[PATCH v3 2/4] rust: str: implement `strip_prefix` for `BStr`

Andreas Hindborg
2024-12-13T11:33:40Z

Implement `strip_prefix` for `BStr` by deferring to `slice::strip_prefix`
on the underlying `&[u8]`.

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 c441acf76ebd1f14919b6d233edffbbbbf944619..9c446ff1ad7adba7ca09a5ae9df00fd369a32899 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")));
+ /// ```
+ pub fn strip_prefix(&self, pattern: &Self) -> Option<&BStr> {
+ self.deref()
+ .strip_prefix(pattern.deref())
+ .map(Self::from_bytes)
+ }
}

impl fmt::Display for BStr {

--
2.47.0