channeldb/invoices: special-case all zeros pay addr

Avoids indexing the all-zeros pay addr, since it is still in use by
legacy keysend. Without this, the pay addr index will reject all but the
first keysend since they will be detected as duplicates within the set
id index.

channeldb/invoice_test.go

@@ -313,6 +313,48 @@ func TestAddDuplicatePayAddr(t *testing.T) {
 	require.Error(t, err, ErrDuplicatePayAddr)
 }
 
+// TestAddDuplicateKeysendPayAddr asserts that we permit duplicate payment
+// addresses to be inserted if they are blank to support JIT legacy keysend
+// invoices.
+func TestAddDuplicateKeysendPayAddr(t *testing.T) {
+	db, cleanUp, err := makeTestDB()
+	defer cleanUp()
+	require.NoError(t, err)
+
+	// Create two invoices with the same _blank_ payment addr.
+	invoice1, err := randInvoice(1000)
+	require.NoError(t, err)
+	invoice1.Terms.PaymentAddr = BlankPayAddr
+
+	invoice2, err := randInvoice(20000)
+	require.NoError(t, err)
+	invoice2.Terms.PaymentAddr = BlankPayAddr
+
+	// Inserting both should succeed without a duplicate payment address
+	// failure.
+	inv1Hash := invoice1.Terms.PaymentPreimage.Hash()
+	_, err = db.AddInvoice(invoice1, inv1Hash)
+	require.NoError(t, err)
+
+	inv2Hash := invoice2.Terms.PaymentPreimage.Hash()
+	_, err = db.AddInvoice(invoice2, inv2Hash)
+	require.NoError(t, err)
+
+	// Querying for each should succeed. Here we use hash+addr refs since
+	// the lookup will fail if the hash and addr point to different
+	// invoices, so if both succeed we can be assured they aren't included
+	// in the payment address index.
+	ref1 := InvoiceRefByHashAndAddr(inv1Hash, BlankPayAddr)
+	dbInv1, err := db.LookupInvoice(ref1)
+	require.NoError(t, err)
+	require.Equal(t, invoice1, &dbInv1)
+
+	ref2 := InvoiceRefByHashAndAddr(inv2Hash, BlankPayAddr)
+	dbInv2, err := db.LookupInvoice(ref2)
+	require.NoError(t, err)
+	require.Equal(t, invoice2, &dbInv2)
+}
+
 // TestInvRefEquivocation asserts that retrieving or updating an invoice using
 // an equivocating InvoiceRef results in ErrInvRefEquivocation.
 func TestInvRefEquivocation(t *testing.T) {