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Rollup merge of #73139 - poliorcetics:cstring-from-vec-with-nul, r=dt…
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…olnay

Add methods to go from a nul-terminated Vec<u8> to a CString

Fixes #73100.

Doc tests have been written and the documentation on the error type
updated too.

I used `#[stable(feature = "cstring_from_vec_with_nul", since = "1.46.0")]` but I don't know if the version is correct.
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@RalfJung
RalfJung authored Jun 15, 2020
2 parents 7c8b941 + 47cc5cc commit ec6fe42
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Showing 2 changed files with 183 additions and 6 deletions.
187 changes: 181 additions & 6 deletions src/libstd/ffi/c_str.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -234,15 +234,14 @@ pub struct NulError(usize, Vec<u8>);

/// An error indicating that a nul byte was not in the expected position.
///
/// The slice used to create a [`CStr`] must have one and only one nul
/// byte at the end of the slice.
/// The slice used to create a [`CStr`] must have one and only one nul byte,
/// positioned at the end.
///
/// This error is created by the
/// [`from_bytes_with_nul`][`CStr::from_bytes_with_nul`] method on
/// [`CStr`]. See its documentation for more.
/// This error is created by the [`from_bytes_with_nul`] method on [`CStr`].
/// See its documentation for more.
///
/// [`CStr`]: struct.CStr.html
/// [`CStr::from_bytes_with_nul`]: struct.CStr.html#method.from_bytes_with_nul
/// [`from_bytes_with_nul`]: struct.CStr.html#method.from_bytes_with_nul
///
/// # Examples
///
Expand All @@ -257,6 +256,32 @@ pub struct FromBytesWithNulError {
kind: FromBytesWithNulErrorKind,
}

/// An error indicating that a nul byte was not in the expected position.
///
/// The vector used to create a [`CString`] must have one and only one nul byte,
/// positioned at the end.
///
/// This error is created by the [`from_vec_with_nul`] method on [`CString`].
/// See its documentation for more.
///
/// [`CString`]: struct.CString.html
/// [`from_vec_with_nul`]: struct.CString.html#method.from_vec_with_nul
///
/// # Examples
///
/// ```
/// #![feature(cstring_from_vec_with_nul)]
/// use std::ffi::{CString, FromVecWithNulError};
///
/// let _: FromVecWithNulError = CString::from_vec_with_nul(b"f\0oo".to_vec()).unwrap_err();
/// ```
#[derive(Clone, PartialEq, Eq, Debug)]
#[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
pub struct FromVecWithNulError {
error_kind: FromBytesWithNulErrorKind,
bytes: Vec<u8>,
}

#[derive(Clone, PartialEq, Eq, Debug)]
enum FromBytesWithNulErrorKind {
InteriorNul(usize),
Expand All @@ -272,6 +297,59 @@ impl FromBytesWithNulError {
}
}

#[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
impl FromVecWithNulError {
/// Returns a slice of [`u8`]s bytes that were attempted to convert to a [`CString`].
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(cstring_from_vec_with_nul)]
/// use std::ffi::CString;
///
/// // Some invalid bytes in a vector
/// let bytes = b"f\0oo".to_vec();
///
/// let value = CString::from_vec_with_nul(bytes.clone());
///
/// assert_eq!(&bytes[..], value.unwrap_err().as_bytes());
/// ```
///
/// [`CString`]: struct.CString.html
pub fn as_bytes(&self) -> &[u8] {
&self.bytes[..]
}

/// Returns the bytes that were attempted to convert to a [`CString`].
///
/// This method is carefully constructed to avoid allocation. It will
/// consume the error, moving out the bytes, so that a copy of the bytes
/// does not need to be made.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(cstring_from_vec_with_nul)]
/// use std::ffi::CString;
///
/// // Some invalid bytes in a vector
/// let bytes = b"f\0oo".to_vec();
///
/// let value = CString::from_vec_with_nul(bytes.clone());
///
/// assert_eq!(bytes, value.unwrap_err().into_bytes());
/// ```
///
/// [`CString`]: struct.CString.html
pub fn into_bytes(self) -> Vec<u8> {
self.bytes
}
}

/// An error indicating invalid UTF-8 when converting a [`CString`] into a [`String`].
///
/// `CString` is just a wrapper over a buffer of bytes with a nul
Expand Down Expand Up @@ -643,6 +721,86 @@ impl CString {
let this = mem::ManuallyDrop::new(self);
unsafe { ptr::read(&this.inner) }
}

/// Converts a `Vec` of `u8` to a `CString` without checking the invariants
/// on the given `Vec`.
///
/// # Safety
///
/// The given `Vec` **must** have one nul byte as its last element.
/// This means it cannot be empty nor have any other nul byte anywhere else.
///
/// # Example
///
/// ```
/// #![feature(cstring_from_vec_with_nul)]
/// use std::ffi::CString;
/// assert_eq!(
/// unsafe { CString::from_vec_with_nul_unchecked(b"abc\0".to_vec()) },
/// unsafe { CString::from_vec_unchecked(b"abc".to_vec()) }
/// );
/// ```
#[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
pub unsafe fn from_vec_with_nul_unchecked(v: Vec<u8>) -> Self {
Self { inner: v.into_boxed_slice() }
}

/// Attempts to converts a `Vec` of `u8` to a `CString`.
///
/// Runtime checks are present to ensure there is only one nul byte in the
/// `Vec`, its last element.
///
/// # Errors
///
/// If a nul byte is present and not the last element or no nul bytes
/// is present, an error will be returned.
///
/// # Examples
///
/// A successful conversion will produce the same result as [`new`] when
/// called without the ending nul byte.
///
/// ```
/// #![feature(cstring_from_vec_with_nul)]
/// use std::ffi::CString;
/// assert_eq!(
/// CString::from_vec_with_nul(b"abc\0".to_vec())
/// .expect("CString::from_vec_with_nul failed"),
/// CString::new(b"abc".to_vec()).expect("CString::new failed")
/// );
/// ```
///
/// A incorrectly formatted vector will produce an error.
///
/// ```
/// #![feature(cstring_from_vec_with_nul)]
/// use std::ffi::{CString, FromVecWithNulError};
/// // Interior nul byte
/// let _: FromVecWithNulError = CString::from_vec_with_nul(b"a\0bc".to_vec()).unwrap_err();
/// // No nul byte
/// let _: FromVecWithNulError = CString::from_vec_with_nul(b"abc".to_vec()).unwrap_err();
/// ```
///
/// [`new`]: #method.new
#[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
pub fn from_vec_with_nul(v: Vec<u8>) -> Result<Self, FromVecWithNulError> {
let nul_pos = memchr::memchr(0, &v);
match nul_pos {
Some(nul_pos) if nul_pos + 1 == v.len() => {
// SAFETY: We know there is only one nul byte, at the end
// of the vec.
Ok(unsafe { Self::from_vec_with_nul_unchecked(v) })
}
Some(nul_pos) => Err(FromVecWithNulError {
error_kind: FromBytesWithNulErrorKind::InteriorNul(nul_pos),
bytes: v,
}),
None => Err(FromVecWithNulError {
error_kind: FromBytesWithNulErrorKind::NotNulTerminated,
bytes: v,
}),
}
}
}

// Turns this `CString` into an empty string to prevent
Expand Down Expand Up @@ -976,6 +1134,23 @@ impl fmt::Display for FromBytesWithNulError {
}
}

#[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
impl Error for FromVecWithNulError {}

#[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
impl fmt::Display for FromVecWithNulError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self.error_kind {
FromBytesWithNulErrorKind::InteriorNul(pos) => {
write!(f, "data provided contains an interior nul byte at pos {}", pos)
}
FromBytesWithNulErrorKind::NotNulTerminated => {
write!(f, "data provided is not nul terminated")
}
}
}
}

impl IntoStringError {
/// Consumes this error, returning original [`CString`] which generated the
/// error.
Expand Down
2 changes: 2 additions & 0 deletions src/libstd/ffi/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -157,6 +157,8 @@

#[stable(feature = "cstr_from_bytes", since = "1.10.0")]
pub use self::c_str::FromBytesWithNulError;
#[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
pub use self::c_str::FromVecWithNulError;
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::c_str::{CStr, CString, IntoStringError, NulError};

Expand Down

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