aperture+challenger: add error channel to challenger

To make sure we can capture errors in the challenger's invoice
subscription, we hand the main error channel to the challenger so it can
report back errors on it.

aperture.go

@@ -110,7 +110,10 @@ func run() error {
 			Value: price,
 		}, nil
 	}
-	challenger, err := NewLndChallenger(cfg.Authenticator, genInvoiceReq)
+	errChan := make(chan error)
+	challenger, err := NewLndChallenger(
+		cfg.Authenticator, genInvoiceReq, errChan,
+	)
 	if err != nil {
 		return err
 	}
@@ -164,7 +167,6 @@ func run() error {
 	)
 	log.Infof("Starting the server, listening on %s.", cfg.ListenAddr)
 
-	errChan := make(chan error)
 	wg.Add(1)
 	go func() {
 		defer wg.Done()

challenger.go

@@ -49,6 +49,8 @@ type LndChallenger struct {
 	invoicesCancel func()
 	invoicesCond   *sync.Cond
 
+	errChan chan<- error
+
 	quit chan struct{}
 	wg   sync.WaitGroup
 }
@@ -66,8 +68,8 @@ const (
 
 // NewLndChallenger creates a new challenger that uses the given connection
 // details to connect to an lnd backend to create payment challenges.
-func NewLndChallenger(cfg *authConfig, genInvoiceReq InvoiceRequestGenerator) (
+func NewLndChallenger(cfg *authConfig, genInvoiceReq InvoiceRequestGenerator,
-	*LndChallenger, error) {
+	errChan chan<- error) (*LndChallenger, error) {
 
 	if genInvoiceReq == nil {
 		return nil, fmt.Errorf("genInvoiceReq cannot be nil")
@@ -89,6 +91,7 @@ func NewLndChallenger(cfg *authConfig, genInvoiceReq InvoiceRequestGenerator) (
 		invoicesMtx:   invoicesMtx,
 		invoicesCond:  sync.NewCond(invoicesMtx),
 		quit:          make(chan struct{}),
+		errChan:       errChan,
 	}, nil
 }
 

challenger_test.go

@@ -20,6 +20,7 @@ type invoiceStreamMock struct {
 	lnrpc.Lightning_SubscribeInvoicesClient
 
 	updateChan chan *lnrpc.Invoice
+	errChan    chan error
 	quit       chan struct{}
 }
 
@@ -28,6 +29,9 @@ func (i *invoiceStreamMock) Recv() (*lnrpc.Invoice, error) {
 	case msg := <-i.updateChan:
 		return msg, nil
 
+	case err := <-i.errChan:
+		return nil, err
+
 	case <-i.quit:
 		return nil, context.Canceled
 	}
@@ -36,6 +40,7 @@ func (i *invoiceStreamMock) Recv() (*lnrpc.Invoice, error) {
 type mockInvoiceClient struct {
 	invoices   []*lnrpc.Invoice
 	updateChan chan *lnrpc.Invoice
+	errChan    chan error
 	quit       chan struct{}
 
 	lastAddIndex uint64
@@ -60,6 +65,7 @@ func (m *mockInvoiceClient) SubscribeInvoices(_ context.Context,
 
 	return &invoiceStreamMock{
 		updateChan: m.updateChan,
+		errChan:    m.errChan,
 		quit:       m.quit,
 	}, nil
 }
@@ -81,9 +87,10 @@ func (m *mockInvoiceClient) stop() {
 	close(m.quit)
 }
 
-func newChallenger() (*LndChallenger, *mockInvoiceClient) {
+func newChallenger() (*LndChallenger, *mockInvoiceClient, chan error) {
 	mockClient := &mockInvoiceClient{
 		updateChan: make(chan *lnrpc.Invoice),
+		errChan:    make(chan error, 1),
 		quit:       make(chan struct{}),
 	}
 	genInvoiceReq := func(price int64) (*lnrpc.Invoice, error) {
@@ -91,6 +98,7 @@ func newChallenger() (*LndChallenger, *mockInvoiceClient) {
 			nil
 	}
 	invoicesMtx := &sync.Mutex{}
+	mainErrChan := make(chan error)
 	return &LndChallenger{
 		client:        mockClient,
 		genInvoiceReq: genInvoiceReq,
@@ -98,7 +106,8 @@ func newChallenger() (*LndChallenger, *mockInvoiceClient) {
 		quit:          make(chan struct{}),
 		invoicesMtx:   invoicesMtx,
 		invoicesCond:  sync.NewCond(invoicesMtx),
-	}, mockClient
+		errChan:       mainErrChan,
+	}, mockClient, mainErrChan
 }
 
 func newInvoice(hash lntypes.Hash, addIndex uint64,
@@ -119,12 +128,13 @@ func TestLndChallenger(t *testing.T) {
 
 	// First of all, test that the NewLndChallenger doesn't allow a nil
 	// invoice generator function.
-	_, err := NewLndChallenger(nil, nil)
+	errChan := make(chan error)
+	_, err := NewLndChallenger(nil, nil, errChan)
 	require.Error(t, err)
 
 	// Now mock the lnd backend and create a challenger instance that we can
 	// test.
-	c, invoiceMock := newChallenger()
+	c, invoiceMock, _ := newChallenger()
 
 	// Creating a new challenge should add an invoice to the lnd backend.
 	req, hash, err := c.NewChallenge(1337)