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Diffstat (limited to 'library/std/src/sys/windows/ext/ffi.rs')
| -rw-r--r-- | library/std/src/sys/windows/ext/ffi.rs | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/library/std/src/sys/windows/ext/ffi.rs b/library/std/src/sys/windows/ext/ffi.rs new file mode 100644 index 00000000000..6e78119383f --- /dev/null +++ b/library/std/src/sys/windows/ext/ffi.rs @@ -0,0 +1,142 @@ +//! Windows-specific extensions to the primitives in the `std::ffi` module. +//! +//! # Overview +//! +//! For historical reasons, the Windows API uses a form of potentially +//! ill-formed UTF-16 encoding for strings. Specifically, the 16-bit +//! code units in Windows strings may contain [isolated surrogate code +//! points which are not paired together][ill-formed-utf-16]. The +//! Unicode standard requires that surrogate code points (those in the +//! range U+D800 to U+DFFF) always be *paired*, because in the UTF-16 +//! encoding a *surrogate code unit pair* is used to encode a single +//! character. For compatibility with code that does not enforce +//! these pairings, Windows does not enforce them, either. +//! +//! While it is not always possible to convert such a string losslessly into +//! a valid UTF-16 string (or even UTF-8), it is often desirable to be +//! able to round-trip such a string from and to Windows APIs +//! losslessly. For example, some Rust code may be "bridging" some +//! Windows APIs together, just passing `WCHAR` strings among those +//! APIs without ever really looking into the strings. +//! +//! If Rust code *does* need to look into those strings, it can +//! convert them to valid UTF-8, possibly lossily, by substituting +//! invalid sequences with [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], as is +//! conventionally done in other Rust APIs that deal with string +//! encodings. +//! +//! # `OsStringExt` and `OsStrExt` +//! +//! [`OsString`] is the Rust wrapper for owned strings in the +//! preferred representation of the operating system. On Windows, +//! this struct gets augmented with an implementation of the +//! [`OsStringExt`] trait, which has a [`from_wide`] method. This +//! lets you create an [`OsString`] from a `&[u16]` slice; presumably +//! you get such a slice out of a `WCHAR` Windows API. +//! +//! Similarly, [`OsStr`] is the Rust wrapper for borrowed strings from +//! preferred representation of the operating system. On Windows, the +//! [`OsStrExt`] trait provides the [`encode_wide`] method, which +//! outputs an [`EncodeWide`] iterator. You can [`collect`] this +//! iterator, for example, to obtain a `Vec<u16>`; you can later get a +//! pointer to this vector's contents and feed it to Windows APIs. +//! +//! These traits, along with [`OsString`] and [`OsStr`], work in +//! conjunction so that it is possible to **round-trip** strings from +//! Windows and back, with no loss of data, even if the strings are +//! ill-formed UTF-16. +//! +//! [ill-formed-utf-16]: https://simonsapin.github.io/wtf-8/#ill-formed-utf-16 +//! [`OsString`]: ../../../ffi/struct.OsString.html +//! [`OsStr`]: ../../../ffi/struct.OsStr.html +//! [`OsStringExt`]: trait.OsStringExt.html +//! [`OsStrExt`]: trait.OsStrExt.html +//! [`EncodeWide`]: struct.EncodeWide.html +//! [`from_wide`]: trait.OsStringExt.html#tymethod.from_wide +//! [`encode_wide`]: trait.OsStrExt.html#tymethod.encode_wide +//! [`collect`]: ../../../iter/trait.Iterator.html#method.collect +//! [U+FFFD]: ../../../char/constant.REPLACEMENT_CHARACTER.html + +#![stable(feature = "rust1", since = "1.0.0")] + +use crate::ffi::{OsStr, OsString}; +use crate::sys::os_str::Buf; +use crate::sys_common::wtf8::Wtf8Buf; +use crate::sys_common::{AsInner, FromInner}; + +#[stable(feature = "rust1", since = "1.0.0")] +pub use crate::sys_common::wtf8::EncodeWide; + +/// Windows-specific extensions to [`OsString`]. +/// +/// [`OsString`]: ../../../../std/ffi/struct.OsString.html +#[stable(feature = "rust1", since = "1.0.0")] +pub trait OsStringExt { + /// Creates an `OsString` from a potentially ill-formed UTF-16 slice of + /// 16-bit code units. + /// + /// This is lossless: calling [`encode_wide`] on the resulting string + /// will always return the original code units. + /// + /// # Examples + /// + /// ``` + /// use std::ffi::OsString; + /// use std::os::windows::prelude::*; + /// + /// // UTF-16 encoding for "Unicode". + /// let source = [0x0055, 0x006E, 0x0069, 0x0063, 0x006F, 0x0064, 0x0065]; + /// + /// let string = OsString::from_wide(&source[..]); + /// ``` + /// + /// [`encode_wide`]: ./trait.OsStrExt.html#tymethod.encode_wide + #[stable(feature = "rust1", since = "1.0.0")] + fn from_wide(wide: &[u16]) -> Self; +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl OsStringExt for OsString { + fn from_wide(wide: &[u16]) -> OsString { + FromInner::from_inner(Buf { inner: Wtf8Buf::from_wide(wide) }) + } +} + +/// Windows-specific extensions to [`OsStr`]. +/// +/// [`OsStr`]: ../../../../std/ffi/struct.OsStr.html +#[stable(feature = "rust1", since = "1.0.0")] +pub trait OsStrExt { + /// Re-encodes an `OsStr` as a wide character sequence, i.e., potentially + /// ill-formed UTF-16. + /// + /// This is lossless: calling [`OsString::from_wide`] and then + /// `encode_wide` on the result will yield the original code units. + /// Note that the encoding does not add a final null terminator. + /// + /// # Examples + /// + /// ``` + /// use std::ffi::OsString; + /// use std::os::windows::prelude::*; + /// + /// // UTF-16 encoding for "Unicode". + /// let source = [0x0055, 0x006E, 0x0069, 0x0063, 0x006F, 0x0064, 0x0065]; + /// + /// let string = OsString::from_wide(&source[..]); + /// + /// let result: Vec<u16> = string.encode_wide().collect(); + /// assert_eq!(&source[..], &result[..]); + /// ``` + /// + /// [`OsString::from_wide`]: ./trait.OsStringExt.html#tymethod.from_wide + #[stable(feature = "rust1", since = "1.0.0")] + fn encode_wide(&self) -> EncodeWide<'_>; +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl OsStrExt for OsStr { + fn encode_wide(&self) -> EncodeWide<'_> { + self.as_inner().inner.encode_wide() + } +} |