function_selector_json

Builds the canonical signature for a JSON ABI function fragment and returns its 4-byte Keccak-256 selector.

Example

Local

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SELECT function_selector_json(json('{
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"type": "function",
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"name": "transfer",
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"inputs": [
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{"name": "to", "type": "address"},
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{"name": "value", "type": "uint256"}
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]
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}')) AS selector;
Notebook ready in readonly mode.

API reference

Exact signatures with descriptions, requirements, inputs, returns, and examples.

function_selector_json(JSON) #

Canonicalizes one JSON ABI function fragment, then hashes the derived signature.

Inputs

Name Type Use
abi JSON

A single function ABI object with name and inputs. Tuple and array structure is preserved while uint/int aliases are normalized to uint256/int256.

 required positional

Returns

Name Type
selector BYTES4

Function selector. Returns the first four bytes of Keccak-256 over the canonical function signature as BYTES4.

Guidance

Choose a selector source

Use function_selector_json when the source of truth is a JSON ABI fragment. It preserves tuple and array structure and normalizes uint and int aliases before hashing.

  • Use function_selector for signature text that is already canonical.
  • Use encode_function_data when complete selector-prefixed calldata is required.
  • Use event_signature for event topic0.

Local SQL

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SELECT function_selector('transfer(address,uint256)') AS selector;
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Choose the right ABI primitive

Choose by byte framing and direction: selector construction, standard arguments, calldata, packed bytes, raw words, calldata decoding, and return-data decoding are distinct operations.

  • function_selector hashes already-canonical signature text exactly; function_selector_json builds a canonical signature from one JSON ABI fragment first.
  • encode_function_args emits selector-free standard ABI arguments; encode_function_data prefixes those same bytes with the 4-byte selector.
  • abi_encode_packed concatenates compact scalar encodings without standard ABI offsets, lengths, or 32-byte padding; evm_abi_word always emits exactly one padded 32-byte word.
  • decode_function_data consumes and validates selector-prefixed calldata inputs; call_decode consumes selector-free function return bytes.

Local SQL

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SELECT
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function_selector('transfer(address,uint256)') AS selector,
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encode_function_data(
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'[{"type":"function","name":"transfer","inputs":[{"type":"address"},{"type":"uint256"}]}]'::JSON,
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'transfer(address,uint256)',
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'0x000000000000000000000000000000000000dEaD'::ADDRESS,
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1::UINT256
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) AS calldata;
Notebook ready in readonly mode.

Related functions

Category and tags

Tag
ABI