Introduce net package

Introduces a new net package, which defines networking interfaces used
throughout the pion/dtls code base, as well as utilities to help
consumers convert standard library net types into pion/dtls compatible
ones.

Signed-off-by: Daniel Mangum <georgedanielmangum@gmail.com>

pkg/net/net.go

@@ -0,0 +1,108 @@
+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+// Package net defines packet-oriented primitives that are compatible with net
+// in the standard library.
+package net
+
+import (
+	"net"
+	"time"
+)
+
+// A PacketListener is the same as net.Listener but returns a net.PacketConn on
+// Accept() rather than a net.Conn.
+//
+// Multiple goroutines may invoke methods on a PacketListener simultaneously.
+type PacketListener interface {
+	// Accept waits for and returns the next connection to the listener.
+	Accept() (net.PacketConn, net.Addr, 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() net.Addr
+}
+
+// PacketListenerFromListener converts a net.Listener into a
+// dtlsnet.PacketListener.
+func PacketListenerFromListener(l net.Listener) PacketListener {
+	return &packetListenerWrapper{
+		l: l,
+	}
+}
+
+// packetListenerWrapper wraps a net.Listener and implements
+// dtlsnet.PacketListener.
+type packetListenerWrapper struct {
+	l net.Listener
+}
+
+// Accept calls Accept on the underlying net.Listener and converts the returned
+// net.Conn into a net.PacketConn.
+func (p *packetListenerWrapper) Accept() (net.PacketConn, net.Addr, error) {
+	c, err := p.l.Accept()
+	if err != nil {
+		return PacketConnFromConn(c), nil, err
+	}
+	return PacketConnFromConn(c), c.RemoteAddr(), nil
+}
+
+// Close closes the underlying net.Listener.
+func (p *packetListenerWrapper) Close() error {
+	return p.l.Close()
+}
+
+// Addr returns the address of the underlying net.Listener.
+func (p *packetListenerWrapper) Addr() net.Addr {
+	return p.l.Addr()
+}
+
+// PacketConnFromConn converts a net.Conn into a net.PacketConn.
+func PacketConnFromConn(conn net.Conn) net.PacketConn {
+	return &packetConnWrapper{conn}
+}
+
+// packetConnWrapper wraps a net.Conn and implements net.PacketConn.
+type packetConnWrapper struct {
+	conn net.Conn
+}
+
+// ReadFrom reads from the underlying net.Conn and returns its remote address.
+func (p *packetConnWrapper) ReadFrom(b []byte) (int, net.Addr, error) {
+	n, err := p.conn.Read(b)
+	return n, p.conn.RemoteAddr(), err
+}
+
+// WriteTo writes to the underlying net.Conn.
+func (p *packetConnWrapper) WriteTo(b []byte, _ net.Addr) (int, error) {
+	n, err := p.conn.Write(b)
+	return n, err
+}
+
+// Close closes the underlying net.Conn.
+func (p *packetConnWrapper) Close() error {
+	return p.conn.Close()
+}
+
+// LocalAddr returns the local address of the underlying net.Conn.
+func (p *packetConnWrapper) LocalAddr() net.Addr {
+	return p.conn.LocalAddr()
+}
+
+// SetDeadline sets the deadline on the underlying net.Conn.
+func (p *packetConnWrapper) SetDeadline(t time.Time) error {
+	return p.conn.SetDeadline(t)
+}
+
+// SetReadDeadline sets the read deadline on the underlying net.Conn.
+func (p *packetConnWrapper) SetReadDeadline(t time.Time) error {
+	return p.conn.SetReadDeadline(t)
+}
+
+// SetWriteDeadline sets the write deadline on the underlying net.Conn.
+func (p *packetConnWrapper) SetWriteDeadline(t time.Time) error {
+	return p.conn.SetWriteDeadline(t)
+}