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Add in missing nullptr check when calling std::slice::from_raw_parts #416

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merged 2 commits into from
Sep 29, 2024
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Add in missing nullptr check when calling std::slice::from_raw_parts #416

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a5b5a0b
Add in missing nullptr check when calling `std::slice::from_raw_parts`
maspe36 Sep 22, 2024
54180dc
Added missing testcase
maspe36 Sep 24, 2024
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20 changes: 14 additions & 6 deletions rosidl_runtime_rs/src/sequence.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -261,18 +261,26 @@ where
///
/// Equivalent to `&seq[..]`.
pub fn as_slice(&self) -> &[T] {
// SAFETY: self.data points to self.size consecutive, initialized elements and
// isn't modified externally.
unsafe { std::slice::from_raw_parts(self.data, self.size) }
if self.data.is_null() {
&[]
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Taken from this example in the stdlib

https://doc.rust-lang.org/std/slice/fn.from_raw_parts.html#ffi-handling-null-pointers

} else {
// SAFETY: self.data is not null and points to self.size consecutive,
// initialized elements and isn't modified externally.
unsafe { std::slice::from_raw_parts(self.data, self.size) }
}
}

/// Extracts a mutable slice containing the entire sequence.
///
/// Equivalent to `&mut seq[..]`.
pub fn as_mut_slice(&mut self) -> &mut [T] {
// SAFETY: self.data points to self.size consecutive, initialized elements and
// isn't modified externally.
unsafe { std::slice::from_raw_parts_mut(self.data, self.size) }
if self.data.is_null() {
&mut []
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Actually, now that I'm looking at this, I'm not sure this would work. If someone started pushing to this mutable slice self.data would never get updated, so this likely would compile but exhibit incorrect runtime behavior.

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Is it possible to write a unit test for this scenario? Just to make sure that it's working, and also as a warning sign in case future changes cause it to break?

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Is it possible to write a unit test for this scenario?

Good point, added a unit test for the base cases. But also, just digging around the slice API, doesn't seem like this is really a concern to mutate the slice as its empty, and the only mutation that can be done will be with the fixed size.

i.e.

let mut slice = Sequence::<i32>::default().as_mut_slice();

// I can't do anything useful with slice now
// slice[0] = 42 will segfault because the len of the slice is zero.
// I actually don't think it matters, its just not really idiomatic rust

} else {
// SAFETY: self.data is not null and points to self.size consecutive,
// initialized elements and isn't modified externally.
unsafe { std::slice::from_raw_parts_mut(self.data, self.size) }
}
}
}

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