Channels in Golang with TCP/IP socket not working

Question

I just started writting a Golang client for a server that I've made in C with TCP/IP sockets, then I figured out that my channel wasn't working.

Any ideas why ?

func reader(r io.Reader, channel chan<- []byte) {
  buf := make([]byte, 2048)
  for {
    n, err := r.Read(buf[:])
    if err != nil {
        return
    }
    channel <- buf[0:n]
  }
}
func client(e *gowd.Element) {
 f, err := os.Create("/tmp/dat2")
 if err != nil {
    log.Fatal()
 }
 read := make(chan []byte)
 c, err := net.Dial("tcp", "127.0.0.1:4242")
 if err != nil {
    log.Fatal(err)
 }
 go reader(c, read)
 for {
    buf := <-read
    n := strings.Index(string(buf), "\n")
    if n == -1 {
        continue
 }
 msg := string(buf[0:n])
 if msg == "WELCOME" {
    fmt.Fprint(c, "GRAPHIC\n")
 }
 f.WriteString(msg + "\n")
}

Testing my server with netcat results in the following output : http://pasted.co/a37b2954

But i only have : http://pasted.co/f13d56b4

I'm new to chan in Golang so maybe I'm wrong (I probably am)

Can you define "not working" within the question itself? – Adrian Jul 03 '17 at 12:34 — Adrian, Jul 03 '17 at 12:34

jeevatkm · Accepted Answer · 2017-07-03T20:43:52.943

Channel usage looks alright, however retrieving value from channel would overwrite previously read value at buf := <-read since your waiting for newline.

Also you can use bufio.Reader to read string upto newline.

Your code snippet is partial so its not feasible to execute, try and let me know:

func reader(r io.Reader, channel chan<- string) {
    bufReader := bufio.NewReader(conn)
    for {
        msg, err := bufReader.ReadString('\n')
        if err != nil { // connection error or connection reset error, etc
           break
        }
        channel <- msg
    }
}

func client(e *gowd.Element) {
    f, err := os.Create("/tmp/dat2")
    if err != nil {
        log.Fatal()
    }
    read := make(chan string)
    c, err := net.Dial("tcp", "127.0.0.1:4242")
    if err != nil {
        log.Fatal(err)
    }
    go reader(c, read)
    for {
        msg := <-read
        if msg == "WELCOME" {
            fmt.Fprint(c, "GRAPHIC\n")
        }
        f.WriteString(msg + "\n")
    }
    //...
}

EDIT:

Please find example of generic TCP client to read data. Also I have removed scanner from above code snippet and added buffer reader.

func main() {
    conn, err := net.Dial("tcp", "127.0.0.1:4242")
    if err != nil {
        log.Fatal(err)
    }

    reader := bufio.NewReader(conn)
    for {
        msg, err := reader.ReadString('\n')
        if err != nil {
            break
        }
        fmt.Println(msg)
    }
}

Thank you, the whole code is garbage with html and whatever, unreadable. I use your code, but it produces nothing, i have no more message in my file... — Boris Le Méec, Jul 03 '17 at 02:14
Sorry, my english is a total disaster tonight. I haven't published the entire code because it would be unreadable. Anyway i tried your code but now I can't even receive one message from the server, at the end of the execution, the file in tmp is still empty — Boris Le Méec, Jul 03 '17 at 02:20
I do not have knowledge on your code. However I will create generic TCP socket read and will update the answer. Then you can customize it for your need. — jeevatkm, Jul 03 '17 at 02:29

Channels in Golang with TCP/IP socket not working

1 Answers1