[Go] TCP Server

Posted on | In , |

A bunch of brief intro of writing TCP server from scratch code.

Write to connection

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
import (
    "fmt"
    "io"
    "log"
    "net"
)

func main() {
    li, err := net.Listen("tcp", ":8080") // return Listener(Accept(), Close(), Addr()), Error
    if err != nil {
        log.Panic(err)
    }
    defer li.Close()

    for { // Infinite loop
        conn, err := li.Accept() // Conn: Connection: reader + writer
        if err != nil {
            log.Println(err)
        }

        io.WriteString(conn, "\nHello from TCP server\n")
        fmt.Fprintln(conn, "How is your day")
        fmt.Fprintf(conn, "%v", "Well, I hope!")

        conn.Close()
    }
}

Read from connection

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
func main() {
	li, err := net.Listen("tcp", ":8080")
	if err != nil {
		log.Panic(err)
	}
	defer li.Close()

	for { // Infinite loop
		conn, err := li.Accept()
		if err != nil {
			log.Println(err)
		}

		go handle(conn)
	}
}

func handle(conn net.Conn) {
	scanner := bufio.NewScanner(conn)
	for scanner.Scan() { // return boolean, stops when reach the end of line
		ln := scanner.Text() // Scan() keeps listening to the conn's port, 
		fmt.Println(ln)
	}

	defer conn.Close()
}

Response and request

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
func handle(conn net.Conn) {
    defer conn.Close()

    // read request
    request(conn)

    // write resposne
    respond(conn)
}

func request(conn net.Conn) { // PRINT request connection OUT
    i := 0
    scanner := bufio.NewScanner(conn)
    for scanner.Scan() {
        ln := scanner.Text()
        fmt.Println(ln)
        if i == 0 {
            // request line
            m := strings.Fields(ln)[0]
            fmt.Println("***METHOD", m)
        }
        if ln == "" {
            break
        }
        i++
    }
}

func respond(conn net.Conn) {
    body := `<!DOCTYPE html><html lang="en"><body>hello</body></html>`
    fmt.Fprint(conn, "HTTP/1.1 200 OK\r\n")
    fmt.Fprint(conn, body)
}