std/io/

stdio.rs

#![cfg_attr(test, allow(unused))]

#[cfg(test)]
mod tests;

use crate::cell::{Cell, RefCell};
use crate::fmt;
use crate::fs::File;
use crate::io::prelude::*;
use crate::io::{
    self, BorrowedCursor, BufReader, IoSlice, IoSliceMut, LineWriter, Lines, SpecReadByte,
};
use crate::panic::{RefUnwindSafe, UnwindSafe};
use crate::sync::atomic::{Atomic, AtomicBool, Ordering};
use crate::sync::{Arc, Mutex, MutexGuard, OnceLock, ReentrantLock, ReentrantLockGuard};
use crate::sys::stdio;
use crate::thread::AccessError;

type LocalStream = Arc<Mutex<Vec<u8>>>;

thread_local! {
    /// Used by the test crate to capture the output of the print macros and panics.
    static OUTPUT_CAPTURE: Cell<Option<LocalStream>> = const {
        Cell::new(None)
    }
}

/// Flag to indicate OUTPUT_CAPTURE is used.
///
/// If it is None and was never set on any thread, this flag is set to false,
/// and OUTPUT_CAPTURE can be safely ignored on all threads, saving some time
/// and memory registering an unused thread local.
///
/// Note about memory ordering: This contains information about whether a
/// thread local variable might be in use. Although this is a global flag, the
/// memory ordering between threads does not matter: we only want this flag to
/// have a consistent order between set_output_capture and print_to *within
/// the same thread*. Within the same thread, things always have a perfectly
/// consistent order. So Ordering::Relaxed is fine.
static OUTPUT_CAPTURE_USED: Atomic<bool> = AtomicBool::new(false);

/// A handle to a raw instance of the standard input stream of this process.
///
/// This handle is not synchronized or buffered in any fashion. Constructed via
/// the `std::io::stdio::stdin_raw` function.
struct StdinRaw(stdio::Stdin);

/// A handle to a raw instance of the standard output stream of this process.
///
/// This handle is not synchronized or buffered in any fashion. Constructed via
/// the `std::io::stdio::stdout_raw` function.
struct StdoutRaw(stdio::Stdout);

/// A handle to a raw instance of the standard output stream of this process.
///
/// This handle is not synchronized or buffered in any fashion. Constructed via
/// the `std::io::stdio::stderr_raw` function.
struct StderrRaw(stdio::Stderr);

/// Constructs a new raw handle to the standard input of this process.
///
/// The returned handle does not interact with any other handles created nor
/// handles returned by `std::io::stdin`. Data buffered by the `std::io::stdin`
/// handles is **not** available to raw handles returned from this function.
///
/// The returned handle has no external synchronization or buffering.
#[unstable(feature = "libstd_sys_internals", issue = "none")]
const fn stdin_raw() -> StdinRaw {
    StdinRaw(stdio::Stdin::new())
}

/// Constructs a new raw handle to the standard output stream of this process.
///
/// The returned handle does not interact with any other handles created nor
/// handles returned by `std::io::stdout`. Note that data is buffered by the
/// `std::io::stdout` handles so writes which happen via this raw handle may
/// appear before previous writes.
///
/// The returned handle has no external synchronization or buffering layered on
/// top.
#[unstable(feature = "libstd_sys_internals", issue = "none")]
const fn stdout_raw() -> StdoutRaw {
    StdoutRaw(stdio::Stdout::new())
}

/// Constructs a new raw handle to the standard error stream of this process.
///
/// The returned handle does not interact with any other handles created nor
/// handles returned by `std::io::stderr`.
///
/// The returned handle has no external synchronization or buffering layered on
/// top.
#[unstable(feature = "libstd_sys_internals", issue = "none")]
const fn stderr_raw() -> StderrRaw {
    StderrRaw(stdio::Stderr::new())
}

#[cfg(windows)]
impl StdoutRaw {
    /// Starts a new lock session: stream state cached per lock session (the
    /// handle and its console mode) is re-queried at the next write, so that
    /// changing the process stdio handles (e.g. with `SetStdHandle`) between
    /// lock sessions keeps working.
    #[inline]
    fn refresh(&mut self) {
        self.0.refresh();
    }
}

#[cfg(windows)]
impl StderrRaw {
    /// See `StdoutRaw::refresh`.
    #[inline]
    fn refresh(&mut self) {
        self.0.refresh();
    }
}

impl Read for StdinRaw {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        handle_ebadf(self.0.read(buf), || Ok(0))
    }

    fn read_buf(&mut self, buf: BorrowedCursor<'_, u8>) -> io::Result<()> {
        handle_ebadf(self.0.read_buf(buf), || Ok(()))
    }

    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        handle_ebadf(self.0.read_vectored(bufs), || Ok(0))
    }

    #[inline]
    fn is_read_vectored(&self) -> bool {
        self.0.is_read_vectored()
    }

    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
        if buf.is_empty() {
            return Ok(());
        }
        handle_ebadf(self.0.read_exact(buf), || Err(io::Error::READ_EXACT_EOF))
    }

    fn read_buf_exact(&mut self, buf: BorrowedCursor<'_, u8>) -> io::Result<()> {
        if buf.capacity() == 0 {
            return Ok(());
        }
        handle_ebadf(self.0.read_buf_exact(buf), || Err(io::Error::READ_EXACT_EOF))
    }

    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
        handle_ebadf(self.0.read_to_end(buf), || Ok(0))
    }

    fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
        handle_ebadf(self.0.read_to_string(buf), || Ok(0))
    }
}

impl Write for StdoutRaw {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        handle_ebadf(self.0.write(buf), || Ok(buf.len()))
    }

    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        let total = || Ok(bufs.iter().map(|b| b.len()).sum());
        handle_ebadf(self.0.write_vectored(bufs), total)
    }

    #[inline]
    fn is_write_vectored(&self) -> bool {
        self.0.is_write_vectored()
    }

    fn flush(&mut self) -> io::Result<()> {
        handle_ebadf(self.0.flush(), || Ok(()))
    }

    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
        handle_ebadf(self.0.write_all(buf), || Ok(()))
    }

    fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> io::Result<()> {
        handle_ebadf(self.0.write_all_vectored(bufs), || Ok(()))
    }

    fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
        handle_ebadf(self.0.write_fmt(fmt), || Ok(()))
    }
}

impl Write for StderrRaw {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        handle_ebadf(self.0.write(buf), || Ok(buf.len()))
    }

    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        let total = || Ok(bufs.iter().map(|b| b.len()).sum());
        handle_ebadf(self.0.write_vectored(bufs), total)
    }

    #[inline]
    fn is_write_vectored(&self) -> bool {
        self.0.is_write_vectored()
    }

    fn flush(&mut self) -> io::Result<()> {
        handle_ebadf(self.0.flush(), || Ok(()))
    }

    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
        handle_ebadf(self.0.write_all(buf), || Ok(()))
    }

    fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> io::Result<()> {
        handle_ebadf(self.0.write_all_vectored(bufs), || Ok(()))
    }

    fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
        handle_ebadf(self.0.write_fmt(fmt), || Ok(()))
    }
}

fn handle_ebadf<T>(r: io::Result<T>, default: impl FnOnce() -> io::Result<T>) -> io::Result<T> {
    match r {
        Err(ref e) if stdio::is_ebadf(e) => default(),
        r => r,
    }
}

/// A handle to the standard input stream of a process.
///
/// Each handle is a shared reference to a global buffer of input data to this
/// process. A handle can be `lock`'d to gain full access to [`BufRead`] methods
/// (e.g., `.lines()`). Reads to this handle are otherwise locked with respect
/// to other reads.
///
/// This handle implements the `Read` trait, but beware that concurrent reads
/// of `Stdin` must be executed with care.
///
/// Created by the [`io::stdin`] method.
///
/// [`io::stdin`]: stdin
///
/// ### Note: Windows Portability Considerations
///
/// When operating in a console, the Windows implementation of this stream does not support
/// non-UTF-8 byte sequences. Attempting to read bytes that are not valid UTF-8 will return
/// an error.
///
/// In a process with a detached console, such as one using
/// `#![windows_subsystem = "windows"]`, or in a child process spawned from such a process,
/// the contained handle will be null. In such cases, the standard library's `Read` and
/// `Write` will do nothing and silently succeed. All other I/O operations, via the
/// standard library or via raw Windows API calls, will fail.
///
/// # Examples
///
/// ```no_run
/// use std::io;
///
/// fn main() -> io::Result<()> {
///     let mut buffer = String::new();
///     let stdin = io::stdin(); // We get `Stdin` here.
///     stdin.read_line(&mut buffer)?;
///     Ok(())
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[cfg_attr(not(test), rustc_diagnostic_item = "Stdin")]
pub struct Stdin {
    inner: &'static Mutex<BufReader<StdinRaw>>,
}

/// A locked reference to the [`Stdin`] handle.
///
/// This handle implements both the [`Read`] and [`BufRead`] traits, and
/// is constructed via the [`Stdin::lock`] method.
///
/// ### Note: Windows Portability Considerations
///
/// When operating in a console, the Windows implementation of this stream does not support
/// non-UTF-8 byte sequences. Attempting to read bytes that are not valid UTF-8 will return
/// an error.
///
/// In a process with a detached console, such as one using
/// `#![windows_subsystem = "windows"]`, or in a child process spawned from such a process,
/// the contained handle will be null. In such cases, the standard library's `Read` and
/// `Write` will do nothing and silently succeed. All other I/O operations, via the
/// standard library or via raw Windows API calls, will fail.
///
/// # Examples
///
/// ```no_run
/// use std::io::{self, BufRead};
///
/// fn main() -> io::Result<()> {
///     let mut buffer = String::new();
///     let stdin = io::stdin(); // We get `Stdin` here.
///     {
///         let mut handle = stdin.lock(); // We get `StdinLock` here.
///         handle.read_line(&mut buffer)?;
///     } // `StdinLock` is dropped here.
///     Ok(())
/// }
/// ```
#[must_use = "if unused stdin will immediately unlock"]
#[stable(feature = "rust1", since = "1.0.0")]
#[cfg_attr(not(test), rustc_diagnostic_item = "StdinLock")]
pub struct StdinLock<'a> {
    inner: MutexGuard<'a, BufReader<StdinRaw>>,
}

/// Constructs a new handle to the standard input of the current process.
///
/// Each handle returned is a reference to a shared global buffer whose access
/// is synchronized via a mutex. If you need more explicit control over
/// locking, see the [`Stdin::lock`] method.
///
/// ### Note: Windows Portability Considerations
///
/// When operating in a console, the Windows implementation of this stream does not support
/// non-UTF-8 byte sequences. Attempting to read bytes that are not valid UTF-8 will return
/// an error.
///
/// In a process with a detached console, such as one using
/// `#![windows_subsystem = "windows"]`, or in a child process spawned from such a process,
/// the contained handle will be null. In such cases, the standard library's `Read` and
/// `Write` will do nothing and silently succeed. All other I/O operations, via the
/// standard library or via raw Windows API calls, will fail.
///
/// # Examples
///
/// Using implicit synchronization:
///
/// ```no_run
/// use std::io;
///
/// fn main() -> io::Result<()> {
///     let mut buffer = String::new();
///     io::stdin().read_line(&mut buffer)?;
///     Ok(())
/// }
/// ```
///
/// Using explicit synchronization:
///
/// ```no_run
/// use std::io::{self, BufRead};
///
/// fn main() -> io::Result<()> {
///     let mut buffer = String::new();
///     let stdin = io::stdin();
///     let mut handle = stdin.lock();
///
///     handle.read_line(&mut buffer)?;
///     Ok(())
/// }
/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn stdin() -> Stdin {
    static INSTANCE: OnceLock<Mutex<BufReader<StdinRaw>>> = OnceLock::new();
    Stdin {
        inner: INSTANCE.get_or_init(|| {
            Mutex::new(BufReader::with_capacity(stdio::STDIN_BUF_SIZE, stdin_raw()))
        }),
    }
}

impl Stdin {
    /// Locks this handle to the standard input stream, returning a readable
    /// guard.
    ///
    /// The lock is released when the returned lock goes out of scope. The
    /// returned guard also implements the [`Read`] and [`BufRead`] traits for
    /// accessing the underlying data.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::io::{self, BufRead};
    ///
    /// fn main() -> io::Result<()> {
    ///     let mut buffer = String::new();
    ///     let stdin = io::stdin();
    ///     let mut handle = stdin.lock();
    ///
    ///     handle.read_line(&mut buffer)?;
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn lock(&self) -> StdinLock<'static> {
        // Locks this handle with 'static lifetime. This depends on the
        // implementation detail that the underlying `Mutex` is static.
        StdinLock { inner: self.inner.lock().unwrap_or_else(|e| e.into_inner()) }
    }

    /// Locks this handle and reads a line of input, appending it to the specified buffer.
    ///
    /// For detailed semantics of this method, see the documentation on
    /// [`BufRead::read_line`]. In particular:
    /// * Previous content of the buffer will be preserved. To avoid appending
    ///   to the buffer, you need to [`clear`] it first.
    /// * The trailing newline character, if any, is included in the buffer.
    ///
    /// [`clear`]: String::clear
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::io;
    ///
    /// let mut input = String::new();
    /// match io::stdin().read_line(&mut input) {
    ///     Ok(n) => {
    ///         println!("{n} bytes read");
    ///         println!("{input}");
    ///     }
    ///     Err(error) => println!("error: {error}"),
    /// }
    /// ```
    ///
    /// You can run the example one of two ways:
    ///
    /// - Pipe some text to it, e.g., `printf foo | path/to/executable`
    /// - Give it text interactively by running the executable directly,
    ///   in which case it will wait for the Enter key to be pressed before
    ///   continuing
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_confusables("get_line")]
    pub fn read_line(&self, buf: &mut String) -> io::Result<usize> {
        self.lock().read_line(buf)
    }

    /// Consumes this handle and returns an iterator over input lines.
    ///
    /// For detailed semantics of this method, see the documentation on
    /// [`BufRead::lines`].
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::io;
    ///
    /// let lines = io::stdin().lines();
    /// for line in lines {
    ///     println!("got a line: {}", line.unwrap());
    /// }
    /// ```
    #[must_use = "`self` will be dropped if the result is not used"]
    #[stable(feature = "stdin_forwarders", since = "1.62.0")]
    pub fn lines(self) -> Lines<StdinLock<'static>> {
        self.lock().lines()
    }
}

#[stable(feature = "std_debug", since = "1.16.0")]
impl fmt::Debug for Stdin {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Stdin").finish_non_exhaustive()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Read for Stdin {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        self.lock().read(buf)
    }
    fn read_buf(&mut self, buf: BorrowedCursor<'_, u8>) -> io::Result<()> {
        self.lock().read_buf(buf)
    }
    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        self.lock().read_vectored(bufs)
    }
    #[inline]
    fn is_read_vectored(&self) -> bool {
        self.lock().is_read_vectored()
    }
    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
        self.lock().read_to_end(buf)
    }
    fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
        self.lock().read_to_string(buf)
    }
    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
        self.lock().read_exact(buf)
    }
    fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_, u8>) -> io::Result<()> {
        self.lock().read_buf_exact(cursor)
    }
}

#[stable(feature = "read_shared_stdin", since = "1.78.0")]
impl Read for &Stdin {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        self.lock().read(buf)
    }
    fn read_buf(&mut self, buf: BorrowedCursor<'_, u8>) -> io::Result<()> {