Simon Zimmermann

I had some time to research the net-package in Go today. Here is what I found. It’s really not meant to be a tutorial or anything like that. It’s just my notes.

net-package is used to abstract some of the lower level socket things. This allows us to create more platform independent programs. A small illustration of a comparision of C and Go can be like this:

C	Go
socket()	…
bind()	…
listen()	Listen(network, addr)
accept()	Listen().Accept()

Listen(network, addr) returns a Listener interface used for stream-oriented protocol network: “tcp”, “tcp4”, “tcp6”, or “unix”. Listen() will take care of calling the socket() and bind() syscalls and set the correct parameters depending on what kind of network you set-up.

For example creating a tcp server we can call Listen("tcp", "127.0.0.1") which in net.go will run through a switch case and call the appropriate network Listen function(ListenTCP(), ListenUnix()). ListenTCP, for instance, will then create a internetSocket with all correct settings in order: syscall.SOCKSTREAM, syscall.AF_INET(IPv4), syscall.Sockaddr, syscall.Socket, syscall.Bind and a non-blocking I/O to syscall.Accept using the thread safe syscall.ForkLock (see l.fd.accept() in fd.go). Thats why leave out the syscall socket() and bind() in Go when using the net-package.

Listen(net, laddr string) (l Listener, err os.Error)

type Listener interface {
        Accept() (c Conn, err os.Error);
        Close() os.Error;
        Addr() Addr;    // Listener's network address
 }
func Accept(fd int) (nfd int, sa Sockaddr, errno int)

http- and websocket[1]-packages are making things even simpler. An example found in pkg.http.server.go for creating a trivial server:

 
package main

import (
    "http";
    "io";
)
// hello world, the web server
func HelloServer(c http.Conn, req http.Request) {
    io.WriteString(c, "hello, world!n");
}
func main() {
    http.Handle("/hello", http.HandlerFunc(HelloServer));
    err := http.ListenAndServe(":12345", nil);
    if err != nil {
        panic("ListenAndServe: ", err.String())
    }
}

[1] websocket package is per date only available in the development trunk.