[bug] simulate transaction - return data truncates 0 trailing zero bytes

[ngundotra]

Problem

Here's the output of connection.simulateTransaction(...)

value.logs:

[
  'Program F96CHxPDRgjUypdUqpJocgT59vEPT79AFJXjtyPCBaRt invoke [1]',
 ...
  'Program return: F96CHxPDRgjUypdUqpJocgT59vEPT79AFJXjtyPCBaRt CgAAAGqESwQbOhmSyJ05YcX8yuNd0njURaxOHDYINR4MYbMsAAEojRw9Os+/4K0ZpeJWw/3v8PboPlgkFx4n0ld1IP747AABPu+weEw0Q/3awCJDGdE4AeW7NRpNrlCaBi5txpV4jTUAADIZojUTiD7oHHgzCQXAuZXenMlh3zh7I2cL6rQZ7/hBAACcte7UwJZd0Ds9bHif7Z3TAwmi3JGxths2aoEaBkaCzgABnwlgIBRezTwnbIydryTVyUOR7ZyFLFOah/zvvilCq2wAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAGp9UXGHvRZjXa1ARV/cLAwSTGjyFWdaXbustfCAAAAAAABt324ddloZPZy+FGzut5rBy0he1fWzeROoz1hX7/AKkAAIyXJY9OJInxuz0QKRSODYMLWhOZ2v8QhASOe9jb6fhZAAA=',
  'Program F96CHxPDRgjUypdUqpJocgT59vEPT79AFJXjtyPCBaRt success'
] 

This is a problem because its unexpected behavior. It's not high priority because devs can just parse the 2nd to last log line for their untruncated return data.

Proposed Solution

Just return the full 1024 (MAX_CPI_DATA) slab length in RPC response value.return_data

[CriesofCarrots]

Why would you parse the log line instead of just adding back the padding, if for some reason you need it to be 1024 bytes?

[ngundotra]

That's another great alternative solution.

The issue is .value.return_data['data'] actually truncates the trailing 0s of what I put in set_return_data.

[tkporter]

Also hitting this - would love to see this fixed

[tkporter]

Not sure what's different about my setup but I'm not able to use the logs workaround - my logs don't show a Program return at all. This is when using a BanksClient fwiw

TransactionSimulationDetails {
  logs: ["Program 2YjtZDiUoptoSsA5eVrDCcX6wxNK6YoEVW7y82x5Z2fw invoke [1]", "Program 2YjtZDiUoptoSsA5eVrDCcX6wxNK6YoEVW7y82x5Z2fw invoke [1]", "Program 2YjtZDiUoptoSsA5eVrDCcX6wxNK6YoEVW7y82x5Z2fw success", "Program 2YjtZDiUoptoSsA5eVrDCcX6wxNK6YoEVW7y82x5Z2fw success"],
  units_consumed: 0,
  return_data: Some(TransactionReturnData { program_id: 2YjtZDiUoptoSsA5eVrDCcX6wxNK6YoEVW7y82x5Z2fw, data: [1, 0, 0, 0, 208, 33, 109, 56, 119, 42, 118, 230, 38, 41, 226, 35, 34, 241, 83, 38, 4, 160, 7, 87, 162, 113, 226, 54, 205, 242, 16, 94, 4, 142, 139, 151] })
}

My return data is truncated and ordinarily has two zero bytes at the end

[tkporter]

My sad workaround is a wrapper type like this to always ensure there are no trailing 0 bytes :(

#[derive(Debug, BorshSerialize, BorshDeserialize)]
pub struct SimulationReturnData<T>
where
    T: BorshSerialize + BorshDeserialize,
{
    pub return_data: T,
    trailing_byte: u8,
}

impl<T> SimulationReturnData<T>
where
    T: BorshSerialize + BorshDeserialize,
{
    pub fn new(return_data: T) -> Self {
        Self {
            return_data,
            trailing_byte: u8::MAX,
        }
    }
}