ℹ️ NOTE: This section has been recently added to the course and is an early draft that may still be awaiting review. Caveat reader.
This section explains how to interact with bitcoind using the NodeJS programming language and the BCRPC package.
BCRPC is built on node.js. Thus, you'll first need to install the node.js and npm (the node package manager) packages for your system.
If you're using a Ubuntu machine, you can run the following commands to get a new version of node.js (as opposed to the horribly out-of-date version in the Ubuntu package system).
$ curl -sL https://deb.nodesource.com/setup_14.x | sudo bash -
$ sudo apt-get install -y nodejs
$ sudo npm install mocha -g
You can now clone the BCRPC package from GitHub and install its dependencies.
$ git clone https://github.com/dgarage/bcrpc.git
$ cd bcrpc
$ npm install
To test the BCRPC package, you must first set environmental variables for your rpcuser and rpcpassword. As usual, these come from ~/.bitcoin/bitcoin.conf. You must also set the RPC port to 18332 which should be correct for the standard testnet setup described in these documents.
$ export BITCOIND_USER=StandUp
$ export BITCOIND_PASS=d8340efbcd34e312044c8431c59c792c
$ export BITCOIND_PORT=18332
⚠️ WARNING: Obviously, you'd never put your password in an environmental variable in a production environment.
🔗 MAINNET VS TESTNET: The port would be 8332 for a mainnet setup.
You can now verify everything is working correctly:
$ npm test
> bcrpc@0.2.2 test /home/user1/bcrpc
> mocha tests.js
BitcoinD
✓ is running
bcrpc
✓ can get info
2 passing (36ms)
Congratulations, you now have a Bitcoin-ready RPC wrapper for Node.js that is working with your Bitcoin setup.
You can now create a new Node.js project and install BCRPC via npm.
$ cd ~
$ mkdir myproject
$ cd myproject
$ npm init
[continue with default options]
$ npm install bcrpc
In your myproject directory, create a .js file where you JavaScript code will be executed.
You can initiate an RPC connection by creating an RpcAgent:
const RpcAgent = require('bcrpc');
agent = new RpcAgent({port: 18332, user: 'StandUp', pass: 'd8340efbcd34e312044c8431c59c792c'});
Obviously, your user and pass should again match what's in your ~/.bitcoin/bitcoin.conf, and you use port 18332 if you're on testnet.
Using BCRPC, you can use the same RPC commands you would usually use via bitcoin-cli with your RpcAgent, except they need to be in camelCase. For example, getblockhash would be getBlockHash instead.
To print the newest block number, you just call getBlockCount thourgh your RpcAgent:
agent.getBlockCount(function (err, blockCount) {
if (err)
throw Error(JSON.stringify(err));
console.log(blockCount.result);
});
The BCRPC functions can accept arguments. For example, getBlockHash takes blockCount.result as an input.
agent.getBlockHash(blockCount.result, function (err, hash) {
if (err)
throw Error(JSON.stringify(err));
console.log(hash.result);
})
The result of the BCRPC functions is a JSON object containing information about any errors and the id of the request. When accessing your result, you add .result to the end of it to specify that you are interested in the actual result, not information about errors.
You can find the getinfo code in the src directory.
$ node getinfo.js
1831094
00000000000002bf8b522a830180ad3a93b8eed33121f54b3842d8838580a53c
This is what output of the above example would look like if you replaced console.log(blockCount.result); and console.log(hash.result); with console.log(blockCount); and console.log(hash);, respectively:
{ result: 1774686, error: null, id: null }
{
result: '00000000000000d980c495a2b7addf09bb0a9c78b5b199c8e965ee54753fa5da',
error: null,
id: null
}
It's useful when accepting Bitcoin to check the received Bitcoin on a specific address in your wallet. For example, if you were running an online store accepting Bitcoin, for each payment from a customer, you would generate a new address, show that address to the customer, then check the balance of the address after some time, to make sure the correct amount has been received:
agent.getReceivedByAddress('mpGpCMX6SuUimDZKiVViuhd7EGyVxkNnha', function (err, addressInfo) {
if (err)
throw Error(JSON.stringify(err));
console.log(addressInfo.result);
});
ℹ️ NOTE: Obviously, you'll need to enter an address recognized by your machine.
By default this functions checks the transactions that have been confirmed once, however you can increase this to a higher number such as 6:
agent.getReceivedByAddress('mpGpCMX6SuUimDZKiVViuhd7EGyVxkNnha', 6, function (err, addressInfo) {
if (err)
throw Error(JSON.stringify(err));
console.log(addressInfo.result);
});
You can also look up additional information about your wallet and view your balance, transaction count, et cetera:
agent.getWalletInfo(function (err, walletInfo) {
if (err)
throw Error(JSON.stringify(err));
console.log(walletInfo.result);
});
The source is available as walletinfo.js.
$ node walletinfo.js
0.008498
{
walletname: '',
walletversion: 169900,
balance: 0.010438,
unconfirmed_balance: 0,
immature_balance: 0,
txcount: 4,
keypoololdest: 1596567843,
keypoolsize: 999,
hdseedid: 'da5a1b058deb9e51ecffef1b0ddc069a5dfb2c5f',
keypoolsize_hd_internal: 1000,
paytxfee: 0,
private_keys_enabled: true,
avoid_reuse: false,
scanning: false
}
Instead of printing all the details associated with your wallet, you can print specific information, such as your balance. Since a JSON object is being accessed, this can be done by changing the line console.log(walletInfo.result); to console.log(walletInfo.result.balance);:
You can also pass additional arguments to RPC commands. For example, the following generates a new legacy address, with the -addresstype flag.
agent.getNewAddress('-addresstype', 'legacy', function (err, newAddress) {
if (err)
throw Error(JSON.stringify(err));
console.log(newAddress.result);
});
This is the same as running the following from the command line:
$ bitcoin-cli getnewaddress -addresstype legacy
mtGPcBvRPZFEHo2YX8un9qqPBydhG82uuZ
In BCRPC, you can generally use the same flags as in bitcoin-cli in BCRPC. Though you use camelCase (getNewAddress) for the methods, the flags, which are normally separated by spaces on the command line, are instead placed in strings and separated by commas.
You can send coins to an address most easily using the sendToAddress function:
agent.sendToAddress(newAddress.result, 0.00001, function(err, txid) {
if (err)
throw Error(JSON.stringify(err));
console.log(txid.result);
});
This should print the txid of the transaction:
1679bee019c61608340b79810377be2798efd4d2ec3ace0f00a1967af70666b9
You may now wish to view a transaction, such as the one you just sent.
agent.getTransaction(txid.result, function (err, transaction) {
if (err)
throw Error(JSON.stringify(err));
console.log(transaction.result);
});
You should get an output similar to this:
{
amount: 0.001,
confirmations: 4776,
blockhash: '000000006628870b0a8a66abea9cf0d4e815c491f079e3fa9e658a87b5dc863a',
blockindex: 117,
blocktime: 1591857418,
txid: '1661ce322c128e053b8ea8fcc22d17df680d2052983980e2281d692b9b4ab7df',
walletconflicts: [],
time: 1591857343,
timereceived: 1591857343,
'bip125-replaceable': 'no',
details: [
{
address: 'mpGpCMX6SuUimDZKiVViuhd7EGyVxkNnha',
category: 'receive',
amount: 0.001,
label: '',
vout: 0
}
],
hex: '02000000000101e9e8c3bd057d54e73baadc60c166860163b0e7aa60cab33a03e89fb44321f8d5010000001716001435c2aa3fc09ea53c3e23925c5b2e93b9119b2568feffffff02a0860100000000001976a914600c8c6a4abb0a502ea4de01681fe4fa1ca7800688ac65ec1c000000000017a91425b920efb2fde1a0277d3df11d0fd7249e17cf8587024730440220403a863d312946aae3f3ef0a57206197bc67f71536fb5f4b9ca71a7e226b6dc50220329646cf786cfef79d60de3ef54f702ab1073694022f0618731902d926918c3e012103e6feac9d7a8ad1ac6b36fb4c91c1c9f7fff1e7f63f0340e5253a0e4478b7b13f41fd1a00'
}
The full code is available as sendtx.js.
With BCRPC you can access all the RPC commands available through bitcoin-cli, in JavaScript. The BCRPC README has some examples which use promises (the examples in this document use callbacks). The JavaScript behind it is short and readable.
Based on these examples you should be able to incorporate Bitcoin in a Node.js project and do things like sending and receiving coins.
Learn more about "Talking to Bitcoin in Other Languages" in 18.4: Accessing Bitcoin with Python.