code review 4437053: net: use C library resolver on FreeBSD, Linux, OS X / a...

src/pkg/net/cgo_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.
 
 package net
 
 /*
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
@@ skipping 14 matching lines @@
         ip, err, completed := cgoLookupIP(name)
         for _, p := range ip {
                 addrs = append(addrs, p.String())
         }
         return
 }
 
 func cgoLookupPort(net, service string) (port int, err os.Error, completed bool) {
         var res *C.struct_addrinfo
         var hints C.struct_addrinfo
-        
+
         switch net {
         case "":
                 // no hints
         case "tcp", "tcp4", "tcp6":
                 hints.ai_socktype = C.SOCK_STREAM
                 hints.ai_protocol = C.IPPROTO_TCP
         case "udp", "udp4", "udp6":
                 hints.ai_socktype = C.SOCK_DGRAM
                 hints.ai_protocol = C.IPPROTO_UDP
         default:
                 return 0, UnknownNetworkError(net), true
         }
         if len(net) >= 4 {
                 switch net[3] {
                 case '4':
                         hints.ai_family = C.AF_INET
                 case '6':
                         hints.ai_family = C.AF_INET6
                 }
         }
-        
+
         s := C.CString(service)
         defer C.free(unsafe.Pointer(s))
         if C.getaddrinfo(nil, s, &hints, &res) == 0 {
                 defer C.freeaddrinfo(res)
                 for r := res; r != nil; r = r.ai_next {
                         switch r.ai_family {
                         default:
                                 continue
                         case C.AF_INET:
                                 sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(r.ai_addr))
                                 p := (*[2]byte)(unsafe.Pointer(&sa.Port))
                                 return int(p[0])<<8 | int(p[1]), nil, true
                         case C.AF_INET6:
                                 sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(r.ai_addr))
                                 p := (*[2]byte)(unsafe.Pointer(&sa.Port))
                                 return int(p[0])<<8 | int(p[1]), nil, true
                         }
                 }
         }
         return 0, &AddrError{"unknown port", net + "/" + service}, true
 }
 
 func cgoLookupIPCNAME(name string) (addrs []IP, cname string, err os.Error, completed bool) {
         var res *C.struct_addrinfo
         var hints C.struct_addrinfo
 
-        hints.ai_flags = C.AI_CANONNAME | C.AI_ALL | C.AI_V4MAPPED | C.AI_ADDRCONFIG
+        // NOTE(rsc): In theory there are approximately balanced
+        // arguments for and against including AI_ADDRCONFIG
+        // in the flags (it includes IPv4 results only on IPv4 systems,
+        // and similarly for IPv6), but in practice setting it causes
+        // getaddrinfo to return the wrong canonical name on Linux.
+        // So definitely leave it out.
+        hints.ai_flags = C.AI_ALL | C.AI_V4MAPPED | C.AI_CANONNAME
 
         h := C.CString(name)
         defer C.free(unsafe.Pointer(h))
-        gerrno := C.getaddrinfo(h, nil, &hints, &res)
+        gerrno, err := C.getaddrinfo(h, nil, &hints, &res)
         if gerrno != 0 {
                 var str string
                 if gerrno == C.EAI_NONAME {
                         str = noSuchHost
+                } else if gerrno == C.EAI_SYSTEM {
+                        str = err.String()
                 } else {
                         str = C.GoString(C.gai_strerror(gerrno))
                 }
                 return nil, "", &DNSError{Error: str, Name: name}, true
         }
         defer C.freeaddrinfo(res)
         if res != nil {
                 cname = C.GoString(res.ai_canonname)
                 if cname == "" {
                         cname = name
                 }
                 if len(cname) > 0 && cname[len(cname)-1] != '.' {
                         cname += "."
                 }
         }
         for r := res; r != nil; r = r.ai_next {
+                // Everything comes back twice, once for UDP and once for TCP.
+                if r.ai_socktype != C.SOCK_STREAM {
+                        continue
+                }
                 switch r.ai_family {
                 default:
                         continue
                 case C.AF_INET:
                         sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(r.ai_addr))
                         addrs = append(addrs, copyIP(sa.Addr[:]))
                 case C.AF_INET6:
                         sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(r.ai_addr))
                         addrs = append(addrs, copyIP(sa.Addr[:]))
                 }
         }
         return addrs, cname, nil, true
 }
 
 func cgoLookupIP(name string) (addrs []IP, err os.Error, completed bool) {
         addrs, _, err, completed = cgoLookupIPCNAME(name)
         return
 }
 
 func cgoLookupCNAME(name string) (cname string, err os.Error, completed bool) {
         _, cname, err, completed = cgoLookupIPCNAME(name)
         return
 }
 
 func copyIP(x IP) IP {
         y := make(IP, len(x))
         copy(y, x)
         return y
 }