Funding transaction withholding support

.msggen.json

@@ -1698,7 +1698,8 @@
         },
         "FundchannelCompleteRequest": {
             "FundChannel_Complete.id": 1,
-            "FundChannel_Complete.psbt": 2
+            "FundChannel_Complete.psbt": 2,
+            "FundChannel_Complete.withhold": 3
         },
         "FundchannelCompleteResponse": {
             "FundChannel_Complete.channel_id": 1,
@@ -2075,8 +2076,10 @@
             "ListClosedChannels.closedchannels[].funding_fee_paid_msat": 15,
             "ListClosedChannels.closedchannels[].funding_fee_rcvd_msat": 16,
             "ListClosedChannels.closedchannels[].funding_outnum": 13,
+            "ListClosedChannels.closedchannels[].funding_psbt": 26,
             "ListClosedChannels.closedchannels[].funding_pushed_msat": 17,
             "ListClosedChannels.closedchannels[].funding_txid": 12,
+            "ListClosedChannels.closedchannels[].funding_withheld": 27,
             "ListClosedChannels.closedchannels[].last_commitment_fee_msat": 23,
             "ListClosedChannels.closedchannels[].last_commitment_txid": 22,
             "ListClosedChannels.closedchannels[].last_stable_connection": 25,
@@ -2844,8 +2847,10 @@
             "ListPeerChannels.channels[].funding.fee_paid_msat": 4,
             "ListPeerChannels.channels[].funding.fee_rcvd_msat": 5,
             "ListPeerChannels.channels[].funding.local_funds_msat": 2,
+            "ListPeerChannels.channels[].funding.psbt": 6,
             "ListPeerChannels.channels[].funding.pushed_msat": 1,
-            "ListPeerChannels.channels[].funding.remote_funds_msat": 3
+            "ListPeerChannels.channels[].funding.remote_funds_msat": 3,
+            "ListPeerChannels.channels[].funding.withheld": 7
         },
         "ListpeerchannelsChannelsHtlcs": {
             "ListPeerChannels.channels[].htlcs[].amount_msat": 3,
@@ -7318,6 +7323,10 @@
             "added": "pre-v0.10.1",
             "deprecated": null
         },
+        "FundChannel_Complete.withhold": {
+            "added": "v25.12",
+            "deprecated": null
+        },
         "FundChannel_Start": {
             "added": "pre-v0.10.1",
             "deprecated": null
@@ -8350,6 +8359,10 @@
             "added": "pre-v0.10.1",
             "deprecated": null
         },
+        "ListClosedChannels.closedchannels[].funding_psbt": {
+            "added": "v25.12",
+            "deprecated": null
+        },
         "ListClosedChannels.closedchannels[].funding_pushed_msat": {
             "added": "pre-v0.10.1",
             "deprecated": null
@@ -8358,6 +8371,10 @@
             "added": "pre-v0.10.1",
             "deprecated": null
         },
+        "ListClosedChannels.closedchannels[].funding_withheld": {
+            "added": "v25.12",
+            "deprecated": null
+        },
         "ListClosedChannels.closedchannels[].last_commitment_fee_msat": {
             "added": "pre-v0.10.1",
             "deprecated": null
@@ -10342,6 +10359,10 @@
             "added": "v23.02",
             "deprecated": null
         },
+        "ListPeerChannels.channels[].funding.psbt": {
+            "added": "v25.12",
+            "deprecated": null
+        },
         "ListPeerChannels.channels[].funding.pushed_msat": {
             "added": "v23.02",
             "deprecated": null
@@ -10350,6 +10371,10 @@
             "added": "v23.02",
             "deprecated": null
         },
+        "ListPeerChannels.channels[].funding.withheld": {
+            "added": "v25.12",
+            "deprecated": null
+        },
         "ListPeerChannels.channels[].funding_outnum": {
             "added": "v23.02",
             "deprecated": null

channeld/watchtower.c

@@ -79,8 +79,11 @@ penalty_tx_create(const tal_t *ctx,
 	if (final_index) {
 		size_t script_len = tal_bytelen(final_scriptpubkey);
 		bool is_tr = is_p2tr(final_scriptpubkey, script_len, NULL);
-		psbt_add_keypath_to_last_output(tx, *final_index,
-						final_ext_key, is_tr);
+		if (!psbt_add_keypath_to_last_output(tx, *final_index,
+						     final_ext_key, is_tr))
+			status_failed(STATUS_FAIL_INTERNAL_ERROR,
+				      "Cannot add final keypath?");
+
         }
 
 	/* Worst-case sig is 73 bytes */

common/close_tx.c

@@ -54,9 +54,11 @@ struct bitcoin_tx *create_close_tx(const tal_t *ctx,
 		assert((local_wallet_index == NULL) == (local_wallet_ext_key == NULL));
 		if (local_wallet_index) {
 			size_t script_len = tal_bytelen(script);
-			psbt_add_keypath_to_last_output(
-				tx, *local_wallet_index, local_wallet_ext_key,
-				is_p2tr(script, script_len, NULL));
+			/* Should not happen! */
+			if (!psbt_add_keypath_to_last_output(
+				    tx, *local_wallet_index, local_wallet_ext_key,
+				    is_p2tr(script, script_len, NULL)))
+				return tal_free(tx);
                 }
 		num_outputs++;
 	}

common/psbt_keypath.c

@@ -3,7 +3,11 @@
 #include <common/psbt_keypath.h>
 #include <common/utils.h>
 
-void psbt_output_set_keypath(u32 index, const struct ext_key *ext, bool is_taproot, struct wally_psbt_output *output) {
+bool psbt_output_set_keypath(u32 index,
+			     const struct ext_key *ext,
+			     bool is_taproot,
+			     struct wally_psbt_output *output)
+{
 	u8 fingerprint[BIP32_KEY_FINGERPRINT_LEN];
 	if (bip32_key_get_fingerprint(
 		    (struct ext_key *) ext, fingerprint, sizeof(fingerprint)) != WALLY_OK)
@@ -18,24 +22,29 @@ void psbt_output_set_keypath(u32 index, const struct ext_key *ext, bool is_tapro
 							  NULL, 0,
 							  fingerprint, sizeof(fingerprint),
 							  path, 1) != WALLY_OK)
-			abort();
+			return false;
 	} else {
 		if (wally_psbt_output_keypath_add(output,
 						  ext->pub_key, sizeof(ext->pub_key),
 						  fingerprint, sizeof(fingerprint),
 						  path, 1) != WALLY_OK)
-			abort();
+			return false;
 	}
 
+	return true;
 }
 
-void psbt_add_keypath_to_last_output(struct bitcoin_tx *tx,
+bool psbt_add_keypath_to_last_output(struct bitcoin_tx *tx,
 				     u32 key_index,
-					 const struct ext_key *ext,
-					 bool is_taproot) {
+				     const struct ext_key *ext,
+				     bool is_taproot)
+{
 	size_t outndx = tx->psbt->num_outputs - 1;
+	bool ok;
 
 	tal_wally_start();
-	psbt_output_set_keypath(key_index, ext, is_taproot, &tx->psbt->outputs[outndx]);
+	ok = psbt_output_set_keypath(key_index, ext, is_taproot, &tx->psbt->outputs[outndx]);
 	tal_wally_end(tx->psbt);
+
+	return ok;
 }

common/psbt_keypath.h

@@ -2,6 +2,7 @@
 #define LIGHTNING_COMMON_PSBT_KEYPATH_H
 
 #include "config.h"
+#include <ccan/compiler/compiler.h>
 #include <ccan/short_types/short_types.h>
 #include <wally_psbt.h>
 
@@ -15,11 +16,14 @@ struct wally_map;
  * @ext - extended public key of the immediate parent of the wallet key
  * @is_taproot - PSBT output has taproot script
  * @output - PSBT output to set
+ *
+ * This can fail, if it's adding the same thing twice (taproot only)
  */
-void psbt_output_set_keypath(u32 index,
-		      const struct ext_key *ext,
-			  bool is_taproot,
-		      struct wally_psbt_output *output);
+WARN_UNUSED_RESULT
+bool psbt_output_set_keypath(u32 index,
+			     const struct ext_key *ext,
+			     bool is_taproot,
+			     struct wally_psbt_output *output);
 
 /* psbt_add_keypath_to_last_output - augment the last output with the
  * given wallet keypath
@@ -29,9 +33,10 @@ void psbt_output_set_keypath(u32 index,
  * @ext - extended public key of the immediate parent of the wallet key
  * @is_taproot - if the output is taproot
  */
-void psbt_add_keypath_to_last_output(struct bitcoin_tx *tx,
+WARN_UNUSED_RESULT
+bool psbt_add_keypath_to_last_output(struct bitcoin_tx *tx,
 				     u32 index,
 				     const struct ext_key *ext,
-					 bool is_taproot);
+				     bool is_taproot);
 
 #endif /* LIGHTNING_COMMON_PSBT_KEYPATH_H */

contrib/msggen/msggen/schema.json

@@ -13594,6 +13594,13 @@
             "description": [
               "Transaction to use for funding (does not need to be signed but must be otherwise complete)."
             ]
+          },
+          "withhold": {
+            "type": "boolean",
+            "added": "v25.12",
+            "description": [
+              "Mark this channel 'withheld' so we know we haven't broadcast the funding transaction.  If the channel is closed before we call `sendpsbt` on this psbt, it will simply be closed immediately."
+            ]
           }
         }
       },
@@ -18439,6 +18446,7 @@
                 "total_htlcs_sent",
                 "funding_txid",
                 "funding_outnum",
+                "funding_withheld",
                 "leased",
                 "final_to_us_msat",
                 "min_to_us_msat",
@@ -18584,6 +18592,20 @@
                     "The 0-based output number of the funding transaction which opens the channel."
                   ]
                 },
+                "funding_psbt": {
+                  "type": "string",
+                  "added": "v25.12",
+                  "description": [
+                    "The PSBT (may be non-final or unsigned) we should use to open the channel, if any"
+                  ]
+                },
+                "funding_withheld": {
+                  "type": "boolean",
+                  "added": "v25.12",
+                  "description": [
+                    "True if we have not broadcast the funding transaction (see fundchannel_complete)."
+                  ]
+                },
                 "leased": {
                   "type": "boolean",
                   "description": [
@@ -24327,6 +24349,20 @@
                       "description": [
                         "Amount we were paid by peer at open."
                       ]
+                    },
+                    "psbt": {
+                      "type": "string",
+                      "added": "v25.12",
+                      "description": [
+                        "The PSBT (may be non-final or unsigned) we should use to open the channel, if any.  This is initially from `fundchannel_complete`, but will be updated with if `sendpsbt` is called with an updated PSBT."
+                      ]
+                    },
+                    "withheld": {
+                      "type": "boolean",
+                      "added": "v25.12",
+                      "description": [
+                        "True if `fundchannel_complete` told us it will not broadcast the funding transaction (so we know not to bother with any other onchain transactions in the case of this channel).  This is set to false if `sendpsbt` is send on the above PSBT."
+                      ]
                     }
                   }
                 },
@@ -32300,7 +32336,7 @@
       "rpc": "sendpsbt",
       "title": "Command to finalize, extract and send a partially signed bitcoin transaction (PSBT).",
       "description": [
-        "The **sendpsbt** is a low-level RPC command which sends a fully-signed PSBT."
+        "The **sendpsbt** is a low-level RPC command which sends a fully-signed PSBT.  If the PSBT is the same one promised by a channel (via fundchannel_complete) it will also be associated with that channel and re-transmitted if necessary on restart."
       ],
       "request": {
         "required": [

contrib/pyln-client/pyln/client/lightning.py

@@ -847,13 +847,14 @@ def fundchannel_cancel(self, node_id):
         }
         return self.call("fundchannel_cancel", payload)
 
-    def fundchannel_complete(self, node_id, psbt):
+    def fundchannel_complete(self, node_id, psbt, withhold=True):
         """
         Complete channel establishment with {id}, using {psbt}.
         """
         payload = {
             "id": node_id,
             "psbt": psbt,
+            "withhold": withhold,
         }
         return self.call("fundchannel_complete", payload)