net: use slightly less predictable dns request id

not trying to be secure, just not repetitive
(sending with the same id repeatedly makes
some resolvers stop replying.)

eventually we'll replace this with linking against
the system's native resolver.

R=p
CC=golang-dev
https://golang.org/cl/207051

diff --git a/src/pkg/net/dnsclient.go b/src/pkg/net/dnsclient.go
index 7820244b280d49399e98f60b462609081fbfaffc..0a6fca0115220bda56a420e1fdaef42f3fe82115 100644 (file)
--- a/src/pkg/net/dnsclient.go
+++ b/src/pkg/net/dnsclient.go
@@ -17,6 +17,8 @@ package net
 import (
        "once"
        "os"
+       "rand"
+       "time"
 )
 
 // DNSError represents a DNS lookup error.
@@ -44,7 +46,7 @@ func _Exchange(cfg *_DNS_Config, c Conn, name string) (m *_DNS_Msg, err os.Error
                return nil, &DNSError{"name too long", name, ""}
        }
        out := new(_DNS_Msg)
-       out.id = 0x1234
+       out.id = uint16(rand.Int()) ^ uint16(time.Nanoseconds())
        out.question = []_DNS_Question{
                _DNS_Question{name, _DNS_TypeA, _DNS_ClassINET},
        }