Rendering & Updating AJAX Expected Real-Time Singularity

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REST GET DELETE POST PUT Resources ?

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REST (Representational State Transfer) - Defined by Roy T. Fielding in his dissertation: “Architectural Styles and the Design of Network-based Software Architectures” - Fielding: there are two perspectives on the process of architectural design - Build the architecture from familiar components until needs are satisfied - Start with system needs; incrementally add constraints when needed - First one emphasizes creativity and unbound vision - Second one emphasizes restraint and understanding the system context

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Client-Server

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Client-Server Stateless

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Client-Server Stateless Cache

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Client-Server Stateless Cache Uniform Interface

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Client-Server Stateless Cache Uniform Interface Layered System

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Client-Server Stateless Cache Uniform Interface Layered System Code on Demand

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WebSockets

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Chats Games

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GET ws://localhost:4000/ HTTP/1.1 Origin: http://localhost:4000 Host: localhost:4000 Connection: Upgrade Upgrade: websocket Sec-WebSocket-Key: zy6Dy9mSAIM7GJZNf9rI1A== Sec-WebSocket-Version: 13 Open Handshake Request

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HTTP/1.1 101 Switching Protocols Connection: Upgrade Upgrade: websocket Sec-WebSocket-Accept: EDJa7WCAQQzMCYNJM42Syuo9SqQ= Open Handshake Response

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Server ws://… Client Messages Text/Binary

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Server ws://… Client Messages Text/Binary - Message-oriented protocol - Messages are split into frames - Payload can be binary or text - Supports fragmentation

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Server ws://… Client Messages Text/Binary - Message-oriented protocol - Messages are split into frames - Payload can be binary or text - Supports fragmentation

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package main import ( "net/http" ) func main() { err := http.ListenAndServe(":4000", nil) if err != nil { panic(err) } }

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package main import ( "net/http" "golang.org/x/net/websocket" ) func main() { http.Handle("/websocket", websocket.Handler(nil)) err := http.ListenAndServe(":4000", nil) if err != nil { panic(err) } }

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package main import ( "net/http" "golang.org/x/net/websocket" ) func Handle(ws *websocket.Conn) { // TODO } func main() { http.Handle("/websocket", websocket.Handler(Handle)) err := http.ListenAndServe(":4000", nil) if err != nil { panic(err) } }

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package main import ( "net/http" "golang.org/x/net/websocket" ) func Handle(ws *websocket.Conn) { ws.Write([]byte("I am alive")) } func main() { http.Handle("/websocket", websocket.Handler(Handle)) err := http.ListenAndServe(":4000", nil) if err != nil { panic(err) } }

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package main import ( "net/http" "golang.org/x/net/websocket" ) func main() { origin := "http://localhost/" _, err := websocket.Dial("ws://localhost:4000/websocket", "", origin) if err != nil { panic(err) } }

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package main import ( "net/http" "golang.org/x/net/websocket" ) func main() { origin := "http://localhost/" ws, err := websocket.Dial("ws://localhost:4000/websocket", "", origin) if err != nil { panic(err) } _, err := ws.Write([]byte("Hello? Anybody here?")) if err != nil { panic(err) } }

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https://godoc.org/?q=websocket

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github.com/gorilla/websocket 3958 stars, 2393 imports golang.org/x/net/websocket 1412 imports

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github.com/gorilla/websocket golang.org/x/net RFC 6455 Features Passes Autobahn Test Suite Yes No Receive fragmented message Yes No Send close message Yes No Send pings and receive pongs Yes No Get the type of a received data message Yes Yes Other Features Read message using io.Reader Yes No? Write message using io.WriterCloser Yes No?

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Message 1

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Frame 1 Message 1

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Frame 1 Frame 2 Message 1

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Frame 1 Frame 2 Frame 3 Message 1

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Frame 1 Frame 2 Frame 3 Frame 1 Message 1 Frame 2 Message 2

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Frame 1 Frame 2 Frame 3 Frame 1 Message 1 Frame 2 Message 2

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Frame 1 Frame 2 Frame 3 Frame 1 Message 1 Frame 2 Message 2 Read() / Write() golang.org/x/net/websocket

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Frame 1 Frame 2 Frame 3 Frame 1 Message 1 Frame 2 Message 2 Read() / Write() Read() / Write() golang.org/x/net/websocket

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Frame 1 Frame 2 Frame 3 Frame 1 Message 1 Frame 2 Message 2 Read() / Write() Read() / Write() Read() / Write() golang.org/x/net/websocket

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Frame 1 Frame 2 Frame 3 Frame 1 Message 1 Frame 2 Message 2 github.com/gorilla/websocket Read() / Write() Read() / Write() Read() / Write() Read() / Write() Read() / Write() golang.org/x/net/websocket

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package main import ( "log" "net/http" ) func handleUpgrade(w http.ResponseWriter, r *http.Request) { // TODO } func main() { http.HandleFunc("/websocket", handleUpgrade) err := http.ListenAndServe(":4000", nil) if err != nil { panic(err) } }

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package main import ( "log" "net/http" ) var upgrader = websocket.Upgrader{} func handleUpgrade(w http.ResponseWriter, r *http.Request) { // TODO } func main() { http.HandleFunc("/websocket", handleUpgrade) err := http.ListenAndServe(":4000", nil) if err != nil { panic(err) } }

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package main import ( "log" "net/http" ) var upgrader = websocket.Upgrader{} func handleUpgrade(w http.ResponseWriter, r *http.Request) { conn, err := upgrader.Upgrade(w, r, nil) if err != nil { panic(err) } defer conn.Close() // TODO } func main() { http.HandleFunc("/websocket", handleUpgrade) // …

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package main import ( "log" "net/http" ) var upgrader = websocket.Upgrader{} func handleUpgrade(w http.ResponseWriter, r *http.Request) { conn, err := upgrader.Upgrade(w, r, nil) if err != nil { panic(err) } defer conn.Close() handleConnection(conn) } func main() { http.HandleFunc("/websocket", handleUpgrade) // …

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func handleConnection(conn *websocket.Conn) { for { messageType, message, err := c.ReadMessage() if err != nil { break } log.Println(message) err = c.WriteMessage(messageType, message) if err != nil { break } } }

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https://github.com/gobwas/ws - Efficient low-level WebSocket library - Allow users to reuse I/O buffers between connections - Export efficient low-level interface for working with the protocol Zero-Copy Upgrade - Skips the need to use HTTP for upgrading - ws.Upgrade() accepts io.ReadWriter (net.Conn)

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Backend Clients API Database HTTP

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Backend Clients API Database HTTP Polling

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Push Backend Clients API Database WebSocket Bus

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Push Backend Clients API Database WebSocket Bus Subscribe Publish State change

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Push Backend Clients API Database WebSocket Bus Subscribe Publish State change

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Push Backend Clients API Database WebSocket {"cmd”:"listUsers"}

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Push Backend Clients API Database WebSocket "CONNECT" "LIST_USERS"

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type MessageEndpoint func(ctx context.Context, m Message, w *Writer) error type Router struct { endpoints map[string]MessageEndpoint writer map[string]*Writer } func (r *Router) HandleConnection(conn *websocket.Conn) { w := r.NewWriter(conn) for { _, message, err := conn.ReadMessage() if err != nil { break } request := string(message) r.writer[w.ID] = w r.Route(context.Background(), w, request) } delete(r.writer, r.ID(conn)) }

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type MessageEndpoint func(ctx context.Context, m Message, w *Writer) error type Router struct { endpoints map[string]MessageEndpoint writer map[string]*Writer } func (r *Router) HandleConnection(conn *websocket.Conn) { w := r.NewWriter(conn) for { _, message, err := conn.ReadMessage() if err != nil { break } request := string(message) r.writer[w.ID] = w go r.Route(context.Background(), w, request) } delete(r.writer, r.ID(conn)) }

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type Writer struct { ID int conn *websocket.Conn } func (w *Writer) Write(data []byte) (int, error) { err := w.conn.WriteMessage(websocket.TextMessage, data) if err != nil { return 0, err } return len(data), nil }

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type Writer struct { ID int mu sync.RWMutex conn *websocket.Conn } func (w *Writer) Write(data []byte) (int, error) { w.mu.Lock() defer w.mu.Unlock() err := w.conn.WriteMessage(websocket.TextMessage, data) if err != nil { return 0, err } return len(data), nil }

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Summary - REST can be implemented using WebSockets - WebSockets allow us to implement a push architecture - Freedom in designing a sub-protocol tailored to your system’s needs - Also useful for connecting backend components - Gorilla WebSocket is a great implementation of RFC 6455 - Rolling your own implementation can be costly - Bad compatibility to the outside world