英文:
Can I create a callback wrapper with Rust?
问题
I want to call the native Windows CopyFileEx function from within a Rust program but I am having trouble getting a working example of LPPROGRESS_ROUTINE. I am a Java programmer learning Rust and the lack of OOP paradigms is a challenge for me. In Java, I would use a class that implemented an interface as my callback. However, it looks like the lpprogressroutine parameter is a pointer to a function, rather than a polymorphic object. But this should be fine; I can just declare a function and create a pointer to it.
我想在Rust程序中调用本机的Windows CopyFileEx函数，但我在获取LPPROGRESS_ROUTINE的工作示例时遇到了问题。我是一名学习Rust的Java程序员，缺乏面向对象的编程范式对我来说是一个挑战。在Java中，我会使用实现接口的类作为我的回调。然而，看起来lpprogressroutine参数是一个指向函数的指针，而不是多态对象。但这应该没问题；我可以只需声明一个函数并创建一个指针。
I want the callback function to call a different function with additional arguments, so I created a wrapper struct to contain those additional arguments and the callback function:
我希望回调函数能够调用一个带有额外参数的不同函数，因此我创建了一个包装结构来包含这些额外参数和回调函数：
use jni::objects::{JObject, JString, JValueGen};use jni::strings::JavaStr;use jni::sys::jint;use jni::JNIEnv;use windows::core::*;use windows::Win32::Foundation::HANDLE;use windows::Win32::Storage::FileSystem::{CopyFileExA, LPPROGRESS_ROUTINE, LPPROGRESS_ROUTINE_CALLBACK_REASON,};struct Callback<'a> {env: JNIEnv<'a>,ext_callback: JObject<'a>,}impl<'a> Callback<'a> {fn new(env: JNIEnv<'a>, ext_callback: JObject<'a>) -> Self {Callback {env: env,ext_callback: ext_callback,}}unsafe extern "system" fn invoke(&mut self,totalfilesize: i64,totalbytestransferred: i64,streamsize: i64,streambytestransferred: i64,_dwstreamnumber: u32,_dwcallbackreason: LPPROGRESS_ROUTINE_CALLBACK_REASON,_hsourcefile: HANDLE,_hdestinationfile: HANDLE,_lpdata: *const ::core::ffi::c_void,) -> u32 {let arr = [JValueGen::Long(totalfilesize),JValueGen::Long(totalbytestransferred),JValueGen::Long(streamsize),JValueGen::Long(streambytestransferred),];self.env.call_method(&self.callback, "onProgressEvent", "(IIII)V", &arr).expect("Java callback failed");return 0;}}
Now in order to access the env and ext_callback fields that I defined on the struct, I had to add the &mut self parameter to my invoke function. I think already this ruins the function signature so it wont work as a LPPROGRESS_ROUTINE, but perhaps not.
现在，为了访问我在结构体上定义的env和ext_callback字段，我不得不将&mut self参数添加到我的invoke函数中。我认为这已经破坏了函数签名，因此它可能无法作为LPPROGRESS_ROUTINE工作，但也许不是。
Continuing the endeavor, I create a method which will construct my Callback implementation and invoke the CopyFileExA function with a pointer to my method. This is where I am having trouble. I cannot figure out how to create a pointer to the callback method, since it is not static:
继续努力，我创建了一个方法，用于构建我的Callback实现并使用指向我的方法的指针调用CopyFileExA函数。这是我遇到困难的地方。我无法弄清如何创建回调方法的指针，因为它不是静态的：
pub extern "system" fn Java_com_nhbb_util_natives_WindowsCopy_copy<'local>(mut env: JNIEnv<'local>,_object: JObject<'local>,source: JString<'local>,dest: JString<'local>,flags: jint,ext_callback: JObject<'local>,) {let source_jstr: JavaStr = env.get_string(&source).expect("Invalid source string");let dest_jstr: JavaStr = env.get_string(&dest).expect("Invalid dest string");let source_arr = source_jstr.get_raw();let dest_arr = dest_jstr.get_raw();let source = source_arr as *const u8;let dest = dest_arr as *const u8;let flags: u32 = flags.try_into().unwrap();let callback = Callback::new(env, ext_callback);unsafe {CopyFileExA(PCSTR(source),PCSTR(dest),LPPROGRESS_ROUTINE::Some(callback::invoke),// ^^^^^^^^ use of undeclared crate or module `callback`None,None,flags,);}}
I think I am just struggling from lack of experience working with this new language. Am I taking the correct approach using struct? Is there a better way to do this?
我认为我只是因为缺乏使用这种新语言的经验而感到困难。我是否采取了正确的方法使用struct？是否有更好的方法来做这个？
英文:
I want to call the native Windows CopyFileEx function from within a Rust program but I am having trouble getting a working example of LPPROGRESS_ROUTINE. I am a Java programmer learning Rust and the lack of OOP paradigms is a challenge for me. In Java, I would use a class that implemented an interface as my callback. However, it looks like the lpprogressroutine parameter is a pointer to a function, rather than a polymorphic object. But this should be fine; I can just declare a function and create a pointer to it.
I want the callback function to call a different function with additional arguments, so I created a wrapper struct to contain those additional arguments and the callback function:
use jni::objects::{JObject, JString, JValueGen};use jni::strings::JavaStr;use jni::sys::jint;use jni::JNIEnv;use windows::core::*;use windows::Win32::Foundation::HANDLE;use windows::Win32::Storage::FileSystem::{CopyFileExA, LPPROGRESS_ROUTINE, LPPROGRESS_ROUTINE_CALLBACK_REASON,};struct Callback<'a> {env: JNIEnv<'a>,ext_callback: JObject<'a>,}impl<'a> Callback<'a> {fn new(env: JNIEnv<'a>, ext_callback: JObject<'a>) -> Self {Callback {env: env,ext_callback: ext_callback,}}unsafe extern "system" fn invoke(&mut self,totalfilesize: i64,totalbytestransferred: i64,streamsize: i64,streambytestransferred: i64,_dwstreamnumber: u32,_dwcallbackreason: LPPROGRESS_ROUTINE_CALLBACK_REASON,_hsourcefile: HANDLE,_hdestinationfile: HANDLE,_lpdata: *const ::core::ffi::c_void,) -> u32 {let arr = [JValueGen::Long(totalfilesize),JValueGen::Long(totalbytestransferred),JValueGen::Long(streamsize),JValueGen::Long(streambytestransferred),];self.env.call_method(&self.callback, "onProgressEvent", "(IIII)V", &arr).expect("Java callback failed");return 0;}}
Now in order to access the env and ext_callback fields that I defined on the struct, I had to add the &mut self parameter to my invoke function. I think already this ruins the function signature so it wont work as a LPPROGRESS_ROUTINE, but perhaps not.
Continuing the endeavor, I create a method which will construct my Callback implementation and invoke the CopyFileExA function with a pointer to my method. This is where I am having trouble. I cannot figure out how to create a pointer to the callback method, since it is not static:
pub extern "system" fn Java_com_nhbb_util_natives_WindowsCopy_copy<'local>(mut env: JNIEnv<'local>,_object: JObject<'local>,source: JString<'local>,dest: JString<'local>,flags: jint,ext_callback: JObject<'local>,) {let source_jstr: JavaStr = env.get_string(&source).expect("Invalid source string");let dest_jstr: JavaStr = env.get_string(&dest).expect("Invalid dest string");let source_arr = source_jstr.get_raw();let dest_arr = dest_jstr.get_raw();let source = source_arr as *const u8;let dest = dest_arr as *const u8;let flags: u32 = flags.try_into().unwrap();let callback = Callback::new(env, ext_callback);unsafe {CopyFileExA(PCSTR(source),PCSTR(dest),LPPROGRESS_ROUTINE::Some(callback::invoke),// ^^^^^^^^ use of undeclared crate or module `callback`None,None,flags,);}}
I think I am just struggling from lack of experience working with this new language. Am I taking the correct approach using struct? Is there a better way to do this?
答案1
得分: 2
这是您提供的代码的中文翻译部分：
重要的是要理解的是，callback::invoke 不是 已绑定到 Callback 对象的普通函数。不存在隐式结构绑定；Callback::invoke 需要作为其第一个参数的 Callback 选项。这意味着它不会直接与 LPPROGRESS_ROUTINE 一起使用，也永远不会这样做。LPPROGRESS_ROUTINE 需要一个静态函数。
因此，您的解决方案是创建一个静态函数，通过其 lpdata 参数传递 callback 选项。这正是 lpdata 参数的用途。
请注意，由于 lpdata 参数在 C 中传递回来，它将是原始指针，您将需要使用 unsafe 来使用它。
这是演示如何工作的示例。请注意，我剥离了所有 JNI 相关的内容，但相同的原则也适用于 JNI。
请注意，PCSTR 的编码取决于区域设置，因此不建议如前所示使用它。建议改用 PCWSTR，这是全局不含糊的。根据 Windows API 文档，PCWSTR 编码为 UTF-16LE。以下是使用 PCWSTR 的示例代码。
希望这有所帮助！
英文:
The important thing to understand here is that callback::invoke is not a normal function already bound to the Callback object. There is no such thing as an implicit struct binding; Callback::invoke requires the Callback option as its first argument. This means it does not and will never work with LPPROGRESS_ROUTINE directly. LPPROGRESS_ROUTINE expects a static function.
So your solution is to create a static function that gets the callback option passed through its lpdata argument. That's exactly what the lpdata argument is for.
Note that because the lpdata argument gets passed to C and back, it will be a raw pointer and you will require unsafe to use it.
Here is a demonstration of how this would work. Note that I stripped out all the JNI stuff, but the same principle should work with JNI as well.
use std::ffi::c_void;use encoding_rs::WINDOWS_1252;use windows::core::*;use windows::Win32::Foundation::HANDLE;use windows::Win32::Storage::FileSystem::{CopyFileExA, LPPROGRESS_ROUTINE, LPPROGRESS_ROUTINE_CALLBACK_REASON,};struct Callback<'a> {ext_callback: &'a mut dyn FnMut(i64, i64, i64, i64) -> u32,}impl<'a> Callback<'a> {fn new(ext_callback: &'a mut dyn FnMut(i64, i64, i64, i64) -> u32) -> Self {Callback { ext_callback }}unsafe extern "system" fn invoke(totalfilesize: i64,totalbytestransferred: i64,streamsize: i64,streambytestransferred: i64,_dwstreamnumber: u32,_dwcallbackreason: LPPROGRESS_ROUTINE_CALLBACK_REASON,_hsourcefile: HANDLE,_hdestinationfile: HANDLE,lpdata: *const c_void,) -> u32 {let this_ptr: *mut Self = lpdata.cast_mut().cast();let this = this_ptr.as_mut().unwrap();(this.ext_callback)(totalfilesize,totalbytestransferred,streamsize,streambytestransferred,)}}fn main() {let mut ext_callback =|totalfilesize, totalbytestransferred, streamsize, streambytestransferred| {println!("Progress: File: {}/{}, Stream Size: {}, Stream bytes transferred: {}",totalbytestransferred, totalfilesize, streamsize, streambytestransferred,);0};let mut callback = Callback::new(&mut ext_callback);// IMPORTANT: Rust strings are UTF-8, but `CopyFileExA` requires an ANSI/Windows-1252 string!// Use `encoding_rs` to convert between the two.let mut source = WINDOWS_1252.encode("file_a.txt").0.into_owned();let mut dest = WINDOWS_1252.encode("file_b.txt").0.into_owned();// Add null terminationsource.push(0);dest.push(0);unsafe {CopyFileExA(PCSTR::from_raw(source.as_ptr()),PCSTR::from_raw(dest.as_ptr()),LPPROGRESS_ROUTINE::Some(Callback::invoke),Some(((&mut callback) as *mut Callback).cast()),None,0,);}}
Progress: File: 0/23, Stream Size: 23, Stream bytes transferred: 0Progress: File: 23/23, Stream Size: 23, Stream bytes transferred: 23
FURTHER REMARKS, IMPORANT:
The encoding of PCSTR depends on the locale, and should therefore not be used as shown previously. While most western locales do indeed use Windows-1252, many others do not.
It is therefore recommended to use PCWSTR instead, which is globally unambiguous.
According to the Windows API docs, a PCWSTR is encoded as UTF-16LE.
This is how the previous code would be rewritten for it:
use std::ffi::c_void;use std::iter;use windows::core::*;use windows::Win32::Foundation::HANDLE;use windows::Win32::Storage::FileSystem::{CopyFileExW, LPPROGRESS_ROUTINE, LPPROGRESS_ROUTINE_CALLBACK_REASON,};struct Callback<'a> {ext_callback: &'a mut dyn FnMut(i64, i64, i64, i64) -> u32,}impl<'a> Callback<'a> {fn new(ext_callback: &'a mut dyn FnMut(i64, i64, i64, i64) -> u32) -> Self {Callback { ext_callback }}unsafe extern "system" fn invoke(totalfilesize: i64,totalbytestransferred: i64,streamsize: i64,streambytestransferred: i64,_dwstreamnumber: u32,_dwcallbackreason: LPPROGRESS_ROUTINE_CALLBACK_REASON,_hsourcefile: HANDLE,_hdestinationfile: HANDLE,lpdata: *const c_void,) -> u32 {let this_ptr: *mut Self = lpdata.cast_mut().cast();let this = this_ptr.as_mut().unwrap();(this.ext_callback)(totalfilesize,totalbytestransferred,streamsize,streambytestransferred,)}}fn main() {let mut ext_callback =|totalfilesize, totalbytestransferred, streamsize, streambytestransferred| {println!("Progress: File: {}/{}, Stream Size: {}, Stream bytes transferred: {}",totalbytestransferred, totalfilesize, streamsize, streambytestransferred,);0};let mut callback = Callback::new(&mut ext_callback);// IMPORTANT: Rust strings are UTF-8, but `CopyFileExW`// requires UTF-16 with null termination.let source: Vec<u16> = "file_😀_a.txt".encode_utf16().chain(iter::once(0)) // null termination.collect();let dest: Vec<u16> = "file_😀_b.txt".encode_utf16().chain(iter::once(0)) // null termination.collect();unsafe {CopyFileExW(PCWSTR::from_raw(source.as_ptr()),PCWSTR::from_raw(dest.as_ptr()),LPPROGRESS_ROUTINE::Some(Callback::invoke),Some(((&mut callback) as *mut Callback).cast()),None,0,);}}
Progress: File: 0/30, Stream Size: 30, Stream bytes transferred: 0Progress: File: 30/30, Stream Size: 30, Stream bytes transferred: 30
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