Improve runtime error message when not enough memory is available when saving ciphertexts

[codedust]

When trying to save a ciphertext to a byte-array less than the size needed to export the ciphertext, a generic "I/O error" gets thrown instead of some more descriptive error message like "not enough space to save the ciphertext".

Pseudo-code:

std::byte ciphertext_exported[4242];
ciphertext.save(ciphertext_exported, 4242);

Generic error message:

terminate called after throwing an instance of 'std::runtime_error'
  what():  I/O error

[WeiDaiWD]

Let's me try to reproduce that and trace down why the error condition is skipped in our error messaging logic.

[fionser]

Also, I think the exception throw by SEAL is so information-less, and hard to trace down the point that throws the exception...

[kimlaine]

This issue will be fixed in SEAL 3.5: the message will clearly indicate an insufficient buffer size.

@fionser: overall, the error messaging of SEAL is indeed problematic. There are many runtime errors (decryption, decoding, etc.) that are hard to trace back to their causes. We are working on compiler tools to help with this. Then there are logic errors that are in principle easily explainable, e.g. the user setting bad parameters and SEALContext validation failing, which then causes some confusing issues with KeyGenerator etc. creation failing. We'll address this specific issue in SEAL 3.5. In the future we'll definitely want to make all errors/exceptions easier to understand.