whispering_gophers/part3/main.go

// Solution to part 3 of the Whispering Gophers code lab.
//
// This program listens on the host and port specified by the -listen flag.
// For each incoming connection, it launches a goroutine that reads and decodes
// JSON-encoded messages from the connection and prints them to standard
// output.
//
// You can test this program by running it in one terminal:
// 	$ part3 -listen=localhost:8000
// And running part2 in another terminal:
// 	$ part2 -dial=localhost:8000
// Lines typed in the second terminal should appear as JSON objects in the
// first terminal.
//
package main

import (
	"bufio"
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"log"
	"net"
)

var listenAddr = flag.String("listen", "localhost:8000", "host:port to listen on")

type Message struct {
	Body string
}

func main() {
	flag.Parse()

	// Create a net.Listener listening from the address in the "listen" flag.
	l, err := net.Listen("tcp4", *listenAddr)
	if err != nil {
		log.Fatal(err)
	}

	for {
		// Accept a new connection from the listener.
		c, err := l.Accept()
		if err != nil {
			log.Fatal(err)
		}

		go serve(c)
	}
}

func serve(c net.Conn) {
	// Use defer to Close the connection when this function returns.
	defer c.Close()

	// Create a new json.Decoder reading from the connection.
	d := json.NewDecoder(bufio.NewReader(c)) // NewDecoder(c) would loop on EOF
	for {
		// Create an empty message.
		m := Message{}
		// Decode a new message into the variable you just created.
		err := d.Decode(&m)
		if err == io.EOF {
			break
		}
		if err != nil {
			log.Fatal(err)
		}
		// Print the message to the standard output.
		fmt.Println(m)
	}
	log.Println("Closing connection on EOF.")
}