Go net

The following are my notes on the Go net package (https://golang.org/pkg/net/). Much of these are director quotes from the official docs.

The net package provides access to low-level networking primitives. However, many projects only need the basic Dial, Listen, and Accept functions, and the associated Conn and Listener interfaces.

The Dial function connects to a server:

package main
import ("bufio"; "fmt"; "log"; "net")
func main() {
	conn, err := net.Dial("tcp", "golang.org:80")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Fprintf(conn, "GET / HTTP/1.0\r\n\r\n")
	status, err := bufio.NewReader(conn).ReadString('\n')
	fmt.Printf(string(status))
}

The Listen function creates servers:

package main
import ("log"; "net")
func main() {
	ln, err := net.Listen("tcp", ":8080")
	if err != nil {
		log.Fatal(err)
	}
	for {
		conn, err := ln.Accept()
		if err != nil {
			log.Println(err)
		}
		go func(c net.Conn) {
			defer c.Close()
			c.Write([]byte("Hello.\n"))
		}(conn)
	}
}

(Hit the above like nc 127.0.0.1 8080.)

Conn

Conn is an interface for generic stream-oriented network connections. (Comments abbreviated below. See the docs for full comments.)

type Conn interface {
	// Read data from the connection.
	Read(b []byte) (n int, err error)
	// Write data to the connection.
	Write(b []byte) (n int, err error)
	// Close the connection, unbocking any blocked r/w operations.
	Close() error
	// LocalAddr returns the local network address.
	LocalAddr() Addr
	// RemoteAddr returns the remote network address.
	RemoteAddr() Addr
	// SetDeadline for reads and writes.
	SetDeadline(t time.Time) error
	// SetReadDeadline sets the deadline for Read calls.
	SetReadDeadline(t time.Time) error
	// SetWriteDeadline sets the deadline for Write calls.
	SetWriteDeadline(t time.Time) error
}

Listener

A Listener is an interface for generic stream-oriented protocols.

type Listener interface {
		// Accept waits for and returns the next connection to the listener.
		Accept() (Conn, error)
		// Close closes the listener.
		// Any blocked Accept operations will be unblocked and return errors.
		Close() error
		// Addr returns the listener's network address.
		Addr() Addr
}

PacketConn and IPConn

Although, Conn and Listener are stream-oriented, the net package also offers packet-oriented tools.

PacketConn is a generic packet-oriented network connection. (Comments abbreviated below. See the docs for full comments.)

type PacketConn interface {
	// ReadFrom reads a packet from the connection,
	// copying the payload into b. It returns the number of
	// bytes copied into b and the return address on the packet.
	ReadFrom(b []byte) (n int, addr Addr, err error)
	// WriteTo writes a packet with payload b to addr.
	WriteTo(b []byte, addr Addr) (n int, err error)
	// Close closes the connection.
	Close() error
	// LocalAddr returns the local network address.
	LocalAddr() Addr
	// SetDeadline sets read and write deadlines for a connection.
	SetDeadline(t time.Time) error
	// SetReadDeadline sets the deadline for future ReadFrom calls.
	SetReadDeadline(t time.Time) error
	// SetWriteDeadline sets the deadline for future WriteTo calls.
	SetWriteDeadline(t time.Time) error
}

IPConn implements the Conn and PacketConn interfaces for IP network connections. IPConn offers DialIP and ListenIP functions.

The net package offers still more specialized tools, like UDPConn.

Mon Oct 23 17:11:11 EDT 2017