Google Go EOF on reading from connection using Read()

Question

I am trying to create a simple TCP server using the Google Go language. I have a client which points to 127.0.0.1:8484. When my server code tries to read the buffer I receive an EOF error on line 37. The client sends an initial tcp packet denoting its client version and other settings (the client is from a game therefore I know that I am doing something wrong). I am trying to read this packet. However, it seems I call the read too late and the client has already sent the packet and is waiting for its response. Any help would be appreciated, as I am truly stumped.

package main

import (
    "fmt"
    "net"
    "os"
)

func main() {

    service := ":8484"
    listener, err := net.Listen("tcp", service)
    checkError(err)

    fmt.Println("Login Server Started\nListening on port:", service[1:])

    for {
        conn, err := listener.Accept()
        if err != nil {
            continue
        }

        go handleClient(conn)
    }
}

func handleClient(conn net.Conn) {

    const BUFFER_LENGTH = 1024

    defer conn.Close()

    fmt.Println("Client connected from", conn.RemoteAddr())
    var buf [BUFFER_LENGTH]byte

    for {
        n, err := conn.Read(buf[0:])
        if err != nil {
            checkError(err)
            return
        }

        _, err2 := conn.Write(buf[0:n])
        if err2 != nil {
            checkError(err)
            return
        }

    }
}

func checkError(err error) {
    if err != nil {
        fmt.Fprintf(os.Stderr, "Fatal error: %s\n", err.Error())
        os.Exit(1)
    }
}

Edit for clarity: 1. Client connects to server. 2. Client sends initial information to server e.g. client version. 3. Server reads the buffer. 4. Server responds (currently I am just echoing the buffer).

It is currently failing at the read buffer stage "n, err := conn.Read(buf[0:])".

Fixed: I was being an idiot and realised I needed to send a handshake packet to the client.

score 1 · Answer 1 · answered Jun 06 '14 at 11:37

Well, in checkError you do an explicit os.Exit(1), which kills your server if there is a Read() error from the client.

Instead of:

    n, err := conn.Read(buf[0:])
    if err != nil {
        checkError(err)
        return
    }

You can do

    n, err := conn.Read(buf[0:])
    if err != nil {
        fmt.Printf(err)
        conn.Close()
        return
    }

Which will print the error on the server side and will go back to listening for next connection / continue to operate.

score 0 · Accepted Answer · answered May 26 '14 at 18:14

0

This works for me using nc:

$ nc localhost 8484
Client connected from 127.0.0.1:46464
hello
hello
world
world
^D
Fatal error: EOF
exit status 1

So I think there's nothing wrong with your connection handling. You might just be sending data that the client isn't expecting, and it's closing the connection because of that.

answered May 26 '14 at 18:14

Thomas

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Thanks for the reply. I get the error when the server is trying to read data that the client has sent. So the order of things is: 1. Client connects to server. 2. Client sends initial information to server e.g. client version. 3. Server reads the buffer. 4. Server responds (currently I am just echoing the buffer). It is currently failing at the read buffer stage "n, err := conn.Read(buf[0:])". Sorry if my original post was not clear. – John May 26 '14 at 18:42

Google Go EOF on reading from connection using Read()

2 Answers2