qubit-fs 0.2.2

Provider-neutral synchronous and asynchronous filesystem abstraction for Rust
Documentation 
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// =============================================================================
//    Copyright (c) 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================
// facade tests.
//! Concrete asynchronous file reader handle.

use std::fmt::Debug;
use std::fmt::Formatter;
use std::fmt::Result as FmtResult;
use std::io::Result as IoResult;
use std::pin::Pin;
use std::task::Context;
use std::task::Poll;

use qubit_io::AsyncInput;
use qubit_io::BoxAsyncInput;

use crate::metadata::OpenedFileInfo;

/// Type-erased asynchronous byte input associated with an opened file.
///
/// # Examples
///
/// This example uses an isolated in-memory provider fixture.
///
/// ```rust
/// # mod support { include!(concat!(env!("CARGO_MANIFEST_DIR"), "/tests/common/rustdoc_support.rs")); }
/// # use support::*;
/// # let (filesystem, _) = async_recording_spi::async_recording_file_system(Default::default());
/// # poll_support::ready(async {
/// use qubit_fs::Path;
/// use qubit_fs::read::ReadOptions;
/// use qubit_io::AsyncInput;
///
/// let mut reader = filesystem.open_reader(&Path::parse("/report")?, ReadOptions::default()).await?;
/// let mut prefix = [0; 3];
/// assert_eq!(3, reader.read_fully_async(&mut prefix).await?);
/// assert_eq!(*b"byt", prefix);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// # }).unwrap();
/// ```
pub struct AsyncFileReader {
    /// Pinned provider byte input.
    inner: BoxAsyncInput<dyn AsyncInput<Item = u8> + Send>,
    /// Stable identity and metadata captured at open time.
    info: OpenedFileInfo,
}

impl AsyncFileReader {
    /// Wraps an already-open asynchronous provider byte input.
    ///
    /// # Parameters
    /// - `inner`: Runtime-neutral asynchronous byte input.
    /// - `info`: File identity and optional open-time metadata snapshot.
    ///
    /// # Returns
    /// A pinned, type-erased asynchronous file reader.
    #[inline]
    #[must_use]
    pub(crate) fn new(info: OpenedFileInfo, inner: Box<dyn AsyncInput<Item = u8> + Send>) -> Self {
        Self {
            inner: BoxAsyncInput::new(inner),
            info,
        }
    }

    /// Returns the fixed identity and open-time metadata snapshot.
    ///
    /// # Returns
    /// Information captured when the reader was opened.
    #[inline]
    #[must_use]
    pub fn info(&self) -> &OpenedFileInfo {
        &self.info
    }
}

impl AsyncInput for AsyncFileReader {
    type Item = u8;

    #[inline]
    fn is_buffered(&self) -> bool {
        self.inner.is_buffered()
    }

    #[inline]
    unsafe fn poll_read_unchecked(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        output: &mut [u8],
        index: usize,
        count: usize,
    ) -> Poll<IoResult<usize>> {
        let this = self.get_mut();
        // SAFETY: The caller guarantees the same range contract required by
        // the wrapped asynchronous input.
        unsafe {
            Pin::new(&mut this.inner)
                .get_pin_mut()
                .poll_read_unchecked(cx, output, index, count)
        }
    }
}

impl Debug for AsyncFileReader {
    #[inline]
    fn fmt(&self, formatter: &mut Formatter<'_>) -> FmtResult {
        formatter
            .debug_struct("AsyncFileReader")
            .field("info", &self.info)
            .finish_non_exhaustive()
    }
}