dlrkit 0.1.3

dlrkit provides an API for interacting with the dynamic linker and loading libraries at runtime such as .so files and .dll files. Useful for executing code from external libraries using the C ABI.
Documentation 
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use core::ffi::{c_char, c_void};

use std::{error::Error, ffi::CString, path::Path};

use crate::OpenMode;

// GetModuleHandleExW constants:
pub const GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS: u32 = 0x00000004;
pub const GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT: u32 = 0x00000002;

#[link(name = "kernel32")]
extern "system" {
    fn GetModuleHandleExW(
        dwflags: u32,
        lp_module_name: *const u16,
        ph_module: *mut *mut c_void,
    ) -> bool;

    fn LoadLibraryExW(
        lp_lib_file_name: *const u16,
        hfile: *mut c_void,
        dwflags: u32,
    ) -> *mut c_void;

    fn GetProcAddress(hmodule: *mut c_void, lp_proc_name: *const c_char) -> *mut c_void;

    fn FreeLibrary(hlibmodule: *mut c_void) -> bool;
}

pub unsafe fn load_library_or_get_module_handle<P: AsRef<Path>>(
    lp_lib_file_name: Option<P>,
    mode: OpenMode,
) -> Result<*mut c_void, Box<dyn Error>> {
    let maybe_path = path_to_utf16(lp_lib_file_name)
        .map_err(|err| format!("failed to convert lp_lib_file_name to utf-16 - {err}"))?;

    let dwflags: u32 = match mode {
        OpenMode::Win32(v) => v,
        _ => return Err(format!("unknown open mode: {mode}").into()),
    };

    match maybe_path {
        Some(path) => load_library_exw(path, core::ptr::null_mut(), dwflags),
        None => get_module_handle_exw(dwflags, None),
    }
}

pub enum GetModuleHandleModuleName {
    Name(Vec<u16>),
    Address(usize),
}

pub unsafe fn get_module_handle_exw(
    dwflags: u32,
    lp_module_name: Option<GetModuleHandleModuleName>,
) -> Result<*mut c_void, Box<dyn Error>> {
    let lp_module_name_ptr: *const u16 = match lp_module_name {
        Some(path) => match path {
            GetModuleHandleModuleName::Name(name) => name.as_ptr(),
            GetModuleHandleModuleName::Address(addr) => addr as *const u16,
        },
        None => core::ptr::null_mut(),
    };

    let mut ph_module: *mut c_void = core::ptr::null_mut();

    if !GetModuleHandleExW(dwflags, lp_module_name_ptr, &mut ph_module) {
        return Err(format!(
            "get_module_handle_exw failed - {}",
            std::io::Error::last_os_error()
        ))?;
    }

    Ok(ph_module)
}

pub unsafe fn load_library_exw(
    lp_lib_file_name: Vec<u16>,
    hfile: *mut c_void,
    dwflags: u32,
) -> Result<*mut c_void, Box<dyn Error>> {
    let result = LoadLibraryExW(lp_lib_file_name.as_ptr(), hfile, dwflags);
    if result.is_null() {
        return Err(format!(
            "load_library_exw failed - {}",
            std::io::Error::last_os_error()
        ))?;
    }

    Ok(result)
}

pub fn path_to_utf16<P: AsRef<Path>>(path: Option<P>) -> Result<Option<Vec<u16>>, Box<dyn Error>> {
    match path {
        Some(p) => match p.as_ref().to_str() {
            Some(s) => {
                let mut utf16 = s.encode_utf16().collect::<Vec<_>>();
                utf16.push(0);

                Ok(Some(utf16))
            }
            None => return Err("str conversaion failed")?,
        },
        None => Ok(None),
    }
}

pub unsafe fn get_proc_address(
    hmodule: *mut c_void,
    lp_proc_name: &str,
) -> Result<*mut c_void, Box<dyn Error>> {
    let lp_proc_name = CString::new(lp_proc_name)?;

    let result = GetProcAddress(hmodule, lp_proc_name.as_ptr());
    if result.is_null() {
        return Err(format!(
            "get_proc_address failed - {}",
            std::io::Error::last_os_error()
        ))?;
    }

    Ok(result)
}

pub unsafe fn free_library(hmodule: *mut c_void) -> Result<(), Box<dyn Error>> {
    if !FreeLibrary(hmodule) {
        return Err(format!(
            "free_library failed - {}",
            std::io::Error::last_os_error()
        ))?;
    }

    Ok(())
}