fix: survive bad dns record (#313)

There's currently a bad txt record in the libp2p bootstrap DNS
record so filter out anything that's not in the correct format.

src/resolvers/index.ts

@@ -49,7 +49,7 @@ export async function dnsaddrResolver (addr: Multiaddr, options: AbortOptions =
 
   const records = await resolver.resolveTxt(`_dnsaddr.${hostname}`)
 
-  let addresses = records.flat().map((a) => a.split('=')[1])
+  let addresses = records.flat().map((a) => a.split('=')[1]).filter(Boolean)
 
   if (peerId != null) {
     addresses = addresses.filter((entry) => entry.includes(peerId))

test/resolvers.spec.ts

@@ -23,6 +23,14 @@ const dnsaddrStub2 = [
   ['dnsaddr=/ip6/2604:1380:2000:7a00::1/udp/4001/quic/p2p/QmbLHAnMoJPWSCR5Zhtx6BHJX9KiKNN6tpvbUcqanj75Nb']
 ]
 
+const dnsaddrStub3 = [
+  ['dnsaddr=/dnsaddr/sv15.bootstrap.libp2p.io/p2p/QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN'],
+  ['dnsaddr=/dnsaddr/ny5.bootstrap.libp2p.io/p2p/QmQCU2EcMqAqQPR2i9bChDtGNJchTbq5TbXJJ16u19uLTa'],
+  ['dnsaddr_record_value'],
+  ['dnsaddr=/dnsaddr/am6.bootstrap.libp2p.io/p2p/QmbLHAnMoJPWSCR5Zhtx6BHJX9KiKNN6tpvbUcqanj75Nb'],
+  ['dnsaddr=/dnsaddr/sg1.bootstrap.libp2p.io/p2p/QmcZf59bWwK5XFi76CZX8cbJ4BhTzzA3gU1ZjYZcYW3dwt']
+]
+
 describe('multiaddr resolve', () => {
   it('should throw if no resolver is available', async () => {
     const ma = multiaddr('/dnsaddr/bootstrap.libp2p.io')
@@ -98,6 +106,20 @@ describe('multiaddr resolve', () => {
       })
     })
 
+    it('can resolve dnsaddr with bad record', async () => {
+      const ma = multiaddr('/dnsaddr/am6.bootstrap.libp2p.io/p2p/QmbLHAnMoJPWSCR5Zhtx6BHJX9KiKNN6tpvbUcqanj75Nb')
+
+      const stub = sinon.stub(Resolver.prototype, 'resolveTxt')
+      stub.onCall(0).returns(Promise.resolve(dnsaddrStub3))
+
+      // Resolve
+      const resolvedMas = await ma.resolve()
+
+      // Should only have one address with the same peer id and should ignore the bad record
+      expect(resolvedMas).to.have.lengthOf(1)
+      expect(resolvedMas[0].toString()).to.equal(ma.toString())
+    })
+
     it('can cancel resolving', async () => {
       const ma = multiaddr('/dnsaddr/bootstrap.libp2p.ii/p2p/QmbLHAnMoJPWSCR5Zhtx6BHJX9KiKNN6tpvbUcqanj75Nc')
       const controller = new AbortController()