feat: improve circuit err messages (libp2p#250)

* feat: improve circuit err handling

* feat: add test to to validate err when circuit not enabled

src/dial.js

@@ -89,18 +89,20 @@ function dial (swtch) {
 
       const tKeys = swtch.availableTransports(pi)
 
+      const circuitEnabled = Boolean(swtch.transports[Circuit.tag])
       let circuitTried = false
       nextTransport(tKeys.shift())
 
       function nextTransport (key) {
         let transport = key
         if (!transport) {
-          if (circuitTried) {
-            return cb(new Error(`Circuit already tried!`))
+          if (!circuitEnabled) {
+            const msg = `Circuit not enabled and all transports failed to dial peer ${pi.id.toB58String()}!`
+            return cb(new Error(msg))
           }
 
-          if (!swtch.transports[Circuit.tag]) {
-            return cb(new Error(`Circuit not enabled!`))
+          if (circuitTried) {
+            return cb(new Error(`No available transports to dial peer ${pi.id.toB58String()}!`))
           }
 
           log(`Falling back to dialing over circuit`)

test/circuit-relay.node.js

@@ -54,6 +54,15 @@ describe(`circuit`, function () {
     ], done)
   })
 
+  it('circuit not enabled and all transports failed', (done) => {
+    swarmA.dial(swarmC._peerInfo, (err, conn) => {
+      expect(err).to.exist()
+      expect(err).to.match(/Circuit not enabled and all transports failed to dial peer/)
+      expect(conn).to.not.exist()
+      done()
+    })
+  })
+
   it('.enableCircuitRelay', () => {
     swarmA.connection.enableCircuitRelay({ enabled: true })
     expect(Object.keys(swarmA.transports).length).to.equal(3)
@@ -88,7 +97,7 @@ describe(`circuit`, function () {
 
     swarmA.dial(swarmC._peerInfo, (err, conn) => {
       expect(err).to.exist()
-      expect(err).to.match(/Circuit already tried!/)
+      expect(err).to.match(/No available transports to dial peer/)
       expect(conn).to.not.exist()
       expect(dialSpyA.callCount).to.be.eql(1)
       done()