dns.lookup fails when offline on Windows

[seanpoulter]

From dns.js, dns.lookup for "localhost" fails, throwing an ENOENT error from getaddrinfo. It's reproducible with the following block:

var dns = require("dns");
dns.lookup("localhost", {"hints":3072}, function(err, ip, addressType) {
  console.log(err, ip, addressType);
})

Running it when connected produces the output:

null '127.0.0.1' 4

but without a network connection:

{ [Error: getaddrinfo ENOENT]
  code: 'ENOENT',
  errno: 'ENOENT',
  syscall: 'getaddrinfo',
  hostname: 'localhost' } undefined undefined

Unfortunately debugging even this simple block with node debug <file> fails trying to connect to port 5858:

>node debug troubleshoot-dns.js
< Debugger listening on port 5858
connecting to port 5858.............There was an internal error in Node's debugger. Please report this bug.
getaddrinfo ENOENT
Error: getaddrinfo ENOENT
    at Object.exports._errnoException (util.js:746:11)
    at errnoException (dns.js:49:15)
    at GetAddrInfoReqWrap.onlookup [as oncomplete] (dns.js:94:26)

One solution is to patch dns.js to replace "localhost" with "127.0.0.1" which produces the expected output, but I think the better solution is to fix the getaddrinfo calls.

[dnakamura]

which node version are you running?

[seanpoulter]

Running v0.12.2 x64.

[dnakamura]

First off you should really be using the constants, ie:

var dns = require("dns");
dns.lookup("localhost", {"hints":dns.ADDRCONFIG | dns.V4MAPPED}, function(err, ip, addressType) {
  console.log(err, ip, addressType);
})

Secondly the behaviour you describe is expected. From the documentation:

dns.ADDRCONFIG: Returned address types are determined by the types of addresses supported by the current system. For example, IPv4 addresses are only returned if the current system has at least one IPv4 address configured. Loopback addresses are not considered.

[seanpoulter]

Thanks for piecing that together and correcting the example code @dnakamura.

Since the API confirms this expected behaviour, I guess we should close this issue and open one against Socket.prototype.connect for improperly handling the ENOENT error thrown when performing the dns.lookup on localhost. Sound good?

[dnakamura]

yeah

[jasnell]

@seanpoulter @dnakamura ... did the other issue get opened? Closing this but want to make sure the other issue is not dropped.

[seanpoulter]

Thanks @jasnell. I hadn't opened the other yet.

Refer to: #25489