ABI Decoding Issue with go-ethereum: "Improperly Formatted Output" for Complex Tuple Array

[m-quigley]

I'm encountering an issue with decoding ABI data using go-ethereum's abi.Unpack or UnpackIntoInterface method. Here are the details:

Go Code Attempt:

type Route struct {
  From    common.Address
  To      common.Address
  Stable  bool
  Factory common.Address
}

type SwapExactTokensForTokensInput struct {
  AmountIn     *big.Int
  AmountOutMin *big.Int
  Routes       []Route
  To           common.Address
  Deadline     *big.Int
}

	abiJSON := `[
  {
    "inputs": [
      {
        "internalType": "uint256",
        "name": "amountIn",
        "type": "uint256"
      },
      {
        "internalType": "uint256",
        "name": "amountOutMin",
        "type": "uint256"
      },
      {
        "components": [
          {
            "internalType": "address",
            "name": "from",
            "type": "address"
          },
          {
            "internalType": "address",
            "name": "to",
            "type": "address"
          },
          {
            "internalType": "bool",
            "name": "stable",
            "type": "bool"
          },
          {
            "internalType": "address",
            "name": "factory",
            "type": "address"
          }
        ],
        "internalType": "struct IRouter.Route[]",
        "name": "routes",
        "type": "tuple[]"
      },
      {
        "internalType": "address",
        "name": "to",
        "type": "address"
      },
      {
        "internalType": "uint256",
        "name": "deadline",
        "type": "uint256"
      }
    ],
    "name": "swapExactTokensForTokens",
    "outputs": [
      {
        "internalType": "uint256[]",
        "name": "amounts",
        "type": "uint256[]"
      }
    ],
    "stateMutability": "nonpayable",
    "type": "function"
  }]`

	parsedABI, err := abi.JSON(strings.NewReader(abiJSON))
	if err != nil {
		log.Fatalf("Error parsing ABI: %v", err)
	}

	input := "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"

	var inputStruct SwapExactTokensForTokensInput
	if err := parsedABI.UnpackIntoInterface(&inputStruct, "swapExactTokensForTokens", common.FromHex(input)); err != nil {
		log.Fatalf("Error unpacking input: %v", err)
	}

Error Received:

Error unpacking input: abi: improperly formatted output: "\xcaȎ\xa9\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\xc9\xf7\x8d(\x93\xe4\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\xb4\xc0YZ\x86\xaa\x1c\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xa0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x1ab(\xe2\xf0^\xe0\xc0\xe8\"\xbe\b$\x9c\x81[7F\x7f@\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00g`5\xba\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00B\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x06\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\b\"\xd3a3[M_5-\xac)<\xa4\x12\x8b[`_\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00B\rӁ\xb3\x1a\xeff\x83\xdbk\x90 \x84\xcb\x0f\xfe\xce@\xda" - Bytes: [202 200 142 169 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 201 247 141 40 147 228 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 180 192 89 90 134 170 28 16 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 160 0 0 0 0 0 0 0 0 0 0 0 0 26 98 40 226 240 94 224 192 232 34 190 8 36 156 129 91 55 70 127 64 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 103 96 53 186 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 66 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 0 128 8 34 211 97 51 91 77 95 53 45 172 41 60 164 18 139 91 96 95 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 66 13 211 129 179 26 239 102 131 219 107 144 32 132 203 15 254 206 64 218]

Steps Taken:

• Verified that the ABI matches the function signature in the smart contract.
• Checked that the hex input is correctly formatted and converted to bytes.
• Tested decoding in JavaScript with ethers.js, which works without issues.
• Tested decoding in https://lab.miguelmota.com/ethereum-input-data-decoder/example/, which works without issues.
• Ensured struct definitions match ABI specifications.

Question:

Can anyone identify why this decoding fails in Go, or is there a known issue with decoding such complex tuple arrays with go-ethereum? Any suggestions or fixes would be greatly appreciated.
I've used this same approach for decoding calldata hundreds of times, first time facing this issue

Additional Info:

go-ethereum version: 1.22
Go version: v1.14.12

any help would be hugely appreciated

[m-quigley]

the ABI is a subset of this CAs abi, if that helps at all
https://basescan.org/address/0xcf77a3ba9a5ca399b7c97c74d54e5b1beb874e43

[m-quigley]

also, slicing off the method selector

if err := parsedABI.UnpackIntoInterface(&inputStruct, "swapExactTokensForTokens", common.FromHex(input)[4:]); err != nil {

results in

2024/12/18 12:02:51 Error unpacking input: abi: cannot marshal in to go slice: offset 33000000000000000032 would go over slice boundary (len=320)

[m-quigley]

Found #26242 which is the same issue, never fully resolved. I have the same result, if I use method.Inputs.Unpack it works

[jwasinger]

For contract methods, the unpack methods decode the provided data against the specified output of the given method, not the input. This is the source of your error.

To do what you want, you'd want something like the following:

func UnpackMethoInputIntoInterface(abi ABI, outp interface{}, name string, data []byte) error {
	var (
		args Arguments
		err  error
	)
	method := abi.Methods[name]
	args = method.Inputs

	unpacked, err := args.Unpack(data)
	if err != nil {
		return err
	}
	return args.Copy(outp, unpacked)
}