Read faults from socket in go

Question

I am trying to learn a translation language and I am writing a simple echo server. I have difficulty getting this to work.

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 result 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, go documentation on the socket API is poor).

Thanks,

Nathan

Answer 1

In your example, buf should have a specific size. You declared it as a slice of length 0.

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); } }