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Calculate Gas

Vara nodes charge gas fees for all network operations, including executing a program’s code or processing a message. This gas is paid for by the initiator of these actions.

To ensure successful message processing and avoid errors like Gas limit exceeded, simulate the execution in advance to calculate the exact amount of gas that will be consumed.

Calculate Gas for Messages​

To determine the minimum gas amount required to send an extrinsic, use api.program.calculateGas.[method]. Depending on the conditions, calculate gas for initializing a program or processing a message in handle() or reply().

info

Gas calculation returns the GasInfo object, which contains 5 parameters:

  • min_limit - minimum gas limit required for execution
  • reserved - gas amount reserved for other on-chain interactions
  • burned - number of gas units burned during message processing
  • may_be_returned - value that can be returned in some cases
  • waited - notification that the message will be added to the waitlist

Init (for upload_program extrinsic)​

const code = fs.readFileSync('demo_ping.opt.wasm');

const gas = await api.program.calculateGas.initUpload(
  '0xd43593c715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d', // source id
  code,
  '0x00', // payload
  0,      // value
  true,   // allow other panics
);

console.log(gas.toHuman());

Init (for create_program extrinsic)​

const codeId = '0x…';

const gas = await api.program.calculateGas.initCreate(
  '0xd43593c715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d', // source id
  codeId,
  '0x00', // payload
  0,      // value
  true,   // allow other panics
);
console.log(gas.toHuman());

Handle​

import { getProgramMetadata } from '@gear-js/api';
const metadata = await getProgramMetadata('0x' + fs.readFileSync('demo_new_meta.meta.txt'));
const gas = await api.program.calculateGas.handle(
  '0xd43593c715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d', // source id
  '0xa178362715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d', // program id
  {
    id: {
      decimal: 64,
      hex: '0xd43593c715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d',
    },
  },      // payload
  0,      // value
  false,  // allow other panics
  metadata,
);
console.log(gas.toHuman());

Reply to a Message​

import { getProgramMetadata } from '@gear-js/api';
const metadata = await getProgramMetadata('0x' + fs.readFileSync('demo_async.meta.txt'));
const gas = await api.program.calculateGas.reply(
  '0xd43593c715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d', // source id
  '0x518e6bc03d274aadb3454f566f634bc2b6aef9ae6faeb832c18ae8300fd72635', // message id
  'PONG', // payload
  0,      // value
  true,   // allow other panics
  metadata,
);
console.log(gas.toHuman());