std/os/windows/
ffi.rs

1//! Windows-specific extensions to primitives in the [`std::ffi`] module.
2//!
3//! # Overview
4//!
5//! For historical reasons, the Windows API uses a form of potentially
6//! ill-formed UTF-16 encoding for strings. Specifically, the 16-bit
7//! code units in Windows strings may contain [isolated surrogate code
8//! points which are not paired together][ill-formed-utf-16]. The
9//! Unicode standard requires that surrogate code points (those in the
10//! range U+D800 to U+DFFF) always be *paired*, because in the UTF-16
11//! encoding a *surrogate code unit pair* is used to encode a single
12//! character. For compatibility with code that does not enforce
13//! these pairings, Windows does not enforce them, either.
14//!
15//! While it is not always possible to convert such a string losslessly into
16//! a valid UTF-16 string (or even UTF-8), it is often desirable to be
17//! able to round-trip such a string from and to Windows APIs
18//! losslessly. For example, some Rust code may be "bridging" some
19//! Windows APIs together, just passing `WCHAR` strings among those
20//! APIs without ever really looking into the strings.
21//!
22//! If Rust code *does* need to look into those strings, it can
23//! convert them to valid UTF-8, possibly lossily, by substituting
24//! invalid sequences with [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], as is
25//! conventionally done in other Rust APIs that deal with string
26//! encodings.
27//!
28//! # `OsStringExt` and `OsStrExt`
29//!
30//! [`OsString`] is the Rust wrapper for owned strings in the
31//! preferred representation of the operating system. On Windows,
32//! this struct gets augmented with an implementation of the
33//! [`OsStringExt`] trait, which has an [`OsStringExt::from_wide`] method. This
34//! lets you create an [`OsString`] from a `&[u16]` slice; presumably
35//! you get such a slice out of a `WCHAR` Windows API.
36//!
37//! Similarly, [`OsStr`] is the Rust wrapper for borrowed strings from
38//! preferred representation of the operating system. On Windows, the
39//! [`OsStrExt`] trait provides the [`OsStrExt::encode_wide`] method, which
40//! outputs an [`EncodeWide`] iterator. You can [`collect`] this
41//! iterator, for example, to obtain a `Vec<u16>`; you can later get a
42//! pointer to this vector's contents and feed it to Windows APIs.
43//!
44//! These traits, along with [`OsString`] and [`OsStr`], work in
45//! conjunction so that it is possible to **round-trip** strings from
46//! Windows and back, with no loss of data, even if the strings are
47//! ill-formed UTF-16.
48//!
49//! [ill-formed-utf-16]: https://simonsapin.github.io/wtf-8/#ill-formed-utf-16
50//! [`collect`]: crate::iter::Iterator::collect
51//! [U+FFFD]: crate::char::REPLACEMENT_CHARACTER
52//! [`std::ffi`]: crate::ffi
53
54#![stable(feature = "rust1", since = "1.0.0")]
55
56use alloc::wtf8::Wtf8Buf;
57
58use crate::ffi::{OsStr, OsString};
59use crate::fmt;
60use crate::iter::FusedIterator;
61use crate::sys::os_str::Buf;
62use crate::sys::{AsInner, FromInner};
63
64/// Windows-specific extensions to [`OsString`].
65#[stable(feature = "rust1", since = "1.0.0")]
66pub impl(self) trait OsStringExt {
67    /// Creates an `OsString` from a potentially ill-formed UTF-16 slice of
68    /// 16-bit code units.
69    ///
70    /// This is lossless: calling [`OsStrExt::encode_wide`] on the resulting string
71    /// will always return the original code units.
72    ///
73    /// # Examples
74    ///
75    /// ```
76    /// use std::ffi::OsString;
77    /// use std::os::windows::prelude::*;
78    ///
79    /// // UTF-16 encoding for "Unicode".
80    /// let source = [0x0055, 0x006E, 0x0069, 0x0063, 0x006F, 0x0064, 0x0065];
81    ///
82    /// let string = OsString::from_wide(&source[..]);
83    /// ```
84    #[stable(feature = "rust1", since = "1.0.0")]
85    fn from_wide(wide: &[u16]) -> Self;
86}
87
88#[stable(feature = "rust1", since = "1.0.0")]
89impl OsStringExt for OsString {
90    fn from_wide(wide: &[u16]) -> OsString {
91        FromInner::from_inner(Buf { inner: Wtf8Buf::from_wide(wide) })
92    }
93}
94
95/// Windows-specific extensions to [`OsStr`].
96#[stable(feature = "rust1", since = "1.0.0")]
97pub impl(self) trait OsStrExt {
98    /// Re-encodes an `OsStr` as a wide character sequence, i.e., potentially
99    /// ill-formed UTF-16.
100    ///
101    /// This is lossless: calling [`OsStringExt::from_wide`] and then
102    /// `encode_wide` on the result will yield the original code units.
103    /// Note that the encoding does not add a final null terminator.
104    ///
105    /// # Examples
106    ///
107    /// ```
108    /// use std::ffi::OsString;
109    /// use std::os::windows::prelude::*;
110    ///
111    /// // UTF-16 encoding for "Unicode".
112    /// let source = [0x0055, 0x006E, 0x0069, 0x0063, 0x006F, 0x0064, 0x0065];
113    ///
114    /// let string = OsString::from_wide(&source[..]);
115    ///
116    /// let result: Vec<u16> = string.encode_wide().collect();
117    /// assert_eq!(&source[..], &result[..]);
118    /// ```
119    #[stable(feature = "rust1", since = "1.0.0")]
120    fn encode_wide(&self) -> EncodeWide<'_>;
121}
122
123#[stable(feature = "rust1", since = "1.0.0")]
124impl OsStrExt for OsStr {
125    #[inline]
126    fn encode_wide(&self) -> EncodeWide<'_> {
127        EncodeWide { inner: self.as_inner().inner.encode_wide() }
128    }
129}
130
131/// Iterator returned by [`OsStrExt::encode_wide`].
132#[stable(feature = "rust1", since = "1.0.0")]
133#[derive(Clone)]
134pub struct EncodeWide<'a> {
135    inner: alloc::wtf8::EncodeWide<'a>,
136}
137#[stable(feature = "encode_wide_debug", since = "1.91.0")]
138impl fmt::Debug for EncodeWide<'_> {
139    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
140        fmt::Debug::fmt(&self.inner, f)
141    }
142}
143#[stable(feature = "rust1", since = "1.0.0")]
144impl Iterator for EncodeWide<'_> {
145    type Item = u16;
146
147    #[inline]
148    fn next(&mut self) -> Option<u16> {
149        self.inner.next()
150    }
151
152    #[inline]
153    fn size_hint(&self) -> (usize, Option<usize>) {
154        self.inner.size_hint()
155    }
156}
157#[stable(feature = "encode_wide_fused_iterator", since = "1.62.0")]
158impl FusedIterator for EncodeWide<'_> {}
std/os/windows/ffi.rs

std/os/windows/
ffi.rs
