code review 5313043: net: allow LookupSRV on non-standard DNS names

net: allow LookupSRV on non-standard DNS names

[rsc, 2011-10-18 17:48:16]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://go.googlecode.com/hg/

[bradfitz, 2011-10-18 17:53:10]

LGTM

On Tue, Oct 18, 2011 at 10:48 AM, <rsc@golang.org> wrote:

> Reviewers: golang-dev_googlegroups.com,
>
> Message:
> Hello golang-dev@googlegroups.com,
>
> I'd like you to review this change to
> https://go.googlecode.com/hg/
>
>
> Description:
> net: allow LookupSRV on non-standard DNS names
>
> Please review this at
http://codereview.appspot.com/**5313043/<http://codereview.appspot.com/5313043/>
>
> Affected files:
>  M src/pkg/net/lookup_plan9.go
>  M src/pkg/net/lookup_test.go
>  M src/pkg/net/lookup_unix.go
>  M src/pkg/net/lookup_windows.go
>
>
> Index: src/pkg/net/lookup_plan9.go
> ==============================**==============================**=======
> --- a/src/pkg/net/lookup_plan9.go
> +++ b/src/pkg/net/lookup_plan9.go
> @@ -157,12 +157,21 @@
>  }
>
>  // LookupSRV tries to resolve an SRV query of the given service,
> -// protocol, and domain name, as specified in RFC 2782. In most cases
> -// the proto argument can be the same as the corresponding
> -// Addr.Network(). The returned records are sorted by priority
> -// and randomized by weight within a priority.
> +// protocol, and domain name.  The proto is "tcp" or "udp".
> +// The returned records are sorted by priority and randomized
> +// by weight within a priority.
> +//
> +// LookupSRV constructs the DNS name to look up following RFC 2782.
> +// That is, it looks up _service._proto.name.  To accommodate services
> +// publishing SRV records under non-standard names, if both service
> +// and proto are empty strings, LookupSRV looks up name directly.
>  func LookupSRV(service, proto, name string) (cname string, addrs []*SRV,
> err os.Error) {
> -       target := "_" + service + "._" + proto + "." + name
> +       var target string
> +       if service == "" && proto == "" {
> +               target = name
> +       } else {
> +               target = "_" + service + "._" + proto + "." + name
> +       }
>        lines, err := queryDNS(target, "srv")
>        if err != nil {
>                return
> Index: src/pkg/net/lookup_test.go
> ==============================**==============================**=======
> --- a/src/pkg/net/lookup_test.go
> +++ b/src/pkg/net/lookup_test.go
> @@ -26,6 +26,15 @@
>        if len(addrs) == 0 {
>                t.Errorf("no results")
>        }
> +
> +       // Non-standard back door.
> +       _, addrs, err = LookupSRV("", "", "_xmpp-server._tcp.google.com"**
> )
> +       if err != nil {
> +               t.Errorf("back door failed: %s", err)
> +       }
> +       if len(addrs) == 0 {
> +               t.Errorf("back door no results")
> +       }
>  }
>
>  func TestGmailMX(t *testing.T) {
> Index: src/pkg/net/lookup_unix.go
> ==============================**==============================**=======
> --- a/src/pkg/net/lookup_unix.go
> +++ b/src/pkg/net/lookup_unix.go
> @@ -94,12 +94,21 @@
>  }
>
>  // LookupSRV tries to resolve an SRV query of the given service,
> -// protocol, and domain name, as specified in RFC 2782. In most cases
> -// the proto argument can be the same as the corresponding
> -// Addr.Network(). The returned records are sorted by priority
> -// and randomized by weight within a priority.
> +// protocol, and domain name.  The proto is "tcp" or "udp".
> +// The returned records are sorted by priority and randomized
> +// by weight within a priority.
> +//
> +// LookupSRV constructs the DNS name to look up following RFC 2782.
> +// That is, it looks up _service._proto.name.  To accommodate services
> +// publishing SRV records under non-standard names, if both service
> +// and proto are empty strings, LookupSRV looks up name directly.
>  func LookupSRV(service, proto, name string) (cname string, addrs []*SRV,
> err os.Error) {
> -       target := "_" + service + "._" + proto + "." + name
> +       var target string
> +       if service == "" && proto == "" {
> +               target = name
> +       } else {
> +               target = "_" + service + "._" + proto + "." + name
> +       }
>        var records []dnsRR
>        cname, records, err = lookup(target, dnsTypeSRV)
>        if err != nil {
> Index: src/pkg/net/lookup_windows.go
> ==============================**==============================**=======
> --- a/src/pkg/net/lookup_windows.**go
> +++ b/src/pkg/net/lookup_windows.**go
> @@ -91,9 +91,23 @@
>        return
>  }
>
> +// LookupSRV tries to resolve an SRV query of the given service,
> +// protocol, and domain name.  The proto is "tcp" or "udp".
> +// The returned records are sorted by priority and randomized
> +// by weight within a priority.
> +//
> +// LookupSRV constructs the DNS name to look up following RFC 2782.
> +// That is, it looks up _service._proto.name.  To accommodate services
> +// publishing SRV records under non-standard names, if both service
> +// and proto are empty strings, LookupSRV looks up name directly.
>  func LookupSRV(service, proto, name string) (cname string, addrs []*SRV,
> err os.Error) {
> +       var target string
> +       if service == "" && proto == "" {
> +               target = name
> +       } else {
> +               target = "_" + service + "._" + proto + "." + name
> +       }
>        var r *syscall.DNSRecord
> -       target := "_" + service + "._" + proto + "." + name
>        e := syscall.DnsQuery(target, syscall.DNS_TYPE_SRV, 0, nil, &r, nil)
>        if int(e) != 0 {
>                return "", nil, os.NewSyscallError("LookupSRV"**, int(e))
>
>
>

[rsc, 2011-10-18 17:57:07]

*** Submitted as http://code.google.com/p/go/source/detail?r=3198ce30ea39 ***

net: allow LookupSRV on non-standard DNS names

R=golang-dev, bradfitz
CC=golang-dev
http://codereview.appspot.com/5313043