IdleTimeout in tcp server

Question

I am working on a project in the Go language which includes TCP server. I am trying to implement an idle timeout on server sockets, but couldn't do it. The Go code I am using goes like this:

package main

import (
    "bufio"
    "fmt"
    "net"
    "os"
    "strconv"
    "time"
)

func main() {
    startServer(6666, time.Duration(2)*time.Second)
}

func startServer(port int, deadline time.Duration) {
    // Listen for incoming connections.
    strPort := strconv.Itoa(port)
    l, err := net.Listen("tcp", ":"+strPort)
    if err != nil {
        fmt.Println("Error listening:", err.Error())
        os.Exit(1)
    }
    // Close the listener when the application closes.
    defer l.Close()
    fmt.Println("Listening on port:" + strPort)
    for {
        // Listen for an incoming connection.
        conn, err := l.Accept()
        if err != nil {
            fmt.Println("Error accepting: ", err.Error())
            os.Exit(1)
        }

        fmt.Println("Got new connection")

        // Set read timeout
        conn.SetReadDeadline(time.Now().Add(deadline))

        // Handle connections in a new goroutine.
        go handleRequest(conn)
    }
}

func handleRequest(conn net.Conn) {
    reader := bufio.NewReader(conn)
    scanner := bufio.NewScanner(reader)

    for scanner.Scan() {
        fmt.Println(scanner.Bytes())
    }
}

I want it to timeout and close the connection after 2 seconds. Could anybody please tell me what I might be doing wrong. In order to test it, I am using a TCP client I wrote as Python scipt. The client code goes like this:

λ python
Python 3.5.1 (v3.5.1:37a07cee5969, Dec  6 2015, 01:54:25) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from socket import *
>>> c = socket(family=AF_INET, type=SOCK_STREAM)
>>> c.connect(('localhost', 6666))

I can always keep track of all the open connections, along with their last active time in some sort of data structure and launch a goroutine which periodically checks for time elapsed for every connection, closing the ones I haven't heard from in a while. But I wanted to utilize the built-in method SetReadDeadline() for the job.

Answer 1

In the net package documentation for SetDeadline, it states

   // An idle timeout can be implemented by repeatedly extending
   // the deadline after successful Read or Write calls.

You do this by creating your own net.Conn type to implement the call you want to have timeout. Since an idle connection would normally be waiting in Read, that is usually where you want to set the deadline.

type Conn struct {
    net.Conn
    idleTimeout time.Duration
}

func (c *Conn) Read(b []byte) (int, error) {
    err := c.Conn.SetReadDeadline(time.Now().Add(c.idleTimeout))
    if err != nil {
        return 0, err
    }
    return c.Conn.Read(b)
}