Feature #4788: resolv.rb refactoring

• Status: Closed
• Assignee: akr (Akira Tanaka)
• Target version: 2.6

[metanest (Makoto Kishimoto)]

このようなモンキーパッチが（私のコードではありませんが）
https://github.com/ioquatix/rubydns/blob/master/lib/rubydns/resolv.rb
#3835 （ [ruby-core:32407] ）の結果、動かなくなっていたのでパッチを検討していたわけですが、
結論としてresolv.rbに以下のようなリファクタリングを施すのがいいのではないかと考えました。
パッチを添付します。

---

diff --git a/lib/resolv.rb b/lib/resolv.rb
index 1e18893..e9c2432 100644
--- a/lib/resolv.rb
+++ b/lib/resolv.rb
@@ -491,6 +491,12 @@ class Resolv
# #getresource for argument details.

 def each_resource(name, typeclass, &proc)

•  each_resource_(name, typeclass) {|reply, reply_name|
  

•    extract_resources(reply, reply_name, typeclass, &proc)
  

•  }
  

• end
• def each_resource_(name, typeclass)
  lazy_initialize
  requester = make_udp_requester
  senders = {}
  @@ -517,7 +523,7 @@ class Resolv
  # response will not fit in an untruncated UDP packet.
  redo
  else

•          extract_resources(reply, reply_name, typeclass, &proc)
  

•          yield(reply, reply_name)
         end
         return
       when RCode::NXDomain
  

[metanest (Makoto Kishimoto)]

とりあえず思いつかなかったのでパッチでは each_resource_ という名前にしてしまいましたが、fetch_resource という名前でどうでしょうか。

[nahi (Hiroshi Nakamura)]

• Assignee set to akr (Akira Tanaka)

[ioquatix (Samuel Williams)]

I have a vested interest in this patch since I am the developer of RubyDNS. This update will allow RubyDNS to hook into resolve.rb more efficiently. Right now, I have to duplicate code in resolve.rb to get the right behaviour.

Also, I originally suggested then name fetch_resource and thus I support Makoto Kishimoto's proposal about this change.

Lets work to get this updated so that I can add good support for RubyDNS and Ruby 1.9.

Thanks.

[naruse (Yui NARUSE)]

• Target version changed from 1.9.3 to 2.0.0

[metanest (Makoto Kishimoto)]

• File resolv_rb_patch.txt resolv_rb_patch.txt added

[akr (Akira Tanaka)]

2011/5/27 Makoto Kishimoto [e-mail]:

このようなモンキーパッチが（私のコードではありませんが）
https://github.com/ioquatix/rubydns/blob/master/lib/rubydns/resolv.rb
#3835 （ [ruby-core:32407] ）の結果、動かなくなっていたのでパッチを検討していたわけですが、
結論としてresolv.rbに以下のようなリファクタリングを施すのがいいのではないかと考えました。

なぜそうするのがいいのか書いていないのでなんとも言い難いものがあります。

モンキーパッチがうまくいかないから、という理由は受け入れ難いです。

後で調べるはめになったときのために、
変更するときには意図をどこかに残しておきたいと思うのですが、
上記はその記述として十分なものとは思えません。

[田中 哲][たなか あきら][Tanaka Akira]

[metanest (Makoto Kishimoto)]

元の問題は、lib/resolv.rb が、TCP へのフォールバックに対応して、その際に
make_requester --> make_udp_requester という名前の変更があったために、
（公開インターフェースではない）それに依存していたコードが動かなくなった、
というものです。

しかし、make_requester のような内部の非常に低いレイヤにあるメソッドに
rubydns ライブラリのコードが依存していた理由は、DNS#each_resource
メソッド中に、個々のリソースを取得するコードが一体不可分に含まれてしまって
いるため、DNS プロキシのようなものを作る場合、each_resource メソッド中の
リソース取得部分のコードの duplicate が、このようなライブラリの実装において
不可避であったためです。

パッチで示したように、リソース取得部分を切り離し、また、一種のコールバックで
ある extract_resources を、現状のハードコーディング状態から抽象化する
リファクタリングによって、ライブラリ側でのコード duplicate が必要なくなります。

パッチで追加される fetch_resource メソッドのユースケースとして、
ライブラリ側のコードがどうなるかというパッチを示します。

--- resolv.rb.orig 2011-05-27 18:15:59.000000000 +0900
+++ resolv.rb 2011-08-03 10:38:43.000000000 +0900
@@ -24,6 +24,13 @@
# This allows such responses to be passed upstream with little or no
# modification/reinterpretation.
def query(name, typeclass)

•   	if respond_to?(:fetch_resource) then
  

•   		fetch_resource(name, typeclass) do |reply, reply_name|
  

•   			return reply, reply_name
  

•   		end
  

•   		return
  

•   	end
  

•   	lazy_initialize
    	requester = make_requester
    	senders = {}
  

[ioquatix (Samuel Williams)]

It would be nice to get some movement on this - I'm getting bug reports from people trying to use 1.9.x and RubyDNS.

Kind regards,
Samuel

[shyouhei (Shyouhei Urabe)]

• Status changed from Open to Assigned

[ioquatix (Samuel Williams)]

Hi, still having users with problems and no consistent way to solve it. Merging this patch would be a great addition. Let me know if you require any further support or have any questions.

[ioquatix (Samuel Williams)]

Here is a translation into English for the most recent message from Makoto:

The original problem is that 'lib/resolv.rb' had a fallback to TCP which was broken. There was a patch (#3835) which renamed ‘make_requester' to 'make_udp_requester’. This is not a public interface so the code which depended on it stopped working.

However, the reason why RubyDNS depended on such a method is because the high level interface performs breaks the response up into individual records but we are actually interested in the response in its entirety. This is specifically a problem when creating a DNS proxy where you want to forward requests with minimal changes. Duplicating the code for each_resource was unavoidable in the implementation of RubyDNS.

As in the patch provided by Makoto, code duplication can be reduced by removing the direct connection between each_resource and fetch_resource, and providing a block to be executed per successful response.

A second patch shows how RubyDNS can be simplified once the proposed change is applied.

[ioquatix (Samuel Williams)]

Hi, still waiting for some progress on this issue. Lots of people are bugging me about it.

[ioquatix (Samuel Williams)]

Bump

[shyouhei (Shyouhei Urabe)]

@ioquatix (Samuel Williams) isn't the only one who's interested in it (read: me too).

[akr (Akira Tanaka)]

• Target version changed from 2.0.0 to 2.6

[akr (Akira Tanaka)]

• Status changed from Assigned to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r40159.
Makoto, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

• lib/resolv.rb (Resolv::DNS.fetch_resource): New method to obtain
  full result.
  [ruby-dev:43587] [Feature #4788] proposed by Makoto Kishimoto.

[ioquatix (Samuel Williams)]

I'm happy to se this has been completed. I just thought I'd mention that I reimplemented the DNS resolver in RubyDNS using EventMachine as I couldn't wait for this bug fix. The new EventMachine resolver is asynchronous which makes it useful in the event driven server, such as the one in RubyDNS. Thanks for everyone's effort getting this bug resolved.