fix: do not emit empty peer info objects (#85)

I noticed stack traces in the logs from trying to access properties
of `undefined`. It seems this module emits `undefined` `peerInfo`
values, for example when recieving a response to your own mDNS
query or a response with an invalid PeerID.

This PR guards on empty PeerInfo objects from `query.gotResponse`

Author: achingbrain

src/index.js

@@ -56,7 +56,10 @@ class MulticastDNS extends EventEmitter {
   async _onMdnsResponse (event) {
     try {
       const foundPeer = await query.gotResponse(event, this.peerInfo, this.serviceTag)
-      this.emit('peer', foundPeer)
+
+      if (foundPeer) {
+        this.emit('peer', foundPeer)
+      }
     } catch (err) {
       log('Error processing peer response', err)
     }

test/multicast-dns.spec.js

@@ -160,4 +160,35 @@ describe('MulticastDNS', () => {
     await mdns.start()
     await mdns.stop()
   })
+
+  it('should not emit undefined peer ids', async () => {
+    const mdns = new MulticastDNS({ peerInfo: pA, port: 50004 })
+    await mdns.start()
+
+    return new Promise((resolve, reject) => {
+      mdns.on('peer', (peerInfo) => {
+        if (!peerInfo) {
+          reject(new Error('peerInfo was not set'))
+        }
+      })
+
+      mdns.mdns.on('response', () => {
+        // query.gotResponse is async - we'll bail from that method when
+        // comparing the senders PeerId to our own but it'll happen later
+        // so allow enough time for the test to have failed if we emit
+        // empty PeerInfo objects
+        setTimeout(() => {
+          resolve()
+        }, 100)
+      })
+
+      // this will cause us to respond to ourselves
+      mdns.mdns.query({
+        questions: [{
+          name: 'localhost',
+          type: 'A'
+        }]
+      })
+    })
+  })
 })