failed-result

A small crate for converting various failed value to result with corresponding error type

Motivation

Somtimes, in order to implement some features, we have to call native interface via FFI in Rust, and the conversion between native error with Rust error is commonly painful, so we need a more convenient way to do this.

In general, the error type is std::io::Error, which correspond the common error type in each platform.

This crate introduces a trait LastError, provides a method LastError::last_error to get the last error by std::io::Error::last_os_error, ant it is implemented by default for general types whose one of value represents a failed result, such as bool(false), Option(None), u32(0, the FALSE value of BOOL type on Windows) and any Null-Pointer.

You can get the error as a Result more easily, like this

use failed_result::*;

let res = OpenProcess(PROCESS_ALL_ACCESS, 0, 0).last_error();
assert_eq!(res.unwrap_err().kind(), ErrorKind::InvalidInput);

And the convenience becomes significant when the parent function returns a Result

fn get_process_path(pid: u32) -> anyhow::Result<String> {
    unsafe {
        let handle = OpenProcess(PROCESS_ALL_ACCESS, 0, pid).last_error()?;

        let mut buf = [0u16; MAX_PATH];
        GetModuleFileNameExW(handle, core::ptr::null_mut(), buf.as_mut_ptr(), buf.len() as u32).last_error()?;
        CloseHandle(handle);

        Ok(String::from_utf16(&buf)?)
    }
}

In addition, there is also a trait AsHResult on Windows platform, represents a result whose root type is HRESULT, you can convert these types easily to a windows::core::Result by using this trait.

I will implement more failed type includes other platform, depending on people's needs, and any feedback is welcome.

Example

use failed_result::*;
use std::io::ErrorKind;
use winapi::um::{processthreadsapi::*, winnt::PROCESS_ALL_ACCESS};

unsafe {
    let res = OpenProcess(PROCESS_ALL_ACCESS, 0, 0).last_error();
    assert_eq!(res.unwrap_err().kind(), ErrorKind::InvalidInput);

    let res = OpenProcess(PROCESS_ALL_ACCESS, 0, std::process::id()).last_error();
    assert!(res.is_ok());
}