qubit_io/ext/
write_ext.rs

1// =============================================================================
2//    Copyright (c) 2026 Haixing Hu.
3//
4//    SPDX-License-Identifier: Apache-2.0
5//
6//    Licensed under the Apache License, Version 2.0.
7// =============================================================================
8
9use std::io::{
10    Result,
11    Write,
12};
13
14/// Extension methods for [`Write`] values.
15///
16/// `WriteExt` provides small method-style helpers for byte writers. The
17/// methods are implemented for every type that implements [`Write`], including
18/// `dyn Write` trait objects.
19pub trait WriteExt: Write {
20    /// Writes bytes from a range of `buffer` without checking the range bounds
21    /// in release builds.
22    ///
23    /// This method delegates to [`Write::write`] after creating the source
24    /// slice with raw pointer arithmetic. It performs at most one write
25    /// operation and returns the number of bytes written, keeping the same
26    /// short-write and error behavior as [`Write::write`].
27    ///
28    /// # Parameters
29    /// - `buffer`: Source buffer.
30    /// - `start_index`: Start offset inside `buffer`.
31    /// - `count`: Maximum number of bytes to write.
32    ///
33    /// # Returns
34    /// The number of bytes written from `buffer[start_index..start_index +
35    /// count]`. The value is in `0..=count`.
36    ///
37    /// # Errors
38    /// Returns the error reported by [`Write::write`].
39    ///
40    /// # Safety
41    /// The caller must guarantee that `start_index..start_index + count` is a
42    /// valid range within `buffer` and that `start_index + count` does not
43    /// overflow `usize`.
44    unsafe fn write_unchecked(
45        &mut self,
46        buffer: &[u8],
47        start_index: usize,
48        count: usize,
49    ) -> Result<usize> {
50        debug_assert!(
51            start_index
52                .checked_add(count)
53                .is_some_and(|end_index| end_index <= buffer.len()),
54            "unchecked write range exceeds buffer"
55        );
56        // SAFETY: The caller guarantees that the computed pointer and length
57        // form a valid subslice of `buffer`.
58        let source = unsafe {
59            core::slice::from_raw_parts(buffer.as_ptr().add(start_index), count)
60        };
61        self.write(source)
62    }
63
64    /// Writes exactly `count` bytes from a range of `buffer` without checking
65    /// the range bounds in release builds.
66    ///
67    /// This method delegates to [`Write::write_all`] after creating the source
68    /// slice with raw pointer arithmetic. It keeps the same short-write,
69    /// [`std::io::ErrorKind::Interrupted`], and
70    /// [`std::io::ErrorKind::WriteZero`] behavior as [`Write::write_all`].
71    ///
72    /// # Parameters
73    /// - `buffer`: Source buffer.
74    /// - `start_index`: Start offset inside `buffer`.
75    /// - `count`: Number of bytes to write.
76    ///
77    /// # Errors
78    /// Returns the error reported by [`Write::write_all`].
79    ///
80    /// # Safety
81    /// The caller must guarantee that `start_index..start_index + count` is a
82    /// valid range within `buffer` and that `start_index + count` does not
83    /// overflow `usize`.
84    unsafe fn write_all_unchecked(
85        &mut self,
86        buffer: &[u8],
87        start_index: usize,
88        count: usize,
89    ) -> Result<()> {
90        debug_assert!(
91            start_index
92                .checked_add(count)
93                .is_some_and(|end_index| end_index <= buffer.len()),
94            "unchecked write range exceeds buffer"
95        );
96        // SAFETY: The caller guarantees that the computed pointer and length
97        // form a valid subslice of `buffer`.
98        let source = unsafe {
99            core::slice::from_raw_parts(buffer.as_ptr().add(start_index), count)
100        };
101        self.write_all(source)
102    }
103}
104
105impl<T> WriteExt for T where T: Write + ?Sized {}
qubit_io/ext/write_ext.rs

qubit_io/ext/
write_ext.rs
