ndless 0.8.8

use crate::file_io::sys::cvt;
use crate::file_io::sys_common::AsInner;
use crate::io::{self, Initializer, Read};
use core::cmp;
use core::mem;
use core::sync::atomic::{AtomicBool, Ordering};

use crate::libc;
use alloc::vec::Vec;
use libc::{c_int, c_void, ssize_t};

#[derive(Debug)]
pub struct FileDesc {
	fd: c_int,
}

fn max_len() -> usize {
	// The maximum read limit on most posix-like systems is `SSIZE_MAX`,
	// with the man page quoting that if the count of bytes to read is
	// greater than `SSIZE_MAX` the result is "unspecified".
	//
	// On macOS, however, apparently the 64-bit libc is either buggy or
	// intentionally showing odd behavior by rejecting any read with a size
	// larger than or equal to INT_MAX. To handle both of these the read
	// size is capped on both platforms.
	if cfg!(target_os = "macos") {
		<c_int>::max_value() as usize - 1
	} else {
		<ssize_t>::max_value() as usize
	}
}

impl FileDesc {
	pub fn new(fd: c_int) -> FileDesc {
		FileDesc { fd }
	}

	pub fn raw(&self) -> c_int {
		self.fd
	}

	/// Extracts the actual file descriptor without closing it.
	pub fn into_raw(self) -> c_int {
		let fd = self.fd;
		mem::forget(self);
		fd
	}

	pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
		let ret = cvt(unsafe {
			libc::read(
				self.fd,
				buf.as_mut_ptr() as *mut c_void,
				cmp::min(buf.len(), max_len()),
			)
		})?;
		Ok(ret as usize)
	}

	pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
		let mut me = self;
		(&mut me).read_to_end(buf)
	}

	pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
		let ret = cvt(unsafe {
			libc::write(
				self.fd,
				buf.as_ptr() as *const c_void,
				cmp::min(buf.len(), max_len()),
			)
		})?;
		Ok(ret as usize)
	}

	pub fn set_cloexec(&self) -> io::Result<()> {
		unsafe {
			let previous = cvt(libc::fcntl(self.fd, libc::F_GETFD))?;
			let new = previous | libc::FD_CLOEXEC;
			if new != previous {
				cvt(libc::fcntl(self.fd, libc::F_SETFD, new))?;
			}
			Ok(())
		}
	}

	pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
		unsafe {
			let previous = cvt(libc::fcntl(self.fd, libc::F_GETFL))?;
			let new = if nonblocking {
				previous | libc::O_NONBLOCK
			} else {
				previous & !libc::O_NONBLOCK
			};
			if new != previous {
				cvt(libc::fcntl(self.fd, libc::F_SETFL, new))?;
			}
			Ok(())
		}
	}

	pub fn duplicate(&self) -> io::Result<FileDesc> {
		// We want to atomically duplicate this file descriptor and set the
		// CLOEXEC flag, and currently that's done via F_DUPFD_CLOEXEC. This
		// flag, however, isn't supported on older Linux kernels (earlier than
		// 2.6.24).
		//
		// To detect this and ensure that CLOEXEC is still set, we
		// follow a strategy similar to musl [1] where if passing
		// F_DUPFD_CLOEXEC causes `fcntl` to return EINVAL it means it's not
		// supported (the third parameter, 0, is always valid), so we stop
		// trying that.
		//
		// Also note that Android doesn't have F_DUPFD_CLOEXEC, but get it to
		// resolve so we at least compile this.
		//
		// [1]: http://comments.gmane.org/gmane.linux.lib.musl.general/2963
		use libc::F_DUPFD as F_DUPFD_CLOEXEC;

		let make_filedesc = |fd| {
			let fd = FileDesc::new(fd);
			fd.set_cloexec()?;
			Ok(fd)
		};
		static TRY_CLOEXEC: AtomicBool = AtomicBool::new(!cfg!(target_os = "android"));
		let fd = self.raw();
		if TRY_CLOEXEC.load(Ordering::Relaxed) {
			match cvt(unsafe { libc::fcntl(fd, F_DUPFD_CLOEXEC, 0) }) {
				// We *still* call the `set_cloexec` method as apparently some
				// linux kernel at some point stopped setting CLOEXEC even
				// though it reported doing so on F_DUPFD_CLOEXEC.
				Ok(fd) => {
					return Ok(if cfg!(target_os = "linux") {
						make_filedesc(fd)?
					} else {
						FileDesc::new(fd)
					})
				}
				Err(ref e) if e.raw_os_error() == Some(libc::EINVAL) => {
					TRY_CLOEXEC.store(false, Ordering::Relaxed);
				}
				Err(e) => return Err(e),
			}
		}
		cvt(unsafe { libc::fcntl(fd, libc::F_DUPFD, 0) }).and_then(make_filedesc)
	}
}

impl<'a> Read for &'a FileDesc {
	fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
		(**self).read(buf)
	}

	#[inline]
	unsafe fn initializer(&self) -> Initializer {
		Initializer::nop()
	}
}

impl AsInner<c_int> for FileDesc {
	fn as_inner(&self) -> &c_int {
		&self.fd
	}
}

impl Drop for FileDesc {
	fn drop(&mut self) {
		// Note that errors are ignored when closing a file descriptor. The
		// reason for this is that if an error occurs we don't actually know if
		// the file descriptor was closed or not, and if we retried (for
		// something like EINTR), we might close another valid file descriptor
		// opened after we closed ours.
		let _ = unsafe { libc::close(self.fd) };
	}
}