Trouble reading from a socket in go - sockets

Question

I'm trying to learn the go language, and I'm writing a simple echo server. I'm having difficulty making it work, though.
func listen(server string) {
var buf []byte
listener, ok := net.Listen("tcp", server)
if ok != nil {
fmt.Fprintf(os.Stderr, "Could not listen on socket: %s\n", ok.String())
return
}
conn, ok := listener.Accept()
if ok != nil {
fmt.Fprintf(os.Stderr, "Could not accept connection on socket: %s\n", ok.String())
return
}
writelen, ok := conn.Write(strings.Bytes("Ready to receive\n"))
if ok != nil {
fmt.Fprintf(os.Stderr, "Could not write to socket: %s\n", ok.String())
} else {
fmt.Printf("Wrote %d bytes to socket\n", writelen)
}
for ;; {
readlen, ok := conn.Read(buf)
if ok != nil {
fmt.Fprintf(os.Stderr, "Error when reading from socket: %s\n", ok.String())
return
}
if readlen == 0 {
fmt.Printf("Connection closed by remote host\n")
return
}
fmt.Printf("Client at %s says '%s'\n", conn.RemoteAddr().String(), buf)
}
}
I get the following output from this function:
[nathan#ebisu ~/src/go/echo_server] ./6.out 1234
Using port 1234
Wrote 17 bytes to socket
Error when reading from socket: EOF
This is what I see on the client:
[nathan#ebisu ~] telnet 127.0.0.1 1234
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
Ready to receive
Connection closed by foreign host.
Any help would be appreciated (or pointers to resources; the go documentation on the sockets API leaves a little to be desired).
Thanks,
Nathan

Answer 1

In your example, buf needs to have a definite size. You've declared it as a 0-length slice.
Declare it as:
var buf = make([]byte, 1024)

Answer 2

Of course, if you want to learn, it is better to write it yourself but, if it helps, here is my own echo server in Go.
package main
import (
"net";
"os";
"fmt";
)
func handle(conn *net.TCPConn) {
fmt.Printf("Connection from %s\n", conn.RemoteAddr());
message := make([]byte, 1024);
// TODO: loop the read, we can have >1024 bytes
n1, error := conn.Read(message);
if error != nil {
fmt.Printf("Cannot read: %s\n", error);
os.Exit(1);
}
n2, error := conn.Write(message[0:n1]);
if error != nil || n2 != n1 {
fmt.Printf("Cannot write: %s\n", error);
os.Exit(1);
}
fmt.Printf("Echoed %d bytes\n", n2);
conn.Close(); // TODO: wait to see if more data? It would be better with telnet...
}
func main() {
listen := ":7";
addr, error := net.ResolveTCPAddr(listen);
if error != nil {
fmt.Printf("Cannot parse \"%s\": %s\n", listen, error);
os.Exit(1);
}
listener, error := net.ListenTCP("tcp", addr);
if error != nil {
fmt.Printf("Cannot listen: %s\n", error);
os.Exit(1);
}
for { // ever...
conn, error := listener.AcceptTCP();
if error != nil {
fmt.Printf("Cannot accept: %s\n", error);
os.Exit(1);
}
go handle(conn);
}
}