net: reject invalid net:proto network names

R=rsc
CC=golang-dev
https://golang.org/cl/4129042

src/pkg/net/dial.go

@@ -24,7 +24,7 @@ import "os"
 //	Dial("tcp", "127.0.0.1:123", "127.0.0.1:88")
 //
 func Dial(net, laddr, raddr string) (c Conn, err os.Error) {
-	switch prefixBefore(net, ':') {
+	switch net {
 	case "tcp", "tcp4", "tcp6":
 		var la, ra *TCPAddr
 		if laddr != "" {
@@ -137,7 +137,7 @@ func Listen(net, laddr string) (l Listener, err os.Error) {
 // The network string net must be a packet-oriented network:
 // "udp", "udp4", "udp6", or "unixgram".
 func ListenPacket(net, laddr string) (c PacketConn, err os.Error) {
-	switch prefixBefore(net, ':') {
+	switch net {
 	case "udp", "udp4", "udp6":
 		var la *UDPAddr
 		if laddr != "" {
@@ -162,18 +162,24 @@ func ListenPacket(net, laddr string) (c PacketConn, err os.Error) {
 			return nil, err
 		}
 		return c, nil
-	case "ip", "ip4", "ip6":
-		var la *IPAddr
-		if laddr != "" {
-			if la, err = ResolveIPAddr(laddr); err != nil {
+	}
+
+	if i := last(net, ':'); i > 0 {
+		switch net[0:i] {
+		case "ip", "ip4", "ip6":
+			var la *IPAddr
+			if laddr != "" {
+				if la, err = ResolveIPAddr(laddr); err != nil {
+					return nil, err
+				}
+			}
+			c, err := ListenIP(net, la)
+			if err != nil {
 				return nil, err
 			}
+			return c, nil
 		}
-		c, err := ListenIP(net, la)
-		if err != nil {
-			return nil, err
-		}
-		return c, nil
 	}
+
 	return nil, UnknownNetworkError(net)
 }

src/pkg/net/iprawsock.go

@@ -311,7 +311,7 @@ func DialIP(netProto string, laddr, raddr *IPAddr) (c *IPConn, err os.Error) {
 	if err != nil {
 		return
 	}
-	switch prefixBefore(net, ':') {
+	switch net {
 	case "ip", "ip4", "ip6":
 	default:
 		return nil, UnknownNetworkError(net)
@@ -335,7 +335,7 @@ func ListenIP(netProto string, laddr *IPAddr) (c *IPConn, err os.Error) {
 	if err != nil {
 		return
 	}
-	switch prefixBefore(net, ':') {
+	switch net {
 	case "ip", "ip4", "ip6":
 	default:
 		return nil, UnknownNetworkError(net)

src/pkg/net/parse.go

@@ -192,16 +192,6 @@ func count(s string, b byte) int {
 	return n
 }
 
-// Returns the prefix of s up to but not including the character c
-func prefixBefore(s string, c byte) string {
-	for i, v := range s {
-		if v == int(c) {
-			return s[0:i]
-		}
-	}
-	return s
-}
-
 // Index of rightmost occurrence of b in s.
 func last(s string, b byte) int {
 	i := len(s)