plugin/offers: add inject_onionmessage helper.

This will obsolete the existing calls to RPC "sendonionmessage", but
we transition by introducing it separately.  It's designed to work with
the common/onion_message routines and "injectonionmessage".

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

plugins/Makefile

@@ -208,7 +208,7 @@ $(PLUGIN_KEYSEND_OBJS): $(PLUGIN_PAY_LIB_HEADER)
 
 plugins/spenderp: bitcoin/block.o bitcoin/preimage.o bitcoin/psbt.o common/psbt_open.o common/json_channel_type.o common/channel_type.o common/features.o wire/peer_wiregen.o $(PLUGIN_SPENDER_OBJS) $(PLUGIN_LIB_OBJS) $(PLUGIN_COMMON_OBJS) $(JSMN_OBJS)
 
-plugins/offers: $(PLUGIN_OFFERS_OBJS) $(PLUGIN_LIB_OBJS) $(PLUGIN_COMMON_OBJS) common/addr.o common/bolt12.o common/bolt12_merkle.o common/bolt11_json.o common/iso4217.o $(WIRE_OBJS) $(WIRE_BOLT12_OBJS) bitcoin/block.o common/channel_id.o bitcoin/preimage.o common/blindedpath.o common/invoice_path_id.o common/blinding.o common/hmac.o common/json_blinded_path.o common/gossmap.o common/fp16.o $(JSMN_OBJS) common/dijkstra.o common/route.o common/gossmods_listpeerchannels.o 
+plugins/offers: $(PLUGIN_OFFERS_OBJS) $(PLUGIN_LIB_OBJS) $(PLUGIN_COMMON_OBJS) common/addr.o common/bolt12.o common/bolt12_merkle.o common/bolt11_json.o common/iso4217.o $(WIRE_OBJS) $(WIRE_BOLT12_OBJS) bitcoin/block.o common/channel_id.o bitcoin/preimage.o common/blindedpath.o common/invoice_path_id.o common/blinding.o common/hmac.o common/json_blinded_path.o common/gossmap.o common/fp16.o $(JSMN_OBJS) common/dijkstra.o common/route.o common/gossmods_listpeerchannels.o common/onion_message.o
 
 plugins/funder: bitcoin/psbt.o common/psbt_open.o $(PLUGIN_FUNDER_OBJS) $(PLUGIN_LIB_OBJS) $(PLUGIN_COMMON_OBJS) $(JSMN_OBJS)
 

plugins/offers.c

@@ -17,6 +17,7 @@
 #include <common/json_param.h>
 #include <common/json_stream.h>
 #include <common/memleak.h>
+#include <common/onion_message.h>
 #include <errno.h>
 #include <plugins/fetchinvoice.h>
 #include <plugins/offers.h>
@@ -109,6 +110,35 @@ bool convert_to_scidd(struct command *cmd,
 	return true;
 }
 
+struct command_result *
+inject_onionmessage_(struct command *cmd,
+		     const struct onion_message *omsg,
+		     struct command_result *(*cb)(struct command *command,
+						  const char *buf,
+						  const jsmntok_t *result,
+						  void *arg),
+		     struct command_result *(*errcb)(struct command *command,
+						     const char *buf,
+						     const jsmntok_t *result,
+						     void *arg),
+		     void *arg)
+{
+	struct out_req *req;
+
+	req = jsonrpc_request_start(cmd->plugin, cmd, "injectonionmessage",
+				    cb, errcb, arg);
+	json_add_pubkey(req->js, "blinding", &omsg->first_blinding);
+	json_array_start(req->js, "hops");
+	for (size_t i = 0; i < tal_count(omsg->hops); i++) {
+		json_object_start(req->js, NULL);
+		json_add_pubkey(req->js, "id", &omsg->hops[i]->pubkey);
+		json_add_hex_talarr(req->js, "tlv", omsg->hops[i]->raw_payload);
+		json_object_end(req->js);
+	}
+	json_array_end(req->js);
+	return send_outreq(cmd->plugin, req);
+}
+
 struct command_result *
 send_onion_reply(struct command *cmd,
 		 struct blinded_path *reply_path,

plugins/offers.h

@@ -4,6 +4,7 @@
 
 struct command_result;
 struct command;
+struct onion_message;
 struct plugin;
 
 /* This is me. */
@@ -29,6 +30,34 @@ send_onion_reply(struct command *cmd,
 		 struct blinded_path *reply_path,
 		 struct tlv_onionmsg_tlv *payload);
 
+/* Helper to send an onion message */
+#define inject_onionmessage(cmd, omsg, success, fail, arg)		\
+	inject_onionmessage_((cmd), (omsg),				\
+			     typesafe_cb_preargs(struct command_result *, void *, \
+						 (success), (arg),	\
+						 struct command *,	\
+						 const char *,		\
+						 const jsmntok_t *),	\
+			     typesafe_cb_preargs(struct command_result *, void *, \
+						 (fail), (arg),		\
+						 struct command *,	\
+						 const char *,		\
+						 const jsmntok_t *),	\
+			     (arg))
+
+struct command_result *
+inject_onionmessage_(struct command *cmd,
+		     const struct onion_message *omsg,
+		     struct command_result *(*cb)(struct command *command,
+						  const char *buf,
+						  const jsmntok_t *result,
+						  void *arg),
+		     struct command_result *(*errcb)(struct command *command,
+						     const char *buf,
+						     const jsmntok_t *result,
+						     void *arg),
+		     void *arg);
+
 /* Get the (latest) gossmap */
 struct gossmap *get_gossmap(struct plugin *plugin);
 #endif /* LIGHTNING_PLUGINS_OFFERS_H */