Query JSON RPC endpoints

Overview

The JSON-RPC layer of the xBuildApp provides developers with the functionality of easily interacting with the blockchain, through HTTP requests.

This example covers using tools like curl to query information, as well as starting the chain with a premined account, and sending a transaction.

Step 1: Create a genesis file with a premined account

To generate a genesis file, run the following command:

polygon-edge genesis --premine 0x1010101010101010101010101010101010101010

The premine flag sets the address that should be included with a starting balance in the genesis file. In this case, the address 0x1010101010101010101010101010101010101010 will have a starting default balance of 0x3635C9ADC5DEA00000 wei.

The balance can be either a hex or uint256 value.

:::warning Only premine accounts for which you have a private key! If you premine accounts and do not have a private key to access them, you premined balance will not be usable :::

Step 2: Start the xBuildApp in dev mode

To start the xBuildApp in development mode, which is explained in the CLI Commands section, run the following:

polygon-edge server --chain genesis.json --dev --log-level debug

Step 3: Query the account balance

Now that the client is up and running in dev mode, using the genesis file generated in step 1, we can use a tool like curl to query the account balance:

curl -X POST --data '{"jsonrpc":"2.0","method":"eth_getBalance","params":["0x1010101010101010101010101010101010101010", "latest"],"id":1}' localhost:8545

The command should return the following output:

{
  "id":1,
  "result":"0x100000000000000000000000000"
}

Step 4: Send a transfer transaction

Now that we've confirmed the account we set up as premined has the correct balance, we can transfer some ether:

var Web3 = require("web3");

const web3 = new Web3("<provider's websocket jsonrpc address>"); //example: ws://localhost:10002/ws
web3.eth.accounts
  .signTransaction(
    {
      to: "<recipient address>",
      value: web3.utils.toWei("<value in ETH>"),
      gas: 21000,
    },
    "<private key from premined account>"
  )
  .then((signedTxData) => {
    web3.eth
      .sendSignedTransaction(signedTxData.rawTransaction)
      .on("receipt", console.log);
  });