Implement timeout for dns and set default to 5s. Close #6

src/probeDns.js

@@ -1,14 +1,23 @@
 const measureDurationInMs = require('./measureDurationInMs');
 const probeStatus = require('./probeStatus');
-const dns = require('dns');
-module.exports = (config) => {
-  return new Promise((resolve) => {
+const { Resolver } = require('dns');
+module.exports = (config, DNSResolver = Resolver) => {
+  return new Promise((resolvePromise) => {
+    let timedOut = false;
+    const resolve = (value) => {
+      clearTimeout(timeout);
+      resolvePromise(value);
+    };
     const getDurationInMs = measureDurationInMs();
-    dns.resolveAny(config.host, (err, rawAddresses) => {
+    const resolver = new DNSResolver();
+    resolver.resolveAny(config.host, (err, rawAddresses) => {
       const result = {
         duration: getDurationInMs()
       };
-      if (err) {
+      if (timedOut) {
+        result.err_code = 'TIMEOUT';
+        result.probe_status = probeStatus.error
+      } else if (err) {
         result.err_code = err.code;
         if (config.expect.err_code) {
           if (config.expect.err_code == err.code) {
@@ -35,5 +44,9 @@ module.exports = (config) => {
       }
       resolve(result);
     });
+    const timeout = setTimeout(() => {
+      timedOut = true;
+      resolver.cancel();
+    }, config.timeout || 5000);
   });
 };

test/probeDnsTest.js

@@ -105,4 +105,32 @@ describe('probeDns', () => {
       res_addresses: 's3-website.eu-central-1.amazonaws.com'
     }, metrics);
   });
+
+  it('returns metrics for timeout', async () => {
+    class ResolverMock {
+      resolveAny(host, callback) {
+        setTimeout(() => {
+          callback()
+        }, 1000)
+      }
+      cancel() {
+        ResolverMock.cancelled = true
+      }
+    }
+    ResolverMock.cancelled = false
+    const metrics = await probeDns({
+      host: 'example.s3-website.eu-central-1.amazonaws.com',
+      expect: {
+        err_code: 'TIMEOUT'
+      },
+      timeout: 500
+    }, ResolverMock);
+    assert(metrics.duration >= 500, `duration >= 500, but was ${metrics.duration}`);
+    delete metrics.duration;
+    assert.deepEqual({
+      probe_status: 2,
+      err_code: 'TIMEOUT'
+    }, metrics);
+    assert.deepEqual(ResolverMock.cancelled, true)
+  });
 });