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//! A wide string FFI module for converting to and from wide string variants. //! //! This module provides multiple types of wide strings: `U16String`, `U16CString`, `U32String`, //! and `U32CString`. These types are backed by two generic implementations parameterized by //! element size: `UString<C>` and `UCString<C>`. The `UCString` types are analogous to the //! standard `CString` FFI type, while the `UString` types are analogous to `OsString`. Otherwise, //! `U16` and `U32` types differ only in character width and encoding methods. //! //! For `U16String` and `U32String`, no guarantees are made about the underlying string data; they //! are simply a sequence of UTF-16 *code units* or UTF-32 code points, both of which may be //! ill-formed or contain nul values. `U16CString` and `U32CString`, on the other hand, are aware //! of nul values and are guaranteed to be terminated with a nul value (unless unchecked methods //! are used to construct the strings). Because `U16CString` and `U32CString` are C-style, //! nul-terminated strings, they will have no interior nul values. All four string types may still //! have unpaired UTF-16 surrogates or invalid UTF-32 code points; ill-formed data is preserved //! until conversion to a basic Rust `String`. //! //! Use `U16String` or `U32String` when you simply need to pass-through strings, or when you know //! or don't care if you're not dealing with a nul-terminated string, such as when string lengths //! are provided and you are only reading strings from FFI, not writing them out to a FFI. //! //! Use `U16CString` or `U32CString` when you must properly handle nul values, and must deal with //! nul-terminated C-style wide strings, such as when you pass strings into FFI functions. //! //! # Relationship to other Rust Strings //! //! Standard Rust strings `String` and `str` are well-formed Unicode data encoded as UTF-8. The //! standard strings provide proper handling of Unicode and ensure strong safety guarantees. //! //! `CString` and `CStr` are strings used for C FFI. They handle nul-terminated C-style strings. //! However, they do not have a builtin encoding, and conversions between C-style and other Rust //! strings must specifically encode and decode the strings, and handle possibly invalid encoding //! data. They are safe to use only in passing string-like data back and forth from C APIs but do //! not provide any other guarantees, so may not be well-formed. //! //! `OsString` and `OsStr` are also strings for use with FFI. Unlike `CString`, they do no special //! handling of nul values, but instead have an OS-specified encoding. While, for example, on Linux //! systems this is usually the UTF-8 encoding, this is not the case for every platform. The //! encoding may not even be 8-bit: on Windows, `OsString` uses a malformed encoding sometimes //! referred to as "WTF-8". In any case, like `CString`, `OsString` has no additional guarantees //! and may not be well-formed. //! //! Due to the loss of safety of these other string types, conversion to standard Rust `String` is //! lossy, and may require knowledge of the underlying encoding, including platform-specific //! quirks. //! //! The wide strings in this crate are roughly based on the principles of the string types in //! `std::ffi`, though there are differences. `U16String`, `U32String`, `U16Str`, and `U32Str` are //! roughly similar in role to `OsString` and `OsStr`, while `U16CString`, `U32CString`, `U16CStr`, //! and `U32CStr` are roughly similar in role to `CString` and `CStr`. Conversion to FFI string //! types is generally very straight forward and safe, while conversion directly between standard //! Rust `String` is a lossy conversion just as `OsString` is. //! //! `U16String` and `U16CString` are treated as though they use UTF-16 encoding, even if they may //! contain unpaired surrogates. `U32String` and `U32CString` are treated as though they use UTF-32 //! encoding, even if they may contain values outside the valid Unicode character range. //! //! # Remarks on UTF-16 Code Units //! //! *Code units* are the 16-bit units that comprise UTF-16 sequences. Code units //! can specify Unicode code points either as single units or in *surrogate pairs*. Because every //! code unit might be part of a surrogate pair, many regular string operations, including //! indexing into a wide string, writing to a wide string, or even iterating a wide string should //! be handled with care and are greatly discouraged. Some operations have safer alternatives //! provided, such as Unicode code point iteration instead of code unit iteration. Always keep in //! mind that the number of code units (`len()`) of a wide string is **not** equivalent to the //! number of Unicode characters in the string, merely the length of the UTF-16 encoding sequence. //! In fact, Unicode code points do not even have a one-to-one mapping with characters! //! //! UTF-32 simply encodes Unicode code points as-is in 32-bit values, but Unicode character code //! points are reserved only for 21-bits. Again, Unicode code points do not have a one-to-one //! mapping with the concept of a visual character glyph. //! //! # FFI with C/C++ `wchar_t` //! //! C/C++'s `wchar_t` (and C++'s corresponding `widestring`) varies in size depending on compiler //! and platform. Typically, `wchar_t` is 16-bits on Windows and 32-bits on most Unix-based //! platforms. For convenience when using `wchar_t`-based FFI's, type aliases for the corresponding //! string types are provided: `WideString` aliases `U16String` on Windows or `U32String` //! elsewhere, `WideCString` aliases `U16CString` or `U32CString`, etc. The `WideChar` alias //! is also provided, aliasing `u16` or `u32`. //! //! When not interacting with a FFI using `wchar_t`, it is recommended to use the string types //! directly rather than via the wide alias. //! //! This crate supports `no_std` when default features are disabled. The `std` and `alloc` features //! (enabled by default) enable the `U16String`, `U32String`, `U16CString`, and `U32CString` types //! and aliases. Other types do not require allocation and can be used in a `no_std` environment. //! //! # Examples //! //! The following example uses `U16String` to get Windows error messages, since `FormatMessageW` //! returns a string length for us and we don't need to pass error messages into other FFI //! functions so we don't need to worry about nul values. //! //! ```rust //! # #[cfg(not(windows))] //! # fn main() {} //! # extern crate winapi; //! # extern crate widestring; //! # #[cfg(windows)] //! # fn main() { //! use winapi::um::winbase::{FormatMessageW, LocalFree, FORMAT_MESSAGE_FROM_SYSTEM, //! FORMAT_MESSAGE_ALLOCATE_BUFFER, FORMAT_MESSAGE_IGNORE_INSERTS}; //! use winapi::shared::ntdef::LPWSTR; //! use winapi::shared::minwindef::HLOCAL; //! use std::ptr; //! use widestring::U16String; //! # use winapi::shared::minwindef::DWORD; //! # let error_code: DWORD = 0; //! //! let U16Str: U16String; //! unsafe { //! // First, get a string buffer from some windows api such as FormatMessageW... //! let mut buffer: LPWSTR = ptr::null_mut(); //! let strlen = FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM | //! FORMAT_MESSAGE_ALLOCATE_BUFFER | //! FORMAT_MESSAGE_IGNORE_INSERTS, //! ptr::null(), //! error_code, // error code from GetLastError() //! 0, //! (&mut buffer as *mut LPWSTR) as LPWSTR, //! 0, //! ptr::null_mut()); //! //! // Get the buffer as a wide string //! U16Str = U16String::from_ptr(buffer, strlen as usize); //! // Since U16String creates an owned copy, it's safe to free original buffer now //! // If you didn't want an owned copy, you could use &U16Str. //! LocalFree(buffer as HLOCAL); //! } //! // Convert to a regular Rust String and use it to your heart's desire! //! let message = U16Str.to_string_lossy(); //! # assert_eq!(message, "The operation completed successfully.\r\n"); //! # } //! ``` //! //! The following example is the functionally the same, only using `U16CString` instead. //! //! ```rust //! # #[cfg(not(windows))] //! # fn main() {} //! # extern crate winapi; //! # extern crate widestring; //! # #[cfg(windows)] //! # fn main() { //! use winapi::um::winbase::{FormatMessageW, LocalFree, FORMAT_MESSAGE_FROM_SYSTEM, //! FORMAT_MESSAGE_ALLOCATE_BUFFER, FORMAT_MESSAGE_IGNORE_INSERTS}; //! use winapi::shared::ntdef::LPWSTR; //! use winapi::shared::minwindef::HLOCAL; //! use std::ptr; //! use widestring::U16CString; //! # use winapi::shared::minwindef::DWORD; //! # let error_code: DWORD = 0; //! //! let U16Str: U16CString; //! unsafe { //! // First, get a string buffer from some windows api such as FormatMessageW... //! let mut buffer: LPWSTR = ptr::null_mut(); //! FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM | //! FORMAT_MESSAGE_ALLOCATE_BUFFER | //! FORMAT_MESSAGE_IGNORE_INSERTS, //! ptr::null(), //! error_code, // error code from GetLastError() //! 0, //! (&mut buffer as *mut LPWSTR) as LPWSTR, //! 0, //! ptr::null_mut()); //! //! // Get the buffer as a wide string //! U16Str = U16CString::from_ptr_str(buffer); //! // Since U16CString creates an owned copy, it's safe to free original buffer now //! // If you didn't want an owned copy, you could use &U16CStr. //! LocalFree(buffer as HLOCAL); //! } //! // Convert to a regular Rust String and use it to your heart's desire! //! let message = U16Str.to_string_lossy(); //! # assert_eq!(message, "The operation completed successfully.\r\n"); //! # } //! ``` #![deny(future_incompatible)] #![warn( unused, anonymous_parameters, missing_docs, missing_copy_implementations, missing_debug_implementations, trivial_casts, trivial_numeric_casts )] #![cfg_attr(not(feature = "std"), no_std)] #[cfg(all(feature = "alloc", not(feature = "std")))] extern crate alloc; #[cfg(feature = "std")] extern crate core; use core::fmt::Debug; #[cfg(feature = "std")] mod platform; mod ucstr; #[cfg(feature = "alloc")] mod ucstring; mod ustr; #[cfg(feature = "alloc")] mod ustring; pub use crate::ucstr::*; #[cfg(feature = "alloc")] pub use crate::ucstring::*; pub use crate::ustr::*; #[cfg(feature = "alloc")] pub use crate::ustring::*; /// Marker trait for primitive types used to represent UTF character data. Should not be used /// directly. pub trait UChar: Debug + Sized + Copy + Ord + Eq { /// NUL character value const NUL: Self; } impl UChar for u16 { const NUL: u16 = 0; } impl UChar for u32 { const NUL: u32 = 0; } #[cfg(not(windows))] /// Alias for `u16` or `u32` depending on platform. Intended to match typical C `wchar_t` size on platform. pub type WideChar = u32; #[cfg(windows)] /// Alias for `u16` or `u32` depending on platform. Intended to match typical C `wchar_t` size on platform. pub type WideChar = u16;