"Balance change does not match transfer value" ignore statement will ignore "fee base" tokens

[DenisCarriere]

Tokens that deduct a fee when transferring would be entirely ignored by this if statement.

Ex: User A transfers 1.0000 XYZ token to user B, protocol deducts 0.0500 XYZ (as 5% transfer tax), user A deducts 1.0000 XYZ full amount (✅ not ignored), however user B only receive an increase in 0.9500 XYZ tokens (❌ this balance change would be ignored)

substreams-erc20-balance-changes/src/maps.rs

Lines 177 to 180 in 99907f0

	if balance_change_abs != transfer_value_abs {
	info!("Balance change does not match transfer value. Balance change: {}, transfer value: {}", balance_change_abs, transfer_value_abs);
	continue;
	}

[maoueh]

Algorithm #2 seems to deal with that case, trying to gather storage changes with the diff, see https://github.com/streamingfast/substreams-erc20-balance-changes/blob/master/src/maps.rs#L308-L314

Do you have an example that generates a wrong input, we could easily create a unit test for that based on real data.

Overall, agreed they should be handled.

[DenisCarriere]

The "safemoon" types of tokens have a transfer fee.

Perhaps the current logic is accurate since it's tracking the "value" from the logs and not the "call" itself (which would have a different value from the diff balances vs. value amount)

https://bscscan.com/tx/0x76d98d01c220234ab1ae1f13044ff4c613264a6d6f6e80135bb121910e54ff32