code review 12898045: net: use protocol number literals instead of names in r...

src/pkg/net/lookup_unix.go

 // Copyright 2011 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.
 
 // +build darwin freebsd linux netbsd openbsd
 
 package net
 
 import (
         "errors"
         "sync"
 )
 
-var (
-        protocols         map[string]int
-        onceReadProtocols sync.Once
-)
+var onceReadProtocols sync.Once
 
 // readProtocols loads contents of /etc/protocols into protocols map
 // for quick access.
 func readProtocols() {
-        protocols = make(map[string]int)
         if file, err := open("/etc/protocols"); err == nil {
                 for line, ok := file.readLine(); ok; line, ok = file.readLine() {
                         // tcp    6   TCP    # transmission control protocol
                         if i := byteIndex(line, '#'); i >= 0 {
                                 line = line[0:i]
                         }
                         f := getFields(line)
                         if len(f) < 2 {
                                 continue
                         }
                         if proto, _, ok := dtoi(f[1], 0); ok {
-                                protocols[f[0]] = proto
+                                if _, ok := protocols[f[0]]; !ok {
+                                        protocols[f[0]] = proto
+                                }
                                 for _, alias := range f[2:] {
-                                        protocols[alias] = proto
+                                        if _, ok := protocols[alias]; !ok {
+                                                protocols[alias] = proto
+                                        }
                                 }
                         }
                 }
                 file.close()
         }
 }
 
 // lookupProtocol looks up IP protocol name in /etc/protocols and
 // returns correspondent protocol number.
 func lookupProtocol(name string) (proto int, err error) {
@@ skipping 112 matching lines @@
         if err != nil {
                 return
         }
         name = make([]string, len(records))
         for i := range records {
                 r := records[i].(*dnsRR_PTR)
                 name[i] = r.Ptr
         }
         return
 }