library/std/src/sys/windows/stdio.rs - toolchain/rustc - Git at Google

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

 use crate::char::decode_utf16;
 use crate::cmp;
 use crate::io;
 use crate::os::windows::io::{FromRawHandle, IntoRawHandle};
 use crate::ptr;
 use crate::str;
 use crate::sys::c;
 use crate::sys::cvt;
 use crate::sys::handle::Handle;
 use core::str::utf8_char_width;

 // 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 {
     incomplete_utf8: IncompleteUtf8,
 }

 pub struct Stderr {
     incomplete_utf8: IncompleteUtf8,
 }

 struct IncompleteUtf8 {
     bytes: [u8; 4],
     len: u8,
 }

 // 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],
     incomplete_utf8: &mut IncompleteUtf8,
 ) -> io::Result<usize> {
     if data.is_empty() {
         return Ok(0);
     }

     let handle = get_handle(handle_id)?;
     if !is_console(handle) {
         unsafe {
             let handle = Handle::from_raw_handle(handle);
             let ret = handle.write(data);
             handle.into_raw_handle(); // Don't close the handle
             return ret;
         }
     }

     if incomplete_utf8.len > 0 {
         assert!(
             incomplete_utf8.len < 4,
             "Unexpected number of bytes for incomplete UTF-8 codepoint."
         );
         if data[0] >> 6 != 0b10 {
             // not a continuation byte - reject
             incomplete_utf8.len = 0;
             return Err(io::Error::new_const(
                 io::ErrorKind::InvalidData,
                 &"Windows stdio in console mode does not support writing non-UTF-8 byte sequences",
             ));
         }
         incomplete_utf8.bytes[incomplete_utf8.len as usize] = data[0];
         incomplete_utf8.len += 1;
         let char_width = utf8_char_width(incomplete_utf8.bytes[0]);
         if (incomplete_utf8.len as usize) < char_width {
             // more bytes needed
             return Ok(1);
         }
         let s = str::from_utf8(&incomplete_utf8.bytes[0..incomplete_utf8.len as usize]);
         incomplete_utf8.len = 0;
         match s {
             Ok(s) => {
                 assert_eq!(char_width, s.len());
                 let written = write_valid_utf8_to_console(handle, s)?;
                 assert_eq!(written, s.len()); // guaranteed by write_valid_utf8_to_console() for single codepoint writes
                 return Ok(1);
             }
             Err(_) => {
                 return Err(io::Error::new_const(
                     io::ErrorKind::InvalidData,
                     &"Windows stdio in console mode does not support writing non-UTF-8 byte sequences",
                 ));
             }
         }
     }

     // As the console is meant for presenting text, we assume bytes of `data` 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.
     // If the first byte is invalid it is either first byte of a multi-byte sequence but the
     // provided byte slice is too short or it is the first byte of an invalide multi-byte sequence.
     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 => {
             let first_byte_char_width = utf8_char_width(data[0]);
             if first_byte_char_width > 1 && data.len() < first_byte_char_width {
                 incomplete_utf8.bytes[0] = data[0];
                 incomplete_utf8.len = 1;
                 return Ok(1);
             } else {
                 return Err(io::Error::new_const(
                     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(),
     };

     write_valid_utf8_to_console(handle, utf8)
 }

 fn write_valid_utf8_to_console(handle: c::HANDLE, utf8: &str) -> io::Result<usize> {
     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 const fn new() -> Stdin {
         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) {
             unsafe {
                 let handle = Handle::from_raw_handle(handle);
                 let ret = handle.read(buf);
                 handle.into_raw_handle(); // Don't close the handle
                 return ret;
             }
         }

         if buf.len() == 0 {
             return Ok(0);
         } else if buf.len() < 4 {
             return Err(io::Error::new_const(
                 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, a UTF-8 string can take 3 bytes for every `u16` of a 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 might 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_const(
                     io::ErrorKind::InvalidData,
                     &"Windows stdin in console mode does not support non-UTF-16 input; \
                      encountered unpaired surrogate",
                 ));
             }
         }
     }
     Ok(written)
 }

 impl IncompleteUtf8 {
     pub const fn new() -> IncompleteUtf8 {
         IncompleteUtf8 { bytes: [0; 4], len: 0 }
     }
 }

 impl Stdout {
     pub const fn new() -> Stdout {
         Stdout { incomplete_utf8: IncompleteUtf8::new() }
     }
 }

 impl io::Write for Stdout {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         write(c::STD_OUTPUT_HANDLE, buf, &mut self.incomplete_utf8)
     }

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

 impl Stderr {
     pub const fn new() -> Stderr {
         Stderr { incomplete_utf8: IncompleteUtf8::new() }
     }
 }

 impl io::Write for Stderr {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         write(c::STD_ERROR_HANDLE, buf, &mut self.incomplete_utf8)
     }

     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> {
     Some(Stderr::new())
 }
	#![unstable(issue = "none", feature = "windows_stdio")]

	use crate::char::decode_utf16;
	use crate::cmp;
	use crate::io;
	use crate::os::windows::io::{FromRawHandle, IntoRawHandle};
	use crate::ptr;
	use crate::str;
	use crate::sys::c;
	use crate::sys::cvt;
	use crate::sys::handle::Handle;
	use core::str::utf8_char_width;

	// 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 {
	incomplete_utf8: IncompleteUtf8,
	}

	pub struct Stderr {
	incomplete_utf8: IncompleteUtf8,
	}

	struct IncompleteUtf8 {
	bytes: [u8; 4],
	len: u8,
	}

	// 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],
	incomplete_utf8: &mut IncompleteUtf8,
	) -> io::Result<usize> {
	if data.is_empty() {
	return Ok(0);
	}

	let handle = get_handle(handle_id)?;
	if !is_console(handle) {
	unsafe {
	let handle = Handle::from_raw_handle(handle);
	let ret = handle.write(data);
	handle.into_raw_handle(); // Don't close the handle
	return ret;
	}
	}

	if incomplete_utf8.len > 0 {
	assert!(
	incomplete_utf8.len < 4,
	"Unexpected number of bytes for incomplete UTF-8 codepoint."
	);
	if data[0] >> 6 != 0b10 {
	// not a continuation byte - reject
	incomplete_utf8.len = 0;
	return Err(io::Error::new_const(
	io::ErrorKind::InvalidData,
	&"Windows stdio in console mode does not support writing non-UTF-8 byte sequences",
	));
	}
	incomplete_utf8.bytes[incomplete_utf8.len as usize] = data[0];
	incomplete_utf8.len += 1;
	let char_width = utf8_char_width(incomplete_utf8.bytes[0]);
	if (incomplete_utf8.len as usize) < char_width {
	// more bytes needed
	return Ok(1);
	}
	let s = str::from_utf8(&incomplete_utf8.bytes[0..incomplete_utf8.len as usize]);
	incomplete_utf8.len = 0;
	match s {
	Ok(s) => {
	assert_eq!(char_width, s.len());
	let written = write_valid_utf8_to_console(handle, s)?;
	assert_eq!(written, s.len()); // guaranteed by write_valid_utf8_to_console() for single codepoint writes
	return Ok(1);
	}
	Err(_) => {
	return Err(io::Error::new_const(
	io::ErrorKind::InvalidData,
	&"Windows stdio in console mode does not support writing non-UTF-8 byte sequences",
	));
	}
	}
	}

	// As the console is meant for presenting text, we assume bytes of `data` 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.
	// If the first byte is invalid it is either first byte of a multi-byte sequence but the
	// provided byte slice is too short or it is the first byte of an invalide multi-byte sequence.
	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 => {
	let first_byte_char_width = utf8_char_width(data[0]);
	if first_byte_char_width > 1 && data.len() < first_byte_char_width {
	incomplete_utf8.bytes[0] = data[0];
	incomplete_utf8.len = 1;
	return Ok(1);
	} else {
	return Err(io::Error::new_const(
	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(),
	};

	write_valid_utf8_to_console(handle, utf8)
	}

	fn write_valid_utf8_to_console(handle: c::HANDLE, utf8: &str) -> io::Result<usize> {
	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 const fn new() -> Stdin {
	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) {
	unsafe {
	let handle = Handle::from_raw_handle(handle);
	let ret = handle.read(buf);
	handle.into_raw_handle(); // Don't close the handle
	return ret;
	}
	}

	if buf.len() == 0 {
	return Ok(0);
	} else if buf.len() < 4 {
	return Err(io::Error::new_const(
	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, a UTF-8 string can take 3 bytes for every `u16` of a 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 might 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_const(
	io::ErrorKind::InvalidData,
	&"Windows stdin in console mode does not support non-UTF-16 input; \
	encountered unpaired surrogate",
	));
	}
	}
	}
	Ok(written)
	}

	impl IncompleteUtf8 {
	pub const fn new() -> IncompleteUtf8 {
	IncompleteUtf8 { bytes: [0; 4], len: 0 }
	}
	}

	impl Stdout {
	pub const fn new() -> Stdout {
	Stdout { incomplete_utf8: IncompleteUtf8::new() }
	}
	}

	impl io::Write for Stdout {
	fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
	write(c::STD_OUTPUT_HANDLE, buf, &mut self.incomplete_utf8)
	}

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

	impl Stderr {
	pub const fn new() -> Stderr {
	Stderr { incomplete_utf8: IncompleteUtf8::new() }
	}
	}

	impl io::Write for Stderr {
	fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
	write(c::STD_ERROR_HANDLE, buf, &mut self.incomplete_utf8)
	}

	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> {
	Some(Stderr::new())
	}