net: add Source field to OpError

Not only by network, transport-layer intermediaries but by
virtualization stuff in a node, it is hard to identify the root cause of
weird faults without information of packet flows after disaster
happened.

This change adds Source field to OpError to be able to represent a
5-tuple of internet transport protocols for helping dealing with
complicated systems.

Also clarifies the usage of Source and Addr fields.

Updates #4856.

Change-Id: I96a523fe391ed14406bfb21604c461d4aac2fa19
Reviewed-on: https://go-review.googlesource.com/9231
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/dial.go

diff --git a/src/net/dial.go b/src/net/dial.go
index feca759..4f0c6cb 100644
--- a/src/net/dial.go
+++ b/src/net/dial.go
@@ -161,7 +161,7 @@
 func (d *Dialer) Dial(network, address string) (Conn, error) {
 	addrs, err := resolveAddrList("dial", network, address, d.deadline())
 	if err != nil {
-		return nil, &OpError{Op: "dial", Net: network, Addr: nil, Err: err}
+		return nil, &OpError{Op: "dial", Net: network, Source: nil, Addr: nil, Err: err}
 	}
 	var dialer func(deadline time.Time) (Conn, error)
 	if d.DualStack && network == "tcp" {
@@ -235,7 +235,7 @@
 // the destination address.
 func dialSingle(net, addr string, la, ra Addr, deadline time.Time) (c Conn, err error) {
 	if la != nil && la.Network() != ra.Network() {
-		return nil, &OpError{Op: "dial", Net: net, Addr: ra, Err: errors.New("mismatched local address type " + la.Network())}
+		return nil, &OpError{Op: "dial", Net: net, Source: la, Addr: ra, Err: errors.New("mismatched local address type " + la.Network())}
 	}
 	switch ra := ra.(type) {
 	case *TCPAddr:
@@ -251,7 +251,7 @@
 		la, _ := la.(*UnixAddr)
 		c, err = dialUnix(net, la, ra, deadline)
 	default:
-		return nil, &OpError{Op: "dial", Net: net, Addr: ra, Err: &AddrError{Err: "unexpected address type", Addr: addr}}
+		return nil, &OpError{Op: "dial", Net: net, Source: la, Addr: ra, Err: &AddrError{Err: "unexpected address type", Addr: addr}}
 	}
 	if err != nil {
 		return nil, err // c is non-nil interface containing nil pointer
@@ -266,7 +266,7 @@
 func Listen(net, laddr string) (Listener, error) {
 	addrs, err := resolveAddrList("listen", net, laddr, noDeadline)
 	if err != nil {
-		return nil, &OpError{Op: "listen", Net: net, Addr: nil, Err: err}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: nil, Err: err}
 	}
 	var l Listener
 	switch la := addrs.first(isIPv4).(type) {
@@ -275,7 +275,7 @@
 	case *UnixAddr:
 		l, err = ListenUnix(net, la)
 	default:
-		return nil, &OpError{Op: "listen", Net: net, Addr: la, Err: &AddrError{Err: "unexpected address type", Addr: laddr}}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: la, Err: &AddrError{Err: "unexpected address type", Addr: laddr}}
 	}
 	if err != nil {
 		return nil, err // l is non-nil interface containing nil pointer
@@ -290,7 +290,7 @@
 func ListenPacket(net, laddr string) (PacketConn, error) {
 	addrs, err := resolveAddrList("listen", net, laddr, noDeadline)
 	if err != nil {
-		return nil, &OpError{Op: "listen", Net: net, Addr: nil, Err: err}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: nil, Err: err}
 	}
 	var l PacketConn
 	switch la := addrs.first(isIPv4).(type) {
@@ -301,7 +301,7 @@
 	case *UnixAddr:
 		l, err = ListenUnixgram(net, la)
 	default:
-		return nil, &OpError{Op: "listen", Net: net, Addr: la, Err: &AddrError{Err: "unexpected address type", Addr: laddr}}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: la, Err: &AddrError{Err: "unexpected address type", Addr: laddr}}
 	}
 	if err != nil {
 		return nil, err // l is non-nil interface containing nil pointer

src/net/dial_gen.go

diff --git a/src/net/dial_gen.go b/src/net/dial_gen.go
index 3816844..a628f71 100644
--- a/src/net/dial_gen.go
+++ b/src/net/dial_gen.go
@@ -17,7 +17,7 @@
 	}
 	timeout := deadline.Sub(time.Now())
 	if timeout <= 0 {
-		return nil, &OpError{Op: "dial", Net: net, Addr: ra, Err: errTimeout}
+		return nil, &OpError{Op: "dial", Net: net, Source: nil, Addr: ra, Err: errTimeout}
 	}
 	t := time.NewTimer(timeout)
 	defer t.Stop()
@@ -33,7 +33,7 @@
 	}()
 	select {
 	case <-t.C:
-		return nil, &OpError{Op: "dial", Net: net, Addr: ra, Err: errTimeout}
+		return nil, &OpError{Op: "dial", Net: net, Source: nil, Addr: ra, Err: errTimeout}
 	case racer := <-ch:
 		return racer.Conn, racer.error
 	}

src/net/error_test.go

diff --git a/src/net/error_test.go b/src/net/error_test.go
index 03c646c..75b125d 100644
--- a/src/net/error_test.go
+++ b/src/net/error_test.go
@@ -32,34 +32,13 @@
 	if e.Net == "" {
 		return fmt.Errorf("OpError.Net is empty: %v", e)
 	}
-	switch addr := e.Addr.(type) {
-	case *TCPAddr:
-		if addr == nil {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
-		}
-	case *UDPAddr:
-		if addr == nil {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
-		}
-	case *IPAddr:
-		if addr == nil {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
-		}
-	case *IPNet:
-		if addr == nil {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
-		}
-	case *UnixAddr:
-		if addr == nil {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
-		}
-	case *pipeAddr:
-		if addr == nil {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
-		}
-	case fileAddr:
-		if addr == "" {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
+	for _, addr := range []Addr{e.Source, e.Addr} {
+		if addr != nil {
+			switch addr.(type) {
+			case *TCPAddr, *UDPAddr, *IPAddr, *IPNet, *UnixAddr, *pipeAddr, fileAddr:
+			default:
+				return fmt.Errorf("OpError.Source or Addr is unknown type: %T, %v", addr, e)
+			}
 		}
 	}
 	if e.Err == nil {

src/net/file.go

diff --git a/src/net/file.go b/src/net/file.go
index be93e2c..1aad477 100644
--- a/src/net/file.go
+++ b/src/net/file.go
@@ -18,7 +18,7 @@
 func FileConn(f *os.File) (c Conn, err error) {
 	c, err = fileConn(f)
 	if err != nil {
-		err = &OpError{Op: "file", Net: "file+net", Addr: fileAddr(f.Name()), Err: err}
+		err = &OpError{Op: "file", Net: "file+net", Source: nil, Addr: fileAddr(f.Name()), Err: err}
 	}
 	return
 }
@@ -30,7 +30,7 @@
 func FileListener(f *os.File) (ln Listener, err error) {
 	ln, err = fileListener(f)
 	if err != nil {
-		err = &OpError{Op: "file", Net: "file+net", Addr: fileAddr(f.Name()), Err: err}
+		err = &OpError{Op: "file", Net: "file+net", Source: nil, Addr: fileAddr(f.Name()), Err: err}
 	}
 	return
 }
@@ -42,7 +42,7 @@
 func FilePacketConn(f *os.File) (c PacketConn, err error) {
 	c, err = filePacketConn(f)
 	if err != nil {
-		err = &OpError{Op: "file", Net: "file+net", Addr: fileAddr(f.Name()), Err: err}
+		err = &OpError{Op: "file", Net: "file+net", Source: nil, Addr: fileAddr(f.Name()), Err: err}
 	}
 	return
 }

src/net/interface.go

diff --git a/src/net/interface.go b/src/net/interface.go
index e6d874f..9c7b5da 100644
--- a/src/net/interface.go
+++ b/src/net/interface.go
@@ -62,11 +62,11 @@
 // Addrs returns interface addresses for a specific interface.
 func (ifi *Interface) Addrs() ([]Addr, error) {
 	if ifi == nil {
-		return nil, &OpError{Op: "route", Net: "ip+net", Addr: nil, Err: errInvalidInterface}
+		return nil, &OpError{Op: "route", Net: "ip+net", Source: nil, Addr: nil, Err: errInvalidInterface}
 	}
 	ifat, err := interfaceAddrTable(ifi)
 	if err != nil {
-		err = &OpError{Op: "route", Net: "ip+net", Addr: nil, Err: err}
+		err = &OpError{Op: "route", Net: "ip+net", Source: nil, Addr: nil, Err: err}
 	}
 	return ifat, err
 }
@@ -75,11 +75,11 @@
 // a specific interface.
 func (ifi *Interface) MulticastAddrs() ([]Addr, error) {
 	if ifi == nil {
-		return nil, &OpError{Op: "route", Net: "ip+net", Addr: nil, Err: errInvalidInterface}
+		return nil, &OpError{Op: "route", Net: "ip+net", Source: nil, Addr: nil, Err: errInvalidInterface}
 	}
 	ifat, err := interfaceMulticastAddrTable(ifi)
 	if err != nil {
-		err = &OpError{Op: "route", Net: "ip+net", Addr: nil, Err: err}
+		err = &OpError{Op: "route", Net: "ip+net", Source: nil, Addr: nil, Err: err}
 	}
 	return ifat, err
 }
@@ -88,7 +88,7 @@
 func Interfaces() ([]Interface, error) {
 	ift, err := interfaceTable(0)
 	if err != nil {
-		err = &OpError{Op: "route", Net: "ip+net", Addr: nil, Err: err}
+		err = &OpError{Op: "route", Net: "ip+net", Source: nil, Addr: nil, Err: err}
 	}
 	return ift, err
 }
@@ -98,7 +98,7 @@
 func InterfaceAddrs() ([]Addr, error) {
 	ifat, err := interfaceAddrTable(nil)
 	if err != nil {
-		err = &OpError{Op: "route", Net: "ip+net", Addr: nil, Err: err}
+		err = &OpError{Op: "route", Net: "ip+net", Source: nil, Addr: nil, Err: err}
 	}
 	return ifat, err
 }
@@ -106,15 +106,15 @@
 // InterfaceByIndex returns the interface specified by index.
 func InterfaceByIndex(index int) (*Interface, error) {
 	if index <= 0 {
-		return nil, &OpError{Op: "route", Net: "ip+net", Addr: nil, Err: errInvalidInterfaceIndex}
+		return nil, &OpError{Op: "route", Net: "ip+net", Source: nil, Addr: nil, Err: errInvalidInterfaceIndex}
 	}
 	ift, err := interfaceTable(index)
 	if err != nil {
-		return nil, &OpError{Op: "route", Net: "ip+net", Addr: nil, Err: err}
+		return nil, &OpError{Op: "route", Net: "ip+net", Source: nil, Addr: nil, Err: err}
 	}
 	ifi, err := interfaceByIndex(ift, index)
 	if err != nil {
-		err = &OpError{Op: "route", Net: "ip+net", Addr: nil, Err: err}
+		err = &OpError{Op: "route", Net: "ip+net", Source: nil, Addr: nil, Err: err}
 	}
 	return ifi, err
 }
@@ -131,16 +131,16 @@
 // InterfaceByName returns the interface specified by name.
 func InterfaceByName(name string) (*Interface, error) {
 	if name == "" {
-		return nil, &OpError{Op: "route", Net: "ip+net", Addr: nil, Err: errInvalidInterfaceName}
+		return nil, &OpError{Op: "route", Net: "ip+net", Source: nil, Addr: nil, Err: errInvalidInterfaceName}
 	}
 	ift, err := interfaceTable(0)
 	if err != nil {
-		return nil, &OpError{Op: "route", Net: "ip+net", Addr: nil, Err: err}
+		return nil, &OpError{Op: "route", Net: "ip+net", Source: nil, Addr: nil, Err: err}
 	}
 	for _, ifi := range ift {
 		if name == ifi.Name {
 			return &ifi, nil
 		}
 	}
-	return nil, &OpError{Op: "route", Net: "ip+net", Addr: nil, Err: errNoSuchInterface}
+	return nil, &OpError{Op: "route", Net: "ip+net", Source: nil, Addr: nil, Err: errNoSuchInterface}
 }

src/net/iprawsock_plan9.go

diff --git a/src/net/iprawsock_plan9.go b/src/net/iprawsock_plan9.go
index a3d8649..0796290 100644
--- a/src/net/iprawsock_plan9.go
+++ b/src/net/iprawsock_plan9.go
@@ -23,12 +23,12 @@
 // Timeout() == true after a fixed time limit; see SetDeadline and
 // SetReadDeadline.
 func (c *IPConn) ReadFromIP(b []byte) (int, *IPAddr, error) {
-	return 0, nil, &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: syscall.EPLAN9}
+	return 0, nil, &OpError{Op: "read", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: syscall.EPLAN9}
 }
 
 // ReadFrom implements the PacketConn ReadFrom method.
 func (c *IPConn) ReadFrom(b []byte) (int, Addr, error) {
-	return 0, nil, &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: syscall.EPLAN9}
+	return 0, nil, &OpError{Op: "read", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: syscall.EPLAN9}
 }
 
 // ReadMsgIP reads a packet from c, copying the payload into b and the
@@ -36,7 +36,7 @@
 // bytes copied into b, the number of bytes copied into oob, the flags
 // that were set on the packet and the source address of the packet.
 func (c *IPConn) ReadMsgIP(b, oob []byte) (n, oobn, flags int, addr *IPAddr, err error) {
-	return 0, 0, 0, nil, &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: syscall.EPLAN9}
+	return 0, 0, 0, nil, &OpError{Op: "read", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: syscall.EPLAN9}
 }
 
 // WriteToIP writes an IP packet to addr via c, copying the payload
@@ -47,19 +47,19 @@
 // SetWriteDeadline.  On packet-oriented connections, write timeouts
 // are rare.
 func (c *IPConn) WriteToIP(b []byte, addr *IPAddr) (int, error) {
-	return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: syscall.EPLAN9}
+	return 0, &OpError{Op: "write", Net: c.fd.dir, Source: c.fd.laddr, Addr: addr, Err: syscall.EPLAN9}
 }
 
 // WriteTo implements the PacketConn WriteTo method.
 func (c *IPConn) WriteTo(b []byte, addr Addr) (int, error) {
-	return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: syscall.EPLAN9}
+	return 0, &OpError{Op: "write", Net: c.fd.dir, Source: c.fd.laddr, Addr: addr, Err: syscall.EPLAN9}
 }
 
 // WriteMsgIP writes a packet to addr via c, copying the payload from
 // b and the associated out-of-band data from oob.  It returns the
 // number of payload and out-of-band bytes written.
 func (c *IPConn) WriteMsgIP(b, oob []byte, addr *IPAddr) (n, oobn int, err error) {
-	return 0, 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: syscall.EPLAN9}
+	return 0, 0, &OpError{Op: "write", Net: c.fd.dir, Source: c.fd.laddr, Addr: addr, Err: syscall.EPLAN9}
 }
 
 // DialIP connects to the remote address raddr on the network protocol
@@ -70,7 +70,7 @@
 }
 
 func dialIP(netProto string, laddr, raddr *IPAddr, deadline time.Time) (*IPConn, error) {
-	return nil, syscall.EPLAN9
+	return nil, &OpError{Op: "dial", Net: netProto, Source: laddr, Addr: raddr, Err: syscall.EPLAN9}
 }
 
 // ListenIP listens for incoming IP packets addressed to the local
@@ -78,5 +78,5 @@
 // methods can be used to receive and send IP packets with per-packet
 // addressing.
 func ListenIP(netProto string, laddr *IPAddr) (*IPConn, error) {
-	return nil, syscall.EPLAN9
+	return nil, &OpError{Op: "listen", Net: netProto, Source: nil, Addr: laddr, Err: syscall.EPLAN9}
 }

src/net/iprawsock_posix.go

diff --git a/src/net/iprawsock_posix.go b/src/net/iprawsock_posix.go
index 26ef05f..1102823 100644
--- a/src/net/iprawsock_posix.go
+++ b/src/net/iprawsock_posix.go
@@ -81,7 +81,7 @@
 		addr = &IPAddr{IP: sa.Addr[0:], Zone: zoneToString(int(sa.ZoneId))}
 	}
 	if err != nil {
-		err = &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return n, addr, err
 }
@@ -130,7 +130,7 @@
 		addr = &IPAddr{IP: sa.Addr[0:], Zone: zoneToString(int(sa.ZoneId))}
 	}
 	if err != nil {
-		err = &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return
 }
@@ -147,18 +147,18 @@
 		return 0, syscall.EINVAL
 	}
 	if c.fd.isConnected {
-		return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: ErrWriteToConnected}
+		return 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: ErrWriteToConnected}
 	}
 	if addr == nil {
-		return 0, &OpError{Op: "write", Net: c.fd.net, Addr: nil, Err: errMissingAddress}
+		return 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: errMissingAddress}
 	}
 	sa, err := addr.sockaddr(c.fd.family)
 	if err != nil {
-		return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: err}
+		return 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: err}
 	}
 	n, err := c.fd.writeTo(b, sa)
 	if err != nil {
-		err = &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: err}
+		err = &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: err}
 	}
 	return n, err
 }
@@ -170,7 +170,7 @@
 	}
 	a, ok := addr.(*IPAddr)
 	if !ok {
-		return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: syscall.EINVAL}
+		return 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: syscall.EINVAL}
 	}
 	return c.WriteToIP(b, a)
 }
@@ -183,19 +183,19 @@
 		return 0, 0, syscall.EINVAL
 	}
 	if c.fd.isConnected {
-		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: ErrWriteToConnected}
+		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: ErrWriteToConnected}
 	}
 	if addr == nil {
-		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Addr: nil, Err: errMissingAddress}
+		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: errMissingAddress}
 	}
 	var sa syscall.Sockaddr
 	sa, err = addr.sockaddr(c.fd.family)
 	if err != nil {
-		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: err}
+		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: err}
 	}
 	n, oobn, err = c.fd.writeMsg(b, oob, sa)
 	if err != nil {
-		err = &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: err}
+		err = &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: err}
 	}
 	return
 }
@@ -210,19 +210,19 @@
 func dialIP(netProto string, laddr, raddr *IPAddr, deadline time.Time) (*IPConn, error) {
 	net, proto, err := parseNetwork(netProto)
 	if err != nil {
-		return nil, &OpError{Op: "dial", Net: netProto, Addr: raddr, Err: err}
+		return nil, &OpError{Op: "dial", Net: netProto, Source: laddr, Addr: raddr, Err: err}
 	}
 	switch net {
 	case "ip", "ip4", "ip6":
 	default:
-		return nil, &OpError{Op: "dial", Net: netProto, Addr: raddr, Err: UnknownNetworkError(netProto)}
+		return nil, &OpError{Op: "dial", Net: netProto, Source: laddr, Addr: raddr, Err: UnknownNetworkError(netProto)}
 	}
 	if raddr == nil {
-		return nil, &OpError{Op: "dial", Net: netProto, Addr: nil, Err: errMissingAddress}
+		return nil, &OpError{Op: "dial", Net: netProto, Source: laddr, Addr: raddr, Err: errMissingAddress}
 	}
 	fd, err := internetSocket(net, laddr, raddr, deadline, syscall.SOCK_RAW, proto, "dial")
 	if err != nil {
-		return nil, &OpError{Op: "dial", Net: netProto, Addr: raddr, Err: err}
+		return nil, &OpError{Op: "dial", Net: netProto, Source: laddr, Addr: raddr, Err: err}
 	}
 	return newIPConn(fd), nil
 }
@@ -234,16 +234,16 @@
 func ListenIP(netProto string, laddr *IPAddr) (*IPConn, error) {
 	net, proto, err := parseNetwork(netProto)
 	if err != nil {
-		return nil, &OpError{Op: "dial", Net: netProto, Addr: laddr, Err: err}
+		return nil, &OpError{Op: "dial", Net: netProto, Source: nil, Addr: laddr, Err: err}
 	}
 	switch net {
 	case "ip", "ip4", "ip6":
 	default:
-		return nil, &OpError{Op: "listen", Net: netProto, Addr: laddr, Err: UnknownNetworkError(netProto)}
+		return nil, &OpError{Op: "listen", Net: netProto, Source: nil, Addr: laddr, Err: UnknownNetworkError(netProto)}
 	}
 	fd, err := internetSocket(net, laddr, nil, noDeadline, syscall.SOCK_RAW, proto, "listen")
 	if err != nil {
-		return nil, &OpError{Op: "listen", Net: netProto, Addr: laddr, Err: err}
+		return nil, &OpError{Op: "listen", Net: netProto, Source: nil, Addr: laddr, Err: err}
 	}
 	return newIPConn(fd), nil
 }

src/net/ipsock_plan9.go

diff --git a/src/net/ipsock_plan9.go b/src/net/ipsock_plan9.go
index 1c2932d..11b6b32 100644
--- a/src/net/ipsock_plan9.go
+++ b/src/net/ipsock_plan9.go
@@ -152,23 +152,23 @@
 	defer func() { netErr(err) }()
 	f, dest, proto, name, err := startPlan9(net, raddr)
 	if err != nil {
-		return nil, &OpError{"dial", net, raddr, err}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: err}
 	}
 	_, err = f.WriteString("connect " + dest)
 	if err != nil {
 		f.Close()
-		return nil, &OpError{"dial", f.Name(), raddr, err}
+		return nil, &OpError{Op: "dial", Net: f.Name(), Source: laddr, Addr: raddr, Err: err}
 	}
 	data, err := os.OpenFile(netdir+"/"+proto+"/"+name+"/data", os.O_RDWR, 0)
 	if err != nil {
 		f.Close()
-		return nil, &OpError{"dial", net, raddr, err}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: err}
 	}
 	laddr, err = readPlan9Addr(proto, netdir+"/"+proto+"/"+name+"/local")
 	if err != nil {
 		data.Close()
 		f.Close()
-		return nil, &OpError{"dial", proto, raddr, err}
+		return nil, &OpError{Op: "dial", Net: proto, Source: laddr, Addr: raddr, Err: err}
 	}
 	return newFD(proto, name, f, data, laddr, raddr)
 }
@@ -177,52 +177,52 @@
 	defer func() { netErr(err) }()
 	f, dest, proto, name, err := startPlan9(net, laddr)
 	if err != nil {
-		return nil, &OpError{"listen", net, laddr, err}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: err}
 	}
 	_, err = f.WriteString("announce " + dest)
 	if err != nil {
 		f.Close()
-		return nil, &OpError{"announce", proto, laddr, err}
+		return nil, &OpError{Op: "announce", Net: proto, Source: nil, Addr: laddr, Err: err}
 	}
 	laddr, err = readPlan9Addr(proto, netdir+"/"+proto+"/"+name+"/local")
 	if err != nil {
 		f.Close()
-		return nil, &OpError{Op: "listen", Net: net, Err: err}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: err}
 	}
 	return newFD(proto, name, f, nil, laddr, nil)
 }
 
-func (l *netFD) netFD() (*netFD, error) {
-	return newFD(l.net, l.n, l.ctl, l.data, l.laddr, l.raddr)
+func (fd *netFD) netFD() (*netFD, error) {
+	return newFD(fd.net, fd.n, fd.ctl, fd.data, fd.laddr, fd.raddr)
 }
 
-func (l *netFD) acceptPlan9() (fd *netFD, err error) {
+func (fd *netFD) acceptPlan9() (nfd *netFD, err error) {
 	defer func() { netErr(err) }()
-	if err := l.readLock(); err != nil {
+	if err := fd.readLock(); err != nil {
 		return nil, err
 	}
-	defer l.readUnlock()
-	f, err := os.Open(l.dir + "/listen")
+	defer fd.readUnlock()
+	f, err := os.Open(fd.dir + "/listen")
 	if err != nil {
-		return nil, &OpError{"accept", l.dir + "/listen", l.laddr, err}
+		return nil, &OpError{Op: "accept", Net: fd.dir + "/listen", Source: nil, Addr: fd.laddr, Err: err}
 	}
 	var buf [16]byte
 	n, err := f.Read(buf[:])
 	if err != nil {
 		f.Close()
-		return nil, &OpError{"accept", l.dir + "/listen", l.laddr, err}
+		return nil, &OpError{Op: "accept", Net: fd.dir + "/listen", Source: nil, Addr: fd.laddr, Err: err}
 	}
 	name := string(buf[:n])
-	data, err := os.OpenFile(netdir+"/"+l.net+"/"+name+"/data", os.O_RDWR, 0)
+	data, err := os.OpenFile(netdir+"/"+fd.net+"/"+name+"/data", os.O_RDWR, 0)
 	if err != nil {
 		f.Close()
-		return nil, &OpError{"accept", l.net, l.laddr, err}
+		return nil, &OpError{Op: "accept", Net: fd.net, Source: nil, Addr: fd.laddr, Err: err}
 	}
-	raddr, err := readPlan9Addr(l.net, netdir+"/"+l.net+"/"+name+"/remote")
+	raddr, err := readPlan9Addr(fd.net, netdir+"/"+fd.net+"/"+name+"/remote")
 	if err != nil {
 		data.Close()
 		f.Close()
-		return nil, &OpError{"accept", l.net, l.laddr, err}
+		return nil, &OpError{Op: "accept", Net: fd.net, Source: nil, Addr: fd.laddr, Err: err}
 	}
-	return newFD(l.net, name, f, data, l.laddr, raddr)
+	return newFD(fd.net, name, f, data, fd.laddr, raddr)
 }

src/net/net.go

diff --git a/src/net/net.go b/src/net/net.go
index 41fc081..955d018 100644
--- a/src/net/net.go
+++ b/src/net/net.go
@@ -123,12 +123,7 @@
 	}
 	n, err := c.fd.Read(b)
 	if err != nil && err != io.EOF {
-		err = &OpError{Op: "read", Net: c.fd.net, Err: err}
-		if c.fd.raddr != nil {
-			err.(*OpError).Addr = c.fd.raddr
-		} else {
-			err.(*OpError).Addr = c.fd.laddr // for unconnected-mode sockets
-		}
+		err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return n, err
 }
@@ -140,12 +135,7 @@
 	}
 	n, err := c.fd.Write(b)
 	if err != nil {
-		err = &OpError{Op: "write", Net: c.fd.net, Err: err}
-		if c.fd.raddr != nil {
-			err.(*OpError).Addr = c.fd.raddr
-		} else {
-			err.(*OpError).Addr = c.fd.laddr // for unconnected-mode sockets
-		}
+		err = &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return n, err
 }
@@ -157,12 +147,7 @@
 	}
 	err := c.fd.Close()
 	if err != nil {
-		err = &OpError{Op: "close", Net: c.fd.net, Err: err}
-		if c.fd.raddr != nil {
-			err.(*OpError).Addr = c.fd.raddr
-		} else {
-			err.(*OpError).Addr = c.fd.laddr // for unconnected-mode sockets
-		}
+		err = &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return err
 }
@@ -193,7 +178,7 @@
 		return syscall.EINVAL
 	}
 	if err := c.fd.setDeadline(t); err != nil {
-		return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: c.fd.net, Source: nil, Addr: c.fd.laddr, Err: err}
 	}
 	return nil
 }
@@ -204,7 +189,7 @@
 		return syscall.EINVAL
 	}
 	if err := c.fd.setReadDeadline(t); err != nil {
-		return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: c.fd.net, Source: nil, Addr: c.fd.laddr, Err: err}
 	}
 	return nil
 }
@@ -215,7 +200,7 @@
 		return syscall.EINVAL
 	}
 	if err := c.fd.setWriteDeadline(t); err != nil {
-		return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: c.fd.net, Source: nil, Addr: c.fd.laddr, Err: err}
 	}
 	return nil
 }
@@ -227,7 +212,7 @@
 		return syscall.EINVAL
 	}
 	if err := setReadBuffer(c.fd, bytes); err != nil {
-		return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: c.fd.net, Source: nil, Addr: c.fd.laddr, Err: err}
 	}
 	return nil
 }
@@ -239,7 +224,7 @@
 		return syscall.EINVAL
 	}
 	if err := setWriteBuffer(c.fd, bytes); err != nil {
-		return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: c.fd.net, Source: nil, Addr: c.fd.laddr, Err: err}
 	}
 	return nil
 }
@@ -254,7 +239,7 @@
 func (c *conn) File() (f *os.File, err error) {
 	f, err = c.fd.dup()
 	if err != nil {
-		err = &OpError{Op: "file", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		err = &OpError{Op: "file", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return
 }
@@ -352,7 +337,17 @@
 	// such as "tcp" or "udp6".
 	Net string
 
-	// Addr is the network address on which this error occurred.
+	// For operations involving a remote network connection, like
+	// Dial, Read, or Write, Source is the corresponding local
+	// network address.
+	Source Addr
+
+	// Addr is the network address for which this error occurred.
+	// For local operations, like Listen or SetDeadline, Addr is
+	// the address of the local endpoint being manipulated.
+	// For operations involving a remote network connection, like
+	// Dial, Read, or Write, Addr is the remote address of that
+	// connection.
 	Addr Addr
 
 	// Err is the error that occurred during the operation.
@@ -367,8 +362,16 @@
 	if e.Net != "" {
 		s += " " + e.Net
 	}
+	if e.Source != nil {
+		s += " " + e.Source.String()
+	}
 	if e.Addr != nil {
-		s += " " + e.Addr.String()
+		if e.Source != nil {
+			s += "->"
+		} else {
+			s += " "
+		}
+		s += e.Addr.String()
 	}
 	s += ": " + e.Err.Error()
 	return s

src/net/pipe.go

diff --git a/src/net/pipe.go b/src/net/pipe.go
index f1a2eca..5fc830b 100644
--- a/src/net/pipe.go
+++ b/src/net/pipe.go
@@ -55,13 +55,13 @@
 }
 
 func (p *pipe) SetDeadline(t time.Time) error {
-	return errors.New("net.Pipe does not support deadlines")
+	return &OpError{Op: "set", Net: "pipe", Source: nil, Addr: nil, Err: errors.New("deadline not supported")}
 }
 
 func (p *pipe) SetReadDeadline(t time.Time) error {
-	return errors.New("net.Pipe does not support deadlines")
+	return &OpError{Op: "set", Net: "pipe", Source: nil, Addr: nil, Err: errors.New("deadline not supported")}
 }
 
 func (p *pipe) SetWriteDeadline(t time.Time) error {
-	return errors.New("net.Pipe does not support deadlines")
+	return &OpError{Op: "set", Net: "pipe", Source: nil, Addr: nil, Err: errors.New("deadline not supported")}
 }

src/net/tcpsock_plan9.go

diff --git a/src/net/tcpsock_plan9.go b/src/net/tcpsock_plan9.go
index a0b2630..bc3f8fc 100644
--- a/src/net/tcpsock_plan9.go
+++ b/src/net/tcpsock_plan9.go
@@ -25,7 +25,7 @@
 func (c *TCPConn) ReadFrom(r io.Reader) (int64, error) {
 	n, err := genericReadFrom(c, r)
 	if err != nil && err != io.EOF {
-		err = &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.raddr, Err: err}
+		err = &OpError{Op: "read", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return n, err
 }
@@ -38,7 +38,7 @@
 	}
 	err := c.fd.closeRead()
 	if err != nil {
-		err = &OpError{Op: "close", Net: c.fd.net, Addr: c.fd.raddr, Err: err}
+		err = &OpError{Op: "close", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return err
 }
@@ -51,7 +51,7 @@
 	}
 	err := c.fd.closeWrite()
 	if err != nil {
-		err = &OpError{Op: "close", Net: c.fd.net, Addr: c.fd.raddr, Err: err}
+		err = &OpError{Op: "close", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return err
 }
@@ -69,7 +69,7 @@
 // some operating systems after sec seconds have elapsed any remaining
 // unsent data may be discarded.
 func (c *TCPConn) SetLinger(sec int) error {
-	return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: syscall.EPLAN9}
+	return &OpError{Op: "set", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: syscall.EPLAN9}
 }
 
 // SetKeepAlive sets whether the operating system should send
@@ -79,7 +79,7 @@
 		return syscall.EPLAN9
 	}
 	if err := setKeepAlive(c.fd, keepalive); err != nil {
-		return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return nil
 }
@@ -90,7 +90,7 @@
 		return syscall.EPLAN9
 	}
 	if err := setKeepAlivePeriod(c.fd, d); err != nil {
-		return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return nil
 }
@@ -100,7 +100,7 @@
 // algorithm).  The default is true (no delay), meaning that data is
 // sent as soon as possible after a Write.
 func (c *TCPConn) SetNoDelay(noDelay bool) error {
-	return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: syscall.EPLAN9}
+	return &OpError{Op: "set", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: syscall.EPLAN9}
 }
 
 // DialTCP connects to the remote address raddr on the network net,
@@ -117,10 +117,10 @@
 	switch net {
 	case "tcp", "tcp4", "tcp6":
 	default:
-		return nil, &OpError{"dial", net, raddr, UnknownNetworkError(net)}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: UnknownNetworkError(net)}
 	}
 	if raddr == nil {
-		return nil, &OpError{"dial", net, nil, errMissingAddress}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: errMissingAddress}
 	}
 	fd, err := dialPlan9(net, laddr, raddr)
 	if err != nil {
@@ -169,11 +169,11 @@
 	}
 	if _, err := l.fd.ctl.WriteString("hangup"); err != nil {
 		l.fd.ctl.Close()
-		return &OpError{Op: "close", Net: l.fd.net, Addr: l.fd.laddr, Err: err}
+		return &OpError{Op: "close", Net: l.fd.dir, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	err := l.fd.ctl.Close()
 	if err != nil {
-		err = &OpError{Op: "close", Net: l.fd.net, Addr: l.fd.laddr, Err: err}
+		err = &OpError{Op: "close", Net: l.fd.dir, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return err
 }
@@ -190,7 +190,7 @@
 		return syscall.EINVAL
 	}
 	if err := l.fd.setDeadline(t); err != nil {
-		return &OpError{Op: "set", Net: l.fd.net, Addr: l.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: l.fd.dir, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return nil
 }
@@ -205,7 +205,7 @@
 func (l *TCPListener) File() (f *os.File, err error) {
 	f, err = l.dup()
 	if err != nil {
-		err = &OpError{Op: "file", Net: l.fd.net, Addr: l.fd.laddr, Err: err}
+		err = &OpError{Op: "file", Net: l.fd.dir, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return
 }
@@ -218,7 +218,7 @@
 	switch net {
 	case "tcp", "tcp4", "tcp6":
 	default:
-		return nil, &OpError{"listen", net, laddr, UnknownNetworkError(net)}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: UnknownNetworkError(net)}
 	}
 	if laddr == nil {
 		laddr = &TCPAddr{}

src/net/tcpsock_posix.go

diff --git a/src/net/tcpsock_posix.go b/src/net/tcpsock_posix.go
index 62f9ee1..1f43521 100644
--- a/src/net/tcpsock_posix.go
+++ b/src/net/tcpsock_posix.go
@@ -61,13 +61,13 @@
 func (c *TCPConn) ReadFrom(r io.Reader) (int64, error) {
 	if n, err, handled := sendFile(c.fd, r); handled {
 		if err != nil && err != io.EOF {
-			err = &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.raddr, Err: err}
+			err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 		}
 		return n, err
 	}
 	n, err := genericReadFrom(c, r)
 	if err != nil && err != io.EOF {
-		err = &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.raddr, Err: err}
+		err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return n, err
 }
@@ -80,7 +80,7 @@
 	}
 	err := c.fd.closeRead()
 	if err != nil {
-		err = &OpError{Op: "close", Net: c.fd.net, Addr: c.fd.raddr, Err: err}
+		err = &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return err
 }
@@ -93,7 +93,7 @@
 	}
 	err := c.fd.closeWrite()
 	if err != nil {
-		err = &OpError{Op: "close", Net: c.fd.net, Addr: c.fd.raddr, Err: err}
+		err = &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return err
 }
@@ -115,7 +115,7 @@
 		return syscall.EINVAL
 	}
 	if err := setLinger(c.fd, sec); err != nil {
-		return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return nil
 }
@@ -127,7 +127,7 @@
 		return syscall.EINVAL
 	}
 	if err := setKeepAlive(c.fd, keepalive); err != nil {
-		return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return nil
 }
@@ -138,7 +138,7 @@
 		return syscall.EINVAL
 	}
 	if err := setKeepAlivePeriod(c.fd, d); err != nil {
-		return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return nil
 }
@@ -152,7 +152,7 @@
 		return syscall.EINVAL
 	}
 	if err := setNoDelay(c.fd, noDelay); err != nil {
-		return &OpError{Op: "set", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return nil
 }
@@ -164,10 +164,10 @@
 	switch net {
 	case "tcp", "tcp4", "tcp6":
 	default:
-		return nil, &OpError{Op: "dial", Net: net, Addr: raddr, Err: UnknownNetworkError(net)}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: UnknownNetworkError(net)}
 	}
 	if raddr == nil {
-		return nil, &OpError{Op: "dial", Net: net, Addr: nil, Err: errMissingAddress}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: errMissingAddress}
 	}
 	return dialTCP(net, laddr, raddr, noDeadline)
 }
@@ -207,7 +207,7 @@
 	}
 
 	if err != nil {
-		return nil, &OpError{Op: "dial", Net: net, Addr: raddr, Err: err}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: err}
 	}
 	return newTCPConn(fd), nil
 }
@@ -253,7 +253,7 @@
 	}
 	fd, err := l.fd.accept()
 	if err != nil {
-		return nil, &OpError{Op: "accept", Net: l.fd.net, Addr: l.fd.laddr, Err: err}
+		return nil, &OpError{Op: "accept", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return newTCPConn(fd), nil
 }
@@ -276,7 +276,7 @@
 	}
 	err := l.fd.Close()
 	if err != nil {
-		err = &OpError{Op: "close", Net: l.fd.net, Addr: l.fd.laddr, Err: err}
+		err = &OpError{Op: "close", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return err
 }
@@ -293,7 +293,7 @@
 		return syscall.EINVAL
 	}
 	if err := l.fd.setDeadline(t); err != nil {
-		return &OpError{Op: "set", Net: l.fd.net, Addr: l.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return nil
 }
@@ -308,7 +308,7 @@
 func (l *TCPListener) File() (f *os.File, err error) {
 	f, err = l.fd.dup()
 	if err != nil {
-		err = &OpError{Op: "file", Net: l.fd.net, Addr: l.fd.laddr, Err: err}
+		err = &OpError{Op: "file", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return
 }
@@ -321,14 +321,14 @@
 	switch net {
 	case "tcp", "tcp4", "tcp6":
 	default:
-		return nil, &OpError{Op: "listen", Net: net, Addr: laddr, Err: UnknownNetworkError(net)}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: UnknownNetworkError(net)}
 	}
 	if laddr == nil {
 		laddr = &TCPAddr{}
 	}
 	fd, err := internetSocket(net, laddr, nil, noDeadline, syscall.SOCK_STREAM, 0, "listen")
 	if err != nil {
-		return nil, &OpError{Op: "listen", Net: net, Addr: laddr, Err: err}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: err}
 	}
 	return &TCPListener{fd}, nil
 }

src/net/udpsock_plan9.go

diff --git a/src/net/udpsock_plan9.go b/src/net/udpsock_plan9.go
index 8acbb20..949f666 100644
--- a/src/net/udpsock_plan9.go
+++ b/src/net/udpsock_plan9.go
@@ -33,10 +33,10 @@
 	buf := make([]byte, udpHeaderSize+len(b))
 	m, err := c.fd.data.Read(buf)
 	if err != nil {
-		return 0, nil, &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		return 0, nil, &OpError{Op: "read", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	if m < udpHeaderSize {
-		return 0, nil, &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: errors.New("short read reading UDP header")}
+		return 0, nil, &OpError{Op: "read", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: errors.New("short read reading UDP header")}
 	}
 	buf = buf[:m]
 
@@ -59,7 +59,7 @@
 // flags that were set on the packet and the source address of the
 // packet.
 func (c *UDPConn) ReadMsgUDP(b, oob []byte) (n, oobn, flags int, addr *UDPAddr, err error) {
-	return 0, 0, 0, nil, &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: syscall.EPLAN9}
+	return 0, 0, 0, nil, &OpError{Op: "read", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: syscall.EPLAN9}
 }
 
 // WriteToUDP writes a UDP packet to addr via c, copying the payload
@@ -74,7 +74,7 @@
 		return 0, syscall.EINVAL
 	}
 	if addr == nil {
-		return 0, &OpError{Op: "write", Net: c.fd.dir, Addr: nil, Err: errMissingAddress}
+		return 0, &OpError{Op: "write", Net: c.fd.dir, Source: c.fd.laddr, Addr: addr, Err: errMissingAddress}
 	}
 	h := new(udpHeader)
 	h.raddr = addr.IP.To16()
@@ -87,7 +87,7 @@
 	i := copy(buf, h.Bytes())
 	copy(buf[i:], b)
 	if _, err := c.fd.data.Write(buf); err != nil {
-		return 0, &OpError{Op: "write", Net: c.fd.dir, Addr: addr, Err: err}
+		return 0, &OpError{Op: "write", Net: c.fd.dir, Source: c.fd.laddr, Addr: addr, Err: err}
 	}
 	return len(b), nil
 }
@@ -99,7 +99,7 @@
 	}
 	a, ok := addr.(*UDPAddr)
 	if !ok {
-		return 0, &OpError{Op: "write", Net: c.fd.dir, Addr: addr, Err: syscall.EINVAL}
+		return 0, &OpError{Op: "write", Net: c.fd.dir, Source: c.fd.laddr, Addr: addr, Err: syscall.EINVAL}
 	}
 	return c.WriteToUDP(b, a)
 }
@@ -110,7 +110,7 @@
 // out-of-band data is copied from oob.  It returns the number of
 // payload and out-of-band bytes written.
 func (c *UDPConn) WriteMsgUDP(b, oob []byte, addr *UDPAddr) (n, oobn int, err error) {
-	return 0, 0, &OpError{Op: "write", Net: c.fd.dir, Addr: addr, Err: syscall.EPLAN9}
+	return 0, 0, &OpError{Op: "write", Net: c.fd.dir, Source: c.fd.laddr, Addr: addr, Err: syscall.EPLAN9}
 }
 
 // DialUDP connects to the remote address raddr on the network net,
@@ -127,10 +127,10 @@
 	switch net {
 	case "udp", "udp4", "udp6":
 	default:
-		return nil, UnknownNetworkError(net)
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: UnknownNetworkError(net)}
 	}
 	if raddr == nil {
-		return nil, &OpError{"dial", net, nil, errMissingAddress}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: errMissingAddress}
 	}
 	fd, err := dialPlan9(net, laddr, raddr)
 	if err != nil {
@@ -178,7 +178,7 @@
 	switch net {
 	case "udp", "udp4", "udp6":
 	default:
-		return nil, UnknownNetworkError(net)
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: UnknownNetworkError(net)}
 	}
 	if laddr == nil {
 		laddr = &UDPAddr{}
@@ -189,11 +189,11 @@
 	}
 	_, err = l.ctl.WriteString("headers")
 	if err != nil {
-		return nil, err
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: err}
 	}
 	l.data, err = os.OpenFile(l.dir+"/data", os.O_RDWR, 0)
 	if err != nil {
-		return nil, err
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: err}
 	}
 	fd, err := l.netFD()
 	return newUDPConn(fd), err
@@ -204,5 +204,5 @@
 // interface to join.  ListenMulticastUDP uses default multicast
 // interface if ifi is nil.
 func ListenMulticastUDP(net string, ifi *Interface, gaddr *UDPAddr) (*UDPConn, error) {
-	return nil, syscall.EPLAN9
+	return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: gaddr, Err: syscall.EPLAN9}
 }

src/net/udpsock_posix.go

diff --git a/src/net/udpsock_posix.go b/src/net/udpsock_posix.go
index c4bd0bc..2e43068 100644
--- a/src/net/udpsock_posix.go
+++ b/src/net/udpsock_posix.go
@@ -66,7 +66,7 @@
 		addr = &UDPAddr{IP: sa.Addr[0:], Port: sa.Port, Zone: zoneToString(int(sa.ZoneId))}
 	}
 	if err != nil {
-		err = &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return n, addr, err
 }
@@ -101,7 +101,7 @@
 		addr = &UDPAddr{IP: sa.Addr[0:], Port: sa.Port, Zone: zoneToString(int(sa.ZoneId))}
 	}
 	if err != nil {
-		err = &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return
 }
@@ -118,18 +118,18 @@
 		return 0, syscall.EINVAL
 	}
 	if c.fd.isConnected {
-		return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: ErrWriteToConnected}
+		return 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: ErrWriteToConnected}
 	}
 	if addr == nil {
-		return 0, &OpError{Op: "write", Net: c.fd.net, Addr: nil, Err: errMissingAddress}
+		return 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: errMissingAddress}
 	}
 	sa, err := addr.sockaddr(c.fd.family)
 	if err != nil {
-		return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: err}
+		return 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: err}
 	}
 	n, err := c.fd.writeTo(b, sa)
 	if err != nil {
-		err = &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: err}
+		err = &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: err}
 	}
 	return n, err
 }
@@ -141,7 +141,7 @@
 	}
 	a, ok := addr.(*UDPAddr)
 	if !ok {
-		return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: syscall.EINVAL}
+		return 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: syscall.EINVAL}
 	}
 	return c.WriteToUDP(b, a)
 }
@@ -156,19 +156,19 @@
 		return 0, 0, syscall.EINVAL
 	}
 	if c.fd.isConnected && addr != nil {
-		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: ErrWriteToConnected}
+		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: ErrWriteToConnected}
 	}
 	if !c.fd.isConnected && addr == nil {
-		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Addr: nil, Err: errMissingAddress}
+		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: errMissingAddress}
 	}
 	var sa syscall.Sockaddr
 	sa, err = addr.sockaddr(c.fd.family)
 	if err != nil {
-		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: err}
+		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: err}
 	}
 	n, oobn, err = c.fd.writeMsg(b, oob, sa)
 	if err != nil {
-		err = &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: err}
+		err = &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: err}
 	}
 	return
 }
@@ -180,10 +180,10 @@
 	switch net {
 	case "udp", "udp4", "udp6":
 	default:
-		return nil, &OpError{Op: "dial", Net: net, Addr: raddr, Err: UnknownNetworkError(net)}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: UnknownNetworkError(net)}
 	}
 	if raddr == nil {
-		return nil, &OpError{Op: "dial", Net: net, Addr: nil, Err: errMissingAddress}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: errMissingAddress}
 	}
 	return dialUDP(net, laddr, raddr, noDeadline)
 }
@@ -191,7 +191,7 @@
 func dialUDP(net string, laddr, raddr *UDPAddr, deadline time.Time) (*UDPConn, error) {
 	fd, err := internetSocket(net, laddr, raddr, deadline, syscall.SOCK_DGRAM, 0, "dial")
 	if err != nil {
-		return nil, &OpError{Op: "dial", Net: net, Addr: raddr, Err: err}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: err}
 	}
 	return newUDPConn(fd), nil
 }
@@ -207,14 +207,14 @@
 	switch net {
 	case "udp", "udp4", "udp6":
 	default:
-		return nil, &OpError{Op: "listen", Net: net, Addr: laddr, Err: UnknownNetworkError(net)}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: UnknownNetworkError(net)}
 	}
 	if laddr == nil {
 		laddr = &UDPAddr{}
 	}
 	fd, err := internetSocket(net, laddr, nil, noDeadline, syscall.SOCK_DGRAM, 0, "listen")
 	if err != nil {
-		return nil, &OpError{Op: "listen", Net: net, Addr: laddr, Err: err}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: err}
 	}
 	return newUDPConn(fd), nil
 }
@@ -227,25 +227,25 @@
 	switch net {
 	case "udp", "udp4", "udp6":
 	default:
-		return nil, &OpError{Op: "listen", Net: net, Addr: gaddr, Err: UnknownNetworkError(net)}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: gaddr, Err: UnknownNetworkError(net)}
 	}
 	if gaddr == nil || gaddr.IP == nil {
-		return nil, &OpError{Op: "listen", Net: net, Addr: nil, Err: errMissingAddress}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: gaddr, Err: errMissingAddress}
 	}
 	fd, err := internetSocket(net, gaddr, nil, noDeadline, syscall.SOCK_DGRAM, 0, "listen")
 	if err != nil {
-		return nil, &OpError{Op: "listen", Net: net, Addr: gaddr, Err: err}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: gaddr, Err: err}
 	}
 	c := newUDPConn(fd)
 	if ip4 := gaddr.IP.To4(); ip4 != nil {
 		if err := listenIPv4MulticastUDP(c, ifi, ip4); err != nil {
 			c.Close()
-			return nil, &OpError{Op: "listen", Net: net, Addr: &IPAddr{IP: ip4}, Err: err}
+			return nil, &OpError{Op: "listen", Net: net, Source: c.fd.laddr, Addr: &IPAddr{IP: ip4}, Err: err}
 		}
 	} else {
 		if err := listenIPv6MulticastUDP(c, ifi, gaddr.IP); err != nil {
 			c.Close()
-			return nil, &OpError{Op: "listen", Net: net, Addr: &IPAddr{IP: gaddr.IP}, Err: err}
+			return nil, &OpError{Op: "listen", Net: net, Source: c.fd.laddr, Addr: &IPAddr{IP: gaddr.IP}, Err: err}
 		}
 	}
 	return c, nil

src/net/unixsock_plan9.go

diff --git a/src/net/unixsock_plan9.go b/src/net/unixsock_plan9.go
index a2fb862..c31907b 100644
--- a/src/net/unixsock_plan9.go
+++ b/src/net/unixsock_plan9.go
@@ -24,12 +24,12 @@
 // Timeout() == true after a fixed time limit; see SetDeadline and
 // SetReadDeadline.
 func (c *UnixConn) ReadFromUnix(b []byte) (int, *UnixAddr, error) {
-	return 0, nil, &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: syscall.EPLAN9}
+	return 0, nil, &OpError{Op: "read", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: syscall.EPLAN9}
 }
 
 // ReadFrom implements the PacketConn ReadFrom method.
 func (c *UnixConn) ReadFrom(b []byte) (int, Addr, error) {
-	return 0, nil, &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: syscall.EPLAN9}
+	return 0, nil, &OpError{Op: "read", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: syscall.EPLAN9}
 }
 
 // ReadMsgUnix reads a packet from c, copying the payload into b and
@@ -37,7 +37,7 @@
 // bytes copied into b, the number of bytes copied into oob, the flags
 // that were set on the packet, and the source address of the packet.
 func (c *UnixConn) ReadMsgUnix(b, oob []byte) (n, oobn, flags int, addr *UnixAddr, err error) {
-	return 0, 0, 0, nil, &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: syscall.EPLAN9}
+	return 0, 0, 0, nil, &OpError{Op: "read", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: syscall.EPLAN9}
 }
 
 // WriteToUnix writes a packet to addr via c, copying the payload from b.
@@ -47,31 +47,31 @@
 // SetWriteDeadline.  On packet-oriented connections, write timeouts
 // are rare.
 func (c *UnixConn) WriteToUnix(b []byte, addr *UnixAddr) (int, error) {
-	return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: syscall.EPLAN9}
+	return 0, &OpError{Op: "write", Net: c.fd.dir, Source: c.fd.laddr, Addr: addr, Err: syscall.EPLAN9}
 }
 
 // WriteTo implements the PacketConn WriteTo method.
 func (c *UnixConn) WriteTo(b []byte, addr Addr) (int, error) {
-	return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: syscall.EPLAN9}
+	return 0, &OpError{Op: "write", Net: c.fd.dir, Source: c.fd.laddr, Addr: addr, Err: syscall.EPLAN9}
 }
 
 // WriteMsgUnix writes a packet to addr via c, copying the payload
 // from b and the associated out-of-band data from oob.  It returns
 // the number of payload and out-of-band bytes written.
 func (c *UnixConn) WriteMsgUnix(b, oob []byte, addr *UnixAddr) (n, oobn int, err error) {
-	return 0, 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: syscall.EPLAN9}
+	return 0, 0, &OpError{Op: "write", Net: c.fd.dir, Source: c.fd.laddr, Addr: addr, Err: syscall.EPLAN9}
 }
 
 // CloseRead shuts down the reading side of the Unix domain connection.
 // Most callers should just use Close.
 func (c *UnixConn) CloseRead() error {
-	return &OpError{Op: "close", Net: c.fd.net, Addr: c.fd.raddr, Err: syscall.EPLAN9}
+	return &OpError{Op: "close", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: syscall.EPLAN9}
 }
 
 // CloseWrite shuts down the writing side of the Unix domain connection.
 // Most callers should just use Close.
 func (c *UnixConn) CloseWrite() error {
-	return &OpError{Op: "close", Net: c.fd.net, Addr: c.fd.raddr, Err: syscall.EPLAN9}
+	return &OpError{Op: "close", Net: c.fd.dir, Source: c.fd.laddr, Addr: c.fd.raddr, Err: syscall.EPLAN9}
 }
 
 // DialUnix connects to the remote address raddr on the network net,
@@ -82,36 +82,38 @@
 }
 
 func dialUnix(net string, laddr, raddr *UnixAddr, deadline time.Time) (*UnixConn, error) {
-	return nil, syscall.EPLAN9
+	return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: syscall.EPLAN9}
 }
 
 // UnixListener is a Unix domain socket listener.  Clients should
 // typically use variables of type Listener instead of assuming Unix
 // domain sockets.
-type UnixListener struct{}
+type UnixListener struct {
+	fd *netFD
+}
 
 // ListenUnix announces on the Unix domain socket laddr and returns a
 // Unix listener.  The network net must be "unix" or "unixpacket".
 func ListenUnix(net string, laddr *UnixAddr) (*UnixListener, error) {
-	return nil, syscall.EPLAN9
+	return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: syscall.EPLAN9}
 }
 
 // AcceptUnix accepts the next incoming call and returns the new
 // connection.
 func (l *UnixListener) AcceptUnix() (*UnixConn, error) {
-	return nil, &OpError{Op: "accept", Net: "<nil>", Addr: nil, Err: syscall.EPLAN9}
+	return nil, &OpError{Op: "accept", Net: l.fd.dir, Source: nil, Addr: l.fd.laddr, Err: syscall.EPLAN9}
 }
 
 // Accept implements the Accept method in the Listener interface; it
 // waits for the next call and returns a generic Conn.
 func (l *UnixListener) Accept() (Conn, error) {
-	return nil, &OpError{Op: "accept", Net: "<nil>", Addr: nil, Err: syscall.EPLAN9}
+	return nil, &OpError{Op: "accept", Net: l.fd.dir, Source: nil, Addr: l.fd.laddr, Err: syscall.EPLAN9}
 }
 
 // Close stops listening on the Unix address.  Already accepted
 // connections are not closed.
 func (l *UnixListener) Close() error {
-	return &OpError{Op: "close", Net: "<nil>", Addr: nil, Err: syscall.EPLAN9}
+	return &OpError{Op: "close", Net: l.fd.dir, Source: nil, Addr: l.fd.laddr, Err: syscall.EPLAN9}
 }
 
 // Addr returns the listener's network address.
@@ -122,7 +124,7 @@
 // SetDeadline sets the deadline associated with the listener.
 // A zero time value disables the deadline.
 func (l *UnixListener) SetDeadline(t time.Time) error {
-	return &OpError{Op: "set", Net: "<nil>", Addr: nil, Err: syscall.EPLAN9}
+	return &OpError{Op: "set", Net: l.fd.dir, Source: nil, Addr: l.fd.laddr, Err: syscall.EPLAN9}
 }
 
 // File returns a copy of the underlying os.File, set to blocking
@@ -133,7 +135,7 @@
 // connection's.  Attempting to change properties of the original
 // using this duplicate may or may not have the desired effect.
 func (l *UnixListener) File() (*os.File, error) {
-	return nil, &OpError{Op: "file", Net: "<nil>", Addr: nil, Err: syscall.EPLAN9}
+	return nil, &OpError{Op: "file", Net: l.fd.dir, Source: nil, Addr: l.fd.laddr, Err: syscall.EPLAN9}
 }
 
 // ListenUnixgram listens for incoming Unix datagram packets addressed
@@ -141,5 +143,5 @@
 // The returned connection's ReadFrom and WriteTo methods can be used
 // to receive and send packets with per-packet addressing.
 func ListenUnixgram(net string, laddr *UnixAddr) (*UnixConn, error) {
-	return nil, syscall.EPLAN9
+	return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: syscall.EPLAN9}
 }

src/net/unixsock_posix.go

diff --git a/src/net/unixsock_posix.go b/src/net/unixsock_posix.go
index ed5ffd3..005d248 100644
--- a/src/net/unixsock_posix.go
+++ b/src/net/unixsock_posix.go
@@ -126,7 +126,7 @@
 		}
 	}
 	if err != nil {
-		err = &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return n, addr, err
 }
@@ -159,7 +159,7 @@
 		}
 	}
 	if err != nil {
-		err = &OpError{Op: "read", Net: c.fd.net, Addr: c.fd.laddr, Err: err}
+		err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return
 }
@@ -175,18 +175,18 @@
 		return 0, syscall.EINVAL
 	}
 	if c.fd.isConnected {
-		return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: ErrWriteToConnected}
+		return 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: ErrWriteToConnected}
 	}
 	if addr == nil {
-		return 0, &OpError{Op: "write", Net: c.fd.net, Addr: nil, Err: errMissingAddress}
+		return 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: errMissingAddress}
 	}
 	if addr.Net != sotypeToNet(c.fd.sotype) {
-		return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: syscall.EAFNOSUPPORT}
+		return 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: syscall.EAFNOSUPPORT}
 	}
 	sa := &syscall.SockaddrUnix{Name: addr.Name}
 	n, err := c.fd.writeTo(b, sa)
 	if err != nil {
-		err = &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: err}
+		err = &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: err}
 	}
 	return n, err
 }
@@ -198,7 +198,7 @@
 	}
 	a, ok := addr.(*UnixAddr)
 	if !ok {
-		return 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: syscall.EINVAL}
+		return 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: syscall.EINVAL}
 	}
 	return c.WriteToUnix(b, a)
 }
@@ -211,18 +211,18 @@
 		return 0, 0, syscall.EINVAL
 	}
 	if c.fd.sotype == syscall.SOCK_DGRAM && c.fd.isConnected {
-		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: ErrWriteToConnected}
+		return 0, 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: ErrWriteToConnected}
 	}
 	var sa syscall.Sockaddr
 	if addr != nil {
 		if addr.Net != sotypeToNet(c.fd.sotype) {
-			return 0, 0, &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: syscall.EAFNOSUPPORT}
+			return 0, 0, &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: syscall.EAFNOSUPPORT}
 		}
 		sa = &syscall.SockaddrUnix{Name: addr.Name}
 	}
 	n, oobn, err = c.fd.writeMsg(b, oob, sa)
 	if err != nil {
-		err = &OpError{Op: "write", Net: c.fd.net, Addr: addr, Err: err}
+		err = &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addr, Err: err}
 	}
 	return
 }
@@ -235,7 +235,7 @@
 	}
 	err := c.fd.closeRead()
 	if err != nil {
-		err = &OpError{Op: "close", Net: c.fd.net, Addr: c.fd.raddr, Err: err}
+		err = &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return err
 }
@@ -248,7 +248,7 @@
 	}
 	err := c.fd.closeWrite()
 	if err != nil {
-		err = &OpError{Op: "close", Net: c.fd.net, Addr: c.fd.raddr, Err: err}
+		err = &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return err
 }
@@ -260,7 +260,7 @@
 	switch net {
 	case "unix", "unixgram", "unixpacket":
 	default:
-		return nil, &OpError{Op: "dial", Net: net, Addr: raddr, Err: UnknownNetworkError(net)}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: UnknownNetworkError(net)}
 	}
 	return dialUnix(net, laddr, raddr, noDeadline)
 }
@@ -268,7 +268,7 @@
 func dialUnix(net string, laddr, raddr *UnixAddr, deadline time.Time) (*UnixConn, error) {
 	fd, err := unixSocket(net, laddr, raddr, "dial", deadline)
 	if err != nil {
-		return nil, &OpError{Op: "dial", Net: net, Addr: raddr, Err: err}
+		return nil, &OpError{Op: "dial", Net: net, Source: laddr, Addr: raddr, Err: err}
 	}
 	return newUnixConn(fd), nil
 }
@@ -287,16 +287,16 @@
 	switch net {
 	case "unix", "unixpacket":
 	default:
-		return nil, &OpError{Op: "listen", Net: net, Addr: laddr, Err: UnknownNetworkError(net)}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: UnknownNetworkError(net)}
 	}
 	if laddr == nil {
-		return nil, &OpError{Op: "listen", Net: net, Addr: nil, Err: errMissingAddress}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: errMissingAddress}
 	}
 	fd, err := unixSocket(net, laddr, nil, "listen", noDeadline)
 	if err != nil {
-		return nil, &OpError{Op: "listen", Net: net, Addr: laddr, Err: err}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: err}
 	}
-	return &UnixListener{fd, fd.laddr.String()}, nil
+	return &UnixListener{fd: fd, path: fd.laddr.String()}, nil
 }
 
 // AcceptUnix accepts the next incoming call and returns the new
@@ -307,7 +307,7 @@
 	}
 	fd, err := l.fd.accept()
 	if err != nil {
-		return nil, &OpError{Op: "accept", Net: l.fd.net, Addr: l.fd.laddr, Err: err}
+		return nil, &OpError{Op: "accept", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return newUnixConn(fd), nil
 }
@@ -344,7 +344,7 @@
 	}
 	err := l.fd.Close()
 	if err != nil {
-		err = &OpError{Op: "close", Net: l.fd.net, Addr: l.fd.laddr, Err: err}
+		err = &OpError{Op: "close", Net: l.fd.net, Source: l.fd.laddr, Addr: l.fd.raddr, Err: err}
 	}
 	return err
 }
@@ -361,7 +361,7 @@
 		return syscall.EINVAL
 	}
 	if err := l.fd.setDeadline(t); err != nil {
-		return &OpError{Op: "set", Net: l.fd.net, Addr: l.fd.laddr, Err: err}
+		return &OpError{Op: "set", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return nil
 }
@@ -376,7 +376,7 @@
 func (l *UnixListener) File() (f *os.File, err error) {
 	f, err = l.fd.dup()
 	if err != nil {
-		err = &OpError{Op: "file", Net: l.fd.net, Addr: l.fd.laddr, Err: err}
+		err = &OpError{Op: "file", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return
 }
@@ -389,14 +389,14 @@
 	switch net {
 	case "unixgram":
 	default:
-		return nil, &OpError{Op: "listen", Net: net, Addr: laddr, Err: UnknownNetworkError(net)}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: UnknownNetworkError(net)}
 	}
 	if laddr == nil {
-		return nil, &OpError{Op: "listen", Net: net, Addr: nil, Err: errMissingAddress}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: errMissingAddress}
 	}
 	fd, err := unixSocket(net, laddr, nil, "listen", noDeadline)
 	if err != nil {
-		return nil, &OpError{Op: "listen", Net: net, Addr: laddr, Err: err}
+		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: err}
 	}
 	return newUnixConn(fd), nil
 }