invoices+channeldb: Fix AMP invoices behaviour.

We now cancel all HTLCs of an AMP invoice as soon as it expires.
Otherwise because we mark the invoice as cancelled we would not
allow accepted HTLCs to be resolved via the invoiceEventLoop.

invoices/invoiceregistry_test.go

@@ -117,6 +117,10 @@ func TestInvoiceRegistry(t *testing.T) {
 			name: "FailPartialAMPPayment",
 			test: testFailPartialAMPPayment,
 		},
+		{
+			name: "CancelAMPInvoicePendingHTLCs",
+			test: testCancelAMPInvoicePendingHTLCs,
+		},
 	}
 
 	makeKeyValueDB := func(t *testing.T) (invpkg.InvoiceDB,
@@ -2441,3 +2445,130 @@ func testFailPartialAMPPayment(t *testing.T,
 			"expected HTLC to be canceled")
 	}
 }
+
+// testCancelAMPInvoicePendingHTLCs tests the case where an AMP invoice is
+// canceled and the remaining HTLCs are also canceled so that no HTLCs are left
+// in the accepted state.
+func testCancelAMPInvoicePendingHTLCs(t *testing.T,
+	makeDB func(t *testing.T) (invpkg.InvoiceDB, *clock.TestClock)) {
+
+	t.Parallel()
+
+	ctx := newTestContext(t, nil, makeDB)
+	ctxb := context.Background()
+
+	const (
+		expiry    = uint32(testCurrentHeight + 20)
+		numShards = 4
+	)
+
+	var (
+		shardAmt = testInvoiceAmount / lnwire.MilliSatoshi(numShards)
+		payAddr  [32]byte
+	)
+	_, err := rand.Read(payAddr[:])
+	require.NoError(t, err)
+
+	// Create an AMP invoice we are going to pay via a multi-part payment.
+	ampInvoice := newInvoice(t, false, true)
+
+	// An AMP invoice is referenced by the payment address.
+	ampInvoice.Terms.PaymentAddr = payAddr
+
+	_, err = ctx.registry.AddInvoice(
+		ctxb, ampInvoice, testInvoicePaymentHash,
+	)
+	require.NoError(t, err)
+
+	htlcPayloadSet1 := &mockPayload{
+		mpp: record.NewMPP(testInvoiceAmount, payAddr),
+		// We are not interested in settling the AMP HTLC so we don't
+		// use valid shares.
+		amp: record.NewAMP([32]byte{1}, [32]byte{1}, 1),
+	}
+
+	// Send first HTLC which pays part of the invoice.
+	hodlChan1 := make(chan interface{}, 1)
+	resolution, err := ctx.registry.NotifyExitHopHtlc(
+		lntypes.Hash{1}, shardAmt, expiry, testCurrentHeight,
+		getCircuitKey(1), hodlChan1, nil, htlcPayloadSet1,
+	)
+	require.NoError(t, err)
+	require.Nil(t, resolution, "did not expect direct resolution")
+
+	htlcPayloadSet2 := &mockPayload{
+		mpp: record.NewMPP(testInvoiceAmount, payAddr),
+		// We are not interested in settling the AMP HTLC so we don't
+		// use valid shares.
+		amp: record.NewAMP([32]byte{2}, [32]byte{2}, 1),
+	}
+
+	// Send htlc 2 which should be added to the invoice as expected.
+	hodlChan2 := make(chan interface{}, 1)
+	resolution, err = ctx.registry.NotifyExitHopHtlc(
+		lntypes.Hash{2}, shardAmt, expiry, testCurrentHeight,
+		getCircuitKey(2), hodlChan2, nil, htlcPayloadSet2,
+	)
+	require.NoError(t, err)
+	require.Nil(t, resolution, "did not expect direct resolution")
+
+	require.Eventuallyf(t, func() bool {
+		inv, err := ctx.registry.LookupInvoice(
+			ctxb, testInvoicePaymentHash,
+		)
+		require.NoError(t, err)
+
+		return len(inv.Htlcs) == 2
+	}, testTimeout, time.Millisecond*100, "HTLCs not added to invoice")
+
+	// expire the invoice here.
+	ctx.clock.SetTime(testTime.Add(65 * time.Minute))
+
+	// Expect HLTC 1 to be canceled via the MPPTimeout fail resolution.
+	select {
+	case resolution := <-hodlChan1:
+		htlcResolution, _ := resolution.(invpkg.HtlcResolution)
+		_, ok := htlcResolution.(*invpkg.HtlcFailResolution)
+		require.True(
+			t, ok, "expected fail resolution, got: %T", resolution,
+		)
+
+	case <-time.After(testTimeout):
+		t.Fatal("timeout waiting for HTLC resolution")
+	}
+
+	// Expect HLTC 2 to be canceled via the MPPTimeout fail resolution.
+	select {
+	case resolution := <-hodlChan2:
+		htlcResolution, _ := resolution.(invpkg.HtlcResolution)
+		_, ok := htlcResolution.(*invpkg.HtlcFailResolution)
+		require.True(
+			t, ok, "expected fail resolution, got: %T", resolution,
+		)
+
+	case <-time.After(testTimeout):
+		t.Fatal("timeout waiting for HTLC resolution")
+	}
+
+	require.Eventuallyf(t, func() bool {
+		inv, err := ctx.registry.LookupInvoice(
+			ctxb, testInvoicePaymentHash,
+		)
+		require.NoError(t, err)
+
+		return inv.State == invpkg.ContractCanceled
+	}, testTimeout, time.Millisecond*100, "invoice not canceled")
+
+	// Fetch the invoice again and compare the number of cancelled HTLCs.
+	inv, err := ctx.registry.LookupInvoice(
+		ctxb, testInvoicePaymentHash,
+	)
+	require.NoError(t, err)
+
+	// Make sure all HTLCs are in the cancelled state.
+	require.Len(t, inv.Htlcs, 2)
+	for _, htlc := range inv.Htlcs {
+		require.Equal(t, invpkg.HtlcStateCanceled, htlc.State,
+			"expected HTLC to be canceled")
+	}
+}