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如何不在Rust中重写项目

一旦您超过了Borrow-Checker的痛苦阈值，并意识到Rust可以让您完成其他语言无法想象的（有时是危险的）事情，那么您可能也会有同样的不可抗拒的渴望，将所有内容重写为Rust 。 尽管在最好的情况下这是平庸的徒劳（对几个项目毫无意义的浪费），但在最坏的情况下却导致代码质量下降（毕竟，为什么您认为自己在使用库方面比原始作者更有经验？）


通过重用原始代码为原始库提供安全的接口将更加有用。


• 第一步
• 我们收集chmlib-sys
• 在Rust中编写安全的包装器
• 按名称搜索项目
• 通过过滤器绕过元素
• 读取文件内容
• 添加示例
• CHM文件目录
• 将CHM文件解压缩到磁盘
• 接下来呢？


本文讨论了一个真实的项目。 我不得不从现有的CHM文件中提取信息，但是没有时间了解该格式。 懒惰是进步的动力。

chmlib板条箱发布在crates.io上 ，其源代码可在GitHub上获得 。 如果您发现它有用或发现问题，请通过bugtracker告诉我。

第一步


首先，有必要了解库的工作最初是如何构想的。


这不仅会教您如何使用它，而且还会确保一切正常。 如果幸运的话，您甚至可以找到现成的测试和示例。

不要跳过这一步！

我们将使用CHMLib （一个用于读取Microsoft编译的HTML帮助 （ .chm ）文件的C库）进行工作。


首先创建一个新项目，并将CHMLib作为git子模块连接：


 $ git init chmlib && cd chmlib Initialized empty Git repository in /home/michael/Documents/chmlib/.git/ $ touch README.md Cargo.toml $ cargo new --lib chmlib Created library `chmlib` package $ cargo new --lib chmlib-sys Created library `chmlib-sys` package $ cat Cargo.toml [workspace] members = ["chmlib", "chmlib-sys"] $ git submodule add git@github.com:jedwing/CHMLib.git vendor/CHMLib Cloning into '/home/michael/Documents/chmlib/vendor/CHMLib'... remote: Enumerating objects: 99, done. remote: Total 99 (delta 0), reused 0 (delta 0), pack-reused 99 Receiving objects: 100% (99/99), 375.51 KiB | 430.00 KiB/s, done. Resolving deltas: 100% (45/45), done.

之后，看看使用tree的内部内容：


 $ tree vendor/CHMLib vendor/CHMLib ├── acinclude.m4 ├── AUTHORS ├── ChangeLog ├── ChmLib-ce.zip ├── ChmLib-ds6.zip ├── configure.in ├── contrib │ └── mozilla_helper.sh ├── COPYING ├── Makefile.am ├── NEWS ├── NOTES ├── README └── src ├── chm_http.c ├── chm_lib.c ├── chm_lib.h ├── enum_chmLib.c ├── enumdir_chmLib.c ├── extract_chmLib.c ├── lzx.c ├── lzx.h ├── Makefile.am ├── Makefile.simple └── test_chmLib.c 2 directories, 23 files

看起来该库使用GNU Autotools构建。 这不好，因为chmlib板条箱的所有用户（及其用户）都需要安装Autotools。


我们将尝试通过手动收集C代码来摆脱这种“传染性”的依赖关系，但稍后会对此进行更多介绍。

lzx.h和lzx.c文件包含LZX压缩算法的实现。 通常，最好使用某种liblzx库免费获取所有更新，但是愚蠢地编译这些文件可能会更容易。


enum_chmLib.c，enumdir_chmLib.c，extract_chmLib.c似乎是使用函数chm_enumerate（），chm_enumerate_dir（），chm_retrieve_object（）的示例。 它将派上用场...


文件test_chmLib.c包含另一个示例，这次从CHM文件中提取一页到磁盘。


chm_http.c实现了一个简单的HTTP服务器，该浏览器在浏览器中显示.chm文件。 这可能不再有用。


因此，我们整理了供应商/ CHMLib / src中的所有内容。 我们会收集图书馆吗？


老实说，它很小，足以应用科学的戳法。


 $ clang chm_lib.c enum_chmLib.c -o enum_chmLib /usr/bin/ld: /tmp/chm_lib-537dfe.o: in function `chm_close': chm_lib.c:(.text+0x8fa): undefined reference to `LZXteardown' /usr/bin/ld: /tmp/chm_lib-537dfe.o: in function `_chm_decompress_region': chm_lib.c:(.text+0x18ca): undefined reference to `LZXinit' /usr/bin/ld: /tmp/chm_lib-537dfe.o: in function `_chm_decompress_block': chm_lib.c:(.text+0x2900): undefined reference to `LZXreset' /usr/bin/ld: chm_lib.c:(.text+0x2a4b): undefined reference to `LZXdecompress' /usr/bin/ld: chm_lib.c:(.text+0x2abe): undefined reference to `LZXreset' /usr/bin/ld: chm_lib.c:(.text+0x2bf4): undefined reference to `LZXdecompress' clang: error: linker command failed with exit code 1 (use -v to see invocation)

好吧，也许仍然需要此LZX ...


 $ clang chm_lib.c enum_chmLib.c lzx.c -o enum_chmLib

呃...全部？


为了确保代码正常工作，我从互联网上下载了一个示例：


 $ curl http://www.innovasys.com/static/hs/samples/topics.classic.chm.zip \ -o topics.classic.chm.zip $ unzip topics.classic.chm.zip Archive: topics.classic.chm.zip inflating: output/compiled/topics.classic.chm $ file output/compiled/topics.classic.chm output/compiled/topics.classic.chm: MS Windows HtmlHelp Data

让我们看看enum_chmLib是如何处理的：


 $ ./enum_chmLib output/compiled/topics.classic.chm output/compiled/topics.classic.chm: spc start length type name === ===== ====== ==== ==== 0 0 0 normal dir / 1 5125797 4096 special file /#IDXHDR ... 1 4944434 11234 normal file /BrowserView.html ... 0 0 0 normal dir /flash/ 1 532689 727 normal file /flash/expressinstall.swf 0 0 0 normal dir /Images/Commands/RealWorld/ 1 24363 1254 normal file /Images/Commands/RealWorld/BrowserBack.bmp ... 1 35672 1021 normal file /Images/Employees24.gif ... 1 3630715 200143 normal file /template/packages/jquery-mobile/script/ jquery.mobile-1.4.5.min.js ... 0 134 1296 meta file ::DataSpace/Storage/MSCompressed/Transform/ {7FC28940-9D31-11D0-9B27-00A0C91E9C7C}/ InstanceData/ResetTable

主啊， 即使在这里 jQuery¯\ _（ツ）_ /¯


编译chmlib-sys


现在我们知道足够在chmlib -sys crate中使用CHMLib，它负责构建本机库，将其与Rast编译器链接，并提供C函数的接口。


要构建该库，您需要编写build.rs文件。 他将使用cc crate调用C编译器并进行其他友谊操作，以使一切正常工作。


幸运的是，我们可以将大部分工作转移到cc，但是有时要困难得多。 阅读更多有关汇编脚本的文档 。

首先添加cc作为chmlib-sys的依赖项：


 $ cd chmlib-sys $ cargo add --build cc Updating 'https://github.com/rust-lang/crates.io-index' index Adding cc v1.0.46 to build-dependencies

然后我们编写build.rs ：


 // chmlib-sys/build.rs use cc::Build; use std::{env, path::PathBuf}; fn main() { let project_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap()) .canonicalize() .unwrap(); let root_dir = project_dir.parent().unwrap(); let src = root_dir.join("vendor").join("CHMLib").join("src"); Build::new() .file(src.join("chm_lib.c")) .file(src.join("lzx.c")) .include(&src) .warnings(false) .compile("chmlib"); }

您还需要告诉Cargo chmlib-sys链接到chmlib库。 然后，Cargo可以确保在整个依赖关系图中只有一个机架，具体取决于特定的本机库。 这样可以避免有关重复字符或意外使用不兼容库的模糊错误消息。


 --- a/chmlib-sys/Cargo.toml +++ b/chmlib-sys/Cargo.toml @@ -3,7 +3,13 @@ name = "chmlib-sys" version = "0.1.0" authors = ["Michael Bryan <michaelfbryan@gmail.com>"] edition = "2018" description = "Raw bindings to the CHMLib C library" license = "LGPL" repository = "https://github.com/Michael-F-Bryan/chmlib" +links = "chmlib" +build = "build.rs" [dependencies] [build-dependencies] cc = { version = "1.0" }

接下来，我们需要声明chmlib库导出的所有函数，以便可以从Rast使用它们。


为此，有一个很棒的bindgen项目。 将C头文件提供给输入，并输出带有Rast的FFI绑定的文件。


 $ cargo install bindgen $ bindgen ../vendor/CHMLib/src/chm_lib.h \ -o src/lib.rs \ --raw-line '#![allow(non_snake_case, non_camel_case_types)]' $ head src/lib.rs /* automatically generated by rust-bindgen */ #![allow(non_snake_case, non_camel_case_types)] pub const CHM_UNCOMPRESSED: u32 = 0; pub const CHM_COMPRESSED: u32 = 1; pub const CHM_MAX_PATHLEN: u32 = 512; pub const CHM_PARAM_MAX_BLOCKS_CACHED: u32 = 0; pub const CHM_RESOLVE_SUCCESS: u32 = 0; pub const CHM_RESOLVE_FAILURE: u32 = 1; $ tail src/lib.rs extern "C" { pub fn chm_enumerate_dir( h: *mut chmFile, prefix: *const ::std::os::raw::c_char, what: ::std::os::raw::c_int, e: CHM_ENUMERATOR, context: *mut ::std::os::raw::c_void, ) -> ::std::os::raw::c_int; }

我强烈建议您阅读Bindgen用户手册 ，以解决其不足 。

在此阶段，编写冒烟测试将很有用，它将验证所有操作均按预期进行，并且可以实际调用原始C库的函数。


 // chmlib-sys/tests/smoke_test.rs //    Path  char*     . //  , OsStr ( Path)  Windows  [u16]  , //        char*. #![cfg(unix)] use std::{ffi::CString, os::unix::ffi::OsStrExt, path::Path}; #[test] fn open_example_file() { let project_dir = Path::new(env!("CARGO_MANIFEST_DIR")); let sample_chm = project_dir.parent().unwrap().join("topics.classic.chm"); let c_str = CString::new(sample_chm.as_os_str().as_bytes()).unwrap(); unsafe { let handle = chmlib_sys::chm_open(c_str.as_ptr()); assert!(!handle.is_null()); chmlib_sys::chm_close(handle); } }

cargo test一切似乎井井有条：


 $ cargo test Finished test [unoptimized + debuginfo] target(s) in 0.03s Running ~/chmlib/target/debug/deps/chmlib_sys-2ffd7b11a9fd8437 running 1 test test bindgen_test_layout_chmUnitInfo ... ok test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out Running ~/chmlib/target/debug/deps/smoke_test-f7be9810412559dc running 1 test test open_example_file ... ok test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out Doc-tests chmlib-sys running 0 tests test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

在Rust中编写安全包装


从技术上和技术上，我们现在可以从Rasta调用CHMLib，但这需要不安全的堆。 它可能适用于老练的手工艺品，但对于在crates.io上发布，则值得为所有不安全的代码编写安全的包装。


如果使用cargo doc --open查看chmlib-sys API，则可以看到许多将*mut ChmFile作为第一个参数的函数。 这类似于对象和方法。


CHMLib头文件
 /* $Id: chm_lib.h,v 1.10 2002/10/09 01:16:33 jedwin Exp $ */ /*************************************************************************** * chm_lib.h - CHM archive manipulation routines * * ------------------- * * * * author: Jed Wing <jedwin@ugcs.caltech.edu> * * version: 0.3 * * notes: These routines are meant for the manipulation of microsoft * * .chm (compiled html help) files, but may likely be used * * for the manipulation of any ITSS archive, if ever ITSS * * archives are used for any other purpose. * * * * Note also that the section names are statically handled. * * To be entirely correct, the section names should be read * * from the section names meta-file, and then the various * * content sections and the "transforms" to apply to the data * * they contain should be inferred from the section name and * * the meta-files referenced using that name; however, all of * * the files I've been able to get my hands on appear to have * * only two sections: Uncompressed and MSCompressed. * * Additionally, the ITSS.DLL file included with Windows does * * not appear to handle any different transforms than the * * simple LZX-transform. Furthermore, the list of transforms * * to apply is broken, in that only half the required space * * is allocated for the list. (It appears as though the * * space is allocated for ASCII strings, but the strings are * * written as unicode. As a result, only the first half of * * the string appears.) So this is probably not too big of * * a deal, at least until CHM v4 (MS .lit files), which also * * incorporate encryption, of some description. * ***************************************************************************/ /*************************************************************************** * * * This program is free software; you can redistribute it and/or modify * * it under the terms of the GNU Lesser General Public License as * * published by the Free Software Foundation; either version 2.1 of the * * License, or (at your option) any later version. * * * ***************************************************************************/ #ifndef INCLUDED_CHMLIB_H #define INCLUDED_CHMLIB_H #ifdef __cplusplus extern "C" { #endif /* RWE 6/12/1002 */ #ifdef PPC_BSTR #include <wtypes.h> #endif #ifdef WIN32 #ifdef __MINGW32__ #define __int64 long long #endif typedef unsigned __int64 LONGUINT64; typedef __int64 LONGINT64; #else typedef unsigned long long LONGUINT64; typedef long long LONGINT64; #endif /* the two available spaces in a CHM file */ /* NB: The format supports arbitrarily many spaces, but only */ /* two appear to be used at present. */ #define CHM_UNCOMPRESSED (0) #define CHM_COMPRESSED (1) /* structure representing an ITS (CHM) file stream */ struct chmFile; /* structure representing an element from an ITS file stream */ #define CHM_MAX_PATHLEN (512) struct chmUnitInfo { LONGUINT64 start; LONGUINT64 length; int space; int flags; char path[CHM_MAX_PATHLEN+1]; }; /* open an ITS archive */ #ifdef PPC_BSTR /* RWE 6/12/2003 */ struct chmFile* chm_open(BSTR filename); #else struct chmFile* chm_open(const char *filename); #endif /* close an ITS archive */ void chm_close(struct chmFile *h); /* methods for ssetting tuning parameters for particular file */ #define CHM_PARAM_MAX_BLOCKS_CACHED 0 void chm_set_param(struct chmFile *h, int paramType, int paramVal); /* resolve a particular object from the archive */ #define CHM_RESOLVE_SUCCESS (0) #define CHM_RESOLVE_FAILURE (1) int chm_resolve_object(struct chmFile *h, const char *objPath, struct chmUnitInfo *ui); /* retrieve part of an object from the archive */ LONGINT64 chm_retrieve_object(struct chmFile *h, struct chmUnitInfo *ui, unsigned char *buf, LONGUINT64 addr, LONGINT64 len); /* enumerate the objects in the .chm archive */ typedef int (*CHM_ENUMERATOR)(struct chmFile *h, struct chmUnitInfo *ui, void *context); #define CHM_ENUMERATE_NORMAL (1) #define CHM_ENUMERATE_META (2) #define CHM_ENUMERATE_SPECIAL (4) #define CHM_ENUMERATE_FILES (8) #define CHM_ENUMERATE_DIRS (16) #define CHM_ENUMERATE_ALL (31) #define CHM_ENUMERATOR_FAILURE (0) #define CHM_ENUMERATOR_CONTINUE (1) #define CHM_ENUMERATOR_SUCCESS (2) int chm_enumerate(struct chmFile *h, int what, CHM_ENUMERATOR e, void *context); int chm_enumerate_dir(struct chmFile *h, const char *prefix, int what, CHM_ENUMERATOR e, void *context); #ifdef __cplusplus } #endif #endif /* INCLUDED_CHMLIB_H */

让我们从数据类型开始，该数据类型在构造函数中调用chm_open（），在析构函数中调用chm_close（）。


 pub unsafe extern "C" fn chm_open(filename: *const c_char) -> *mut chmFile; pub unsafe extern "C" fn chm_close(h: *mut chmFile);

为了简化错误处理，我们使用thiserror crate ，它会自动实现std::error::Error 。


 $ cd chmlib $ cargo add thiserror

现在您需要弄清楚如何将std::path::Path转换为*const c_char 。 不幸的是，由于各种 具有兼容性的 玩笑 ，这并非易事。


 // chmlib/src/lib.rs use thiserror::Error; use std::{ffi::CString, path::Path}; #[cfg(unix)] fn path_to_cstring(path: &Path) -> Result<CString, InvalidPath> { use std::os::unix::ffi::OsStrExt; let bytes = path.as_os_str().as_bytes(); CString::new(bytes).map_err(|_| InvalidPath) } #[cfg(not(unix))] fn path_to_cstring(path: &Path) -> Result<CString, InvalidPath> { //  ,  Windows CHMLib  CreateFileA(),   //       ASCII.   ...   // ,          ? let rust_str = path.as_os_str().as_str().ok_or(InvalidPath)?; CString::new(rust_str).map_err(|_| InvalidPath) } #[derive(Error, Debug, Copy, Clone, PartialEq)] #[error("Invalid Path")] pub struct InvalidPath;

现在让我们定义ChmFile结构。 它存储指向chmlib_sys :: chmFile的非空指针。 如果chm_open（）返回空指针，则表示由于某种错误她无法打开文件。


 // chmlib/src/lib.rs use std::{ffi::CString, path::Path, ptr::NonNull}; #[derive(Debug)] pub struct ChmFile { raw: NonNull<chmlib_sys::chmFile>, } impl ChmFile { pub fn open<P: AsRef<Path>>(path: P) -> Result<ChmFile, OpenError> { let c_path = path_to_cstring(path.as_ref())?; // ,   c_path  unsafe { let raw = chmlib_sys::chm_open(c_path.as_ptr()); match NonNull::new(raw) { Some(raw) => Ok(ChmFile { raw }), None => Err(OpenError::Other), } } } } impl Drop for ChmFile { fn drop(&mut self) { unsafe { chmlib_sys::chm_close(self.raw.as_ptr()); } } } /// The error returned when we are unable to open a [`ChmFile`]. #[derive(Error, Debug, Copy, Clone, PartialEq)] pub enum OpenError { #[error("Invalid path")] InvalidPath(#[from] InvalidPath), #[error("Unable to open the ChmFile")] Other, }

为了确保没有内存泄漏，请在Valgrind下运行一个简单的测试。 他将创建一个ChmFile并立即释放它。


 // chmlib/src/lib.rs #[test] fn open_valid_chm_file() { let sample = sample_path(); //   let chm_file = ChmFile::open(&sample).unwrap(); //      drop(chm_file); } fn sample_path() -> PathBuf { let project_dir = Path::new(env!("CARGO_MANIFEST_DIR")); let sample = project_dir.parent().unwrap().join("topics.classic.chm"); assert!(sample.exists()); sample }

Valgrind说没有剩余的未记内存：


 $ valgrind ../target/debug/deps/chmlib-8d8c740d578324 open_valid_chm_file ==8953== Memcheck, a memory error detector ==8953== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==8953== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info ==8953== Command: ~/chmlib/target/debug/deps/chmlib-8d8c740d578324 open_valid_chm_file ==8953== running 1 test test tests::open_valid_chm_file ... ok test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out ==8953== ==8953== HEAP SUMMARY: ==8953== in use at exit: 0 bytes in 0 blocks ==8953== total heap usage: 249 allocs, 249 frees, 43,273 bytes allocated ==8953== ==8953== All heap blocks were freed -- no leaks are possible ==8953== ==8953== For counts of detected and suppressed errors, rerun with: -v ==8953== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

按名称搜索项目


接下来的是chm_resolve_object（）函数：


 pub const CHM_RESOLVE_SUCCESS: u32 = 0; pub const CHM_RESOLVE_FAILURE: u32 = 1; /* resolve a particular object from the archive */ pub unsafe extern "C" fn chm_resolve_object( h: *mut chmFile, objPath: *const c_char, ui: *mut chmUnitInfo ) -> c_int;

搜索可能会失败，因此chm_resolve_object（）返回报告成功或失败的错误代码，有关所找到对象的信息将由传递给chmUnitInfo的指针记录。


仅针对我们的案例使用out参数ui创建了std::mem::MaybeUninit类型。


现在，让我们将UnitInfo结构保留为空-这与chmUnitInfo C结构的Rust等效。 从ChmFile开始读取时，我们将添加字段。


 // chmlib/src/lib.rs impl ChmFile { ... /// Find a particular object in the archive. pub fn find<P: AsRef<Path>>(&mut self, path: P) -> Option<UnitInfo> { let path = path_to_cstring(path.as_ref()).ok()?; unsafe { //   chmUnitInfo   let mut resolved = MaybeUninit::<chmlib_sys::chmUnitInfo>::uninit(); //  -  let ret = chmlib_sys::chm_resolve_object( self.raw.as_ptr(), path.as_ptr(), resolved.as_mut_ptr(), ); if ret == chmlib_sys::CHM_RESOLVE_SUCCESS { //    "resolved"   Some(UnitInfo::from_raw(resolved.assume_init())) } else { None } } } } #[derive(Debug)] pub struct UnitInfo; impl UnitInfo { fn from_raw(ui: chmlib_sys::chmUnitInfo) -> UnitInfo { UnitInfo } }

请注意，尽管Rast上的代码不包含显式的状态更改，但ChmFile :: find（）接受&mut self 。 事实是，C实现使用各种fseek（）在文件中移动，因此内部状态在搜索过程中仍会更改。

让我们在先前下载的实验文件中检查ChmFile :: find（）：


 // chmlib/src/lib.rs #[test] fn find_an_item_in_the_sample() { let sample = sample_path(); let chm = ChmFile::open(&sample).unwrap(); assert!(chm.find("/BrowserView.html").is_some()); assert!(chm.find("doesn't exist.txt").is_none()); }

过滤旁路项目


CHMLib提供了一个API，用于通过位掩码过滤器查看CHM文件的内容。


使用方便的位标志板条箱来处理掩码和标志：


 $ cargo add bitflags Updating 'https://github.com/rust-lang/crates.io-index' index Adding bitflags v1.2.1 to dependencies

并根据chm_lib.h中的常量定义“ 过滤器”复选框：


 // chmlib/src/lib.rs bitflags::bitflags! { pub struct Filter: c_int { /// A normal file. const NORMAL = chmlib_sys::CHM_ENUMERATE_NORMAL as c_int; /// A meta file (typically used by the CHM system). const META = chmlib_sys::CHM_ENUMERATE_META as c_int; /// A special file (starts with `#` or `$`). const SPECIAL = chmlib_sys::CHM_ENUMERATE_SPECIAL as c_int; /// It's a file. const FILES = chmlib_sys::CHM_ENUMERATE_FILES as c_int; /// It's a directory. const DIRS = chmlib_sys::CHM_ENUMERATE_DIRS as c_int; } }

我们还需要一个用于Rastovyh闭包的extern "C"适配器，该适配器可以以指向函数的指针的形式传递给C：


 // chmlib/src/lib.rs unsafe extern "C" fn function_wrapper<F>( file: *mut chmlib_sys::chmFile, unit: *mut chmlib_sys::chmUnitInfo, state: *mut c_void, ) -> c_int where F: FnMut(&mut ChmFile, UnitInfo) -> Continuation, { //      FFI- let result = panic::catch_unwind(|| { //   ManuallyDrop    `&mut ChmFile` //        ( double-free). let mut file = ManuallyDrop::new(ChmFile { raw: NonNull::new_unchecked(file), }); let unit = UnitInfo::from_raw(unit.read()); //  state      let closure = &mut *(state as *mut F); closure(&mut file, unit) }); match result { Ok(Continuation::Continue) => { chmlib_sys::CHM_ENUMERATOR_CONTINUE as c_int }, Ok(Continuation::Stop) => chmlib_sys::CHM_ENUMERATOR_SUCCESS as c_int, Err(_) => chmlib_sys::CHM_ENUMERATOR_FAILURE as c_int, } }

function_wrapper包含一个棘手的不安全代码，您需要使用这些代码：

  • state指针必须指向闭包F的实例。
  • 闭包执行的其他代码可能会引起恐慌。 它不应跨越Rast和C之间的边界，因为使用不同语言进行堆栈升级是未定义的行为。 可能的恐慌应该使用std::panic::catch_unwind()拦截。
  • 传递给function_wrapper的指向chmlib_sys :: chmFile的指针也存储在调用ChmFile中。 在调用过程中，必须确保只有闭包才能操作chmlib_sys :: chmFile，否则可能会出现竞争状况。
  • 需要传递闭包&mut ChmFile ，为此，您将需要使用现有指针在堆栈上创建一个临时对象。 但是，如果在这种情况下运行ChmFile析构函数，则chmlib_sys :: chmFile将被释放得太早。 为了解决这个问题，有std::mem::ManuallyDrop 。

这是使用function_wrapper来实现ChmFile::for_each() ：


 // chmlib/src/lib.rs impl ChmFile { ... /// Inspect each item within the [`ChmFile`]. pub fn for_each<F>(&mut self, filter: Filter, mut cb: F) where F: FnMut(&mut ChmFile, UnitInfo) -> Continuation, { unsafe { chmlib_sys::chm_enumerate( self.raw.as_ptr(), filter.bits(), Some(function_wrapper::<F>), &mut cb as *mut _ as *mut c_void, ); } } /// Inspect each item within the [`ChmFile`] inside a specified directory. pub fn for_each_item_in_dir<F, P>( &mut self, filter: Filter, prefix: P, mut cb: F, ) where P: AsRef<Path>, F: FnMut(&mut ChmFile, UnitInfo) -> Continuation, { let path = match path_to_cstring(prefix.as_ref()) { Ok(p) => p, Err(_) => return, }; unsafe { chmlib_sys::chm_enumerate_dir( self.raw.as_ptr(), path.as_ptr(), filter.bits(), Some(function_wrapper::<F>), &mut cb as *mut _ as *mut c_void, ); } } }

注意F参数如何与通用function_wrapper函数交互。 当您需要通过FFI传递Rust闭包以使用另一种语言进行编码时，通常使用此技术。

读取文件内容


我们需要的最后一个函数负责使用chm_retrieve_object（）实际读取文件。


它的实现非常简单。 这类似于典型的std :: io :: Read特性，但显式文件偏移量除外。


 // chmlib/src/lib.rs impl ChmFile { ... pub fn read( &mut self, unit: &UnitInfo, offset: u64, buffer: &mut [u8], ) -> Result<usize, ReadError> { let mut unit = unit.0.clone(); let bytes_written = unsafe { chmlib_sys::chm_retrieve_object( self.raw.as_ptr(), &mut unit, buffer.as_mut_ptr(), offset, buffer.len() as _, ) }; if bytes_written >= 0 { Ok(bytes_written as usize) } else { Err(ReadError) } } } #[derive(Error, Debug, Copy, Clone, PartialEq)] #[error("The read failed")] pub struct ReadError;

, , « », , chm_retrieve_object() :


  • 0, ;
  • 0 : ;
  • −1 ( errno);
  • −1 , , , malloc().

ChmFile::read() :


 // chmlib/src/lib.rs #[test] fn read_an_item() { let sample = sample_path(); let mut chm = ChmFile::open(&sample).unwrap(); let filename = "/template/packages/core-web/css/index.responsive.css"; //        let item = chm.find(filename).unwrap(); //      let mut buffer = vec![0; item.length() as usize]; let bytes_written = chm.read(&item, 0, &mut buffer).unwrap(); //      assert_eq!(bytes_written, item.length() as usize); // ...  ,    let got = String::from_utf8(buffer).unwrap(); assert!(got.starts_with( "html, body, div#i-index-container, div#i-index-body" )); }


API CHMLib , . , . — , Rust Go ( , rustdoc godoc ).


, CHMLib , .


, , .


CHM-


CHM- .


 /* $Id: enum_chmLib.c,v 1.7 2002/10/09 12:38:12 jedwin Exp $ */ /*************************************************************************** * enum_chmLib.c - CHM archive test driver * * ------------------- * * * * author: Jed Wing <jedwin@ugcs.caltech.edu> * * notes: This is a quick-and-dirty test driver for the chm lib * * routines. The program takes as its input the paths to one * * or more .chm files. It attempts to open each .chm file in * * turn, and display a listing of all of the files in the * * archive. * * * * It is not included as a particularly useful program, but * * rather as a sort of "simplest possible" example of how to * * use the enumerate portion of the API. * ***************************************************************************/ /*************************************************************************** * * * This program is free software; you can redistribute it and/or modify * * it under the terms of the GNU Lesser General Public License as * * published by the Free Software Foundation; either version 2.1 of the * * License, or (at your option) any later version. * * * ***************************************************************************/ #include "chm_lib.h" #include <stdio.h> #include <stdlib.h> #include <string.h> /* * callback function for enumerate API */ int _print_ui(struct chmFile *h, struct chmUnitInfo *ui, void *context) { static char szBuf[128]; memset(szBuf, 0, 128); if(ui->flags & CHM_ENUMERATE_NORMAL) strcpy(szBuf, "normal "); else if(ui->flags & CHM_ENUMERATE_SPECIAL) strcpy(szBuf, "special "); else if(ui->flags & CHM_ENUMERATE_META) strcpy(szBuf, "meta "); if(ui->flags & CHM_ENUMERATE_DIRS) strcat(szBuf, "dir"); else if(ui->flags & CHM_ENUMERATE_FILES) strcat(szBuf, "file"); printf(" %1d %8d %8d %s\t\t%s\n", (int)ui->space, (int)ui->start, (int)ui->length, szBuf, ui->path); return CHM_ENUMERATOR_CONTINUE; } int main(int c, char **v) { struct chmFile *h; int i; for (i=1; i<c; i++) { h = chm_open(v[i]); if (h == NULL) { fprintf(stderr, "failed to open %s\n", v[i]); exit(1); } printf("%s:\n", v[i]); printf(" spc start length type\t\t\tname\n"); printf(" === ===== ====== ====\t\t\t====\n"); if (! chm_enumerate(h, CHM_ENUMERATE_ALL, _print_ui, NULL)) printf(" *** ERROR ***\n"); chm_close(h); } return 0; }

_print_ui() Rust. UnitInfo , , .


 // chmlib/examples/enumerate-items.rs fn describe_item(item: UnitInfo) { let mut description = String::new(); if item.is_normal() { description.push_str("normal "); } else if item.is_special() { description.push_str("special "); } else if item.is_meta() { description.push_str("meta "); } if item.is_dir() { description.push_str("dir"); } else if item.is_file() { description.push_str("file"); } println!( " {} {:8} {:8} {}\t\t{}", item.space(), item.start(), item.length(), description, item.path().unwrap_or(Path::new("")).display() ); }

main() , , describe_item() ChmFile::for_each().


 // chmlib/examples/enumerate-items.rs fn main() { let filename = env::args() .nth(1) .unwrap_or_else(|| panic!("Usage: enumerate-items <filename>")); let mut file = ChmFile::open(&filename).expect("Unable to open the file"); println!("{}:", filename); println!(" spc start length type\t\t\tname"); println!(" === ===== ====== ====\t\t\t===="); file.for_each(Filter::all(), |_file, item| { describe_item(item); Continuation::Continue }); }

:


 $ cargo run --example enumerate-items topics.classic.chm > rust-example.txt $ cd vendor/CHMLib/src $ clang chm_lib.c enum_chmLib.c lzx.c -o enum_chmLib $ cd ../../.. $ ./vendor/CHMLib/src/enum_chmLib topics.classic.chm > c-example.txt $ diff -u rust-example.txt c-example.txt $ echo $? 0

diff , , , , . - , diff.


 diff --git a/chmlib/examples/enumerate-items.rs b/chmlib/examples/enumerate-items.rs index e68fa58..ef855ac 100644 --- a/chmlib/examples/enumerate-items.rs +++ b/chmlib/examples/enumerate-items.rs @@ -36,6 +36,10 @@ fn describe_item(item: UnitInfo) { description.push_str("file"); } + if item.length() % 7 == 0 { + description.push_str(" :)"); + } + println!( " {} {:8} {:8} {}\t\t{}", item.space(),

:


 $ cargo run --example enumerate-items topics.classic.chm > rust-example.txt $ diff -u rust-example.txt c-example.txt --- rust-example.txt 2019-10-20 16:51:53.933560892 +0800 +++ c-example.txt 2019-10-20 16:40:42.007053966 +0800 @@ -1,9 +1,9 @@ topics.classic.chm: spc start length type name === ===== ====== ==== ==== - 0 0 0 normal dir :) / + 0 0 0 normal dir / 1 5125797 4096 special file /#IDXHDR - 0 0 0 special file :) /#ITBITS + 0 0 0 special file /#ITBITS 1 5104520 148 special file /#IVB 1 5132009 1227 special file /#STRINGS 0 1430 4283 special file /#SYSTEM @@ -13,9 +13,9 @@ ...

!


CHM-


, CHMLib, «» .


 /* $Id: extract_chmLib.c,v 1.4 2002/10/10 03:24:51 jedwin Exp $ */ /*************************************************************************** * extract_chmLib.c - CHM archive extractor * * ------------------- * * * * author: Jed Wing <jedwin@ugcs.caltech.edu> * * notes: This is a quick-and-dirty chm archive extractor. * ***************************************************************************/ /*************************************************************************** * * * This program is free software; you can redistribute it and/or modify * * it under the terms of the GNU Lesser General Public License as * * published by the Free Software Foundation; either version 2.1 of the * * License, or (at your option) any later version. * * * ***************************************************************************/ #include "chm_lib.h" #include <stdio.h> #include <stdlib.h> #include <string.h> #ifdef WIN32 #include <windows.h> #include <direct.h> #define mkdir(X, Y) _mkdir(X) #define snprintf _snprintf #else #include <unistd.h> #include <sys/stat.h> #include <sys/types.h> #endif struct extract_context { const char *base_path; }; static int dir_exists(const char *path) { #ifdef WIN32 /* why doesn't this work?!? */ HANDLE hFile; hFile = CreateFileA(path, FILE_LIST_DIRECTORY, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL); if (hFile != INVALID_HANDLE_VALUE) { CloseHandle(hFile); return 1; } else return 0; #else struct stat statbuf; if (stat(path, &statbuf) != -1) return 1; else return 0; #endif } static int rmkdir(char *path) { /* * strip off trailing components unless we can stat the directory, or we * have run out of components */ char *i = strrchr(path, '/'); if(path[0] == '\0' || dir_exists(path)) return 0; if (i != NULL) { *i = '\0'; rmkdir(path); *i = '/'; mkdir(path, 0777); } #ifdef WIN32 return 0; #else if (dir_exists(path)) return 0; else return -1; #endif } /* * callback function for enumerate API */ int _extract_callback(struct chmFile *h, struct chmUnitInfo *ui, void *context) { LONGUINT64 ui_path_len; char buffer[32768]; struct extract_context *ctx = (struct extract_context *)context; char *i; if (ui->path[0] != '/') return CHM_ENUMERATOR_CONTINUE; /* quick hack for security hole mentioned by Sven Tantau */ if (strstr(ui->path, "/../") != NULL) { /* fprintf(stderr, "Not extracting %s (dangerous path)\n", ui->path); */ return CHM_ENUMERATOR_CONTINUE; } if (snprintf(buffer, sizeof(buffer), "%s%s", ctx->base_path, ui->path) > 1024) return CHM_ENUMERATOR_FAILURE; /* Get the length of the path */ ui_path_len = strlen(ui->path)-1; /* Distinguish between files and dirs */ if (ui->path[ui_path_len] != '/' ) { FILE *fout; LONGINT64 len, remain=ui->length; LONGUINT64 offset = 0; printf("--> %s\n", ui->path); if ((fout = fopen(buffer, "wb")) == NULL) { /* make sure that it isn't just a missing directory before we abort */ char newbuf[32768]; strcpy(newbuf, buffer); i = strrchr(newbuf, '/'); *i = '\0'; rmkdir(newbuf); if ((fout = fopen(buffer, "wb")) == NULL) return CHM_ENUMERATOR_FAILURE; } while (remain != 0) { len = chm_retrieve_object(h, ui, (unsigned char *)buffer, offset, 32768); if (len > 0) { fwrite(buffer, 1, (size_t)len, fout); offset += len; remain -= len; } else { fprintf(stderr, "incomplete file: %s\n", ui->path); break; } } fclose(fout); } else { if (rmkdir(buffer) == -1) return CHM_ENUMERATOR_FAILURE; } return CHM_ENUMERATOR_CONTINUE; } int main(int c, char **v) { struct chmFile *h; struct extract_context ec; if (c < 3) { fprintf(stderr, "usage: %s <chmfile> <outdir>\n", v[0]); exit(1); } h = chm_open(v[1]); if (h == NULL) { fprintf(stderr, "failed to open %s\n", v[1]); exit(1); } printf("%s:\n", v[1]); ec.base_path = v[2]; if (! chm_enumerate(h, CHM_ENUMERATE_ALL, _extract_callback, (void *)&ec)) printf(" *** ERROR ***\n"); chm_close(h); return 0; }

. , .


extract(). , .


 // chmlib/examples/extract.rs fn extract( root_dir: &Path, file: &mut ChmFile, item: &UnitInfo, ) -> Result<(), Box<dyn Error>> { if !item.is_file() || !item.is_normal() { //      return Ok(()); } let path = match item.path() { Some(p) => p, //     ,   None => return Ok(()), }; let mut dest = root_dir.to_path_buf(); // :  CHM       (  "/"), //     root_dir     "/". dest.extend(path.components().skip(1)); //     if let Some(parent) = dest.parent() { fs::create_dir_all(parent)?; } let mut f = File::create(dest)?; let mut start_offset = 0; // CHMLib      &[u8]    (, //      ),       //      let mut buffer = vec![0; 1 << 16]; loop { let bytes_read = file.read(item, start_offset, &mut buffer)?; if bytes_read == 0 { //     break; } else { //      start_offset += bytes_read as u64; f.write_all(&buffer)?; } } Ok(()) }

main() , extract(), .


 // chmlib/examples/extract.rs fn main() { let args: Vec<_> = env::args().skip(1).collect(); if args.len() != 2 || args.iter().any(|arg| arg.contains("-h")) { println!("Usage: extract <chm-file> <out-dir>"); return; } let mut file = ChmFile::open(&args[0]).expect("Unable to open the file"); let out_dir = PathBuf::from(&args[1]); file.for_each(Filter::all(), |file, item| { match extract(&out_dir, file, &item) { Ok(_) => Continuation::Continue, Err(e) => { eprintln!("Error: {}", e); Continuation::Stop }, } }); }

CHM- HTML-, -.


 $ cargo run --example extract -- ./topics.classic.chm ./extracted $ tree ./extracted ./extracted ├── default.html ├── BrowserForward.html ... ├── Images │ ├── Commands │ │ └── RealWorld │ │ ├── BrowserBack.bmp ... ├── script │ ├── _community │ │ └── disqus.js │ ├── hs-common.js ... └── userinterface.html $ firefox topics.classic/default.html ( default.html  Firefox)

JavaScript ( - Microsoft Help), , .


接下来是什么？


chmlib , , crates.io.


:


  • ChmFile::for_each() ChmFile::for_each_item_in_dir() , , .
  • , ChmFile Continuation::Continue . , F: FnMut(&mut ChmFile, UnitInfo) -> C C: Into<Continuation> , impl From<()> for Continuation .
  • (, extract()) ChmFile::for_each() . impl<E> From<Result<(), E>> for Continuation where E: Error + 'static .
  • - std::fs::File . , ChmFile::read() - std::io::Writer .

Source: https://habr.com/ru/post/zh-CN474666/

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