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Replace CStr::from_ptr() with CStr::from_bytes_with_nul() #82

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Replace CStr::from_ptr() with CStr::from_bytes_with_nul() #82

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86 changes: 48 additions & 38 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -224,9 +224,7 @@ impl Log for AndroidLogger {
.unwrap_or_else(|| module_path.as_bytes());

// truncate the tag here to fit into LOGGING_TAG_MAX_LEN
self.fill_tag_bytes(&mut tag_bytes, tag);
// use stack array as C string
let tag: &CStr = unsafe { CStr::from_ptr(mem::transmute(tag_bytes.as_ptr())) };
let tag = fill_tag_bytes(&mut tag_bytes, tag);

// message must not exceed LOGGING_MSG_MAX_LEN
// therefore split log message into multiple log calls
Expand All @@ -250,23 +248,32 @@ impl Log for AndroidLogger {
fn flush(&self) {}
}

impl AndroidLogger {
fn fill_tag_bytes(&self, array: &mut [MaybeUninit<u8>], tag: &[u8]) {
if tag.len() > LOGGING_TAG_MAX_LEN {
for (input, output) in tag
.iter()
.take(LOGGING_TAG_MAX_LEN - 2)
.chain(b"..\0".iter())
.zip(array.iter_mut())
{
output.write(*input);
}
} else {
for (input, output) in tag.iter().chain(b"\0".iter()).zip(array.iter_mut()) {
output.write(*input);
}
fn fill_tag_bytes<'a>(
array: &'a mut [MaybeUninit<u8>; LOGGING_TAG_MAX_LEN + 1],
tag: &[u8],
) -> &'a CStr {
// FIXME: Simplify when maybe_uninit_fill with MaybeUninit::fill_from() is stabilized
let initialized;
if tag.len() > LOGGING_TAG_MAX_LEN {
for (input, output) in tag
.iter()
.take(LOGGING_TAG_MAX_LEN - 2)
.chain(b"..\0")
.zip(array.iter_mut())
{
output.write(*input);
}
initialized = array.as_slice();
} else {
for (input, output) in tag.iter().chain(b"\0".iter()).zip(array.iter_mut()) {
output.write(*input);
}
initialized = &array[..tag.len() + 1];
}

// 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")
Comment on lines +274 to +276
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This safety comment is a bit too vague for my liking, I'll see if I can update it.

}

/// Filter for android logger.
Expand Down Expand Up @@ -449,7 +456,11 @@ impl<'a> PlatformLogWriter<'a> {
self.buffer.get_unchecked_mut(len)
});

let msg: &CStr = unsafe { CStr::from_ptr(self.buffer.as_ptr().cast()) };
// 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);
Comment on lines +459 to 464
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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.


unsafe { *self.buffer.get_unchecked_mut(len) = last_byte };
Expand Down Expand Up @@ -544,6 +555,11 @@ fn uninit_array<const N: usize, T>() -> [MaybeUninit<T>; N] {
unsafe { MaybeUninit::uninit().assume_init() }
}

// FIXME: Remove when maybe_uninit_slice is stabilized to provide MaybeUninit::slice_assume_init_ref()
unsafe fn slice_assume_init_ref<T>(slice: &[MaybeUninit<T>]) -> &[T] {
&*(slice as *const [MaybeUninit<T>] as *const [T])
}

#[cfg(test)]
mod tests {
use super::*;
Expand Down Expand Up @@ -604,28 +620,26 @@ mod tests {

#[test]
fn fill_tag_bytes_truncates_long_tag() {
let logger = AndroidLogger::new(Config::default());
let too_long_tag: [u8; LOGGING_TAG_MAX_LEN + 20] = [b'a'; LOGGING_TAG_MAX_LEN + 20];
let too_long_tag = [b'a'; LOGGING_TAG_MAX_LEN + 20];

let mut result: [MaybeUninit<u8>; LOGGING_TAG_MAX_LEN + 1] = uninit_array();
logger.fill_tag_bytes(&mut result, &too_long_tag);
let mut result = uninit_array();
let tag = fill_tag_bytes(&mut result, &too_long_tag);

let mut expected_result = [b'a'; LOGGING_TAG_MAX_LEN - 2].to_vec();
let mut expected_result = vec![b'a'; LOGGING_TAG_MAX_LEN - 2];
expected_result.extend("..\0".as_bytes());
assert_eq!(unsafe { assume_init_slice(&result) }, expected_result);
assert_eq!(tag.to_bytes_with_nul(), expected_result);
}

#[test]
fn fill_tag_bytes_keeps_short_tag() {
let logger = AndroidLogger::new(Config::default());
let short_tag: [u8; 3] = [b'a'; 3];
let short_tag = [b'a'; 3];

let mut result: [MaybeUninit<u8>; LOGGING_TAG_MAX_LEN + 1] = uninit_array();
logger.fill_tag_bytes(&mut result, &short_tag);
let mut result = uninit_array();
let tag = fill_tag_bytes(&mut result, &short_tag);

let mut expected_result = short_tag.to_vec();
expected_result.push(0);
assert_eq!(unsafe { assume_init_slice(&result[..4]) }, expected_result);
assert_eq!(tag.to_bytes_with_nul(), expected_result);
}

#[test]
Expand Down Expand Up @@ -654,7 +668,7 @@ mod tests {
assert_eq!(writer.len, 3);
assert_eq!(writer.last_newline_index, 0);
assert_eq!(
unsafe { assume_init_slice(&writer.buffer[..writer.len]) },
unsafe { slice_assume_init_ref(&writer.buffer[..writer.len]) },
"\n90".as_bytes()
);

Expand Down Expand Up @@ -699,7 +713,7 @@ mod tests {
writer.output_specified_len(5);

assert_eq!(
unsafe { assume_init_slice(&writer.buffer[..log_string.len()]) },
unsafe { slice_assume_init_ref(&writer.buffer[..log_string.len()]) },
log_string.as_bytes()
);
}
Expand All @@ -714,7 +728,7 @@ mod tests {
writer.copy_bytes_to_start(3, 2);

assert_eq!(
unsafe { assume_init_slice(&writer.buffer[..10]) },
unsafe { slice_assume_init_ref(&writer.buffer[..10]) },
"3423456789".as_bytes()
);
}
Expand All @@ -731,7 +745,7 @@ mod tests {
writer.copy_bytes_to_start(10, 0);

assert_eq!(
unsafe { assume_init_slice(&writer.buffer[..test_string.len()]) },
unsafe { slice_assume_init_ref(&writer.buffer[..test_string.len()]) },
test_string.as_bytes()
);
}
Expand All @@ -743,8 +757,4 @@ mod tests {
CStr::from_bytes_with_nul(b"tag\0").unwrap(),
)
}

unsafe fn assume_init_slice<T>(slice: &[MaybeUninit<T>]) -> &[T] {
&*(slice as *const [MaybeUninit<T>] as *const [T])
}
}
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