Error: "insufficient data length" when decoding function data

[miguelmota]

Describe the bug

Error when trying to decode transaction function data from etherscan

Tx: https://bscscan.com/tx/0xfa70ffb7ddec8e43728dd710e4f1d240983a502305bbc0c2c845079fc0f154d2

Decode error:

Error: insufficient data length (length=256, count=1000000000, code=BUFFER_OVERRUN, version=abi/5.5.0)

Reproduction steps

Code to reproduce:

const ethers = require('ethers')
const abi = [{
  inputs: [
    { internalType: 'uint256', name: 'amountOutMin', type: 'uint256' },
    { internalType: 'address[]', name: 'path', type: 'address[]' },
    { internalType: 'address', name: 'to', type: 'address' },
    { internalType: 'uint256', name: 'deadline', type: 'uint256' }
  ],
  name: 'swapExactETHForTokens',
  outputs: [ { internalType: 'uint256[]', name: 'amounts', type: 'uint256[]' } ],
  stateMutability: 'payable',
  type: 'function'
}]
const ifc = new ethers.utils.Interface(abi)
const data = '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'
const result = ifc.decodeFunctionData('swapExactETHForTokens', data)
console.log(result)

Version: ethers@5.5.4

Any idea why the error occurs with that tx function data but not with others (for example this tx data)? Thanks!

[ricmoo]

The transaction looks like it failed, and likely because the data was malformed.

It looks like it was encoded with an extra parameter (labeled below with ???) inserted into it. Maybe someone was experimenting with their own encoder, or manually computing the encoded data.

0x
7ff36ab5 // Selector
000000000000000000000000000000000000000000000000000000003b9aca00 // uint256
0000000000000000000000000000000000000000000000000000000000000000 // ???
00000000000000000000000000000000000000000000000000000000000000a0 // address[] => A (slot 5)
000000000000000000000000e2aefb9d145c6633fb019758d532c20b6c2577b2 // address
0000000000000000000000000000000000000000000000000000000060c04576 // uint256
0000000000000000000000000000000000000000000000000000000000000002 // A.length
000000000000000000000000bb4cdb9cbd36b01bd1cbaebf2de08d9173bc095c // A[0]
000000000000000000000000dd80054103cd4cfed6ef2e0afc8a3cb5ec07a585 // A[1]

[miguelmota]

Interesting, thanks for the explanation!