lnrpc: expose commit hashes for waiting close channels

To make it easier to determine which pending sweep to bump in order to
get your anchor commitment tx confirmed.

lnrpc/rpc.proto

@@ -1982,6 +1982,23 @@ message PendingChannelsResponse {
 
         /// The balance in satoshis encumbered in this channel
         int64 limbo_balance = 2;
+
+        /**
+        A list of valid commitment transactions. Any of these can confirm at
+        this point.
+        */
+        Commitments commitments = 3;
+    }
+
+    message Commitments {
+        /// Hash of the local version of the commitment tx.
+        string local_txid = 1;
+
+        /// Hash of the remote version of the commitment tx.
+        string remote_txid = 2;
+        
+        /// Hash of the remote pending version of the commitment tx.
+        string remote_pending_txid = 3;
     }
 
     message ClosedChannel {

lnrpc/rpc.swagger.json

@@ -1603,6 +1603,23 @@
         }
       }
     },
+    "PendingChannelsResponseCommitments": {
+      "type": "object",
+      "properties": {
+        "local_txid": {
+          "type": "string",
+          "description": "/ Hash of the local version of the commitment tx."
+        },
+        "remote_txid": {
+          "type": "string",
+          "description": "/ Hash of the remote version of the commitment tx."
+        },
+        "remote_pending_txid": {
+          "type": "string",
+          "description": "/ Hash of the remote pending version of the commitment tx."
+        }
+      }
+    },
     "PendingChannelsResponseForceClosedChannel": {
       "type": "object",
       "properties": {
@@ -1718,6 +1735,10 @@
           "type": "string",
           "format": "int64",
           "title": "/ The balance in satoshis encumbered in this channel"
+        },
+        "commitments": {
+          "$ref": "#/definitions/PendingChannelsResponseCommitments",
+          "description": "*\nA list of valid commitment transactions. Any of these can confirm at\nthis point."
         }
       }
     },

rpcserver.go

@@ -2756,6 +2756,43 @@ func (r *rpcServer) PendingChannels(ctx context.Context,
 	for _, waitingClose := range waitingCloseChans {
 		pub := waitingClose.IdentityPub.SerializeCompressed()
 		chanPoint := waitingClose.FundingOutpoint
+
+		var commitments lnrpc.PendingChannelsResponse_Commitments
+
+		// Report local commit. May not be present when DLP is active.
+		if waitingClose.LocalCommitment.CommitTx != nil {
+			commitments.LocalTxid =
+				waitingClose.LocalCommitment.CommitTx.TxHash().
+					String()
+		}
+
+		// Report remote commit. May not be present when DLP is active.
+		if waitingClose.RemoteCommitment.CommitTx != nil {
+			commitments.RemoteTxid =
+				waitingClose.RemoteCommitment.CommitTx.TxHash().
+					String()
+		}
+
+		// Report the remote pending commit if any.
+		remoteCommitDiff, err := waitingClose.RemoteCommitChainTip()
+
+		switch {
+
+		// Don't set hash if there is no pending remote commit.
+		case err == channeldb.ErrNoPendingCommit:
+
+		// An unexpected error occurred.
+		case err != nil:
+			return nil, err
+
+		// There is a pending remote commit. Set its hash in the
+		// response.
+		default:
+			hash := remoteCommitDiff.Commitment.CommitTx.TxHash()
+			commitments.RemotePendingTxid = hash.String()
+
+		}
+
 		channel := &lnrpc.PendingChannelsResponse_PendingChannel{
 			RemoteNodePub:        hex.EncodeToString(pub),
 			ChannelPoint:         chanPoint.String(),
@@ -2766,14 +2803,16 @@ func (r *rpcServer) PendingChannels(ctx context.Context,
 			RemoteChanReserveSat: int64(waitingClose.RemoteChanCfg.ChanReserve),
 		}
 
+		waitingCloseResp := &lnrpc.PendingChannelsResponse_WaitingCloseChannel{
+			Channel:      channel,
+			LimboBalance: channel.LocalBalance,
+			Commitments:  &commitments,
+		}
+
 		// A close tx has been broadcasted, all our balance will be in
 		// limbo until it confirms.
 		resp.WaitingCloseChannels = append(
-			resp.WaitingCloseChannels,
-			&lnrpc.PendingChannelsResponse_WaitingCloseChannel{
-				Channel:      channel,
-				LimboBalance: channel.LocalBalance,
-			},
+			resp.WaitingCloseChannels, waitingCloseResp,
 		)
 
 		resp.TotalLimboBalance += channel.LocalBalance