BumpFee

BumpFee bumps the fee of an arbitrary input within a transaction. This RPC takes a different approach than bitcoind's bumpfee command. lnd has a central batching engine in which inputs with similar fee rates are batched together to save on transaction fees. Due to this, we cannot rely on bumping the fee on a specific transaction, since transactions can change at any point with the addition of new inputs. The list of inputs that currently exist within lnd's central batching engine can be retrieved through the PendingSweeps RPC.

When bumping the fee of an input that currently exists within lnd's central batching engine, a higher fee transaction will be created that replaces the lower fee transaction through the Replace-By-Fee (RBF) policy. If it

This RPC also serves useful when wanting to perform a Child-Pays-For-Parent (CPFP), where the child transaction pays for its parent's fee. This can be done by specifying an outpoint within the low fee transaction that is under the control of the wallet.

The fee preference can be expressed either as a specific fee rate or a delta of blocks in which the output should be swept on-chain within. If a fee preference is not explicitly specified, then an error is returned.

Note that this RPC currently doesn't perform any validation checks on the fee preference being provided. For now, the responsibility of ensuring that the new fee preference is sufficient is delegated to the user.

Source: walletrpc/walletkit.proto

gRPC

rpc BumpFee (BumpFeeRequest) returns (BumpFeeResponse);

REST

HTTP Method	Path
POST	/v2/wallet/bumpfee

Code Samples

gRPC

Javascript

const fs = require('fs');
const grpc = require('@grpc/grpc-js');
const protoLoader = require('@grpc/proto-loader');

const GRPC_HOST = 'localhost:10009'
const MACAROON_PATH = 'LND_DIR/data/chain/bitcoin/regtest/admin.macaroon'
const TLS_PATH = 'LND_DIR/tls.cert'

const loaderOptions = {
  keepCase: true,
  longs: String,
  enums: String,
  defaults: true,
  oneofs: true,
};
const packageDefinition = protoLoader.loadSync(['lightning.proto', 'walletrpc/walletkit.proto'], loaderOptions);
const walletrpc = grpc.loadPackageDefinition(packageDefinition).walletrpc;
process.env.GRPC_SSL_CIPHER_SUITES = 'HIGH+ECDSA';
const tlsCert = fs.readFileSync(TLS_PATH);
const sslCreds = grpc.credentials.createSsl(tlsCert);
const macaroon = fs.readFileSync(MACAROON_PATH).toString('hex');
const macaroonCreds = grpc.credentials.createFromMetadataGenerator(function(args, callback) {
  let metadata = new grpc.Metadata();
  metadata.add('macaroon', macaroon);
  callback(null, metadata);
});
let creds = grpc.credentials.combineChannelCredentials(sslCreds, macaroonCreds);
let client = new walletrpc.WalletKit(GRPC_HOST, creds);
let request = {
  outpoint: <OutPoint>,
  target_conf: <uint32>,
  sat_per_byte: <uint32>,
  force: <bool>,
  sat_per_vbyte: <uint64>,
};
client.bumpFee(request, function(err, response) {
  console.log(response);
});
// Console output:
//  {
//  }

Python

import codecs, grpc, os
# Generate the following 2 modules by compiling the walletrpc/walletkit.proto with the grpcio-tools.
# See https://github.com/lightningnetwork/lnd/blob/master/docs/grpc/python.md for instructions.
import walletkit_pb2 as walletrpc, walletkit_pb2_grpc as walletkitstub

GRPC_HOST = 'localhost:10009'
MACAROON_PATH = 'LND_DIR/data/chain/bitcoin/regtest/admin.macaroon'
TLS_PATH = 'LND_DIR/tls.cert'

# create macaroon credentials
macaroon = codecs.encode(open(MACAROON_PATH, 'rb').read(), 'hex')
def metadata_callback(context, callback):
  callback([('macaroon', macaroon)], None)
auth_creds = grpc.metadata_call_credentials(metadata_callback)
# create SSL credentials
os.environ['GRPC_SSL_CIPHER_SUITES'] = 'HIGH+ECDSA'
cert = open(TLS_PATH, 'rb').read()
ssl_creds = grpc.ssl_channel_credentials(cert)
# combine macaroon and SSL credentials
combined_creds = grpc.composite_channel_credentials(ssl_creds, auth_creds)
# make the request
channel = grpc.secure_channel(GRPC_HOST, combined_creds)
stub = walletkitstub.WalletKitStub(channel)
request = walletrpc.BumpFeeRequest(
  outpoint=<OutPoint>,
  target_conf=<uint32>,
  sat_per_byte=<uint32>,
  force=<bool>,
  sat_per_vbyte=<uint64>,
)
response = stub.BumpFee(request)
print(response)
# {
# }

REST

Javascript

const fs = require('fs');
const request = require('request');

const REST_HOST = 'localhost:8080'
const MACAROON_PATH = 'LND_DIR/data/chain/bitcoin/regtest/admin.macaroon'

let requestBody = {
  outpoint: <object>, // <OutPoint> 
  target_conf: <integer>, // <uint32> 
  sat_per_byte: <integer>, // <uint32> 
  force: <boolean>, // <bool> 
  sat_per_vbyte: <string>, // <uint64> 
};
let options = {
  url: `https://${REST_HOST}/v2/wallet/bumpfee`,
  // Work-around for self-signed certificates.
  rejectUnauthorized: false,
  json: true,
  headers: {
    'Grpc-Metadata-macaroon': fs.readFileSync(MACAROON_PATH).toString('hex'),
  },
  form: JSON.stringify(requestBody),
}
request.post(options, function(error, response, body) {
  console.log(body);
});
// Console output:
//  {
//  }

Python

import base64, codecs, json, requests

REST_HOST = 'localhost:8080'
MACAROON_PATH = 'LND_DIR/data/chain/bitcoin/regtest/admin.macaroon'
TLS_PATH = 'LND_DIR/tls.cert'

url = f'https://{REST_HOST}/v2/wallet/bumpfee'
macaroon = codecs.encode(open(MACAROON_PATH, 'rb').read(), 'hex')
headers = {'Grpc-Metadata-macaroon': macaroon}
data = {
  'outpoint': <OutPoint>,
  'target_conf': <uint32>,
  'sat_per_byte': <uint32>,
  'force': <bool>,
  'sat_per_vbyte': <uint64>,
}
r = requests.post(url, headers=headers, data=json.dumps(data), verify=TLS_PATH)
print(r.json())
# {
# }

Shell

# There is no CLI command for this RPC

Messages

walletrpc.BumpFeeRequest

Source: walletrpc/walletkit.proto

Field	gRPC Type	REST Type	REST Placement
outpoint The input we're attempting to bump the fee of.	OutPoint	object	body
target_conf The target number of blocks that the input should be spent within.	uint32	integer	body
sat_per_byte Deprecated, use sat_per_vbyte. The fee rate, expressed in sat/vbyte, that should be used to spend the input with.	uint32	integer	body
force Whether this input must be force-swept. This means that it is swept even if it has a negative yield.	bool	boolean	body
sat_per_vbyte The fee rate, expressed in sat/vbyte, that should be used to spend the input with.	uint64	string	body

walletrpc.BumpFeeResponse

Source: walletrpc/walletkit.proto

note

This response has no parameters.

Nested Messages

lnrpc.OutPoint

Field	gRPC Type	REST Type
txid_bytes Raw bytes representing the transaction id.	bytes	string
txid_str Reversed, hex-encoded string representing the transaction id.	string	string
output_index The index of the output on the transaction.	uint32	integer