code review 4630081: net: break up and simplify Dial a bit

src/pkg/net/dial.go

 // Copyright 2010 The Go Authors.  All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 package net
 
 import "os"
 
 func resolveNetAddr(op, net, addr string) (a Addr, err os.Error) {
         if addr == "" {
                 return nil, &OpError{op, net, nil, errMissingAddress}
         }
         switch net {
         case "tcp", "tcp4", "tcp6":
                 a, err = ResolveTCPAddr(net, addr)
         case "udp", "udp4", "udp6":
                 a, err = ResolveUDPAddr(net, addr)
         case "unix", "unixgram", "unixpacket":
                 a, err = ResolveUnixAddr(net, addr)
         case "ip", "ip4", "ip6":
                 a, err = ResolveIPAddr(net, addr)
         default:
                 err = UnknownNetworkError(net)
         }
-        if err == nil {
-                return
+        if err != nil {
+                return nil, &OpError{op, net + " " + addr, nil, err}
         }
-        return nil, &OpError{op, net + " " + addr, nil, err}
+        return
 }
 
 // Dial connects to the address addr on the network net.
 //
 // Known networks are "tcp", "tcp4" (IPv4-only), "tcp6" (IPv6-only),
 // "udp", "udp4" (IPv4-only), "udp6" (IPv6-only), "ip", "ip4"
 // (IPv4-only), "ip6" (IPv6-only), "unix" and "unixgram".
 //
 // For IP networks, addresses have the form host:port.  If host is
 // a literal IPv6 address, it must be enclosed in square brackets.
@@ skipping 15 matching lines @@
                 c, err = DialTCP(net, nil, ra)
         case *UDPAddr:
                 c, err = DialUDP(net, nil, ra)
         case *UnixAddr:
                 c, err = DialUnix(net, nil, ra)
         case *IPAddr:
                 c, err = DialIP(net, nil, ra)
         default:
                 err = UnknownNetworkError(net)
         }
-        if err == nil {
-                return
+        if err != nil {
+                return nil, &OpError{"dial", net + " " + addr, nil, err}
         }
-        return nil, &OpError{"dial", net + " " + addr, nil, err}
+        return
 }
 
 // Listen announces on the local network address laddr.
 // The network string net must be a stream-oriented
 // network: "tcp", "tcp4", "tcp6", or "unix", or "unixpacket".
 func Listen(net, laddr string) (l Listener, err os.Error) {
         switch net {
         case "tcp", "tcp4", "tcp6":
                 var la *TCPAddr
                 if laddr != "" {
@@ skipping 66 matching lines @@
                         c, err := ListenIP(net, la)
                         if err != nil {
                                 return nil, err
                         }
                         return c, nil
                 }
         }
 
         return nil, UnknownNetworkError(net)
 }