linux-kernel - Re: [PATCH v2] rust: str: add conversion from `CStr` to `CString`

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Date:   Wed, 3 May 2023 16:01:00 -0300
From:   Martin Rodriguez Reboredo <yakoyoku@...il.com>
To:     Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>
Cc:     Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev
Subject: Re: [PATCH v2] rust: str: add conversion from `CStr` to `CString`

On 5/3/23 11:10, Alice Ryhl wrote:
> These methods can be used to copy the data in a temporary c string into
> a separate allocation, so that it can be accessed later even if the
> original is deallocated.
> 
> The API in this change mirrors the standard library API for the `&str`
> and `String` types. The `ToOwned` trait is not implemented because it
> assumes that allocations are infallible.
> 
> Reviewed-by: Benno Lossin <benno.lossin@...ton.me>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
>   rust/kernel/str.rs | 22 ++++++++++++++++++++++
>   1 file changed, 22 insertions(+)
> 
> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> index b771310fa4a4..f3dc5b24ea55 100644
> --- a/rust/kernel/str.rs
> +++ b/rust/kernel/str.rs
> @@ -2,6 +2,7 @@
>   
>   //! String representations.
>   
> +use alloc::alloc::AllocError;
>   use alloc::vec::Vec;
>   use core::fmt::{self, Write};
>   use core::ops::{self, Deref, Index};
> @@ -199,6 +200,12 @@ impl CStr {
>       pub unsafe fn as_str_unchecked(&self) -> &str {
>           unsafe { core::str::from_utf8_unchecked(self.as_bytes()) }
>       }
> +
> +    /// Convert this [`CStr`] into a [`CString`] by allocating memory and
> +    /// copying over the string data.
> +    pub fn to_cstring(&self) -> Result<CString, AllocError> {
> +        CString::try_from(self)
> +    }
>   }
>   
>   impl fmt::Display for CStr {
> @@ -584,6 +591,21 @@ impl Deref for CString {
>       }
>   }
>   
> +impl<'a> TryFrom<&'a CStr> for CString {
> +    type Error = AllocError;
> +
> +    fn try_from(cstr: &'a CStr) -> Result<CString, AllocError> {
> +        let mut buf = Vec::new();
> +
> +        buf.try_extend_from_slice(cstr.as_bytes_with_nul())
> +            .map_err(|_| AllocError)?;
> +
> +        // INVARIANT: The `CStr` and `CString` types have the same invariants for
> +        // the string data, and we copied it over without changes.
> +        Ok(CString { buf })
> +    }
> +}
> +
>   /// A convenience alias for [`core::format_args`].
>   #[macro_export]
>   macro_rules! fmt {
> 
> base-commit: ea76e08f4d901a450619831a255e9e0a4c0ed162

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@...il.com>