Overview of Dune’s Decoded Data Approach

Dune uses the ABI (Application Binary Interface) of smart contracts to decode blockchain transactions into structured tables. Each event log and function call from the ABI are parsed into their own tables. This decoding process transforms the raw, encoded data on the blockchain into human-readable tables, simplifying the analysis of smart contract data.

Dune’s decoded data approach offers several benefits:

  • Enhanced Readability: The decoded data tables provide a clear and intuitive representation of smart contract activities

  • Efficient Analysis: The structured tables enable efficient querying and analysis of smart contract data

  • Handling Multiple Contract Instances: For smart contracts with multiple instances, Dune aggregates the data from these instances into a single table, simplifying the analysis process.

  • Collaborative Mapping: Dune’s smart contract library is continuously expanded through the active participation of the Dune community, ensuring that the decoding coverage remains comprehensive and current.

Which contracts have decoded data?

Contract submission on Dune are driven by the community. Usually the odds are good that the contract you are looking at is already decoded, but esepecially for new projects or new contracts, it might be that the contract is not decoded yet. In those cases you can submit the contract to be decoded. Decoding usually takes about 24 hours, in special cases it might take longer.

You can check if contracts are already decoded by querying [blockchain].contracts tables, the data explorer or use this dashboard.

If you want to submit several contracts at the same time, there is also the possibility of submitting a batch of contracts. To do so, please use this CSV as a template and fill it in with the appropriate information for the contracts you want to decode. Afterwards send the CSV to decoding@dune.com.

How does decoding work?

Smart Contracts on any EVM blockchain are mostly written in high level languages like Solidity or Vyper.

In order for them to be able to be deployed to an EVM execution environment, they need to be compiled to EVM executable bytecode. Once deployed, the bytecode gets associated to an address on the respective chain and is permanently stored in this chain’s state storage.

To be able to interact with this smart contract, which is now just bytecode, we need a guide to be able to call the functions which are defined in the high-level languages. This translation of names and arguments into byte representation is done using an Application Binary Interface (ABI).

The ABI documents names, types, and arguments precisely which allows us to interact with the smart contract using a somewhat human readable format. The ABI can be compiled using the high level language source code.

The ABI is used to call a smart contract or interpret the data it emits.

source: https://hackernoon.com/hn-images/1*Sz1a7G2pQ62UnkHoieve4w.jpeg

Decoding Example

We are going to look at an event log of an ERC20 transfer event from the smart contract that represents the $PICKLE token.

On Etherscan the undecoded event looks like this:


If we query for this transaction in the ethereum.logs table in the Dune database, we will receive the same encoded bytecode as our result dataset.

FROM ethereum.logs
WHERE tx_hash = 0x2bb7c8283b782355875fa37d05e4bd962519ea294678a3dcf2fdffbbd0761bc5

We could make short work of this encoded bytecode by using DuneSQL Varbinary functions to decode it, but having the contract’s ABI at hand makes this process much easier. This contract is decoded in Dune, so we can use the pickle_finance_ethereum.PickleToken_evt_Transfer table to access the decoded event log.

FROM pickle_finance_ethereum.PickleToken_evt_Transfer
WHERE evt_tx_hash = 0x2bb7c8283b782355875fa37d05e4bd962519ea294678a3dcf2fdffbbd0761bc5

Now this is actually useful for analyzing this transaction!

How exactly does this work?

Since we know which event we are looking at here, we can simply convert the encoded bytecode to decoded data by decoding the bytecode according to it’s datatype.

The structure for the Transfer event log of an ERC20 token will always be:

Transfer(address from, address to, uint256 value)

This basically tells us that topic2 and topic3 are of the type address(32bytes) and are respectively the sender and recipient of the token transfer. An event log only has 3 indexed fields, so the data field is used to store the information about how much units of the token have been moved in this transaction. This field is called value.

Since topic0 always is just the Keccak-256 hash of the signature of the event, we are left with decoding topic1, topic2 and data.

In this case, they map out like this:

raw data fielddecoded data descriptionraw datadecoded data
topic0keccak256(“Transfer(address,address,uint256)“)0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3efnot needed, this table only contains event logs from the transfer event log

Now what works for a single erc20 token, works for all erc20 tokens. We can use defined interfaces to decode the data of any erc20 token transfer event log. You can learn more about that in the ERC20 transfer section.

How do I understand decoded data?

Decoded data is the high level programming language representation of two pieces of software talking to each other via the blockchain.

It’s not always easy for a human to understand what exactly is going on in these interactions, but most of the time, looking at column names and the data that is transmitted within them should help you to understand what is happening within that specific log or call.

If you are not able to make sense of the data by just searching the tables, it usually helps to look at single transactions using the transaction hash and Etherscan.

Furthermore, actually going into the smart contracts code (our favorite way to do this is DethCode) to read the comments or the actual logic can help to understand the smart contract’s emitted data.

If that also doesn’t lead to satisfactory results, scouring the relevant docs and GitHub of the project can lead you to the desired answers. Furthermore, talking to the developers and core community of a project can also help you to get an understanding of the smart contracts.