bind: cannot assign requested address on UDPclient in local network

Question

As I'm finding quite some examples how to write a go server and client, this works locally on one machine.

Now I'm trying to communicate in my local network between two PCs, one running the go server script, one the client.

However, I can't establish a connection because of the error:

Error: listen udp 192.168.11.6:10001: bind: cannot assign requested address
panic: runtime error: invalid memory address or nil pointer dereference [signal 0xb code=0x1 addr=0x0 pc=0x401376] // ...

Of course I will post my code (client, where the problem occurs):

package main

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

func CheckError(err error) {
    if err != nil {
        fmt.Println("Error: ", err)
    }
}

func main() {
    ServerAddr, err := net.ResolveUDPAddr("udp", "192.168.11.6:10001")
    CheckError(err)

    Conn, err := net.ListenUDP("udp", ServerAddr)
    CheckError(err)

    defer Conn.Close()
    i := 0
    for {
        msg := strconv.Itoa(i)
        i++
        buf := []byte(msg)
        _, err = Conn.WriteToUDP(buf, ServerAddr)
        time.Sleep(time.Second * 1)
    }
}

Server:

package main
import (
    "fmt"
    "net"
    "os"
)

/* A Simple function to verify error */
func CheckError(err error) {
    if err  != nil {
        fmt.Println("Error: " , err)
        os.Exit(0)
    }
}

func main() {
    ServerAddr,err := net.ResolveUDPAddr("udp",":10001")
    CheckError(err)

    ServerConn, err := net.ListenUDP("udp", ServerAddr)
    CheckError(err)
    defer ServerConn.Close()

    buf := make([]byte, 1024)
    for {
        fmt.Println("Starting...")
        n,addr,err := ServerConn.ReadFromUDP(buf)
        fmt.Println("Received ",string(buf[0:n]), " from ",addr)
        ServerConn.WriteToUDP([]byte("hello there!"), addr)
        if err != nil {
            fmt.Println("Error: ",err)
        }
    }
}

The client has the local network IP address 192.168.11.8 and the server 192.168.11.6. They can also ping each other, and I'm opening the port when Windows asks for it.

I'm happy about all suggestions. I struggle with this because I only find localhost server client go examples.

Thanks for the reply @JimB - what address is the correct one? I thought I listen at the server's ip address — Daniel, Mar 03 '18 at 14:32
@MichaelHampton, there is no client or server in UDP, and you normally bind UDP using Listen regardless, as Dial creates a “connected” UDP socket that has slightly different behavior. — JimB, Mar 03 '18 at 22:55

Daniel · Accepted Answer · 2018-03-03T16:33:21.243

Okay, I figured it out. Weird that I had to allow the app to communicate on public networks? While I am on my home network. When starting the server - I had to enable public networks

I figured out that I do not have to open a socket on the client side, but use DialUDP

Also the server needed the full Ip address in
ServerAddr,err := net.ResolveUDPAddr("udp","192.168.11.6:10001")

Improved Client code: (main func)

ServerAddr, err := net.ResolveUDPAddr("udp", "192.168.11.6:10001")
CheckError(err)
buf := make([]byte, 1024)
Conn, err := net.DialUDP("udp", nil, ServerAddr)
CheckError(err)

defer Conn.Close()
i := 0
for {
    msg := strconv.Itoa(i)
    i++
    fmt.Printf(msg)
    n, err := Conn.Write([]byte(msg))
    CheckError(err)
    fmt.Printf("sent %d bytes", n)
    n, addr, err := Conn.ReadFromUDP(buf)
    if err == nil {
        fmt.Printf("%s %s\n", buf, addr)
    } else {
        fmt.Printf("some err %v\n", err)
    }
    time.Sleep(time.Second * 1)
}

I should clarify that you could also to listen on a socket on both endpoints like in [this answer](https://stackoverflow.com/questions/30563473/golang-udp-server-only-recieving-locally-sent-packets) and [this one](https://stackoverflow.com/questions/26028700/write-to-client-udp-socket-in-go). — Daniel, Mar 15 '18 at 21:24

bind: cannot assign requested address on UDPclient in local network

1 Answers1