Extraneous data in eth_call response is not handled correctly

[onyb]

Per https://community.brave.com/t/wrong-price-to-vusdc/400120.

The result of calling balanceOf(address account) → uint256 on the VUSDC contract (BSC network) returns 0x0000000000000000000000000000000000000000000000000000000000045d120000000000000000000000000000000000000000000000000000000000000000000000000 which is 32 + 32 bytes.

Since we consider the entire hex string as the uint256 response, the resulting balance is incorrect. Etherscan, ethers, and other libraries only extract the first 32 bytes, so we should have same behaviour in brave-core. We should do the same for allowance(address owner, address spender) → uint256 as well.

Note that there's already a function called GetUint256HexFromData in eth_abi_decoder.cc that we can use for this purpose.

Contact me if you need VUSDC on BSC network to test.

[kjozwiak]

The above will require 1.42.69 or higher for 1.42.x verification 👍

[srirambv]

Verification passed on Oppo Reno 5 with Android 12 running 1.42.77 x64 build

• Verified steps from brave/brave-core#14138
• Verified the token balance is correctly shown

23998.mp4

[srirambv]

Brave	1.42.80 Chromium: 104.0.5112.57 (Official Build) (64-bit)
Revision	212fd173a0da1e0a024f328295bb56a2529190bb-refs/branch-heads/5112@{#1042}
OS	☑️ Linux	☑️ Windows 11 Version 21H2 (Build 22000.708)	☑️ macOS Version 12.0.1 (Build 21C52)
Verified steps from https://github.com/brave/brave-core/pull/14138 Verified the token balance is correctly shown
	23998-Linux.mp4	23998-Windows.mp4	23998-macOS.mov