I'm trying to implement a simple socket echo server in go this is the code:
package main
import (
"fmt"
"net"
"sync"
)
func echo_srv(c net.Conn, wg sync.WaitGroup) {
defer c.Close()
defer wg.Done()
for {
var msg []byte
n, err := c.Read(msg)
if err != nil {
fmt.Printf("ERROR: read\n")
fmt.Print(err)
return
}
fmt.Printf("SERVER: received %v bytes\n", n)
n, err = c.Write(msg)
if err != nil {
fmt.Printf("ERROR: write\n")
fmt.Print(err)
return
}
fmt.Printf("SERVER: sent %v bytes\n", n)
}
}
func main() {
var wg sync.WaitGroup
ln, err := net.Listen("unix", "./sock_srv")
if err != nil {
fmt.Print(err)
return
}
defer ln.Close()
conn, err := ln.Accept()
if err != nil {
fmt.Print(err)
return
}
wg.Add(1)
go echo_srv(conn, wg)
wg.Wait()
}
For some reason as soon as a client connects, c.Read() does not block and the error message is printed. So, my first question is: Shouldn't c.Read() block until a client sends something to the socket?
And second: After printing the error message, the server does not terminate. This is what I see when executing the program in gdb:
(gdb) run
Starting program: src/sockets/server/server
warning: Could not load shared library symbols for linux-vdso.so.1.
Do you need "set solib-search-path" or "set sysroot"?
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
[New Thread 0x7fffe7806700 (LWP 28594)]
[New Thread 0x7fffe7005700 (LWP 28595)]
ERROR: read
EOF^C
Program received signal SIGINT, Interrupt.
runtime.epollwait () at /usr/lib/go/src/pkg/runtime/sys_linux_amd64.s:383
383 RET
(gdb) info goroutines
1 waiting runtime.park
2 syscall runtime.goexit
* 3 syscall runtime.entersyscallblock
I have similar echo servers in Python and C and they work fine. For completeness I also post the socket client application below (it works fine with my C and Python servers).
Client:
package main
import (
"bufio"
"fmt"
"net"
"os"
"strings"
)
func main() {
stdin := bufio.NewReader(os.Stdin)
conn, err := net.Dial("unix", "./sock_srv")
if err != nil {
fmt.Print(err)
return
}
defer conn.Close()
for {
fmt.Print("Enter message to transmit: ")
msg, err := stdin.ReadString('\n')
if err != nil {
fmt.Print(err)
return
}
msg = msg[:len(msg)-1]
if (strings.ToLower(msg) == "quit") || (strings.ToLower(msg) == "exit") {
fmt.Println("bye")
return
}
n, err := conn.Write([]byte(msg))
if err != nil {
fmt.Print(err)
return
}
fmt.Printf("CLIENT: sent %v bytes\n", n)
n, err = conn.Read([]byte(msg))
if err != nil {
fmt.Print(err)
return
}
fmt.Printf("CLIENT: received %v bytes\n", n)
fmt.Println("Received message:", msg)
}
}
Here is a working echo_srv
for you. You'll need @jnml's suggestion too!
only write the bytes received with msg[:n]
func echo_srv(c net.Conn, wg *sync.WaitGroup) {
defer c.Close()
defer wg.Done()
for {
msg := make([]byte, 1000)
n, err := c.Read(msg)
if err == io.EOF {
fmt.Printf("SERVER: received EOF (%d bytes ignored)\n", n)
return
} else if err != nil {
fmt.Printf("ERROR: read\n")
fmt.Print(err)
return
}
fmt.Printf("SERVER: received %v bytes\n", n)
n, err = c.Write(msg[:n])
if err != nil {
fmt.Printf("ERROR: write\n")
fmt.Print(err)
return
}
fmt.Printf("SERVER: sent %v bytes\n", n)
}
}
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