conn: make binds replacable

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

conn/bind_std.go

@@ -0,0 +1,180 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2017-2021 WireGuard LLC. All Rights Reserved.
+ */
+
+package conn
+
+import (
+	"errors"
+	"net"
+	"syscall"
+)
+
+// StdNetBind is meant to be a temporary solution on platforms for which
+// the sticky socket / source caching behavior has not yet been implemented.
+// It uses the Go's net package to implement networking.
+// See LinuxSocketBind for a proper implementation on the Linux platform.
+type StdNetBind struct {
+	ipv4       *net.UDPConn
+	ipv6       *net.UDPConn
+	blackhole4 bool
+	blackhole6 bool
+}
+
+func NewStdNetBind() Bind { return &StdNetBind{} }
+
+type StdNetEndpoint net.UDPAddr
+
+var _ Bind = (*StdNetBind)(nil)
+var _ Endpoint = (*StdNetEndpoint)(nil)
+
+func (*StdNetBind) ParseEndpoint(s string) (Endpoint, error) {
+	addr, err := parseEndpoint(s)
+	return (*StdNetEndpoint)(addr), err
+}
+
+func (*StdNetEndpoint) ClearSrc() {}
+
+func (e *StdNetEndpoint) DstIP() net.IP {
+	return (*net.UDPAddr)(e).IP
+}
+
+func (e *StdNetEndpoint) SrcIP() net.IP {
+	return nil // not supported
+}
+
+func (e *StdNetEndpoint) DstToBytes() []byte {
+	addr := (*net.UDPAddr)(e)
+	out := addr.IP.To4()
+	if out == nil {
+		out = addr.IP
+	}
+	out = append(out, byte(addr.Port&0xff))
+	out = append(out, byte((addr.Port>>8)&0xff))
+	return out
+}
+
+func (e *StdNetEndpoint) DstToString() string {
+	return (*net.UDPAddr)(e).String()
+}
+
+func (e *StdNetEndpoint) SrcToString() string {
+	return ""
+}
+
+func listenNet(network string, port int) (*net.UDPConn, int, error) {
+	conn, err := net.ListenUDP(network, &net.UDPAddr{Port: port})
+	if err != nil {
+		return nil, 0, err
+	}
+
+	// Retrieve port.
+	laddr := conn.LocalAddr()
+	uaddr, err := net.ResolveUDPAddr(
+		laddr.Network(),
+		laddr.String(),
+	)
+	if err != nil {
+		return nil, 0, err
+	}
+	return conn, uaddr.Port, nil
+}
+
+func (bind *StdNetBind) Open(uport uint16) (uint16, error) {
+	var err error
+	var tries int
+
+	if bind.ipv4 != nil || bind.ipv6 != nil {
+		return 0, ErrBindAlreadyOpen
+	}
+
+again:
+	port := int(uport)
+
+	bind.ipv4, port, err = listenNet("udp4", port)
+	if err != nil && !errors.Is(err, syscall.EAFNOSUPPORT) {
+		bind.ipv4 = nil
+		return 0, err
+	}
+
+	bind.ipv6, port, err = listenNet("udp6", port)
+	if uport == 0 && err != nil && errors.Is(err, syscall.EADDRINUSE) && tries < 100 {
+		bind.ipv4.Close()
+		bind.ipv4 = nil
+		bind.ipv6 = nil
+		tries++
+		goto again
+	}
+	if err != nil && !errors.Is(err, syscall.EAFNOSUPPORT) {
+		bind.ipv4.Close()
+		bind.ipv4 = nil
+		bind.ipv6 = nil
+		return 0, err
+	}
+	if bind.ipv4 == nil && bind.ipv6 == nil {
+		return 0, syscall.EAFNOSUPPORT
+	}
+	return uint16(port), nil
+}
+
+func (bind *StdNetBind) Close() error {
+	var err1, err2 error
+	if bind.ipv4 != nil {
+		err1 = bind.ipv4.Close()
+		bind.ipv4 = nil
+	}
+	if bind.ipv6 != nil {
+		err2 = bind.ipv6.Close()
+		bind.ipv6 = nil
+	}
+	if err1 != nil {
+		return err1
+	}
+	return err2
+}
+
+func (bind *StdNetBind) ReceiveIPv4(buff []byte) (int, Endpoint, error) {
+	if bind.ipv4 == nil {
+		return 0, nil, syscall.EAFNOSUPPORT
+	}
+	n, endpoint, err := bind.ipv4.ReadFromUDP(buff)
+	if endpoint != nil {
+		endpoint.IP = endpoint.IP.To4()
+	}
+	return n, (*StdNetEndpoint)(endpoint), err
+}
+
+func (bind *StdNetBind) ReceiveIPv6(buff []byte) (int, Endpoint, error) {
+	if bind.ipv6 == nil {
+		return 0, nil, syscall.EAFNOSUPPORT
+	}
+	n, endpoint, err := bind.ipv6.ReadFromUDP(buff)
+	return n, (*StdNetEndpoint)(endpoint), err
+}
+
+func (bind *StdNetBind) Send(buff []byte, endpoint Endpoint) error {
+	var err error
+	nend, ok := endpoint.(*StdNetEndpoint)
+	if !ok {
+		return ErrWrongEndpointType
+	}
+	if nend.IP.To4() != nil {
+		if bind.ipv4 == nil {
+			return syscall.EAFNOSUPPORT
+		}
+		if bind.blackhole4 {
+			return nil
+		}
+		_, err = bind.ipv4.WriteToUDP(buff, (*net.UDPAddr)(nend))
+	} else {
+		if bind.ipv6 == nil {
+			return syscall.EAFNOSUPPORT
+		}
+		if bind.blackhole6 {
+			return nil
+		}
+		_, err = bind.ipv6.WriteToUDP(buff, (*net.UDPAddr)(nend))
+	}
+	return err
+}