Merge pull request #58 from digitalrebar/send-packets-from-the-samne-…

…address-they-were-recieved-by

Make the server side send packets from the same IP address it recieve…

connection.go

@@ -4,6 +4,10 @@ import (
 	"fmt"
 	"net"
 	"time"
+
+	"golang.org/x/net/ipv6"
+
+	"golang.org/x/net/ipv4"
 )
 
 type connectionError struct {
@@ -32,15 +36,29 @@ type connConnection struct {
 }
 
 type chanConnection struct {
-	sendConn net.PacketConn
-	channel  chan []byte
-	addr     *net.UDPAddr
-	timeout  time.Duration
-	complete chan string
+	sendConn      net.PacketConn
+	channel       chan []byte
+	srcAddr, addr *net.UDPAddr
+	timeout       time.Duration
+	complete      chan string
 }
 
 func (c *chanConnection) sendTo(data []byte, addr *net.UDPAddr) error {
-	_, err := c.sendConn.WriteTo(data, addr)
+	var err error
+	if conn, ok := c.sendConn.(*net.UDPConn); ok {
+		srcAddr := c.srcAddr.IP.To4()
+		var cmm []byte
+		if srcAddr != nil {
+			cm := &ipv4.ControlMessage{Src: srcAddr}
+			cmm = cm.Marshal()
+		} else {
+			cm := &ipv6.ControlMessage{Src: c.srcAddr.IP}
+			cmm = cm.Marshal()
+		}
+		_, _, err = conn.WriteMsgUDP(data, cmm, c.addr)
+	} else {
+		_, err = c.sendConn.WriteTo(data, addr)
+	}
 	return err
 }
 

server.go

@@ -323,12 +323,17 @@ func (s *Server) handlePacket(localAddr net.IP, remoteAddr *net.UDPAddr, buffer
 	if err != nil {
 		return err
 	}
+	listenAddr := &net.UDPAddr{IP: localAddr}
 	switch p := p.(type) {
 	case pWRQ:
 		filename, mode, opts, err := unpackRQ(p)
 		if err != nil {
 			return fmt.Errorf("unpack WRQ: %v", err)
 		}
+		//fmt.Printf("got WRQ (filename=%s, mode=%s, opts=%v)\n", filename, mode, opts)
+		if err != nil {
+			return fmt.Errorf("open transmission: %v", err)
+		}
 		wt := &receiver{
 			send:        make([]byte, datagramLength),
 			receive:     make([]byte, datagramLength),
@@ -346,6 +351,7 @@ func (s *Server) handlePacket(localAddr net.IP, remoteAddr *net.UDPAddr, buffer
 		}
 		if s.singlePort {
 			wt.conn = &chanConnection{
+				srcAddr:  listenAddr,
 				addr:     remoteAddr,
 				channel:  listener,
 				timeout:  s.timeout,
@@ -354,7 +360,7 @@ func (s *Server) handlePacket(localAddr net.IP, remoteAddr *net.UDPAddr, buffer
 			}
 			wt.singlePort = true
 		} else {
-			conn, err := net.ListenUDP("udp", &net.UDPAddr{})
+			conn, err := net.ListenUDP("udp", listenAddr)
 			if err != nil {
 				return err
 			}
@@ -379,6 +385,7 @@ func (s *Server) handlePacket(localAddr net.IP, remoteAddr *net.UDPAddr, buffer
 		if err != nil {
 			return fmt.Errorf("unpack RRQ: %v", err)
 		}
+		//fmt.Printf("got RRQ (filename=%s, mode=%s, opts=%v)\n", filename, mode, opts)
 		rf := &sender{
 			send:        make([]byte, datagramLength),
 			sendA:       senderAnticipate{enabled: false},
@@ -398,14 +405,15 @@ func (s *Server) handlePacket(localAddr net.IP, remoteAddr *net.UDPAddr, buffer
 		}
 		if s.singlePort {
 			rf.conn = &chanConnection{
+				srcAddr:  listenAddr,
 				addr:     remoteAddr,
 				channel:  listener,
 				timeout:  s.timeout,
 				sendConn: s.conn,
 				complete: s.gcCollect,
 			}
 		} else {
-			conn, err := net.ListenUDP("udp", &net.UDPAddr{})
+			conn, err := net.ListenUDP("udp", listenAddr)
 			if err != nil {
 				return err
 			}