use ipv6 if that is actually supported

lib/resolver_sequence_tasks.js

@@ -3,6 +3,56 @@ var dns_sd = require('./dns_sd')
   , MDNSService = require('./mdns_service').MDNSService
   ;
 
+// Converts a versionString (v0.11.5) to an array of numbers [0,11,5]
+function versionStringToArray(versionString) {
+  return /^v(\d+(\.\d+)*)/.exec(versionString)[1].split('.').map(Number);
+}
+
+// Accepts versions in the form of v0.11.5.
+// Returns 1 if versionStringA is higher than versionStringB, -1 if lower, 0 if equal.
+function compareVersions(versionStringA, versionStringB) {
+  var versionA = versionStringToArray(versionStringA);
+  var versionB = versionStringToArray(versionStringB);
+
+  // Make sure the versions have just as segments, fill them up with 0's.
+  // Ex. Comparing v0.11 with v0.11.5 will become v0.11.0 and v0.11.5
+  while(versionA.length < versionB.length) { versionA.push(0); }
+  while(versionB.length < versionA.length) { versionB.push(0); }
+
+  var versionLength = versionA.length;
+
+  for(var i=0;i<versionLength;i++) {
+    if (versionA[i] > versionB[i]) {
+      return 1;
+    } else if (versionA[i] < versionB[i]) {
+      return -1;
+    }
+  }
+
+  return 0;
+}
+
+// Checks whether Ipv6 is supported on the OS.
+function hasIpv6Support() {
+  // We presume only Linux has the capability to disable ipv6.
+  if (process.platform !== 'linux') {
+    return true;
+  }
+  // Determine ipv6 support on Linux by checking whether if_inet6 exists.
+  try {
+    fs.statSync('/proc/net/if_inet6')
+    return true;
+  } catch(e) {
+    return false;
+  }
+}
+
+// Checks whether we can use { families: [0] } for getaddrinfo.
+// Support was added in NodeJS v0.11.5
+function hasGetaddrinfoZeroFamilySupport() {
+  return compareVersions(process.version, 'v0.11.5') >= 0;
+}
+
 exports.DNSServiceResolve = function DNSServiceResolve(options) {
   options = options || {};
   options.flags = options.flags || 0;
@@ -141,9 +191,17 @@ try {
   _getaddrinfo = process.binding('net').getaddrinfo;
 }
 
+// Depending on the support for NodeJS and the OS, we use the most supported
+// address families as default for getaddrinfo.
+var defaultFamilies = hasGetaddrinfoZeroFamilySupport()
+  ? [0]
+  : hasIpv6Support()
+    ? [4, 6]
+    : [4];
+
 exports.getaddrinfo = function getaddrinfo(options) {
   options = options || {};
-  var families = options.families || [4, 6];
+  var families = options.families || defaultFamilies;
   return function getaddrinfo(service, next) {
     var last_error
       , counter = 0