fetchinvoice: return the next period for recurring offers.

This is useful for the caller to know when to call again.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

plugins/fetchinvoice.c

@@ -200,6 +200,15 @@ static struct command_result *recv_onion_message(struct command *cmd,
 	} else
 		expected_amount = NULL;
 
+	/* BOLT-offers #12:
+	 * - if the offer contained `recurrence`:
+	 *   - MUST reject the invoice if `recurrence_basetime` is not set.
+	 */
+	if (sent->invreq->recurrence_counter && !inv->recurrence_basetime) {
+		badfield = "recurrence_basetime";
+		goto badinv;
+	}
+
 	/* BOLT-offers #12:
 	 * - SHOULD confirm authorization if the `description` does not exactly
 	 *   match the `offer`
@@ -252,6 +261,44 @@ static struct command_result *recv_onion_message(struct command *cmd,
 					  amount_msat(*inv->amount));
 	json_object_end(out);
 
+	/* We tell them about next period at this point, if any. */
+	if (sent->offer->recurrence) {
+		u64 next_counter, next_period_idx;
+		u64 paywindow_start, paywindow_end;
+
+		next_counter = *sent->invreq->recurrence_counter + 1;
+		if (sent->invreq->recurrence_start)
+			next_period_idx = *sent->invreq->recurrence_start
+				+ next_counter;
+		else
+			next_period_idx = next_counter;
+
+		/* If this was the last, don't tell them about a next! */
+		if (!sent->offer->recurrence_limit
+		    || next_period_idx <= *sent->offer->recurrence_limit) {
+			json_object_start(out, "next_period");
+			json_add_u64(out, "counter", next_counter);
+			json_add_u64(out, "starttime",
+				     offer_period_start(*inv->recurrence_basetime,
+							next_period_idx,
+							sent->offer->recurrence));
+			json_add_u64(out, "endtime",
+				     offer_period_start(*inv->recurrence_basetime,
+							next_period_idx + 1,
+							sent->offer->recurrence) - 1);
+
+			offer_period_paywindow(sent->offer->recurrence,
+					       sent->offer->recurrence_paywindow,
+					       sent->offer->recurrence_base,
+					       *inv->recurrence_basetime,
+					       next_period_idx,
+					       &paywindow_start, &paywindow_end);
+			json_add_u64(out, "paywindow_start", paywindow_start);
+			json_add_u64(out, "paywindow_end", paywindow_end);
+			json_object_end(out);
+		}
+	}
+
 	discard_result(command_finished(sent->cmd, out));
 	return command_hook_success(cmd);
 

tests/test_pay.py

@@ -3856,6 +3856,8 @@ def test_fetchinvoice(node_factory, bitcoind):
     inv1 = l1.rpc.call('fetchinvoice', {'offer': offer})
     inv2 = l1.rpc.call('fetchinvoice', {'offer': offer})
     assert inv1 != inv2
+    assert 'next_period' not in inv1
+    assert 'next_period' not in inv2
     l1.rpc.pay(inv1['invoice'])
     l1.rpc.pay(inv2['invoice'])
 
@@ -3868,6 +3870,8 @@ def test_fetchinvoice(node_factory, bitcoind):
     inv1 = l1.rpc.call('fetchinvoice', {'offer': offer})
     inv2 = l1.rpc.call('fetchinvoice', {'offer': offer})
     assert inv1 != inv2
+    assert 'next_period' not in inv1
+    assert 'next_period' not in inv2
 
     l1.rpc.pay(inv1['invoice'])
 
@@ -3890,12 +3894,23 @@ def test_fetchinvoice(node_factory, bitcoind):
                                        'recurrence_counter': 0,
                                        'recurrence_label': 'test recurrence'})
     print(ret)
+    period1 = ret['next_period']
+    assert period1['counter'] == 1
+    assert period1['endtime'] == period1['starttime'] + 59
+    assert period1['paywindow_start'] == period1['starttime'] - 60
+    assert period1['paywindow_end'] == period1['endtime']
 
     l1.rpc.pay(ret['invoice'], label='test recurrence')
 
     ret = l1.rpc.call('fetchinvoice', {'offer': offer,
                                        'recurrence_counter': 1,
                                        'recurrence_label': 'test recurrence'})
     print(ret)
+    period2 = ret['next_period']
+    assert period2['counter'] == 2
+    assert period2['starttime'] == period1['endtime'] + 1
+    assert period2['endtime'] == period2['starttime'] + 59
+    assert period2['paywindow_start'] == period2['starttime'] - 60
+    assert period2['paywindow_end'] == period2['endtime']
 
     l1.rpc.pay(ret['invoice'], label='test recurrence')