Replace CStr::from_ptr() with CStr::from_bytes_with_nul()
#82
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`CStr::from_ptr()` is `unsafe` because it reads a raw pointer, and searches for a terminating nul character in the pointed region of memory. This is unnecessary as both calls already initialize a given number of characters and terminate with a nul, allowing us to pass a sized and initialized slice (without casting `*const MaybeUninit<u8>` to `*const u8`) directly to `CStr::from_bytes_with_nul()` (available since Rust 1.10, unlike `CStr::from_bytes_until_nul()` which was only stabilized in 1.69). Unfortunately all `std` helper APIs to initialize slices of `MaybeUninit` are still unstable, making this less ideal to write at the moment.
MarijnS95
commented
Sep 10, 2024
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| // TODO: This function must be `unsafe` - or receive an initialized slice or CStr directly - | ||
| // as we can't otherwise guarantee safety here. | ||
| let initialized = unsafe { slice_assume_init_ref(&self.buffer[..len + 1]) }; | ||
| let msg = CStr::from_bytes_with_nul(initialized) | ||
| .expect("Unreachable: nul terminator was placed at `len`"); | ||
| android_log(self.buf_id, self.priority, self.tag, msg); |
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Before merging, we should change the signature of fn output_specified_len() to either be unsafe or already pass an initialized &[u8] slice or CStr. There's no way we can write a valid // SAFETY: here right now.
MarijnS95
commented
Sep 10, 2024
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| // SAFETY: The above code initialized the length of the tag plus a nul terminator, or the whole length of the slice | ||
| let initialized = unsafe { slice_assume_init_ref(initialized) }; | ||
| CStr::from_bytes_with_nul(initialized).expect("Unreachable: we wrote a nul terminator") |
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This safety comment is a bit too vague for my liking, I'll see if I can update it.
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For #81 (comment)
CStr::from_ptr()isunsafebecause it reads a raw pointer, and searches for a terminating nul character in the pointed region of memory.This is unnecessary as both calls already initialize a given number of characters and terminate with a nul, allowing us to pass a sized and initialized slice (without casting
*const MaybeUninit<u8>to*const u8) directly toCStr::from_bytes_with_nul()(available since Rust 1.10, unlikeCStr::from_bytes_until_nul()which was only stabilized in 1.69). Unfortunately allstdhelper APIs to initialize slices ofMaybeUninitare still unstable, making this less ideal to write at the moment.