Fix nix builds: go dependencies are awful

netforward/packet.go

@@ -0,0 +1,102 @@
+// From https://github.com/goburrow/netforward
+package netforward
+
+import (
+	"io"
+	"log"
+	"net"
+	"sync"
+)
+
+type packetConn struct {
+	conn net.PacketConn
+	addr net.Addr
+}
+
+func (p *packetConn) Write(b []byte) (int, error) {
+	return p.conn.WriteTo(b, p.addr)
+}
+
+type syncConns struct {
+	mu    sync.RWMutex
+	conns map[string]net.Conn
+}
+
+func (f *syncConns) get(addr net.Addr) (net.Conn, bool) {
+	var key string
+	if addr != nil {
+		key = addr.String()
+	}
+	f.mu.RLock()
+	defer f.mu.RUnlock()
+	conn, ok := f.conns[key]
+	return conn, ok
+}
+
+func (f *syncConns) set(addr net.Addr, conn net.Conn) {
+	var key string
+	if addr != nil {
+		key = addr.String()
+	}
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.conns[key] = conn
+}
+
+func (f *syncConns) remove(addr net.Addr) {
+	var key string
+	if addr != nil {
+		key = addr.String()
+	}
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	delete(f.conns, key)
+}
+
+func ForwardPacket(remote Dialer, local net.PacketConn) error {
+	conns := syncConns{
+		conns: make(map[string]net.Conn),
+	}
+	buf := getBuffer()
+	defer releaseBuffer(buf)
+	for {
+		nr, addr, err := local.ReadFrom(buf)
+		if err != nil {
+			return err
+		}
+		remoteConn, ok := conns.get(addr)
+		if !ok {
+			remoteConn, err = remote.Dial()
+			if err != nil {
+				log.Printf("%s: dial failed: %v", addr, err)
+				continue
+			}
+			conns.set(addr, remoteConn)
+			// unix datagram does not have a network addr
+			if addr != nil {
+				go forwardPacket(remoteConn, local, addr, &conns)
+			}
+		}
+		nw, err := remoteConn.Write(buf[:nr])
+		if err != nil {
+			log.Printf("%s: write failed: %v", addr, err)
+			continue
+		}
+		if nr != nw {
+			log.Printf("%s: %v", addr, io.ErrShortWrite)
+		}
+	}
+}
+
+func forwardPacket(remote net.Conn, local net.PacketConn, addr net.Addr, conns *syncConns) {
+	defer remote.Close()
+	defer conns.remove(addr)
+
+	buf := getBuffer()
+	defer releaseBuffer(buf)
+
+	_, err := io.CopyBuffer(&packetConn{local, addr}, remote, buf)
+	if err != nil {
+		log.Printf("%s: %v", addr, err)
+	}
+}