How to get caller and block number using Polkadot/Kusama Runtime modules and SubSquid

Question

I'm trying to make my very first indexer. I want to pull the caller (initiator's address) of a runtime system.remark, as well as the block number.

What is the best way to do this via hooking into the runtime modules.

Answer 1

the ID of the account that triggered the extrinsic is present in the ExtrinsicHandlerContext, under extrinsic.signer. You can simply do this to obtain it:

ctx.extrinsic.signer

the block number is available in the block field of the ExtrinsicHandlerContext as height:

ctx.block.height

You could also hook to the system.Remarked event, instead of the system.remark call.

https://polkadot.subscan.io/event?module=System&event=Remarked

The Event should follow the call, if I am not mistaken, and, as a bonus, it reports the sender field as one of the Event's arguments. Subsquid's typegen generates this wrapper for it:

export class SystemRemarkedEvent {
  constructor(private ctx: EventContext) {
    assert(this.ctx.event.name === 'system.Remarked')
  }

  /**
   *  On on-chain remark happened. \[origin, remark_hash\]
   */
  get isV2030(): boolean {
    return this.ctx._chain.getEventHash('system.Remarked') === 'e54ae910805a8a9413af1a7f5885a5d0ba5f4e105175cd6b0ce2a8702ddf1861'
  }

  /**
   *  On on-chain remark happened. \[origin, remark_hash\]
   */
  get asV2030(): [Uint8Array, Uint8Array] {
    assert(this.isV2030)
    return this.ctx._chain.decodeEvent(this.ctx.event)
  }

  /**
   * On on-chain remark happened.
   */
  get isV9160(): boolean {
    return this.ctx._chain.getEventHash('system.Remarked') === 'c58b73482fe762a6dcca2f35266f0d1739333312cf7a50eea55c666d0cda6101'
  }

  /**
   * On on-chain remark happened.
   */
  get asV9160(): {sender: v9160.AccountId32, hash: v9160.H256} {
    assert(this.isV9160)
    return this.ctx._chain.decodeEvent(this.ctx.event)
  }

  get isLatest(): boolean {
    deprecateLatest()
    return this.isV9160
  }

  get asLatest(): {sender: v9160.AccountId32, hash: v9160.H256} {
    deprecateLatest()
    return this.asV9160
  }
}

As for the block number, it's even easier, you can get it like this:

ctx.event.blockNumber