r,s,v for ethereum transaction

ecsign.ts

// ref: https://github.com/ethereumjs/ethereumjs-util/blob/master/src/signature.ts#L15
const secp256k1 = require('secp256k1')

interface ISignature {
  signature: Buffer,
  recovery: number,
}

export const ecsign = function(
  msgHash: Buffer,
  privateKey: Buffer,
  chainId: number,
) {
  const sig: ISignature = secp256k1.sign(msgHash, privateKey)
  const ret = {
    r: sig.signature.slice(0, 32), // buffer
    s: sig.signature.slice(32, 64), // buffer
    v: sig.recovery + (chainId * 2 + 35), // number
  }
  return ret
}