Function Decoding

Decode transaction calldata into structured function call tables using Solidity ABI definitions.

Function decoding transforms raw transaction calldata into structured, typed rows. When configured, the pipeline matches each transaction’s input data against ABI function signatures and produces decoded rows in {chain_name}_fn_{function_name} tables.

How It Works

1. The normalizer produces rows for the transactions table, each containing an input_data field (hex-encoded calldata)
2. The decoder matches the first 4 bytes of input_data (the function selector) against ABI function entries
3. Parameters are decoded from input_data[4:] using ABI type definitions
4. Each decoded call is emitted to a {chain_name}_fn_{function_name_snake_case} table

Only function ABI entries with stateMutability of nonpayable or payable are used. View and pure functions are excluded since they do not appear in transaction calldata.

Output Schema

Each decoded function table includes envelope columns from the source transaction plus the ABI-defined parameters:

Column	Type	Source
block_height	UINT64	From transactions envelope
block_signed_at	TIMESTAMP	From transactions envelope
tx_hash	STRING	From transactions envelope
tx_offset	UINT32	From transactions envelope
from_address	STRING	From transactions envelope
to_address	STRING	From transactions envelope
value	STRING	From transactions envelope
gas_limit	UINT64	From transactions envelope
receipt_status	STRING	From transactions envelope
(ABI parameters)	(mapped type)	Decoded from calldata

Example

For an ERC-20 transfer function call on Base:

function transfer(address to, uint256 amount) external returns (bool);

The output table base_fn_transfer would contain:

Column	Type
block_height	UINT64
block_signed_at	TIMESTAMP
tx_hash	STRING
tx_offset	UINT32
from_address	STRING
to_address	STRING
value	STRING
gas_limit	UINT64
receipt_status	STRING
to	STRING
amount	STRING

Configuration

Function decoding is activated by setting the abi section in your pipeline config and using a transactions topic entity:

topic: "base.mainnet.ref.block.transactions"

abi:
  path: "/etc/pipeline-api/erc20.json"
  contract_addresses:
    - "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48"
  unmatched: "skip"

Contract address filtering matches against the to_address field (the contract being called).

When to Use Function Decoding vs Event Decoding

	Event Decoding	Function Decoding
Source	logs topic entity	transactions topic entity
Decodes	Emitted event logs	Transaction calldata
Output tables	{chain_name}_evt_{name}	{chain_name}_fn_{name}
Best for	Tracking state changes, transfers, approvals	Analyzing what functions were called and with what parameters
Includes failed txs	No (failed txs don’t emit events)	Yes (calldata exists even if tx reverted)

Most use cases are better served by event decoding. Use function decoding when you specifically need to analyze calldata - for example, tracking MEV bot calls, analyzing governance proposals, or monitoring specific function invocations regardless of success.