pay: Have sendpay wait for payment to be saved.

The payment should be stored in a "timely" manner, i.e.
within 10ms.

lightningd/lightningd.c

@@ -68,6 +68,7 @@ static struct lightningd *new_lightningd(const tal_t *ctx)
 	ld->rgb = NULL;
 	list_head_init(&ld->connects);
 	list_head_init(&ld->waitsendpay_commands);
+	list_head_init(&ld->sendpay_commands);
 	ld->wireaddrs = tal_arr(ld, struct wireaddr, 0);
 	ld->portnum = DEFAULT_PORT;
 	timers_init(&ld->timers, time_mono());

lightningd/lightningd.h

@@ -135,6 +135,8 @@ struct lightningd {
 
 	/* Outstanding waitsendpay commands. */
 	struct list_head waitsendpay_commands;
+	/* Outstanding sendpay commands. */
+	struct list_head sendpay_commands;
 
 	/* Maintained by invoices.c */
 	struct invoices *invoices;

lightningd/pay.c

@@ -36,10 +36,28 @@ static void destroy_sendpay_command(struct sendpay_command *pc)
 	list_del(&pc->list);
 }
 
+/* Owned by cxt, if cxt is deleted, then cb will
+ * no longer be called. */
+static void
+add_sendpay_waiter(const tal_t *cxt,
+		   const struct sha256 *payment_hash,
+		   struct lightningd *ld,
+		   void (*cb)(const struct sendpay_result *, void*),
+		   void *cbarg)
+{
+	struct sendpay_command *pc = tal(cxt, struct sendpay_command);
+
+	pc->payment_hash = *payment_hash;
+	pc->cb = cb;
+	pc->cbarg = cbarg;
+	list_add(&ld->sendpay_commands, &pc->list);
+	tal_add_destructor(pc, destroy_sendpay_command);
+}
+
 /* Owned by cxt; if cxt is deleted, then cb will
  * no longer be called. */
 static void
-add_payment_waiter(const tal_t *cxt,
+add_waitsendpay_waiter(const tal_t *cxt,
 		       const struct sha256 *payment_hash,
 		       struct lightningd *ld,
 		       void (*cb)(const struct sendpay_result *, void*),
@@ -368,7 +386,28 @@ static void report_routing_failure(struct log *log,
 void payment_store(struct lightningd *ld,
 		   const struct sha256 *payment_hash)
 {
+	const tal_t *tmpctx = tal_tmpctx(ld);
+	struct sendpay_command *pc;
+	struct sendpay_command *next;
+	struct sendpay_result *result;
+
 	wallet_payment_store(ld->wallet, payment_hash);
+
+	/* Invent a sendpay result with PAY_IN_PROGRESS. */
+	result = sendpay_result_simple_fail(tmpctx, PAY_IN_PROGRESS,
+					    "Payment is still in progress");
+
+	/* Trigger any sendpay commands waiting for the store to occur. */
+	list_for_each_safe(&ld->sendpay_commands, pc, next, list) {
+		if (!structeq(payment_hash, &pc->payment_hash))
+			continue;
+
+		/* Delete later if callback did not delete. */
+		tal_steal(tmpctx, pc);
+		pc->cb(result, pc->cbarg);
+	}
+
+	tal_free(tmpctx);
 }
 
 void payment_failed(struct lightningd *ld, const struct htlc_out *hout,
@@ -490,7 +529,7 @@ bool wait_payment(const tal_t *cxt,
 		  void (*cb)(const struct sendpay_result *, void*),
 		  void *cbarg)
 {
-	const tal_t *tmpctx = tal_tmpctx(cxt);
+	const tal_t *tmpctx = tal_tmpctx(NULL);
 	struct wallet_payment *payment;
 	struct sendpay_result *result;
 	char const *details;
@@ -520,7 +559,7 @@ bool wait_payment(const tal_t *cxt,
 
 	switch (payment->status) {
 	case PAYMENT_PENDING:
-		add_payment_waiter(cxt, payment_hash, ld, cb, cbarg);
+		add_waitsendpay_waiter(cxt, payment_hash, ld, cb, cbarg);
 		cb_not_called = true;
 		goto end;
 
@@ -575,13 +614,14 @@ end:
 	return cb_not_called;
 }
 
-/* Returns the result if available now, or NULL if the
- * sendpay was deferred for later. */
-struct sendpay_result *
+/* Returns false if cb was called, true if cb not yet called. */
+bool
 send_payment(const tal_t *ctx,
 	     struct lightningd* ld,
 	     const struct sha256 *rhash,
-	     const struct route_hop *route)
+	     const struct route_hop *route,
+	     void (*cb)(const struct sendpay_result *, void*),
+	     void *cbarg)
 {
 	const u8 *onion;
 	u8 sessionkey[32];
@@ -629,39 +669,42 @@ send_payment(const tal_t *ctx,
 		log_debug(ld->log, "send_payment: found previous");
 		if (payment->status == PAYMENT_PENDING) {
 			log_add(ld->log, "Payment is still in progress");
-			tal_free(tmpctx);
-			return sendpay_result_simple_fail(ctx,
+			result = sendpay_result_simple_fail(tmpctx,
 							    PAY_IN_PROGRESS,
 							    "Payment is still in progress");
+			cb(result, cbarg);
+			return false;
 		}
 		if (payment->status == PAYMENT_COMPLETE) {
 			log_add(ld->log, "... succeeded");
 			/* Must match successful payment parameters. */
 			if (payment->msatoshi != hop_data[n_hops-1].amt_forward) {
-				char *msg = tal_fmt(ctx,
+				char *msg = tal_fmt(tmpctx,
 						    "Already succeeded "
 						    "with amount %"PRIu64,
 						    payment->msatoshi);
-				tal_free(tmpctx);
-				return sendpay_result_simple_fail(ctx,
+				result = sendpay_result_simple_fail(tmpctx,
 								    PAY_RHASH_ALREADY_USED,
 								    msg);
+				cb(result, cbarg);
+				return false;
 			}
 			if (!structeq(&payment->destination, &ids[n_hops-1])) {
-				char *msg = tal_fmt(ctx,
+				char *msg = tal_fmt(tmpctx,
 						    "Already succeeded to %s",
 						    type_to_string(tmpctx,
 								   struct pubkey,
 								   &payment->destination));
-				tal_free(tmpctx);
-				return sendpay_result_simple_fail(ctx,
+				result = sendpay_result_simple_fail(tmpctx,
 								    PAY_RHASH_ALREADY_USED,
 								    msg);
+				cb(result, cbarg);
+				return false;
 			}
-			result = sendpay_result_success(ctx,
+			result = sendpay_result_success(tmpctx,
 							payment->payment_preimage);
-			tal_free(tmpctx);
-			return result;
+			cb(result, cbarg);
+			return false;
 		}
 		wallet_payment_delete(ld->wallet, rhash);
 		log_add(ld->log, "... retrying");
@@ -676,10 +719,11 @@ send_payment(const tal_t *ctx,
 		report_routing_failure(ld->log, ld->gossip, fail);
 
 		/* Report routing failure to caller */
-		tal_free(tmpctx);
-		return sendpay_result_route_failure(ctx, true, fail, NULL,
+		result = sendpay_result_route_failure(tmpctx, true, fail, NULL,
 						      "No connection to first "
 						      "peer found");
+		cb(result, cbarg);
+		return false;
 	}
 
 	randombytes_buf(&sessionkey, sizeof(sessionkey));
@@ -703,9 +747,10 @@ send_payment(const tal_t *ctx,
 		report_routing_failure(ld->log, ld->gossip, fail);
 
 		/* Report routing failure to caller */
-		tal_free(tmpctx);
-		return sendpay_result_route_failure(ctx, true, fail, NULL,
+		result = sendpay_result_route_failure(tmpctx, true, fail, NULL,
 						      "First peer not ready");
+		cb(result, cbarg);
+		return false;
 	}
 
 	/* Copy channels used along the route. */
@@ -729,8 +774,10 @@ send_payment(const tal_t *ctx,
 	/* We write this into db when HTLC is actually sent. */
 	wallet_payment_setup(ld->wallet, payment);
 
+	add_sendpay_waiter(ctx, rhash, ld, cb, cbarg);
+
 	tal_free(tmpctx);
-	return NULL;
+	return true;
 }
 
 /*-----------------------------------------------------------------------------
@@ -827,6 +874,18 @@ static void json_sendpay_on_resolve(const struct sendpay_result* r,
 				    void *vcmd)
 {
 	struct command *cmd = (struct command*) vcmd;
+	struct json_result *response;
+
+	if (!r->succeeded && r->errorcode == PAY_IN_PROGRESS) {
+		/* This is normal for sendpay. Succeed. */
+		response = new_json_result(cmd);
+		json_object_start(response, NULL);
+		json_add_string(response, "message",
+				"Monitor status with listpayments or waitsendpay");
+		json_add_bool(response, "completed", false);
+		json_object_end(response);
+		command_success(cmd, response);
+	} else
 		json_waitsendpay_on_resolve(r, cmd);
 }
 
@@ -838,8 +897,6 @@ static void json_sendpay(struct command *cmd,
 	size_t n_hops;
 	struct sha256 rhash;
 	struct route_hop *route;
-	struct sendpay_result *r;
-	struct json_result *response;
 
 	if (!json_get_params(cmd, buffer, params,
 			     "route", &routetok,
@@ -918,18 +975,9 @@ static void json_sendpay(struct command *cmd,
 		return;
 	}
 
-	r = send_payment(cmd, cmd->ld, &rhash, route);
-	if (r)
-		json_sendpay_on_resolve(r, cmd);
-	else {
-		response = new_json_result(cmd);
-		json_object_start(response, NULL);
-		json_add_string(response, "message",
-				"Monitor status with listpayments or waitsendpay");
-		json_add_bool(response, "completed", false);
-		json_object_end(response);
-		command_success(cmd, response);
-	}
+	if (send_payment(cmd, cmd->ld, &rhash, route,
+			  &json_sendpay_on_resolve, cmd))
+		command_still_pending(cmd);
 }
 
 static const struct json_command sendpay_command = {

lightningd/pay.h

@@ -40,15 +40,25 @@ struct sendpay_result {
 	const char *details;
 };
 
-/* Initiate a payment.  Return NULL if the payment will be
- * scheduled for later, or a result if the result is available
- * immediately. If returning an immediate result, the returned
- * object is allocated from the given context. Otherwise, the
- * return context is ignored. */
-struct sendpay_result *send_payment(const tal_t *ctx,
+/* Initiate a payment.  Return true if the callback will be
+ * scheduled for later, or false if the callback has already
+ * been called. If the given context is freed before the
+ * callback is called, then the callback will no longer be
+ * called.
+ *
+ * This will call the callback "soon" in 10ms or less.
+ *
+ * Typically the callback will be called with a failed
+ * sendpay_result indicating an error code of PAY_IN_PROGRESS.
+ * It will only call the callback with successful sendpay_result
+ * if the payment has already completed with the same amount
+ * and destination before. */
+bool send_payment(const tal_t *ctx,
 		  struct lightningd* ld,
 		  const struct sha256 *rhash,
-				    const struct route_hop *route);
+		  const struct route_hop *route,
+		  void (*cb)(const struct sendpay_result *, void*),
+		  void *cbarg);
 /* Wait for a previous send_payment to complete in definite
  * success or failure. If the given context is freed before
  * the callback is called, then the callback will no longer

lightningd/payalgo.c

@@ -189,6 +189,12 @@ static void json_pay_sendpay_resolve(const struct sendpay_result *r,
 
 	why = should_delay_retry(pay->try_parent, r);
 	if (why) {
+		/* We have some reason to delay retrying. */
+
+		/* Clear previous try memory. */
+		pay->try_parent = tal_free(pay->try_parent);
+		pay->try_parent = tal(pay, char);
+
 		log_info(pay->cmd->ld->log,
 			 "pay(%p): Delay before retry: %s", pay, why);
 		/* Delay for 3 seconds if needed. FIXME: random
@@ -224,6 +230,26 @@ static void log_route(struct pay *pay, struct route_hop *route)
 	tal_free(tmpctx);
 }
 
+static void json_pay_sendpay_resume(const struct sendpay_result *r,
+				    void *vpay)
+{
+	struct pay *pay = (struct pay *) vpay;
+	bool completed = r->succeeded || r->errorcode != PAY_IN_PROGRESS;
+
+	if (completed)
+		/* Already completed. */
+		json_pay_sendpay_resolve(r, pay);
+	else {
+		/* Clear previous try memory. */
+		pay->try_parent = tal_free(pay->try_parent);
+		pay->try_parent = tal(pay, char);
+
+		/* Not yet complete? Wait for it. */
+		wait_payment(pay->try_parent, pay->cmd->ld, &pay->payment_hash,
+			     json_pay_sendpay_resolve, pay);
+	}
+}
+
 static void json_pay_getroute_reply(struct subd *gossip UNUSED,
 				    const u8 *reply, const int *fds UNUSED,
 				    struct pay *pay)
@@ -234,7 +260,6 @@ static void json_pay_getroute_reply(struct subd *gossip UNUSED,
 	double feepercent;
 	bool fee_too_high;
 	struct json_result *data;
-	struct sendpay_result *result;
 
 	fromwire_gossip_getroute_reply(reply, reply, &route);
 
@@ -295,17 +320,9 @@ static void json_pay_getroute_reply(struct subd *gossip UNUSED,
 
 	log_route(pay, route);
 
-	result = send_payment(pay->try_parent,
-			      pay->cmd->ld, &pay->payment_hash, route);
-	/* Resolved immediately? */
-	if (result)
-		json_pay_sendpay_resolve(result, pay);
-	/* Wait for resolution */
-	else
-		wait_payment(pay->try_parent,
-			     pay->cmd->ld,
-			     &pay->payment_hash,
-			     &json_pay_sendpay_resolve, pay);
+	send_payment(pay->try_parent,
+		     pay->cmd->ld, &pay->payment_hash, route,
+		     &json_pay_sendpay_resume, pay);
 }
 
 /* Start a payment attempt. Return true if deferred,