dns: fix `resolve` failed starts without network #13076

XadillaX · 2017-05-17T09:37:17Z

Fix the bug that you start process without network at first, but it connected lately, dns.resolve will stay failed with ECONNREFUSED because c-ares servers fallback to 127.0.0.1 at the very beginning.

If c-ares servers "127.0.0.1" is detected and its not set by user self, and last query is not OK, recreating ares_channel operation will be triggered to reload servers.

You can test with this script:

const dns = require("dns");

function test() {
    dns.resolve("google.com", function(err, ret) {
        console.log(err, ret, dns.getServers());
        setTimeout(test, 10000);
    });
}

test();

Turn off your network at first before starting this script. Then try to open the network and then turn off. Make the steps above in a loop and you will get the result.

Fixes: #1644

Solutaion

DNS server matches follow conditions is considered as a fallback server of c-ares:

caused last query ECONNREFUSED; (the fallback server very likely to have this error)
is exactly [ "127.0.0.1" ]; (the fallback server is exactly this value)
haven't set by users or developers by dns.setServers.

Because users or developers may do dns.setServers([ "127.0.0.1" ]) or theirs /etc/resolv.conf is 127.0.0.1.

As a result, I gathered those 3 conditions.

I created two flags at the process start up.

cares_query_last_ok_ indicates that is last dns query succeeded or not;
cares_is_servers_use_default_ indicates that whether current dns servers is the fallback 127.0.0.1 that c-ares initialized at the beginning.

If cares_query_last_ok_ is true or cares_is_servers_use_default_ is false, everything will be OK.

If not, the code will check current dns servers to see if it's 127.0.0.1 (maybe c-ares' fallback server). When it's 127.0.0.1, old ares_channel will be released and a new one will be created.

Once one query succeeded or not ECONNREFUSED, cares_query_last_ok_ will be marked as true. And once user set dns servers via dns.setServers, cares_is_servers_use_default_ will be marked as false. And what's more, once the first check found the dns servers is not 127.0.0.1, cares_is_servers_use_default_ also will be marked as false.

Checklist

make -j4 test (UNIX), or vcbuild test (Windows) passes
commit message follows commit guidelines

Affected core subsystem(s)

dns

XadillaX · 2017-05-17T15:43:31Z

Anyone who has time to review this code?

/cc @trevnorris @indutny @addaleax @danbev

addaleax · 2017-05-17T17:19:10Z

src/env-inl.h

+
+inline void Environment::cares_servers_use_default(bool is_default) {
+  cares_is_servers_use_default_ = is_default;
+}


Any chance you could name the setters set_FLAG() and the getters just FLAG() (compare with e.g. using_domains)?

addaleax · 2017-05-17T17:20:03Z

src/cares_wrap.cc

@@ -1306,6 +1373,8 @@ void SetServers(const FunctionCallbackInfo<Value>& args) {

  delete[] servers;

+  if (err == ARES_SUCCESS) env->cares_servers_use_default(false);


Extremely tiny nit: I’d put these on separate lines

addaleax · 2017-05-17T17:21:17Z

src/cares_wrap.cc

@@ -328,10 +386,18 @@ class QueryWrap : public AsyncWrap {
    return static_cast<void*>(this);
  }

+  static void AresQuery(Environment* env, const char* name,
+      int dnsclass, int type, ares_callback callback,


I realize the code around this doesn’t do it either, but once more, would you mind aligning the arguments vertically? 😄

addaleax · 2017-05-17T17:22:01Z

src/cares_wrap.cc

+ * The fallback servers of cares is [ "127.0.0.1" ] with no user additional
+ * setting.
+ */
+void AresCheckServers(Environment* env) {


tiny nit: Check sounds a bit like it’s just testing things, maybe Ensure is better?

addaleax · 2017-05-17T17:23:08Z

src/cares_wrap.cc

+  /* We do the call to ares_init_option for caller. */
+  int r = ares_init_options(env->cares_channel_ptr(),
+      &options,
+      ARES_OPT_FLAGS | ARES_OPT_SOCK_STATE_CB);


(ditto for aligning)

addaleax · 2017-05-17T17:23:59Z

src/cares_wrap.cc

+  memset(&options, 0, sizeof(options));
+  options.flags = ARES_FLAG_NOCHECKRESP;
+  options.sock_state_cb = ares_sockstate_cb;
+  options.sock_state_cb_data = env;


Can we somehow share this code with Initialize, to make it more obviously correct? It looks like there’s quite a bit that could be shared

I'v extracted these code to SetupCaresChannel().

addaleax · 2017-05-17T17:26:58Z

CI: https://ci.nodejs.org/job/node-test-commit/9955/

pmq20 · 2017-05-18T03:43:50Z

One of Windows CI Machines failed. I wonder why.

not ok 2 parallel/test-async-wrap-getasyncid
  ---
  duration_ms: 0.248
  severity: fail
  stack: |-
    Mismatched <anonymous> function calls. Expected 1, actual 0.
        at Object.<anonymous> (c:\workspace\node-test-binary-windows\RUN_SUBSET\0\VS_VERSION\vs2015-x86\label\win2008r2\test\parallel\test-async-wrap-getasyncid.js:155:42)
        at Module._compile (module.js:569:30)
        at Object.Module._extensions..js (module.js:580:10)
        at Module.load (module.js:503:32)
        at tryModuleLoad (module.js:466:12)
        at Function.Module._load (module.js:458:3)
        at Function.Module.runMain (module.js:605:10)
        at startup (bootstrap_node.js:144:16)
        at bootstrap_node.js:561:3
    (node:5140) [DEP0064] DeprecationWarning: tls.createSecurePair() is deprecated. Please use tls.Socket instead.
  ...

XadillaX · 2017-05-18T10:53:34Z

I don't know why, maybe it's the bug of CI? I'm not sure. @addaleax

addaleax · 2017-05-18T10:55:12Z

Yes, the CI failure is nothing to worry about. 👍 (It’s not a bug in the CI but it’s a known failure that’s not related to this PR.)

XadillaX · 2017-05-19T02:53:36Z

Hey @addaleax I've already rebased for some conflicts with master.

addaleax · 2017-05-19T16:36:45Z

CI: https://ci.nodejs.org/job/node-test-commit/10008/

addaleax · 2017-05-19T19:31:50Z

CI is green. Maybe @bnoordhuis or @silverwind could give this a look, too?

bnoordhuis

LGTM modulo comments.

bnoordhuis · 2017-05-19T21:45:52Z

src/cares_wrap.cc

+              ns_c_in,
+              ns_t_a,
+              Callback,
+              GetQueryArg());


This fits on one line now.

bnoordhuis · 2017-05-19T21:46:14Z

src/cares_wrap.cc

+              ns_c_in,
+              ns_t_aaaa,
+              Callback,
+              GetQueryArg());


Likewise. I'll stop pointing it out from here on.

addaleax · 2017-05-19T21:57:10Z

@XadillaX Actually, one more thing: your author name in this commit is given as “XadillaX”. Is that intended or do you prefer to be listed (changelog, git log, AUTHORS file) with some other name? People typically prefer their full name, but ultimately it’s up to you. (Edit: Just to be clear, that name doesn’t have to be ASCII-only – whatever you prefer, really.)

Fix the bug that you start process without network at first, but it connected lately, `dns.resolve` will stay failed with ECONNREFUSED because c-ares servers fallback to 127.0.0.1 at the very beginning. If c-ares servers "127.0.0.1" is detected and its not set by user self, and last query is not OK, recreating `ares_channel` operation will be triggered to reload servers. Fixes: nodejs#1644

XadillaX · 2017-05-20T04:51:39Z

@addaleax I think 'XadillaX - Khaidi Chu' would be fine to me.

XadillaX · 2017-05-21T01:41:02Z

@addaleax I mean I'd like to use XadillaX when in git log, changelog and authors file. And if someday I have the honor of being a collaborator, I'd like to use 'XadillaX - Khaidi Chu' in the list.

addaleax · 2017-05-21T13:53:09Z

Landed in 2b54147

@XadillaX I think you’ve already figured out that you can set this information using git config [--global] user.name and … user.email, but if you need any help, just let us know. :)

Fix the bug that you start process without network at first, but it connected lately, `dns.resolve` will stay failed with ECONNREFUSED because c-ares servers fallback to 127.0.0.1 at the very beginning. If c-ares servers "127.0.0.1" is detected and its not set by user self, and last query is not OK, recreating `ares_channel` operation will be triggered to reload servers. Fixes: #1644 PR-URL: #13076 Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Ben Noordhuis <[email protected]>

XadillaX · 2017-05-21T13:57:43Z

@addaleax Thanks. I wondered if this PR passed the coverity? Shall I trigger that by myself?

addaleax · 2017-05-21T13:59:49Z

@XadillaX I am not sure how to do that. I think the tool gets run periodically without being triggered, but really, I’m not sure.

gibfahn · 2017-05-22T09:28:03Z

@addaleax Thanks. I wondered if this PR passed the coverity? Shall I trigger that by myself?

see #13117 (comment)

MylesBorins · 2017-07-17T14:58:05Z

Should this be backported to v6.x? If so it will require to be done manually

Fix the bug that you start process without network at first, but it connected lately, `dns.resolve` will stay failed with ECONNREFUSED because c-ares servers fallback to 127.0.0.1 at the very beginning. If c-ares servers "127.0.0.1" is detected and its not set by user self, and last query is not OK, recreating `ares_channel` operation will be triggered to reload servers. Fixes: nodejs#1644 PR-URL: nodejs#13076 Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Ben Noordhuis <[email protected]>

XadillaX · 2017-07-23T08:30:31Z

Should this be backported to v6.x? If so it will require to be done manually

#14434

Fix the bug that you start process without network at first, but it connected lately, `dns.resolve` will stay failed with ECONNREFUSED because c-ares servers fallback to 127.0.0.1 at the very beginning. If c-ares servers "127.0.0.1" is detected and its not set by user self, and last query is not OK, recreating `ares_channel` operation will be triggered to reload servers. Fixes: #1644 Backport-PR-URL: #14434 PR-URL: #13076 Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Ben Noordhuis <[email protected]>

nodejs-github-bot added c++ Issues and PRs that require attention from people who are familiar with C++. cares Issues and PRs related to the c-ares dependency or the cares_wrap binding. labels May 17, 2017

XadillaX force-pushed the fix/resolve-fails-when-start-without-network branch from 8662937 to 57f04fd Compare May 17, 2017 09:44

addaleax approved these changes May 17, 2017

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XadillaX force-pushed the fix/resolve-fails-when-start-without-network branch from 57f04fd to 51caf53 Compare May 18, 2017 03:38

XadillaX force-pushed the fix/resolve-fails-when-start-without-network branch from 51caf53 to 490672c Compare May 19, 2017 02:52

bnoordhuis approved these changes May 19, 2017

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XadillaX force-pushed the fix/resolve-fails-when-start-without-network branch from 490672c to 355a33b Compare May 20, 2017 04:48

addaleax closed this May 21, 2017

jasnell mentioned this pull request May 28, 2017

8.0.0 Release Proposal #12220

Closed

gibfahn mentioned this pull request Jun 15, 2017

Auditing for 6.11.1 nodejs/Release#230

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3 tasks

MylesBorins added the lts-watch-v6.x label Jul 17, 2017

XadillaX mentioned this pull request Jul 23, 2017

(v6.x backport) dns: fix resolve failed starts without network #14434

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MylesBorins added backported-to-v6.x and removed lts-watch-v6.x labels Aug 14, 2017

MylesBorins mentioned this pull request Aug 16, 2017

v6.11.3-proposal #14852

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dns: fix `resolve` failed starts without network #13076

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XadillaX commented Jul 23, 2017

		@@ -1306,6 +1373,8 @@ void SetServers(const FunctionCallbackInfo<Value>& args) {

		delete[] servers;

		if (err == ARES_SUCCESS) env->cares_servers_use_default(false);

dns: fix resolve failed starts without network #13076

dns: fix resolve failed starts without network #13076

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XadillaX commented May 17, 2017 • edited Loading

Solutaion

Checklist

Affected core subsystem(s)

XadillaX commented May 17, 2017

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dns: fix `resolve` failed starts without network #13076

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