node-dns-bugfix

Patch for NodeJS bug where calling dns.setServers during dns.resolve* being in progress causes Node process to crash with:

node: ../deps/cares/src/ares_destroy.c:102: ares__destroy_servers_state: Assertion `ares__is_list_empty(&server->queries_to_server)' failed.
Aborted (core dumped)

Some links:

• dns: occasionally crashing in resolve4 and setServers
• dns.setServers() crash
• Traceback with DNS & IPv6

Compatibility

You don't need that for

• Node 10+
• Node 9.3.0+ (but you need it for Node < 9.3.0)
• Node 8.10.0+ (but you need it for Node < 8.10.0)

(you will be warned if imported in your code in these versions)

Tested to work (fixes the bug) with

• Node 6.14.3
• Node 9.2.1

Does not work with

Issue seems to be even bigger in these versions.

• Node 4.9.1
• Node 5.12.0
• Node 7.10.1

How it works

The fix monkey patches setServers and resolve functions of dns module. This makes new setServer calls to wait for all resolve to finish. After last resolve is done it updates the servers settings if setServers was called while resolving.

Note that this causes differences between real Node bugfix and this monkey patch behavior:

• Monkey patched version will not update dns servers until all resolved are completed. If you call resolve always before last one finishes - dns servers may never be updated and Node will be resolving with old servers forever. This is VERY edge-case, but I want you to know that it is possible.
• Real patched Node versions (9.3.0 and up) should use newest servers set with every resolve.

Usage

Do this as soon as possible in your code:

require("node-dns-bugfix");

You will be warned with console if used with Node version that has this fixed already. No patching will occur.

ES5

For Node v6 you probably need to import ES5 version of the code:

require("node-dns-bugfix/dist");

Test

Test files are contained in test directory. Run should-crash.js on broken Node version to see process crash. Run should-not-crash.js on broken Node version to see how this fix prevents the crash.

On fixed Node versions (8.10+, 9.3+) both scripts won't cause crash, but should-not-crash will trigger a warning.

To do

• Make it work with unsupported Node versions? At least for v.4+.

License

MIT