Unix Sockets in Go

Question

I'm trying to make a simple echo client and server that uses Unix sockets. In this example, the connection seems to be unidirectional. The server can receive data from the client, but it can't send the data back. If I use tcp connections instead, it works great. Does anyone know what's wrong?

Server

package main

import "net"
import "fmt"

func echoServer(c net.Conn) {
    for {
        buf := make([]byte, 512)
        nr, err := c.Read(buf)
        if err != nil {
            return
        }

        data := buf[0:nr]
        fmt.Printf("Received: %v", string(data))
        _, err = c.Write(data)
        if err != nil {
            panic("Write: " + err.String())
        }
    }
}

func main() {
    l, err := net.Listen("unix", "/tmp/echo.sock")
    if err != nil {
        println("listen error", err.String())
        return
    }

    for {
        fd, err := l.Accept()
        if err != nil {
            println("accept error", err.String())
            return
        }

        go echoServer(fd)
    }
}

Client

package main

import "net"
import "time"

func main() {
    c,err := net.Dial("unix","", "/tmp/echo.sock")
    if err != nil {
        panic(err.String())
    }
    for {
        _,err := c.Write([]byte("hi\n"))
        if err != nil {
            println(err.String())
        }
        time.Sleep(1e9)
    }
}

Jeff Allen · Accepted Answer · 2014-10-29 10:55:38Z

56

In your example client, you don't seem to be reading the result from the server. When I add code to do that, I see the results from the server.

Also, take a look at how I used defer and break to make the reader goroutine exit.

Server

package main

import (
    "log"
    "net"
)

func echoServer(c net.Conn) {
    for {
        buf := make([]byte, 512)
        nr, err := c.Read(buf)
        if err != nil {
            return
        }

        data := buf[0:nr]
        println("Server got:", string(data))
        _, err = c.Write(data)
        if err != nil {
            log.Fatal("Write: ", err)
        }
    }
}

func main() {
    l, err := net.Listen("unix", "/tmp/echo.sock")
    if err != nil {
        log.Fatal("listen error:", err)
    }

    for {
        fd, err := l.Accept()
        if err != nil {
            log.Fatal("accept error:", err)
        }

        go echoServer(fd)
    }
}

Client

package main

import (
    "io"
    "log"
    "net"
    "time"
)

func reader(r io.Reader) {
    buf := make([]byte, 1024)
    for {
        n, err := r.Read(buf[:])
        if err != nil {
            return
        }
        println("Client got:", string(buf[0:n]))
    }
}

func main() {
    c, err := net.Dial("unix", "/tmp/echo.sock")
    if err != nil {
        panic(err)
    }
    defer c.Close()

    go reader(c)
    for {
        _, err := c.Write([]byte("hi"))
        if err != nil {
            log.Fatal("write error:", err)
            break
        }
        time.Sleep(1e9)
    }
}

edited Oct 29, 2014 at 10:55

answered Jan 21, 2011 at 13:21

Jeff Allen

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1 Comment

nelsonjchen Over a year ago

This no longer compiles with the latest version of Go. The String() function on the error has been replaced by Error() and net's Dial() no longer has whatever that second argument was. Here was the suggested edit with the fix that I made but was rejected: gist.github.com/nelsonjchen/510ab59caa85251c4709 .

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