io.Copy timeout when keepalive is disabled

#php editor Yuzai will introduce to you today a problem about "io.Copy timeout when keepalive is disabled". When using the io.Copy function in the Go language for data transmission, if keepalive is disabled, transmission timeout may occur. This problem may cause some trouble to developers, so we need to know some solutions to avoid this problem from happening. Let’s take a look at how to solve this problem!

Question content

When I disable linux keepalive

sudo sysctl -w net.ipv4.tcp_keepalive_probes=0

And run the following code

package main

import (
    "fmt"
    "io"
    "net"
    "os"
    "sync"
    "time"
)

func main() {
    go func() {
        listen, err := net.Listen("tcp", "127.0.0.1:9390")
        if err != nil {
            fmt.Printf("net listen fail, reason: [%s]\n", err.Error())
            os.Exit(1)
        }
        defer listen.Close()

        for {
            conn, err := listen.Accept()
            if err != nil {
                fmt.Printf("net accept fail, reason: [%s]\n", err.Error())
                continue
            }

            _, err = io.Copy(conn, conn)
            if err != nil {
                fmt.Printf("net Copy fail, reason: [%s]\n", err.Error())
                continue
            }
            conn.Close()
        }
    }()

    var wg sync.WaitGroup
    wg.Add(1)
    go func() {
        defer wg.Done()
        for {
            time.Sleep(1 * time.Second)
            tcpAddr, _ := net.ResolveTCPAddr("tcp", "127.0.0.1:9390")
            fmt.Println("tcp client resolve success: ", tcpAddr.String())
            tcpConn, err := net.DialTCP("tcp", nil, tcpAddr)
            if err != nil {
                fmt.Println("tcp connect fail: ", err.Error())
                return
            }

            time.Sleep(100 * time.Second)
            tcpConn.Close()
            fmt.Println("tcp end")
        }
    }()

    wg.Wait()

}

io.Copy will return "splice: connection timeout"

If I enable keepalive

sudo sysctl -w net.ipv4.tcp_keepalive_probes=3

io.Copy is enough

I tried the tcp client to send packets at 1 second intervals and disable tcp_keepalive, that worked too.

I wrote another code to replace io.Copy

            buf := make([]byte, 10)
            for {
                conn.SetReadDeadline(time.Now().Add(30 * time.Second))
                n, err := conn.Read(buf)
                if err != nil {
                    fmt.Println("read fail: ", err.Error())
                    break
                }

                _, err = conn.Write(buf[:n])
                if err != nil {
                    fmt.Println("write fail: ", err.Error())
                    break
                }
            }
            conn.Close()

Read timeout after 15 seconds, not working for 30 seconds

Why is this so strange?

Solution

Answer: When "kernel tcp stack" uses keepalive to detect the network, when "kernel tcp stack" needs to send keepalive, net.ipv4.tcp_keepalive_probes = 0 will time out

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