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Panic when advance_slices()'ing too far and update docs. #94855

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Jun 20, 2022
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Panic when advance_slices()'ing too far and update docs. #94855

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a23e751
Panic when advance_slices()'ing too far.
m-ou-se Mar 11, 2022
4d7daa0
Update advance and advance_slices docs.
m-ou-se Mar 11, 2022
1890372
Update tests.
m-ou-se Mar 11, 2022
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50 changes: 34 additions & 16 deletions library/std/src/io/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1085,6 +1085,10 @@ impl<'a> IoSliceMut<'a> {
/// Also see [`IoSliceMut::advance_slices`] to advance the cursors of
/// multiple buffers.
///
/// # Panics
///
/// Panics when trying to advance beyond the end of the slice.
///
/// # Examples
///
/// ```
Expand All @@ -1106,15 +1110,18 @@ impl<'a> IoSliceMut<'a> {
self.0.advance(n)
}

/// Advance the internal cursor of the slices.
/// Advance a slice of slices.
///
/// # Notes
/// Shrinks the slice to remove any `IoSliceMut`s that are fully advanced over.
/// If the cursor ends up in the middle of an `IoSliceMut`, it is modified
/// to start at that cursor.
///
/// Elements in the slice may be modified if the cursor is not advanced to
/// the end of the slice. For example if we have a slice of buffers with 2
/// `IoSliceMut`s, both of length 8, and we advance the cursor by 10 bytes
/// the first `IoSliceMut` will be untouched however the second will be
/// modified to remove the first 2 bytes (10 - 8).
/// For example, if we have a slice of two 8-byte `IoSliceMut`s, and we advance by 10 bytes,
/// the result will only include the second `IoSliceMut`, advanced by 2 bytes.
///
/// # Panics
///
/// Panics when trying to advance beyond the end of the slices.
///
/// # Examples
///
Expand Down Expand Up @@ -1155,7 +1162,9 @@ impl<'a> IoSliceMut<'a> {
}

*bufs = &mut replace(bufs, &mut [])[remove..];
if !bufs.is_empty() {
if bufs.is_empty() {
assert!(n == accumulated_len, "advancing io slices beyond their length");
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maybe use assert_eq here to include the expected length in the panic message?

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Then the user would just see left: 200, right: 100, which doesn't mean much. (Also, assert_eq results in mode codegen, which is a bit of a waste.)

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ok

} else {
bufs[0].advance(n - accumulated_len)
}
}
Expand Down Expand Up @@ -1220,6 +1229,10 @@ impl<'a> IoSlice<'a> {
/// Also see [`IoSlice::advance_slices`] to advance the cursors of multiple
/// buffers.
///
/// # Panics
///
/// Panics when trying to advance beyond the end of the slice.
///
/// # Examples
///
/// ```
Expand All @@ -1241,15 +1254,18 @@ impl<'a> IoSlice<'a> {
self.0.advance(n)
}

/// Advance the internal cursor of the slices.
/// Advance a slice of slices.
///
/// # Notes
/// Shrinks the slice to remove any `IoSlice`s that are fully advanced over.
/// If the cursor ends up in the middle of an `IoSlice`, it is modified
/// to start at that cursor.
///
/// Elements in the slice may be modified if the cursor is not advanced to
/// the end of the slice. For example if we have a slice of buffers with 2
/// `IoSlice`s, both of length 8, and we advance the cursor by 10 bytes the
/// first `IoSlice` will be untouched however the second will be modified to
/// remove the first 2 bytes (10 - 8).
/// For example, if we have a slice of two 8-byte `IoSlice`s, and we advance by 10 bytes,
/// the result will only include the second `IoSlice`, advanced by 2 bytes.
///
/// # Panics
///
/// Panics when trying to advance beyond the end of the slices.
///
/// # Examples
///
Expand Down Expand Up @@ -1289,7 +1305,9 @@ impl<'a> IoSlice<'a> {
}

*bufs = &mut replace(bufs, &mut [])[remove..];
if !bufs.is_empty() {
if bufs.is_empty() {
assert!(n == accumulated_len, "advancing io slices beyond their length");
} else {
bufs[0].advance(n - accumulated_len)
}
}
Expand Down
8 changes: 4 additions & 4 deletions library/std/src/io/tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -423,18 +423,18 @@ fn io_slice_mut_advance_slices() {
}

#[test]
#[should_panic]
fn io_slice_mut_advance_slices_empty_slice() {
let mut empty_bufs = &mut [][..];
// Shouldn't panic.
IoSliceMut::advance_slices(&mut empty_bufs, 1);
}

#[test]
#[should_panic]
fn io_slice_mut_advance_slices_beyond_total_length() {
let mut buf1 = [1; 8];
let mut bufs = &mut [IoSliceMut::new(&mut buf1)][..];

// Going beyond the total length should be ok.
IoSliceMut::advance_slices(&mut bufs, 9);
assert!(bufs.is_empty());
}
Expand Down Expand Up @@ -463,18 +463,18 @@ fn io_slice_advance_slices() {
}

#[test]
#[should_panic]
fn io_slice_advance_slices_empty_slice() {
let mut empty_bufs = &mut [][..];
// Shouldn't panic.
IoSlice::advance_slices(&mut empty_bufs, 1);
}

#[test]
#[should_panic]
fn io_slice_advance_slices_beyond_total_length() {
let buf1 = [1; 8];
let mut bufs = &mut [IoSlice::new(&buf1)][..];

// Going beyond the total length should be ok.
IoSlice::advance_slices(&mut bufs, 9);
assert!(bufs.is_empty());
}
Expand Down