JS: JSON RPC client

example-call-bitcoind.js

//
// An example of a bitcoind JSON RPC request.
//
// Example request of curl:
// $ curl --data-binary '{"jsonrpc": "1.0", "id":"hoge", "method": "getblockhash", "params": [9999] }' http://rpc:rpc@127.0.0.1:18332/ 
//

const URL = "http://rpc:rpc@127.0.0.1:18332"; // bitcoind testnet. user:"rpc", password:"rpc"

const RpcClient = require("./rpc-client.js");
const rpc = new RpcClient({ url: URL, debug: true });

const p = {
  // @see: https://en.bitcoin.it/wiki/Original_Bitcoin_client/API_calls_list
  method: "getblockhash",
  params: [9999],
  id: "hoge",
};
rpc.call(p, console.log);

/* [console log]

ON SUCCESS:
null { result: '000000001655e2a7293f28383a2965b2f0add77fd6ac383986e90971a07467d4',
  error: null,
  id: 123 }

ON ERROR:
{ code: -32601, message: 'Method not found' } { result: null,
  error: { code: -32601, message: 'Method not found' },
  id: 'hoge' }
  
*/

rpc-client.js

const util = require("util");
const request = require("request");

// Example of curl to the bitcoind json rpc server:
// $ curl --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "getinfo", "params": [] }' http://rpc:rpc@127.0.0.1:18332/ 

module.exports = class RpcClient {

  constructor({
    url,
    jsonrpc = "2.0",
    debug = false,
    logFn = console.log,
  }) {
    if (!RpcClient.isValidUrl(url))
      throw Error(`invalid parameter: url=${url}`);
    this.url = url;
    this.jsonrpc = jsonrpc;
    this.debug = debug;
    this.logFn = logFn;
  }

  //**************************************************************
  // main methods
  //**************************************************************

  /**
   * RPC Call
   * Example: `request({method:"getblockhash", params:["1"], id:1} (err, res)=>{...});
   * @param {Object} - params:
   *  - method {String} - RPC method
   *  - params {Object} - RPC params
   *  - id {String|Number} - [Optional] RPC request ID
   */
  call({ method, params, id }, cb) {
    const self = this;
    const p = self._createRequestParam(method, params, id);
    request(p, (err, response, body) => {
      err = (body && body.error) ? body.error : err;
      return cb && cb(err, body);
    });
  }

  //**************************************************************
  // sub methods
  //**************************************************************

  /**
   * Creates request parameter
   */
  _createRequestParam(method, params, id) {
    // making form data for example like this:  '{"jsonrpc": "1.0", "id":"curltest", "method": "getinfo", "params": [] }'
    const data = {
      jsonrpc: this.jsonrpc,
      id,
      method,
      params,
    };
    const p = {
      url: this.url,
      form: JSON.stringify(data),
      headers: {
        "Content-Type": "application/json; charset=UTF-8",
        "Accept": "application/json, text/javascript",
      },
      method: "POST", // JSONRPC server handles only POST requests
      encoding: "UTF-8",
      json: true,
    };
    return p;
  }

  //**************************************************************
  // utility static methods
  //**************************************************************

  static isValidUrl(v) {
    return /^https?:\/\/.+$/.test(v);
  }

};