Re: [PATCH v7 4/6] rust: str: implement `strip_prefix` for `BStr`

Daniel Almeida
2025-02-21T16:15:18Z

Hi Andreas,

> On 18 Feb 2025, at 10:00, Andreas Hindborg <a.hindborg@kernel.org> wrote:
>
> Implement `strip_prefix` for `BStr` by deferring to `slice::strip_prefix`
> on the underlying `&[u8]`.
>
> Reviewed-by: Gary Guo <gary@garyguo.net>
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
> ---
>
> It is also possible to get this method by implementing
> `core::slice::SlicePattern` for `BStr`. `SlicePattern` is unstable, so this
> seems more reasonable.
> ---
> rust/kernel/str.rs | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> index c6bd2c69543dc..db272d2198fcc 100644
> --- a/rust/kernel/str.rs
> +++ b/rust/kernel/str.rs
> @@ -31,6 +31,22 @@ pub const fn from_bytes(bytes: &[u8]) -> &Self {
> // SAFETY: `BStr` is transparent to `[u8]`.
> unsafe { &*(bytes as *const [u8] as *const BStr) }
> }
> +
> + /// Strip a prefix from `self`. Delegates to [`slice::strip_prefix`].
> + ///
> + /// # Example
> + /// ```
> + /// use kernel::b_str;
> + /// assert_eq!(Some(b_str!("bar")), b_str!("foobar").strip_prefix(b_str!("foo")));
> + /// assert_eq!(None, b_str!("foobar").strip_prefix(b_str!("bar")));
> + /// assert_eq!(Some(b_str!("foobar")), b_str!("foobar").strip_prefix(b_str!("")));
> + /// assert_eq!(Some(b_str!("")), b_str!("foobar").strip_prefix(b_str!("foobar")));
> + /// ```

This is passing.

> + pub fn strip_prefix(&self, pattern: impl AsRef<Self>) -> Option<&BStr> {
> + self.deref()
> + .strip_prefix(pattern.as_ref().deref())
> + .map(Self::from_bytes)
> + }
> }
>
> impl fmt::Display for BStr {
>
> --
> 2.47.0
>
>

Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>