net: update documentation on Dial{TCP,UDP,IP,Unix}

This change clarifies the documentation on Dial{TCP,UDP,IP,Unix} to
avoid unnecessary confusion about how the arguments for the connection
setup functions are used to make connections.

Change-Id: I2e378182948fbe221f6ae786ab55e77ae90c3f3b
Reviewed-on: https://go-review.googlesource.com/34877Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/iprawsock.go

@@ -200,13 +200,17 @@ func (c *IPConn) WriteMsgIP(b, oob []byte, addr *IPAddr) (n, oobn int, err error
 
 func newIPConn(fd *netFD) *IPConn { return &IPConn{conn{fd}} }
 
-// DialIP connects to the remote address raddr on the network protocol
-// netProto, which must be "ip", "ip4", or "ip6" followed by a colon
-// and a protocol number or name.
-func DialIP(netProto string, laddr, raddr *IPAddr) (*IPConn, error) {
-	c, err := dialIP(context.Background(), netProto, laddr, raddr)
+// DialIP acts like Dial for IP networks.
+//
+// The network must be an IP network name; see func Dial for details.
+//
+// If laddr is nil, a local address is automatically chosen.
+// If the IP field of raddr is nil or an unspecified IP address, the
+// local system is assumed.
+func DialIP(network string, laddr, raddr *IPAddr) (*IPConn, error) {
+	c, err := dialIP(context.Background(), network, laddr, raddr)
 	if err != nil {
-		return nil, &OpError{Op: "dial", Net: netProto, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
+		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
 	}
 	return c, nil
 }

src/net/tcpsock.go

@@ -190,21 +190,25 @@ func newTCPConn(fd *netFD) *TCPConn {
 	return c
 }
 
-// DialTCP connects to the remote address raddr on the network net,
-// which must be "tcp", "tcp4", or "tcp6".  If laddr is not nil, it is
-// used as the local address for the connection.
-func DialTCP(net string, laddr, raddr *TCPAddr) (*TCPConn, error) {
-	switch net {
+// DialTCP acts like Dial for TCP networks.
+//
+// The network must be a TCP network name; see func Dial for details.
+//
+// If laddr is nil, a local address is automatically chosen.
+// If the IP field of raddr is nil or an unspecified IP address, the
+// local system is assumed.
+func DialTCP(network string, laddr, raddr *TCPAddr) (*TCPConn, error) {
+	switch network {
 	case "tcp", "tcp4", "tcp6":
 	default:
-		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(net)}
+		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(network)}
 	}
 	if raddr == nil {
-		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
+		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
 	}
-	c, err := dialTCP(context.Background(), net, laddr, raddr)
+	c, err := dialTCP(context.Background(), network, laddr, raddr)
 	if err != nil {
-		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
+		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
 	}
 	return c, nil
 }

src/net/udpsock.go

@@ -193,21 +193,25 @@ func (c *UDPConn) WriteMsgUDP(b, oob []byte, addr *UDPAddr) (n, oobn int, err er
 
 func newUDPConn(fd *netFD) *UDPConn { return &UDPConn{conn{fd}} }
 
-// DialUDP connects to the remote address raddr on the network net,
-// which must be "udp", "udp4", or "udp6".  If laddr is not nil, it is
-// used as the local address for the connection.
-func DialUDP(net string, laddr, raddr *UDPAddr) (*UDPConn, error) {
-	switch net {
+// DialUDP acts like Dial for UDP networks.
+//
+// The network must be a UDP network name; see func Dial for details.
+//
+// If laddr is nil, a local address is automatically chosen.
+// If the IP field of raddr is nil or an unspecified IP address, the
+// local system is assumed.
+func DialUDP(network string, laddr, raddr *UDPAddr) (*UDPConn, error) {
+	switch network {
 	case "udp", "udp4", "udp6":
 	default:
-		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(net)}
+		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(network)}
 	}
 	if raddr == nil {
-		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
+		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
 	}
-	c, err := dialUDP(context.Background(), net, laddr, raddr)
+	c, err := dialUDP(context.Background(), network, laddr, raddr)
 	if err != nil {
-		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
+		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
 	}
 	return c, nil
 }

src/net/unixsock.go

@@ -196,18 +196,21 @@ func (c *UnixConn) WriteMsgUnix(b, oob []byte, addr *UnixAddr) (n, oobn int, err
 
 func newUnixConn(fd *netFD) *UnixConn { return &UnixConn{conn{fd}} }
 
-// DialUnix connects to the remote address raddr on the network net,
-// which must be "unix", "unixgram" or "unixpacket".  If laddr is not
-// nil, it is used as the local address for the connection.
-func DialUnix(net string, laddr, raddr *UnixAddr) (*UnixConn, error) {
-	switch net {
+// DialUnix acts like Dial for Unix networks.
+//
+// The network must be a Unix network name; see func Dial for details.
+//
+// If laddr is non-nil, it is used as the local address for the
+// connection.
+func DialUnix(network string, laddr, raddr *UnixAddr) (*UnixConn, error) {
+	switch network {
 	case "unix", "unixgram", "unixpacket":
 	default:
-		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(net)}
+		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(network)}
 	}
-	c, err := dialUnix(context.Background(), net, laddr, raddr)
+	c, err := dialUnix(context.Background(), network, laddr, raddr)
 	if err != nil {
-		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
+		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
 	}
 	return c, nil
 }