Add week 3 materials

materials/03-http/seminar/websockets/main.go

@@ -0,0 +1,118 @@
+package main
+
+/*
+Connect client 1:
+
+  wscat --connect 'localhost:8000/connect?author=lupa'
+
+Connect client 2:
+
+    wscat --connect 'localhost:8000/connect?author=lupa'
+Message: {"Text": "hi there"}
+*/
+
+import (
+	"log"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/gorilla/websocket"
+)
+
+type MessageStream struct {
+	Text     string
+	Author   string
+	SendTime *time.Time
+}
+
+type MessengerServer struct {
+	history chan *MessageStream
+	toSend  map[string]chan *MessageStream
+}
+
+var upgrader = websocket.Upgrader{
+	ReadBufferSize:  1024,
+	WriteBufferSize: 1024,
+}
+
+func (s *MessengerServer) Connect(w http.ResponseWriter, r *http.Request) {
+	// Extract author from the URL query parameters
+	author := r.URL.Query().Get("author")
+	if author == "" {
+		w.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	conn, err := upgrader.Upgrade(w, r, nil)
+	if err != nil {
+		log.Printf("failed to upgrade: %s\n", err)
+		return
+	}
+
+	id := uuid.New()
+	s.toSend[id.String()] = make(chan *MessageStream, 1000)
+	log.Printf("Connected: %v\n", id)
+
+	go func() {
+		for {
+			var msg MessageStream
+			err := conn.ReadJSON(&msg)
+			if err != nil {
+				log.Println("Failed to decode a message:", err)
+				return
+			}
+
+			log.Printf("Received from %s: %v\n", author, msg)
+
+			now := time.Now()
+			msg.SendTime = &now
+			msg.Author = author
+			s.history <- &msg
+		}
+	}()
+
+	for {
+		mes := <-s.toSend[id.String()]
+		err := conn.WriteJSON(mes)
+		if err != nil {
+			log.Printf("Deleted %v stream, sending error: %v", id.String(), err)
+			delete(s.toSend, id.String())
+
+			return
+		}
+
+		log.Printf("Sent to stream %v: %v\n", id, mes)
+	}
+}
+
+func (s *MessengerServer) fanout() {
+	for {
+		mes := <-s.history
+
+		log.Printf("Got from history: %v", mes)
+
+		for _, ch := range s.toSend {
+			ch <- mes
+		}
+	}
+}
+
+func main() {
+	port := os.Getenv("MESSENGER_SERVER_PORT")
+	if port == "" {
+		port = "8000"
+		log.Println("Missing MESSENGER_SERVER_PORT, using default value: " + port)
+	}
+	server := MessengerServer{
+		history: make(chan *MessageStream, 1000),
+		toSend:  make(map[string]chan *MessageStream),
+	}
+
+	http.HandleFunc("/connect", server.Connect)
+
+	go server.fanout()
+
+	log.Fatal(http.ListenAndServe("0.0.0.0:"+port, nil))
+}