Dynamic Strings

[stas]

Simple Summary

Velodrome Sugar is an onchain API handling internal and external contract calls. In order to avoid failures to external calls (eg. a random token contract that could be upgraded to a non ERC20 compatible interface), the ERC20 calls are wrapped up for safety using raw_call().

These calls to the ERC20.symbol() do not allow us to dynamically handle arbitrary byte array size returned by the raw_call().

Motivation

There are two aspects in the described limitation.

Consider the following example:

# To test on OP Mainnet, pass these token addresses:
# * 0x4200000000000000000000000000000000000006 (weth)
# * 0x045D841ba37E180bC9b9D4da718E14b9ED7925d6 (large unicode value)

@external
@view
def safe_symbol(_token: address) -> String[10]:
  response: Bytes[100] = raw_call(
      _token,
      method_id("symbol()"),
      max_outsize=100,
      gas=50000,
      is_delegate_call=False,
      is_static_call=True,
      revert_on_failure=False,
  )[1]

  response_len: uint256 = len(response)

  # Min bytes to use abi_decode()
  if response_len > 0 and response_len <= 96:
    return abi_decode(response, String[10])

  return "-???-"

1. using max_outsize=96 we are not able to get the actual size of the response byte array
2. even having the actual size of the response we won't be able to use abi_decode() without having support for dynamic string size allocation

Specification

Suggested approach would be to probably

a) extend the return value of the raw_call to return the actual size of the returned bytes, eg. outsize
b) provide support for dynamic string types, eg symbol: String[outsize] = empty(String[outsize])

Backwards Compatibility

• raw_call() would likely introduce a breaking change for implementations that expect a return value of a tuple with two values
• dynamic strings support would just extend the existing String interface allowing non-static values to be passed

Dependencies

Might need some help if there are duplicates re this.

References

See attached simple example.

Copyright

Copyright and related rights waived via CC0