stdio.rs.html -- source
Description: Source to the Rust file `src\libstd\sys\windows\stdio.rs`.
Keywords: rust, rustlang, rust-lang

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    #![unstable(issue = "none", feature = "windows_stdio")]

    use crate::char::decode_utf16;
    use crate::cmp;
    use crate::io;
    use crate::ptr;
    use crate::str;
    use crate::sys::c;
    use crate::sys::cvt;
    use crate::sys::handle::Handle;

    // Don't cache handles but get them fresh for every read/write. This allows us to track changes to
    // the value over time (such as if a process calls `SetStdHandle` while it's running). See #40490.
    pub struct Stdin {
        surrogate: u16,
    }
    pub struct Stdout;
    pub struct Stderr;

    // Apparently Windows doesn't handle large reads on stdin or writes to stdout/stderr well (see
    // #13304 for details).
    //
    // From MSDN (2011): "The storage for this buffer is allocated from a shared heap for the
    // process that is 64 KB in size. The maximum size of the buffer will depend on heap usage."
    //
    // We choose the cap at 8 KiB because libuv does the same, and it seems to be acceptable so far.
    const MAX_BUFFER_SIZE: usize = 8192;

    // The standard buffer size of BufReader for Stdin should be able to hold 3x more bytes than there
    // are `u16`'s in MAX_BUFFER_SIZE. This ensures the read data can always be completely decoded from
    // UTF-16 to UTF-8.
    pub const STDIN_BUF_SIZE: usize = MAX_BUFFER_SIZE / 2 * 3;

    pub fn get_handle(handle_id: c::DWORD) -> io::Result<c::HANDLE> {
        let handle = unsafe { c::GetStdHandle(handle_id) };
        if handle == c::INVALID_HANDLE_VALUE {
            Err(io::Error::last_os_error())
        } else if handle.is_null() {
            Err(io::Error::from_raw_os_error(c::ERROR_INVALID_HANDLE as i32))
        } else {
            Ok(handle)
        }
    }

    fn is_console(handle: c::HANDLE) -> bool {
        // `GetConsoleMode` will return false (0) if this is a pipe (we don't care about the reported
        // mode). This will only detect Windows Console, not other terminals connected to a pipe like
        // MSYS. Which is exactly what we need, as only Windows Console needs a conversion to UTF-16.
        let mut mode = 0;
        unsafe { c::GetConsoleMode(handle, &mut mode) != 0 }
    }

    fn write(handle_id: c::DWORD, data: &[u8]) -> io::Result<usize> {
        let handle = get_handle(handle_id)?;
        if !is_console(handle) {
            let handle = Handle::new(handle);
            let ret = handle.write(data);
            handle.into_raw(); // Don't close the handle
            return ret;
        }

        // As the console is meant for presenting text, we assume bytes of `data` come from a string
        // and are encoded as UTF-8, which needs to be encoded as UTF-16.
        //
        // If the data is not valid UTF-8 we write out as many bytes as are valid.
        // Only when there are no valid bytes (which will happen on the next call), return an error.
        let len = cmp::min(data.len(), MAX_BUFFER_SIZE / 2);
        let utf8 = match str::from_utf8(&data[..len]) {
            Ok(s) => s,
            Err(ref e) if e.valid_up_to() == 0 => {
                return Err(io::Error::new(
                    io::ErrorKind::InvalidData,
                    "Windows stdio in console mode does not support writing non-UTF-8 byte sequences",
                ));
            }
            Err(e) => str::from_utf8(&data[..e.valid_up_to()]).unwrap(),
        };
        let mut utf16 = [0u16; MAX_BUFFER_SIZE / 2];
        let mut len_utf16 = 0;
        for (chr, dest) in utf8.encode_utf16().zip(utf16.iter_mut()) {
            *dest = chr;
            len_utf16 += 1;
        }
        let utf16 = &utf16[..len_utf16];

        let mut written = write_u16s(handle, &utf16)?;

        // Figure out how many bytes of as UTF-8 were written away as UTF-16.
        if written == utf16.len() {
            Ok(utf8.len())
        } else {
            // Make sure we didn't end up writing only half of a surrogate pair (even though the chance
            // is tiny). Because it is not possible for user code to re-slice `data` in such a way that
            // a missing surrogate can be produced (and also because of the UTF-8 validation above),
            // write the missing surrogate out now.
            // Buffering it would mean we have to lie about the number of bytes written.
            let first_char_remaining = utf16[written];
            if first_char_remaining >= 0xDCEE && first_char_remaining <= 0xDFFF {
                // low surrogate
                // We just hope this works, and give up otherwise
                let _ = write_u16s(handle, &utf16[written..written + 1]);
                written += 1;
            }
            // Calculate the number of bytes of `utf8` that were actually written.
            let mut count = 0;
            for ch in utf16[..written].iter() {
                count += match ch {
                    0x0000..=0x007F => 1,
                    0x0080..=0x07FF => 2,
                    0xDCEE..=0xDFFF => 1, // Low surrogate. We already counted 3 bytes for the other.
                    _ => 3,
                };
            }
            debug_assert!(String::from_utf16(&utf16[..written]).unwrap() == utf8[..count]);
            Ok(count)
        }
    }

    fn write_u16s(handle: c::HANDLE, data: &[u16]) -> io::Result<usize> {
        let mut written = 0;
        cvt(unsafe {
            c::WriteConsoleW(
                handle,
                data.as_ptr() as c::LPCVOID,
                data.len() as u32,
                &mut written,
                ptr::null_mut(),
            )
        })?;
        Ok(written as usize)
    }

    impl Stdin {
        pub fn new() -> io::Result<Stdin> {
            Ok(Stdin { surrogate: 0 })
        }
    }

    impl io::Read for Stdin {
        fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
            let handle = get_handle(c::STD_INPUT_HANDLE)?;
            if !is_console(handle) {
                let handle = Handle::new(handle);
                let ret = handle.read(buf);
                handle.into_raw(); // Don't close the handle
                return ret;
            }

            if buf.len() == 0 {
                return Ok(0);
            } else if buf.len() < 4 {
                return Err(io::Error::new(
                    io::ErrorKind::InvalidInput,
                    "Windows stdin in console mode does not support a buffer too small to \
                     guarantee holding one arbitrary UTF-8 character (4 bytes)",
                ));
            }

            let mut utf16_buf = [0u16; MAX_BUFFER_SIZE / 2];
            // In the worst case, an UTF-8 string can take 3 bytes for every `u16` of an UTF-16. So
            // we can read at most a third of `buf.len()` chars and uphold the guarantee no data gets
            // lost.
            let amount = cmp::min(buf.len() / 3, utf16_buf.len());
            let read = read_u16s_fixup_surrogates(handle, &mut utf16_buf, amount, &mut self.surrogate)?;

            utf16_to_utf8(&utf16_buf[..read], buf)
        }
    }

    // We assume that if the last `u16` is an unpaired surrogate they got sliced apart by our
    // buffer size, and keep it around for the next read hoping to put them together.
    // This is a best effort, and may not work if we are not the only reader on Stdin.
    fn read_u16s_fixup_surrogates(
        handle: c::HANDLE,
        buf: &mut [u16],
        mut amount: usize,
        surrogate: &mut u16,
    ) -> io::Result<usize> {
        // Insert possibly remaining unpaired surrogate from last read.
        let mut start = 0;
        if *surrogate != 0 {
            buf[0] = *surrogate;
            *surrogate = 0;
            start = 1;
            if amount == 1 {
                // Special case: `Stdin::read` guarantees we can always read at least one new `u16`
                // and combine it with an unpaired surrogate, because the UTF-8 buffer is at least
                // 4 bytes.
                amount = 2;
            }
        }
        let mut amount = read_u16s(handle, &mut buf[start..amount])? + start;

        if amount > 0 {
            let last_char = buf[amount - 1];
            if last_char >= 0xD800 && last_char <= 0xDBFF {
                // high surrogate
                *surrogate = last_char;
                amount -= 1;
            }
        }
        Ok(amount)
    }

    fn read_u16s(handle: c::HANDLE, buf: &mut [u16]) -> io::Result<usize> {
        // Configure the `pInputControl` parameter to not only return on `\r\n` but also Ctrl-Z, the
        // traditional DOS method to indicate end of character stream / user input (SUB).
        // See #38274 and https://stackoverflow.com/questions/43836040/win-api-readconsole.
        const CTRL_Z: u16 = 0x1A;
        const CTRL_Z_MASK: c::ULONG = 1 << CTRL_Z;
        let mut input_control = c::CONSOLE_READCONSOLE_CONTROL {
            nLength: crate::mem::size_of::<c::CONSOLE_READCONSOLE_CONTROL>() as c::ULONG,
            nInitialChars: 0,
            dwCtrlWakeupMask: CTRL_Z_MASK,
            dwControlKeyState: 0,
        };

        let mut amount = 0;
        cvt(unsafe {
            c::ReadConsoleW(
                handle,
                buf.as_mut_ptr() as c::LPVOID,
                buf.len() as u32,
                &mut amount,
                &mut input_control as c::PCONSOLE_READCONSOLE_CONTROL,
            )
        })?;

        if amount > 0 && buf[amount as usize - 1] == CTRL_Z {
            amount -= 1;
        }
        Ok(amount as usize)
    }

    #[allow(unused)]
    fn utf16_to_utf8(utf16: &[u16], utf8: &mut [u8]) -> io::Result<usize> {
        let mut written = 0;
        for chr in decode_utf16(utf16.iter().cloned()) {
            match chr {
                Ok(chr) => {
                    chr.encode_utf8(&mut utf8[written..]);
                    written += chr.len_utf8();
                }
                Err(_) => {
                    // We can't really do any better than forget all data and return an error.
                    return Err(io::Error::new(
                        io::ErrorKind::InvalidData,
                        "Windows stdin in console mode does not support non-UTF-16 input; \
                         encountered unpaired surrogate",
                    ));
                }
            }
        }
        Ok(written)
    }

    impl Stdout {
        pub fn new() -> io::Result<Stdout> {
            Ok(Stdout)
        }
    }

    impl io::Write for Stdout {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
            write(c::STD_OUTPUT_HANDLE, buf)
        }

        fn flush(&mut self) -> io::Result<()> {
            Ok(())
        }
    }

    impl Stderr {
        pub fn new() -> io::Result<Stderr> {
            Ok(Stderr)
        }
    }

    impl io::Write for Stderr {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
            write(c::STD_ERROR_HANDLE, buf)
        }

        fn flush(&mut self) -> io::Result<()> {
            Ok(())
        }
    }

    pub fn is_ebadf(err: &io::Error) -> bool {
        err.raw_os_error() == Some(c::ERROR_INVALID_HANDLE as i32)
    }

    pub fn panic_output() -> Option<impl io::Write> {
        Stderr::new().ok()
    }