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HistoricalGasPrice.md

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Type Name

HistoricalGasPrice

Description

This is a query type for the Tellor network, named HistoricalGasPrice, which is engineered to estimate the historical gas price in gwei. This is particularly beneficial for protocols that aim to refund users for their expended gas.

The HistoricalGasPrice query type operates by examining the average gas prices at a given timestamp. It achieves this by reporting the median gas price from the block that corresponds to the given timestamp. Since finding a block that perfectly matches the given timestamp isn't always feasible, the block that is closest to, but not later than, the given timestamp is used. This ensures that the user reimbursement is based on a representative gas price, even when an exact match for the timestamp isn't available.

Query Parameters

The parameters of the HistoricalGasPrice query type will be the chainId and timestamp

1. chainId
    - description: unique id of the EVM chain (ex: rinkeby is 4)
    - value type: `uint256`
2. timestamp
    - description: the unix timestamp to calculate on-chain gas price at
    - value type: `uint256`

Response Type

HistoricalGasPrice's response type is an unpacked 256 bit value with 18 decimals of precision. It's response type is measured in gwei:

- abi_type: ufixed256x18 (18 decimals of precision)
- packed: false

Query Data

queryData = abi.encode("HistoricalGasPrice", abi.encode(1, 1650465649))

Query ID

The Query ID is your new Query's unique identifier. It's important to have one because many kinds of data pass through the Tellor ecosystem.

To generate a query ID, get the bytes32 value of the keccak hash of the query data (defined above). For example, in Solidity:

keccak256(queryData)

You can use this tool to generate query IDs.

JSON Representation

The JSON representation of a HistoricalGasPrice query:

{
    "type": "HistoricalGasPrice",
    "abi": [
        {
            "type": "uint256",
            "name": "chainId",
        },
        {
            "type": "uint256",
            "name": "timestamp",
        },
    ],
    "response": {
        "type": "ufixed256x18",
        "packed": false,
    }
}

Example

A working example mapping of all the various inputs and parameters to a valid queryID.

The queryData for mainnet ethereum (chainId 1) at unix timestamp 1650465649:

queryData = abi.encode("HistoricalGasPrice", abi.encode(1, 1650465649))
queryId = keccack256(queryData)

queryData: 0x000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000800000000000000000000000000000000000000000000000000000000000000012486973746f726963616c47617350726963650000000000000000000000000000000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000062601b71

queryId: 0xf451dd40a7d42f120c488d1b27d148b3deb1293d22bd7378e524e12d0a659584

You can use this tool to generate query IDs.

Dispute Considerations

Note that following this guide does not prevent you from being disputed or guarantee reporters will properly put a value on-chain. Tellor is decentralized. This repo is a start to the education necessary for a fully decentralized oracle, but please focus on communication and working with reporters to prevent unneccesary disputes and at the same time encourage monitoring and punishment of bad data.

don't do this

  • reporting a gas price from one historical transaction. gas prices are very volatile
  • reporting the current gas price from metamask. gas prices are very volatile
  • do not report the base fee and priority fee separately

do this

  • aggregate/medianize gas prices from the relevant block(s)
  • be careful when sourcing data from a black box API
  • use EIP-1559 gas strategy (the sum of the base fee and priority fee)
  • always measured in gwei

Suggested Data Sources

Oracle provides a "gas price history" API. It aggregates gas prices between timestamps, which can be used to calculate a median. It supports the following networks:

  • Ethereum
  • BSC
  • Fantom
  • Polygon
  • Cronos
  • Harmony
  • Celo
  • Heco
  • Moonriver
  • Fuse