fix: return empty array when no multiaddrs are known

Returning `undefined` makes the address length check in [dialler/index.js](https://github.com/libp2p/js-libp2p/blob/master/src/dialer/index.js#L73-L75)
fail with `cannot read property length of undefined` so the change
here is to always return an array, but it might be empty if we don't
know any multiaddrs for the given peer.

doc/API.md

@@ -760,7 +760,7 @@ Get the known [`Addresses`][address] of a provided peer.
 
 | Type | Description |
 |------|-------------|
-| `Array<Address>|undefined` | Array of peer's [`Addresses`][address] containing the multiaddr and its metadata if available, otherwise undefined |
+| `Array<Address>` | Array of peer's [`Addresses`][address] containing the multiaddr and its metadata |
 
 #### Example
 
@@ -797,7 +797,7 @@ Get the known `Multiaddr` of a provided peer. All returned multiaddrs will inclu
 
 | Type | Description |
 |------|-------------|
-| `Array<Multiaddr>|undefined` | Array of peer's multiaddr if available, otherwise undefined |
+| `Array<Multiaddr>` | Array of peer's multiaddr |
 
 #### Example
 

doc/CONFIGURATION.md

@@ -304,7 +304,7 @@ const node = await Libp2p.create({
   },
   config: {
     peerDiscovery: {
-      [WebRTCStar.tag]: {
+      webRTCStar: {
         enabled: true
       }
     }

src/dialer/index.js

@@ -112,7 +112,7 @@ class Dialer {
       this.peerStore.addressBook.add(id, multiaddrs)
     }
 
-    let addrs = this.peerStore.addressBook.getMultiaddrsForPeer(id) || []
+    let addrs = this.peerStore.addressBook.getMultiaddrsForPeer(id)
 
     // If received a multiaddr to dial, it should be the first to use
     // But, if we know other multiaddrs for the peer, we should try them too.

src/peer-store/address-book.js

@@ -168,9 +168,8 @@ class AddressBook extends Book {
   /**
    * Get the known multiaddrs for a given peer. All returned multiaddrs
    * will include the encapsulated `PeerId` of the peer.
-   * Returns `undefined` if there are no known multiaddrs for the given peer.
    * @param {PeerId} peerId
-   * @returns {Array<Multiaddr>|undefined}
+   * @returns {Array<Multiaddr>}
    */
   getMultiaddrsForPeer (peerId) {
     if (!PeerId.isPeerId(peerId)) {
@@ -180,7 +179,7 @@ class AddressBook extends Book {
     const record = this.data.get(peerId.toB58String())
 
     if (!record) {
-      return undefined
+      return []
     }
 
     return record.map((address) => {

src/peer-store/book.js

@@ -77,9 +77,8 @@ class Book {
 
   /**
    * Get the known data of a provided peer.
-   * Returns `undefined` if there is no available data for the given peer.
    * @param {PeerId} peerId
-   * @returns {Array<Data>|undefined}
+   * @returns {Array<Data>}
    */
   get (peerId) {
     if (!PeerId.isPeerId(peerId)) {

test/dialing/direct.node.js

@@ -96,15 +96,6 @@ describe('Dialing (direct, TCP)', () => {
       .and.to.have.nested.property('._errors[0].code', ErrorCodes.ERR_TRANSPORT_UNAVAILABLE)
   })
 
-  it('should fail to connect if peer has no known addresses', async () => {
-    const dialer = new Dialer({ transportManager: localTM, peerStore })
-    const peerId = await PeerId.createFromJSON(Peers[1])
-
-    await expect(dialer.connectToPeer(peerId))
-      .to.eventually.be.rejectedWith(Error)
-      .and.to.have.nested.property('.code', ErrorCodes.ERR_NO_VALID_ADDRESSES)
-  })
-
   it('should be able to connect to a given peer id', async () => {
     const peerStore = new PeerStore()
     const dialer = new Dialer({

test/peer-store/address-book.spec.js

@@ -323,10 +323,10 @@ describe('addressBook', () => {
       throw new Error('invalid peerId should throw error')
     })
 
-    it('returns undefined if no multiaddrs are known for the provided peer', () => {
+    it('returns empty array if no multiaddrs are known for the provided peer', () => {
       const addresses = ab.getMultiaddrsForPeer(peerId)
 
-      expect(addresses).to.not.exist()
+      expect(addresses).to.be.empty()
     })
 
     it('returns the multiaddrs stored', () => {