funding: provide FundingExpiryBlock field in PendingOpenChannel message.

lnrpc/lightning.proto

@@ -2581,6 +2581,17 @@ message PendingChannelsResponse {
 
         // Previously used for confirmation_height. Do not reuse.
         reserved 2;
+
+        // The number of blocks until the funding transaction is considered
+        // expired. If this value gets close to zero, there is a risk that the
+        // channel funding will be canceled by the channel responder. The
+        // channel should be fee bumped using CPFP (see walletrpc.BumpFee) to
+        // ensure that the channel confirms in time. Otherwise a force-close
+        // will be necessary if the channel confirms after the funding
+        // transaction expires. A negative value means the channel responder has
+        // very likely canceled the funding and the channel will never become
+        // fully operational.
+        int32 funding_expiry_blocks = 3;
     }
 
     message WaitingCloseChannel {

lnrpc/lightning.swagger.json

@@ -3052,6 +3052,11 @@
           "type": "string",
           "format": "int64",
           "description": "The required number of satoshis per kilo-weight that the requester will\npay at all times, for both the funding transaction and commitment\ntransaction. This value can later be updated once the channel is open."
+        },
+        "funding_expiry_blocks": {
+          "type": "integer",
+          "format": "int32",
+          "description": "The number of blocks until the funding transaction is considered\nexpired. If this value gets close to zero, there is a risk that the\nchannel funding will be canceled by the channel responder. The\nchannel should be fee bumped using CPFP (see walletrpc.BumpFee) to\nensure that the channel confirms in time. Otherwise a force-close\nwill be necessary if the channel confirms after the funding\ntransaction expires. A negative value means the channel responder has\nvery likely canceled the funding and the channel will never become\nfully operational."
         }
       }
     },

rpcserver.go

@@ -3373,6 +3373,11 @@ func (r *rpcServer) fetchPendingOpenChannels() (pendingOpenChannels, error) {
 		return nil, err
 	}
 
+	_, currentHeight, err := r.server.cc.ChainIO.GetBestBlock()
+	if err != nil {
+		return nil, err
+	}
+
 	result := make(pendingOpenChannels, len(channels))
 	for i, pendingChan := range channels {
 		pub := pendingChan.IdentityPub.SerializeCompressed()
@@ -3389,6 +3394,12 @@ func (r *rpcServer) fetchPendingOpenChannels() (pendingOpenChannels, error) {
 		commitBaseWeight := blockchain.GetTransactionWeight(utx)
 		commitWeight := commitBaseWeight + input.WitnessCommitmentTxWeight
 
+		// FundingExpiryBlocks is the distance from the current block
+		// height to the broadcast height + MaxWaitNumBlocksFundingConf.
+		maxFundingHeight := funding.MaxWaitNumBlocksFundingConf +
+			pendingChan.BroadcastHeight()
+		fundingExpiryBlocks := int32(maxFundingHeight) - currentHeight
+
 		result[i] = &lnrpc.PendingChannelsResponse_PendingOpenChannel{
 			Channel: &lnrpc.PendingChannelsResponse_PendingChannel{
 				RemoteNodePub:        hex.EncodeToString(pub),
@@ -3402,9 +3413,10 @@ func (r *rpcServer) fetchPendingOpenChannels() (pendingOpenChannels, error) {
 				CommitmentType:       rpcCommitmentType(pendingChan.ChanType),
 				Private:              isPrivate(pendingChan),
 			},
-			CommitWeight: commitWeight,
-			CommitFee:    int64(localCommitment.CommitFee),
-			FeePerKw:     int64(localCommitment.FeePerKw),
+			CommitWeight:        commitWeight,
+			CommitFee:           int64(localCommitment.CommitFee),
+			FeePerKw:            int64(localCommitment.FeePerKw),
+			FundingExpiryBlocks: fundingExpiryBlocks,
 			// TODO(roasbeef): need to track confirmation height
 		}
 	}