Golang: Mixing Gin with an UDP server

Question

I'm trying to use both a UDP server to listen continuously to datagrams and a http server, but the string "UDP server up and listening on port..." and command "server.Run()" are never reached.

package main

import (
    "fmt"
    "github.com/gin-gonic/gin"
    "log"
    "net"
)

func handleUDPConnection(conn *net.UDPConn) {
    buffer := make([]byte, 8096)
    n, addr, err := conn.ReadFromUDP(buffer)

    if err != nil {
        log.Fatal(err)
    } else {
        fmt.Println("UDP client: ", addr)
        fmt.Println("Received from UDP client: ", string(buffer[:n]))
    }
}

func main() {
    server := gin.Default()
    host, port := "localhost", "41234"
    udpAddr, err := net.ResolveUDPAddr("udp4", fmt.Sprintf("%s:%s", host, port))

    if err != nil {
        log.Fatal(err)
    }

    conn, err := net.ListenUDP("udp", udpAddr)
    if err != nil {
        log.Fatal(err)
    }

    defer conn.Close()
    server.GET("/ping", func(c *gin.Context) {
        c.JSON(200, gin.H{"message": "pong"})
    })

    for {
        handleUDPConnection(conn)
    }

    fmt.Sprintf("UDP server up and listening on port %s\n", port)
    server.Run()
}

How can I make it work?

Answer 1

There is an infinite loop in your code.

for {
    handleUDPConnection(conn)
}

This will repetedly call the handleUDPConnection function until the program exits without ever moving on to

fmt.Sprintf("UDP server up and listening on port %s\n", port)
server.Run()

Perhaps you want to deal with the connections in a go thread. This would be something more like this:

//define an exit variable
keepListening := true
//spawn a go routine (starts the function on another thread*)
go func() {
    for keepListening {
        handleUDPConnection(conn)
    }
}()
//notify the user that the server is listening
fmt.Sprintf("UDP server up and listening on port %s\n", port)
//run the server (I assume this function call is blocking
server.Run()
//stop the go routine when the server is done running
keepListening = false

Hope this helps!

*a goroutine is not a thread. It can be useful/simple to think of it like that, but they are distinctly different. Here's an article explaining some of the differences and advantages.