lightningd: add start for fundchannel_continue

Add an RPC method (not working at the moment) called
`fundchannel_continue` that takes as its parameters a
node_id and a txid for a transaction (that ostensibly has an output
for a channel)

contrib/pylightning/lightning/lightning.py

@@ -499,6 +499,16 @@ class LightningRpc(UnixDomainSocketRpc):
         }
         return self.call("fundchannel_start", payload)
 
+    def fundchannel_continue(self, node_id, funding_txid):
+        """
+        Complete channel establishment with {id}, using {funding_txid}
+        """
+        payload = {
+            "id": node_id,
+            "txid": funding_txid,
+        }
+        return self.call("fundchannel_continue", payload)
+
     def getinfo(self):
         """
         Show information about this node

lightningd/opening_control.c

@@ -969,6 +969,7 @@ static unsigned int openingd_msg(struct subd *openingd,
 	case WIRE_OPENING_INIT:
 	case WIRE_OPENING_FUNDER:
 	case WIRE_OPENING_FUNDER_START:
+	case WIRE_OPENING_FUNDER_CONTINUE:
 	case WIRE_OPENING_GOT_OFFER_REPLY:
 	case WIRE_OPENING_DEV_MEMLEAK:
 	/* Replies never get here */
@@ -1045,6 +1046,44 @@ void peer_start_openingd(struct peer *peer,
 	subd_send_msg(uc->openingd, take(msg));
 }
 
+static struct command_result *json_fund_channel_continue(struct command *cmd,
+							 const char *buffer,
+							 const jsmntok_t *obj UNNEEDED,
+							 const jsmntok_t *params)
+{
+	u8 *msg;
+	struct node_id *id;
+	struct bitcoin_txid *funding_txid;
+	struct peer *peer;
+	struct channel *channel;
+
+	if (!param(cmd, buffer, params,
+		   p_req("id", param_node_id, &id),
+		   p_req("txid", param_txid, &funding_txid),
+		   NULL))
+		return command_param_failed();
+
+	peer = peer_by_id(cmd->ld, id);
+	if (!peer) {
+		return command_fail(cmd, LIGHTNINGD, "Unknown peer");
+	}
+
+	channel = peer_active_channel(peer);
+	if (channel)
+		return command_fail(cmd, LIGHTNINGD, "Peer already %s",
+				    channel_state_name(channel));
+
+	if (!peer->uncommitted_channel)
+		return command_fail(cmd, LIGHTNINGD, "Peer not connected");
+
+	if (!peer->uncommitted_channel->fc)
+		return command_fail(cmd, LIGHTNINGD, "No channel funding in progress.");
+
+	msg = towire_opening_funder_continue(NULL, funding_txid);
+	subd_send_msg(peer->uncommitted_channel->openingd, take(msg));
+	return command_still_pending(cmd);
+}
+
 static struct command_result *json_fund_channel_start(struct command *cmd,
 						      const char *buffer,
 						      const jsmntok_t *obj UNNEEDED,
@@ -1262,6 +1301,15 @@ static const struct json_command fund_channel_start_command = {
 };
 AUTODATA(json_command, &fund_channel_start_command);
 
+static const struct json_command fund_channel_continue_command = {
+    "fundchannel_continue",
+    "channels",
+    json_fund_channel_continue,
+    "Complete channel establishment with peer {id} for funding transaction"
+    "with {txid}. Returns true on success, false otherwise."
+};
+AUTODATA(json_command, &fund_channel_continue_command);
+
 #if DEVELOPER
  /* Indented to avoid include ordering check */
  #include <lightningd/memdump.h>

openingd/opening_wire.csv

@@ -90,6 +90,12 @@ opening_funder_start_reply,6102
 opening_funder_start_reply,,script_len,u8
 opening_funder_start_reply,,scriptpubkey,script_len*u8
 
+# master->openingd: continue channel establsihment for a funding
+# tx that will be paid for by an external wallet
+# response to this is a normal `opening_funder_reply` ??
+opening_funder_continue,6012
+opening_funder_continue,,funding_txid,struct bitcoin_txid
+
 # Openingd->master: we failed to negotiation channel
 opening_funder_failed,6004
 opening_funder_failed,,reason,wirestring

openingd/openingd.c

@@ -617,6 +617,13 @@ static u8 *funder_channel_start(struct state *state,
 	return towire_opening_funder_start_reply(state, funding_output_script);
 }
 
+static u8 *funder_channel_continue(struct state *state,
+				   struct bitcoin_txid *funding_txid)
+{
+	// now the what. ok we've got a funding_txid..
+	return NULL;
+}
+
 /*~ OK, let's fund a channel!  Returns the reply for lightningd on success,
  * or NULL if something goes wrong. */
 static u8 *funder_channel(struct state *state,
@@ -1565,6 +1572,7 @@ static u8 *handle_master_in(struct state *state)
 	struct amount_sat change;
 	u32 change_keyindex;
 	u8 channel_flags;
+	struct bitcoin_txid funding_txid;
 	struct utxo **utxos;
 	struct ext_key bip32_base;
 
@@ -1596,6 +1604,11 @@ static u8 *handle_master_in(struct state *state)
 		/* We want to keep openingd alive, since we're not done yet */
 		wire_sync_write(REQ_FD, take(msg));
 		return NULL;
+	case WIRE_OPENING_FUNDER_CONTINUE:
+		if (!fromwire_opening_funder_continue(msg,
+						      &funding_txid))
+			master_badmsg(WIRE_OPENING_FUNDER_CONTINUE, msg);
+		return funder_channel_continue(state, &funding_txid);
 	case WIRE_OPENING_DEV_MEMLEAK:
 #if DEVELOPER
 		handle_dev_memleak(state, msg);