Error Handling

LIEF manages the errors using

  1. The exceptions (removed in LIEF 0.13.0)

  2. std::expected (tl::expected)

It turns out that using the C++ exceptions (and the RTTI) were not the better design choice as LIEF (as a library) can be used in -fno-exceptions context. This is why we are slowly moving to the second mechanism which is based on the ResultOrError idiom. We can find this kind idiom in LLVM with llvm::ErrorOr, in Rust with std::result. LIEF is using a std::expected-like to handle errors. Since this interface is only available in C++23, we rely on TartanLlama/expected which provides this interface for C++11/C++17.

Basically, LIEF functions that use this idiom return a LIEF::result which wraps the effective result or an error.

The user can process this result as follows:

result<PE_TYPE> pe_type = PE::get_type("/tmp/NotPE.elf")
if (pe_type) {
  PE_TYPE effective_type = pe_type.value();
} else {
  lief_errors err = as_lief_err(pe_type);

In the case of Python, we leverage the dynamic features of the language to return either: the expected value or an error if the function failed. For instance, if we take the lief.PE.get_type() function, the former implementation of this function raised an exception to inform the user:

  pe_type = lief.PE.get_type("/tmp/NotPE.elf")
  # If it does not fail, pe_type handles a lief.PE.PE_TYPE object
except Exception as e:
  print(f"Error: {e}")

With the new implementation that relies on the ResultOrError idiom, the function returns the lief.PE.PE_TYPE value is everything is ok and in the case of a processing error, it returns a lief.lief_errors.

The user can handle this new interface by using the isinstance() function or by comparing the value with a lief.lief_errors attribute:

pe_type = lief.PE.get_type("/tmp/NotPE.elf")

if pe_type == lief.lief_errors.file_error:
  print("File error")
elif isinstance(pe_type, lief.lief_errors):
  print("Another kind of error")
  print("No error, type is: {}".format(pe_type))