TCP stuck example

client.go

package main

import (
	"bufio"
	"io"
	"log"
	"net"
	"sync"
	"time"
)

func main() {
	conn, err := net.Dial("tcp4", "localhost:8888")
	if err != nil {
		log.Fatal(err)
	}

	var wg sync.WaitGroup
	go func() {
		wg.Add(1)
		defer wg.Done()

		scope := time.Now().Truncate(time.Second)

		var avg time.Duration
		var cnt time.Duration
		for {
			startAt := time.Now()
			startScope := startAt.Truncate(time.Second)
			_, err := io.WriteString(conn, "Hello!\n")
			if err != nil {
				log.Printf("%v (startAt:%v)\n", err, startAt)
				return
			}

			elapsed := time.Now().Sub(startAt)
			if scope.Equal(startScope) {
				avg = (cnt*avg + elapsed) / (cnt + 1)
				cnt++
			} else {
				log.Printf("- %v (%d)\n", avg, cnt)
				scope = startScope
				avg = elapsed
				cnt = 1
			}

			time.Sleep(300 * time.Microsecond)
		}
	}()

	func() {
		wg.Add(1)
		defer wg.Done()

		bufr := bufio.NewReader(conn)
		for {
			line, err := bufr.ReadString('\n')
			if err != nil {
				log.Println(err)
				return
			}

			log.Printf("received: %s", line)
		}
	}()
	wg.Wait()
}

result.txt

2020/05/20 18:14:05 - 21.816µs (2186)
2020/05/20 18:14:06 - 21.257µs (2472)
2020/05/20 18:14:07 - 21.423µs (2472)
2020/05/20 18:14:07 received: Hello!
2020/05/20 18:14:08 - 21.736µs (2474)
2020/05/20 18:14:09 - 21.771µs (2476)
2020/05/20 18:14:10 - 21.649µs (2473)
2020/05/20 18:14:10 received: Hello!
2020/05/20 18:14:11 - 21.389µs (2448)
2020/05/20 18:14:12 - 21.682µs (2473)
2020/05/20 18:14:13 - 21.505µs (2482)
2020/05/20 18:14:13 received: Hello!
2020/05/20 18:14:14 - 21.673µs (2473)
2020/05/20 18:14:15 - 21.43µs (2481)
2020/05/20 18:14:16 - 21.533µs (2461)
2020/05/20 18:14:16 received: Hello!
2020/05/20 18:14:17 - 21.527µs (2469)
2020/05/20 18:14:18 - 22.538µs (2457)
2020/05/20 18:14:19 - 21.3µs (2477)
2020/05/20 18:14:19 received: Hello!
2020/05/20 18:14:20 - 22.237µs (2468)
2020/05/20 18:14:21 - 22.061µs (2469)
2020/05/20 18:14:22 - 22.01µs (2463)
2020/05/20 18:14:22 received: Hello!
2020/05/20 18:14:23 - 21.711µs (2483)
2020/05/20 18:14:24 - 22.5µs (2469)
2020/05/20 18:14:25 - 21.953µs (2467)
2020/05/20 18:14:25 received: Hello!
2020/05/20 18:14:26 - 22.39µs (2457)
2020/05/20 18:14:27 - 22.322µs (2468)
2020/05/20 18:14:28 - 20.327µs (2470)
2020/05/20 18:14:28 received: Hello!
2020/05/20 18:14:29 - 12.092µs (2524)
2020/05/20 18:14:30 - 12.423µs (2515)
2020/05/20 18:14:31 - 12.026µs (2520)
2020/05/20 18:14:31 received: Hello!
2020/05/20 18:14:32 - 12.367µs (2519)
2020/05/20 18:14:33 - 12.221µs (2581)
2020/05/20 18:14:34 - 12.579µs (2537)
2020/05/20 18:14:34 received: Hello!
2020/05/20 18:14:35 - 12.464µs (2521)
2020/05/20 18:14:36 - 12.734µs (2521)
2020/05/20 18:14:37 received: Hello!
2020/05/20 18:14:40 received: Hello!
2020/05/20 18:14:43 received: Hello!
2020/05/20 18:14:46 received: Hello!
2020/05/20 18:14:49 received: Hello!
2020/05/20 18:14:52 received: Hello!
2020/05/20 18:14:55 received: Hello!
2020/05/20 18:14:57 read tcp4 127.0.0.1:59345->127.0.0.1:8888: read: connection reset by peer
2020/05/20 18:14:57 write tcp4 127.0.0.1:59345->127.0.0.1:8888: write: broken pipe (startAt:2020-05-20 18:14:36.058589 +0900 JST m=+31.945740248)

server.go

package main

import (
	"bufio"
	"io"
	"log"
	"net"
	"time"
)

func main() {
	l, err := net.Listen("tcp4", "localhost:8888")
	if err != nil {
		log.Fatal(err)
	}

	for {
		c, err := l.Accept()
		if err != nil {
			log.Println(err)
			return
		}

		go func(c net.Conn) {
			bufr := bufio.NewReader(c)
			for {
				line, err := bufr.ReadString('\n')
				if err != nil {
					log.Println(err)
					break
				}

				time.Sleep(3 * time.Second) # emulate to delay receiving/processing the data
				_, err = io.WriteString(c, line)
				if err != nil {
					log.Println(err)
					break
				}
			}
			err := c.Close()
			if err != nil {
				log.Println(err)
			}
		}(c)
	}
}