mpp: Add CLI option to opt-out of multi-part payments

Several tests are not well-suited for mpp, so I added a CLI option to opt-out
of the MPP support at startup time.

doc/lightningd-config.5

@@ -378,6 +378,16 @@ up space in the database\.
 Control how long invoices must have been expired before they are cleaned
 (if \fIautocleaninvoice-cycle\fR is non-zero)\.
 
+
+Payment control options:
+
+
+ \fBdisable-mpp\fR
+Disable the multi-part payment sending support in the \fBpay\fR plugin\. By default
+the MPP support is enabled, but it can be desirable to disable in situations
+in which each payment should result in a single HTLC being forwarded in the
+network\.
+
 .SH Networking options
 
 Note that for simple setups, the implicit \fIautolisten\fR option does the

doc/lightningd-config.5.md

@@ -309,6 +309,14 @@ up space in the database.
 Control how long invoices must have been expired before they are cleaned
 (if *autocleaninvoice-cycle* is non-zero).
 
+Payment control options:
+
+ **disable-mpp**
+Disable the multi-part payment sending support in the `pay` plugin. By default
+the MPP support is enabled, but it can be desirable to disable in situations
+in which each payment should result in a single HTLC being forwarded in the
+network.
+
 ### Networking options
 
 Note that for simple setups, the implicit *autolisten* option does the

lightningd/options.c

@@ -1201,6 +1201,9 @@ static void add_config(struct lightningd *ld,
 				      feature_offered(ld->our_features
 						      ->bits[INIT_FEATURE],
 						      OPT_LARGE_CHANNELS));
+		} else if (opt->cb == (void *)plugin_opt_flag_set) {
+			/* Noop, they will get added below along with the
+			 * OPT_HASARG options. */
 		} else {
 			/* Insert more decodes here! */
 			assert(!"A noarg option was added but was not handled");

plugins/libplugin-pay.c

@@ -2082,11 +2082,26 @@ REGISTER_PAYMENT_MODIFIER(waitblockheight, void *, NULL, waitblockheight_cb);
 #define MPP_TARGET_MSAT AMOUNT_MSAT(MPP_TARGET_SIZE)
 #define MPP_TARGET_FUZZ ( 1 * 1000 * 1000)
 
-static void presplit_cb(void *d, struct payment *p)
+static struct presplit_mod_data *presplit_mod_data_init(struct payment *p)
+{
+	struct presplit_mod_data *d;
+	if (p->parent == NULL) {
+		d = tal(p, struct presplit_mod_data);
+		d->disable = false;
+		return d;
+	} else {
+		return payment_mod_presplit_get_data(p->parent);
+	}
+}
+
+static void presplit_cb(struct presplit_mod_data *d, struct payment *p)
 {
 	struct payment *root = payment_root(p);
 	struct amount_msat amt = root->amount;
 
+	if (d->disable)
+		return payment_continue(p);
+
 	if (p->step == PAYMENT_STEP_ONION_PAYLOAD) {
 		/* We need to tell the last hop the total we're going to
 		 * send. Presplit disables amount fuzzing, so we should always
@@ -2166,7 +2181,8 @@ static void presplit_cb(void *d, struct payment *p)
 	payment_continue(p);
 }
 
-REGISTER_PAYMENT_MODIFIER(presplit, void *, NULL, presplit_cb);
+REGISTER_PAYMENT_MODIFIER(presplit, struct presplit_mod_data *,
+			  presplit_mod_data_init, presplit_cb);
 
 /*****************************************************************************
  * Adaptive splitter -- Split payment if we can't get it through.
@@ -2179,9 +2195,25 @@ REGISTER_PAYMENT_MODIFIER(presplit, void *, NULL, presplit_cb);
 
 #define MPP_ADAPTIVE_LOWER_LIMIT AMOUNT_MSAT(100 * 1000)
 
-static void adaptive_splitter_cb(void *d, struct payment *p)
+static struct presplit_mod_data *adaptive_splitter_data_init(struct payment *p)
+{
+	struct presplit_mod_data *d;
+	if (p->parent == NULL) {
+		d = tal(p, struct presplit_mod_data);
+		d->disable = false;
+		return d;
+	} else {
+		return payment_mod_presplit_get_data(p->parent);
+	}
+}
+
+static void adaptive_splitter_cb(struct presplit_mod_data *d, struct payment *p)
 {
 	struct payment *root = payment_root(p);
+
+	if (d->disable)
+		return payment_continue(p);
+
 	if (p->step == PAYMENT_STEP_ONION_PAYLOAD) {
 		/* We need to tell the last hop the total we're going to
 		 * send. Presplit disables amount fuzzing, so we should always
@@ -2236,5 +2268,5 @@ static void adaptive_splitter_cb(void *d, struct payment *p)
 	payment_continue(p);
 }
 
-REGISTER_PAYMENT_MODIFIER(adaptive_splitter, void *, NULL,
+REGISTER_PAYMENT_MODIFIER(adaptive_splitter, struct presplit_mod_data *,
-			  adaptive_splitter_cb);
+			  adaptive_splitter_data_init, adaptive_splitter_cb);

plugins/libplugin-pay.h

@@ -319,6 +319,14 @@ struct direct_pay_data {
 	 * attempt against the channel hints. */
 	struct short_channel_id_dir *chan;
 };
+
+/* Since presplit and adaptive mpp modifiers share the same information we
+ * just use the same backing struct. Should they deviate we can create an
+ * adaptive_splitter_mod_data struct and populate that. */
+struct presplit_mod_data {
+	bool disable;
+};
+
 /* List of globally available payment modifiers. */
 REGISTER_PAYMENT_MODIFIER_HEADER(retry, struct retry_mod_data);
 REGISTER_PAYMENT_MODIFIER_HEADER(routehints, struct routehints_data);
@@ -326,8 +334,8 @@ REGISTER_PAYMENT_MODIFIER_HEADER(exemptfee, struct exemptfee_data);
 REGISTER_PAYMENT_MODIFIER_HEADER(shadowroute, struct shadow_route_data);
 REGISTER_PAYMENT_MODIFIER_HEADER(directpay, struct direct_pay_data);
 extern struct payment_modifier waitblockheight_pay_mod;
-extern struct payment_modifier presplit_pay_mod;
+REGISTER_PAYMENT_MODIFIER_HEADER(presplit, struct presplit_mod_data);
-extern struct payment_modifier adaptive_splitter_pay_mod;
+REGISTER_PAYMENT_MODIFIER_HEADER(adaptive_splitter, struct presplit_mod_data);
 
 /* For the root payment we can seed the channel_hints with the result from
  * `listpeers`, hence avoid channels that we know have insufficient capacity

plugins/libplugin.c

@@ -862,6 +862,27 @@ char *u32_option(const char *arg, u32 *i)
 	return NULL;
 }
 
+char *bool_option(const char *arg, bool *i)
+{
+	if (!streq(arg, "true") && !streq(arg, "false"))
+		return tal_fmt(NULL, "'%s' is not a bool, must be \"true\" or \"false\"", arg);
+
+	*i = streq(arg, "true");
+	return NULL;
+}
+
+char *flag_option(const char *arg, bool *i)
+{
+	/* We only get called if the flag was provided, so *i should be false
+	 * by default */
+	assert(*i == false);
+	if (!streq(arg, "true"))
+		return tal_fmt(NULL, "Invalid argument '%s' passed to a flag", arg);
+
+	*i = true;
+	return NULL;
+}
+
 char *charp_option(const char *arg, char **p)
 {
 	*p = tal_strdup(NULL, arg);

plugins/libplugin.h

@@ -239,7 +239,9 @@ void plugin_log(struct plugin *p, enum log_level l, const char *fmt, ...) PRINTF
 /* Standard helpers */
 char *u64_option(const char *arg, u64 *i);
 char *u32_option(const char *arg, u32 *i);
+char *bool_option(const char *arg, bool *i);
 char *charp_option(const char *arg, char **p);
+char *flag_option(const char *arg, bool *i);
 
 /* The main plugin runner: append with 0 or more plugin_option(), then NULL. */
 void NORETURN LAST_ARG_NULL plugin_main(char *argv[],

plugins/pay.c

@@ -25,6 +25,8 @@
 /* Public key of this node. */
 static struct node_id my_id;
 static unsigned int maxdelay_default;
+static bool disablempp = false;
+
 static LIST_HEAD(pay_status);
 
 static LIST_HEAD(payments);
@@ -1955,6 +1957,8 @@ static struct command_result *json_paymod(struct command *cmd,
 
 	payment_mod_exemptfee_get_data(p)->amount = *exemptfee;
 	shadow_route = payment_mod_shadowroute_get_data(p);
+	payment_mod_presplit_get_data(p)->disable = disablempp;
+	payment_mod_adaptive_splitter_get_data(p)->disable = disablempp;
 
 	/* This is an MPP enabled pay command, disable amount fuzzing. */
 	shadow_route->fuzz_amount = false;
@@ -2004,5 +2008,9 @@ int main(int argc, char *argv[])
 {
 	setup_locale();
 	plugin_main(argv, init, PLUGIN_RESTARTABLE, NULL, commands,
-		    ARRAY_SIZE(commands), NULL, 0, NULL, 0, NULL);
+		    ARRAY_SIZE(commands), NULL, 0, NULL, 0,
+		    plugin_option("disable-mpp", "flag",
+				  "Disable multi-part payments.",
+				  flag_option, &disablempp),
+		    NULL);
 }