0079 XLS-79d: Transaction Fee RPC

[tequdev]

1. Abstract

Fees required for a transaction to be accepted into the network depends on the type of transaction and network conditions.

Currently some client libraries such as xrpl.js calculate Fees based on the type of transaction and its fields, but this proposal extends Fee RPC to provide a specification for calculating the Fee required by a transaction without a client library.

Furthermore, in a multi-chain ecosystem with the XRPL protocol, it would be ideal to have multiple networks available in one client library, and even if the network's own transactions require special fees (e.g, for Memo fields or other dynamic fields), it should be possible to obtain the fee.

2. Overview

Add a tx_blob and tx_json field to the already existing fee RPC request and modify it to return the Fee information required for transactions in this field to be accepted into the network.

This change does not require an Amendment because it is only an RPC change that does not affect consensus or transaction processing.

3.Fee RPC Specification

3.1. New Request Fields

Add a new optional field to the existing Fee RPC request:

Field Name	JSON Type	Description
tx_blob	string	(Optional) The transaction to get fee, in binary format.
tx_json	object	(Optional) The transaction to get fee, in JSON format.

If either tx_blob or tx_json is included, the RPC behaves as per the existing fee RPC specification.

Requirements for the tx_blob or tx_json:

• Contains either tx_blob or tx_json or neither
• Valid transaction format

3.2. New Response Fields

No change in the response field.

However, if the request field contains tx_blob or tx_json, fields in result.drops will be values to which the following are taken into account

• base fee
• signerCount
• Special transaction types (e.g.,AccountDelete, AMMCreate, LedgerStateFix)
• Fulfillment field of EscrowCreate

3.3. Error Cases

The RPC should return error messages for invalid tx_blob or tx_json inputs if those fields are included.

4. Example

4.1. Request

{
  "id": 1,
  "command": "fee",
  "tx_blob": "1200152400000000684000000000000000730081142269E8F72D5112F6992818E2B8EC2309EFB9D3C08314046D18FE322220FB5538108533015D485EA2D12E"
}

{
  "id": 1,
  "command": "fee",
  "tx_json": {
    "TransactionType": "AccountDelete",
    "Account": "rh3xiHDPSKvvyFVVYHufgUb7useHNukPr8",
    "Destination": "rQQQrUdN1cLdNmxH4dHfKgmX5P4kf3ZrM"
  }
}

4.2. Response

{
  "id": 1,
  "result": {
    "current_ledger_size": "114",
    "current_queue_size": "0",
    "drops": {
      "base_fee": "200000",
      "median_fee": "100000000",
      "minimum_fee": "200000",
      "open_ledger_fee": "200000"
    },
    "expected_ledger_size": "168",
    "ledger_current_index": 8386800,
    "levels": {
      "median_level": "128000",
      "minimum_level": "256",
      "open_ledger_level": "256",
      "reference_level": "256"
    },
    "max_queue_size": "3360"
  },
  "type": "response"
}

5. Backwards Compatibility

This proposal is backwards compatible as it only extends the existing fee RPC without modifying its current behavior when tx_blob is not provided.

[dangell7]

open_ledger_fee should also be updated for the txn type.

[mvadari]

IMO this should follow the same parameter style as simulate, which autofills Sequence, Fee, and SigningPubKey, and also accepts a tx_json in place of the tx_blob.

[tequdev]

It'd be simpler to support only tx_blob within this standard proposal, as it'd need to be changed for each additional autofill field in the future.

[mvadari]

It'd be simpler to support only tx_blob within this standard proposal

I agree that it'd be simpler, but I don't see why that's a concern. IMO if we're making the change, we should do it completely, rather than halfway.

it'd need to be changed for each additional autofill field in the future

Autofill fields aren't added very often, so I also don't see how that's a concern. Worst case scenario, you just have to autofill it yourself before making the call (until it's patched). Also, adding tx_json doesn't change anything there.

[tequdev]

Updated

• Added tx_json field to request parameter