//! Tokio support for [Windows named pipes].
//!
//! [Windows named pipes]: https://docs.microsoft.com/en-us/windows/win32/ipc/named-pipes

use std::ffi::c_void;
use std::ffi::OsStr;
use std::io;
use std::pin::Pin;
use std::ptr;
use std::task::{Context, Poll};

use crate::io::{AsyncRead, AsyncWrite, Interest, PollEvented, ReadBuf};
use crate::os::windows::io::{AsRawHandle, FromRawHandle, RawHandle};

// Hide imports which are not used when generating documentation.
#[cfg(not(docsrs))]
mod doc {
    pub(super) use crate::os::windows::ffi::OsStrExt;
    pub(super) use crate::winapi::shared::minwindef::{DWORD, FALSE};
    pub(super) use crate::winapi::um::fileapi;
    pub(super) use crate::winapi::um::handleapi;
    pub(super) use crate::winapi::um::namedpipeapi;
    pub(super) use crate::winapi::um::winbase;
    pub(super) use crate::winapi::um::winnt;

    pub(super) use mio::windows as mio_windows;
}

// NB: none of these shows up in public API, so don't document them.
#[cfg(docsrs)]
mod doc {
    pub type DWORD = crate::doc::NotDefinedHere;

    pub(super) mod mio_windows {
        pub type NamedPipe = crate::doc::NotDefinedHere;
    }
}

use self::doc::*;

/// A [Windows named pipe] server.
///
/// Accepting client connections involves creating a server with
/// [`ServerOptions::create`] and waiting for clients to connect using
/// [`NamedPipeServer::connect`].
///
/// To avoid having clients sporadically fail with
/// [`std::io::ErrorKind::NotFound`] when they connect to a server, we must
/// ensure that at least one server instance is available at all times. This
/// means that the typical listen loop for a server is a bit involved, because
/// we have to ensure that we never drop a server accidentally while a client
/// might connect.
///
/// So a correctly implemented server looks like this:
///
/// ```no_run
/// use std::io;
/// use tokio::net::windows::named_pipe::ServerOptions;
///
/// const PIPE_NAME: &str = r"\\.\pipe\named-pipe-idiomatic-server";
///
/// # #[tokio::main] async fn main() -> std::io::Result<()> {
/// // The first server needs to be constructed early so that clients can
/// // be correctly connected. Otherwise calling .wait will cause the client to
/// // error.
/// //
/// // Here we also make use of `first_pipe_instance`, which will ensure that
/// // there are no other servers up and running already.
/// let mut server = ServerOptions::new()
///     .first_pipe_instance(true)
///     .create(PIPE_NAME)?;
///
/// // Spawn the server loop.
/// let server = tokio::spawn(async move {
///     loop {
///         // Wait for a client to connect.
///         let connected = server.connect().await?;
///
///         // Construct the next server to be connected before sending the one
///         // we already have of onto a task. This ensures that the server
///         // isn't closed (after it's done in the task) before a new one is
///         // available. Otherwise the client might error with
///         // `io::ErrorKind::NotFound`.
///         server = ServerOptions::new().create(PIPE_NAME)?;
///
///         let client = tokio::spawn(async move {
///             /* use the connected client */
/// #           Ok::<_, std::io::Error>(())
///         });
/// #       if true { break } // needed for type inference to work
///     }
///
///     Ok::<_, io::Error>(())
/// });
///
/// /* do something else not server related here */
/// # Ok(()) }
/// ```
///
/// [`ERROR_PIPE_BUSY`]: crate::winapi::shared::winerror::ERROR_PIPE_BUSY
/// [Windows named pipe]: https://docs.microsoft.com/en-us/windows/win32/ipc/named-pipes
#[derive(Debug)]
pub struct NamedPipeServer {
    io: PollEvented<mio_windows::NamedPipe>,
}

impl NamedPipeServer {
    /// Construct a new named pipe server from the specified raw handle.
    ///
    /// This function will consume ownership of the handle given, passing
    /// responsibility for closing the handle to the returned object.
    ///
    /// This function is also unsafe as the primitives currently returned have
    /// the contract that they are the sole owner of the file descriptor they
    /// are wrapping. Usage of this function could accidentally allow violating
    /// this contract which can cause memory unsafety in code that relies on it
    /// being true.
    ///
    /// # Errors
    ///
    /// This errors if called outside of a [Tokio Runtime], or in a runtime that
    /// has not [enabled I/O], or if any OS-specific I/O errors occur.
    ///
    /// [Tokio Runtime]: crate::runtime::Runtime
    /// [enabled I/O]: crate::runtime::Builder::enable_io
    pub unsafe fn from_raw_handle(handle: RawHandle) -> io::Result<Self> {
        let named_pipe = mio_windows::NamedPipe::from_raw_handle(handle);

        Ok(Self {
            io: PollEvented::new(named_pipe)?,
        })
    }

    /// Retrieves information about the named pipe the server is associated
    /// with.
    ///
    /// ```no_run
    /// use tokio::net::windows::named_pipe::{PipeEnd, PipeMode, ServerOptions};
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-server-info";
    ///
    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
    /// let server = ServerOptions::new()
    ///     .pipe_mode(PipeMode::Message)
    ///     .max_instances(5)
    ///     .create(PIPE_NAME)?;
    ///
    /// let server_info = server.info()?;
    ///
    /// assert_eq!(server_info.end, PipeEnd::Server);
    /// assert_eq!(server_info.mode, PipeMode::Message);
    /// assert_eq!(server_info.max_instances, 5);
    /// # Ok(()) }
    /// ```
    pub fn info(&self) -> io::Result<PipeInfo> {
        // Safety: we're ensuring the lifetime of the named pipe.
        unsafe { named_pipe_info(self.io.as_raw_handle()) }
    }

    /// Enables a named pipe server process to wait for a client process to
    /// connect to an instance of a named pipe. A client process connects by
    /// creating a named pipe with the same name.
    ///
    /// This corresponds to the [`ConnectNamedPipe`] system call.
    ///
    /// [`ConnectNamedPipe`]: https://docs.microsoft.com/en-us/windows/win32/api/namedpipeapi/nf-namedpipeapi-connectnamedpipe
    ///
    /// ```no_run
    /// use tokio::net::windows::named_pipe::ServerOptions;
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\mynamedpipe";
    ///
    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
    /// let pipe = ServerOptions::new().create(PIPE_NAME)?;
    ///
    /// // Wait for a client to connect.
    /// pipe.connect().await?;
    ///
    /// // Use the connected client...
    /// # Ok(()) }
    /// ```
    pub async fn connect(&self) -> io::Result<()> {
        loop {
            match self.io.connect() {
                Ok(()) => break,
                Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
                    self.io.registration().readiness(Interest::WRITABLE).await?;
                }
                Err(e) => return Err(e),
            }
        }

        Ok(())
    }

    /// Disconnects the server end of a named pipe instance from a client
    /// process.
    ///
    /// ```
    /// use tokio::io::AsyncWriteExt;
    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
    /// use winapi::shared::winerror;
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-disconnect";
    ///
    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
    /// let server = ServerOptions::new()
    ///     .create(PIPE_NAME)?;
    ///
    /// let mut client = ClientOptions::new()
    ///     .open(PIPE_NAME)?;
    ///
    /// // Wait for a client to become connected.
    /// server.connect().await?;
    ///
    /// // Forcibly disconnect the client.
    /// server.disconnect()?;
    ///
    /// // Write fails with an OS-specific error after client has been
    /// // disconnected.
    /// let e = client.write(b"ping").await.unwrap_err();
    /// assert_eq!(e.raw_os_error(), Some(winerror::ERROR_PIPE_NOT_CONNECTED as i32));
    /// # Ok(()) }
    /// ```
    pub fn disconnect(&self) -> io::Result<()> {
        self.io.disconnect()
    }
}

impl AsyncRead for NamedPipeServer {
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        unsafe { self.io.poll_read(cx, buf) }
    }
}

impl AsyncWrite for NamedPipeServer {
    fn poll_write(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        self.io.poll_write(cx, buf)
    }

    fn poll_write_vectored(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        bufs: &[io::IoSlice<'_>],
    ) -> Poll<io::Result<usize>> {
        self.io.poll_write_vectored(cx, bufs)
    }

    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        Poll::Ready(Ok(()))
    }

    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        self.poll_flush(cx)
    }
}

impl AsRawHandle for NamedPipeServer {
    fn as_raw_handle(&self) -> RawHandle {
        self.io.as_raw_handle()
    }
}

/// A [Windows named pipe] client.
///
/// Constructed using [`ClientOptions::open`].
///
/// Connecting a client correctly involves a few steps. When connecting through
/// [`ClientOptions::open`], it might error indicating one of two things:
///
/// * [`std::io::ErrorKind::NotFound`] - There is no server available.
/// * [`ERROR_PIPE_BUSY`] - There is a server available, but it is busy. Sleep
///   for a while and try again.
///
/// So a correctly implemented client looks like this:
///
/// ```no_run
/// use std::time::Duration;
/// use tokio::net::windows::named_pipe::ClientOptions;
/// use tokio::time;
/// use winapi::shared::winerror;
///
/// const PIPE_NAME: &str = r"\\.\pipe\named-pipe-idiomatic-client";
///
/// # #[tokio::main] async fn main() -> std::io::Result<()> {
/// let client = loop {
///     match ClientOptions::new().open(PIPE_NAME) {
///         Ok(client) => break client,
///         Err(e) if e.raw_os_error() == Some(winerror::ERROR_PIPE_BUSY as i32) => (),
///         Err(e) => return Err(e),
///     }
///
///     time::sleep(Duration::from_millis(50)).await;
/// };
///
/// /* use the connected client */
/// # Ok(()) }
/// ```
///
/// [`ERROR_PIPE_BUSY`]: crate::winapi::shared::winerror::ERROR_PIPE_BUSY
/// [Windows named pipe]: https://docs.microsoft.com/en-us/windows/win32/ipc/named-pipes
#[derive(Debug)]
pub struct NamedPipeClient {
    io: PollEvented<mio_windows::NamedPipe>,
}

impl NamedPipeClient {
    /// Construct a new named pipe client from the specified raw handle.
    ///
    /// This function will consume ownership of the handle given, passing
    /// responsibility for closing the handle to the returned object.
    ///
    /// This function is also unsafe as the primitives currently returned have
    /// the contract that they are the sole owner of the file descriptor they
    /// are wrapping. Usage of this function could accidentally allow violating
    /// this contract which can cause memory unsafety in code that relies on it
    /// being true.
    ///
    /// # Errors
    ///
    /// This errors if called outside of a [Tokio Runtime], or in a runtime that
    /// has not [enabled I/O], or if any OS-specific I/O errors occur.
    ///
    /// [Tokio Runtime]: crate::runtime::Runtime
    /// [enabled I/O]: crate::runtime::Builder::enable_io
    pub unsafe fn from_raw_handle(handle: RawHandle) -> io::Result<Self> {
        let named_pipe = mio_windows::NamedPipe::from_raw_handle(handle);

        Ok(Self {
            io: PollEvented::new(named_pipe)?,
        })
    }

    /// Retrieves information about the named pipe the client is associated
    /// with.
    ///
    /// ```no_run
    /// use tokio::net::windows::named_pipe::{ClientOptions, PipeEnd, PipeMode};
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-client-info";
    ///
    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
    /// let client = ClientOptions::new()
    ///     .open(PIPE_NAME)?;
    ///
    /// let client_info = client.info()?;
    ///
    /// assert_eq!(client_info.end, PipeEnd::Client);
    /// assert_eq!(client_info.mode, PipeMode::Message);
    /// assert_eq!(client_info.max_instances, 5);
    /// # Ok(()) }
    /// ```
    pub fn info(&self) -> io::Result<PipeInfo> {
        // Safety: we're ensuring the lifetime of the named pipe.
        unsafe { named_pipe_info(self.io.as_raw_handle()) }
    }
}

impl AsyncRead for NamedPipeClient {
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        unsafe { self.io.poll_read(cx, buf) }
    }
}

impl AsyncWrite for NamedPipeClient {
    fn poll_write(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        self.io.poll_write(cx, buf)
    }

    fn poll_write_vectored(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        bufs: &[io::IoSlice<'_>],
    ) -> Poll<io::Result<usize>> {
        self.io.poll_write_vectored(cx, bufs)
    }

    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        Poll::Ready(Ok(()))
    }

    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        self.poll_flush(cx)
    }
}

impl AsRawHandle for NamedPipeClient {
    fn as_raw_handle(&self) -> RawHandle {
        self.io.as_raw_handle()
    }
}

// Helper to set a boolean flag as a bitfield.
macro_rules! bool_flag {
    ($f:expr, $t:expr, $flag:expr) => {{
        let current = $f;

        if $t {
            $f = current | $flag;
        } else {
            $f = current & !$flag;
        };
    }};
}

/// A builder structure for construct a named pipe with named pipe-specific
/// options. This is required to use for named pipe servers who wants to modify
/// pipe-related options.
///
/// See [`ServerOptions::create`].
#[derive(Debug, Clone)]
pub struct ServerOptions {
    open_mode: DWORD,
    pipe_mode: DWORD,
    max_instances: DWORD,
    out_buffer_size: DWORD,
    in_buffer_size: DWORD,
    default_timeout: DWORD,
}

impl ServerOptions {
    /// Creates a new named pipe builder with the default settings.
    ///
    /// ```
    /// use tokio::net::windows::named_pipe::ServerOptions;
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-new";
    ///
    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
    /// let server = ServerOptions::new().create(PIPE_NAME)?;
    /// # Ok(()) }
    /// ```
    pub fn new() -> ServerOptions {
        ServerOptions {
            open_mode: winbase::PIPE_ACCESS_DUPLEX | winbase::FILE_FLAG_OVERLAPPED,
            pipe_mode: winbase::PIPE_TYPE_BYTE | winbase::PIPE_REJECT_REMOTE_CLIENTS,
            max_instances: winbase::PIPE_UNLIMITED_INSTANCES,
            out_buffer_size: 65536,
            in_buffer_size: 65536,
            default_timeout: 0,
        }
    }

    /// The pipe mode.
    ///
    /// The default pipe mode is [`PipeMode::Byte`]. See [`PipeMode`] for
    /// documentation of what each mode means.
    ///
    /// This corresponding to specifying [`dwPipeMode`].
    ///
    /// [`dwPipeMode`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
    pub fn pipe_mode(&mut self, pipe_mode: PipeMode) -> &mut Self {
        self.pipe_mode = match pipe_mode {
            PipeMode::Byte => winbase::PIPE_TYPE_BYTE,
            PipeMode::Message => winbase::PIPE_TYPE_MESSAGE,
        };

        self
    }

    /// The flow of data in the pipe goes from client to server only.
    ///
    /// This corresponds to setting [`PIPE_ACCESS_INBOUND`].
    ///
    /// [`PIPE_ACCESS_INBOUND`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea#pipe_access_inbound
    ///
    /// # Errors
    ///
    /// Server side prevents connecting by denying inbound access, client errors
    /// with [`std::io::ErrorKind::PermissionDenied`] when attempting to create
    /// the connection.
    ///
    /// ```
    /// use std::io;
    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-access-inbound-err1";
    ///
    /// # #[tokio::main] async fn main() -> io::Result<()> {
    /// let _server = ServerOptions::new()
    ///     .access_inbound(false)
    ///     .create(PIPE_NAME)?;
    ///
    /// let e = ClientOptions::new()
    ///     .open(PIPE_NAME)
    ///     .unwrap_err();
    ///
    /// assert_eq!(e.kind(), io::ErrorKind::PermissionDenied);
    /// # Ok(()) }
    /// ```
    ///
    /// Disabling writing allows a client to connect, but errors with
    /// [`std::io::ErrorKind::PermissionDenied`] if a write is attempted.
    ///
    /// ```
    /// use std::io;
    /// use tokio::io::AsyncWriteExt;
    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-access-inbound-err2";
    ///
    /// # #[tokio::main] async fn main() -> io::Result<()> {
    /// let server = ServerOptions::new()
    ///     .access_inbound(false)
    ///     .create(PIPE_NAME)?;
    ///
    /// let mut client = ClientOptions::new()
    ///     .write(false)
    ///     .open(PIPE_NAME)?;
    ///
    /// server.connect().await?;
    ///
    /// let e = client.write(b"ping").await.unwrap_err();
    /// assert_eq!(e.kind(), io::ErrorKind::PermissionDenied);
    /// # Ok(()) }
    /// ```
    ///
    /// # Examples
    ///
    /// A unidirectional named pipe that only supports server-to-client
    /// communication.
    ///
    /// ```
    /// use std::io;
    /// use tokio::io::{AsyncReadExt, AsyncWriteExt};
    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-access-inbound";
    ///
    /// # #[tokio::main] async fn main() -> io::Result<()> {
    /// let mut server = ServerOptions::new()
    ///     .access_inbound(false)
    ///     .create(PIPE_NAME)?;
    ///
    /// let mut client = ClientOptions::new()
    ///     .write(false)
    ///     .open(PIPE_NAME)?;
    ///
    /// server.connect().await?;
    ///
    /// let write = server.write_all(b"ping");
    ///
    /// let mut buf = [0u8; 4];
    /// let read = client.read_exact(&mut buf);
    ///
    /// let ((), read) = tokio::try_join!(write, read)?;
    ///
    /// assert_eq!(read, 4);
    /// assert_eq!(&buf[..], b"ping");
    /// # Ok(()) }
    /// ```
    pub fn access_inbound(&mut self, allowed: bool) -> &mut Self {
        bool_flag!(self.open_mode, allowed, winbase::PIPE_ACCESS_INBOUND);
        self
    }

    /// The flow of data in the pipe goes from server to client only.
    ///
    /// This corresponds to setting [`PIPE_ACCESS_OUTBOUND`].
    ///
    /// [`PIPE_ACCESS_OUTBOUND`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea#pipe_access_outbound
    ///
    /// # Errors
    ///
    /// Server side prevents connecting by denying outbound access, client
    /// errors with [`std::io::ErrorKind::PermissionDenied`] when attempting to
    /// create the connection.
    ///
    /// ```
    /// use std::io;
    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-access-outbound-err1";
    ///
    /// # #[tokio::main] async fn main() -> io::Result<()> {
    /// let server = ServerOptions::new()
    ///     .access_outbound(false)
    ///     .create(PIPE_NAME)?;
    ///
    /// let e = ClientOptions::new()
    ///     .open(PIPE_NAME)
    ///     .unwrap_err();
    ///
    /// assert_eq!(e.kind(), io::ErrorKind::PermissionDenied);
    /// # Ok(()) }
    /// ```
    ///
    /// Disabling reading allows a client to connect, but attempting to read
    /// will error with [`std::io::ErrorKind::PermissionDenied`].
    ///
    /// ```
    /// use std::io;
    /// use tokio::io::AsyncReadExt;
    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-access-outbound-err2";
    ///
    /// # #[tokio::main] async fn main() -> io::Result<()> {
    /// let server = ServerOptions::new()
    ///     .access_outbound(false)
    ///     .create(PIPE_NAME)?;
    ///
    /// let mut client = ClientOptions::new()
    ///     .read(false)
    ///     .open(PIPE_NAME)?;
    ///
    /// server.connect().await?;
    ///
    /// let mut buf = [0u8; 4];
    /// let e = client.read(&mut buf).await.unwrap_err();
    /// assert_eq!(e.kind(), io::ErrorKind::PermissionDenied);
    /// # Ok(()) }
    /// ```
    ///
    /// # Examples
    ///
    /// A unidirectional named pipe that only supports client-to-server
    /// communication.
    ///
    /// ```
    /// use tokio::io::{AsyncReadExt, AsyncWriteExt};
    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-access-outbound";
    ///
    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
    /// let mut server = ServerOptions::new()
    ///     .access_outbound(false)
    ///     .create(PIPE_NAME)?;
    ///
    /// let mut client = ClientOptions::new()
    ///     .read(false)
    ///     .open(PIPE_NAME)?;
    ///
    /// server.connect().await?;
    ///
    /// let write = client.write_all(b"ping");
    ///
    /// let mut buf = [0u8; 4];
    /// let read = server.read_exact(&mut buf);
    ///
    /// let ((), read) = tokio::try_join!(write, read)?;
    ///
    /// println!("done reading and writing");
    ///
    /// assert_eq!(read, 4);
    /// assert_eq!(&buf[..], b"ping");
    /// # Ok(()) }
    /// ```
    pub fn access_outbound(&mut self, allowed: bool) -> &mut Self {
        bool_flag!(self.open_mode, allowed, winbase::PIPE_ACCESS_OUTBOUND);
        self
    }

    /// If you attempt to create multiple instances of a pipe with this flag
    /// set, creation of the first server instance succeeds, but creation of any
    /// subsequent instances will fail with
    /// [`std::io::ErrorKind::PermissionDenied`].
    ///
    /// This option is intended to be used with servers that want to ensure that
    /// they are the only process listening for clients on a given named pipe.
    /// This is accomplished by enabling it for the first server instance
    /// created in a process.
    ///
    /// This corresponds to setting [`FILE_FLAG_FIRST_PIPE_INSTANCE`].
    ///
    /// # Errors
    ///
    /// If this option is set and more than one instance of the server for a
    /// given named pipe exists, calling [`create`] will fail with
    /// [`std::io::ErrorKind::PermissionDenied`].
    ///
    /// ```
    /// use std::io;
    /// use tokio::net::windows::named_pipe::ServerOptions;
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-first-instance-error";
    ///
    /// # #[tokio::main] async fn main() -> io::Result<()> {
    /// let server1 = ServerOptions::new()
    ///     .first_pipe_instance(true)
    ///     .create(PIPE_NAME)?;
    ///
    /// // Second server errs, since it's not the first instance.
    /// let e = ServerOptions::new()
    ///     .first_pipe_instance(true)
    ///     .create(PIPE_NAME)
    ///     .unwrap_err();
    ///
    /// assert_eq!(e.kind(), io::ErrorKind::PermissionDenied);
    /// # Ok(()) }
    /// ```
    ///
    /// # Examples
    ///
    /// ```
    /// use std::io;
    /// use tokio::net::windows::named_pipe::ServerOptions;
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-first-instance";
    ///
    /// # #[tokio::main] async fn main() -> io::Result<()> {
    /// let mut builder = ServerOptions::new();
    /// builder.first_pipe_instance(true);
    ///
    /// let server = builder.create(PIPE_NAME)?;
    /// let e = builder.create(PIPE_NAME).unwrap_err();
    /// assert_eq!(e.kind(), io::ErrorKind::PermissionDenied);
    /// drop(server);
    ///
    /// // OK: since, we've closed the other instance.
    /// let _server2 = builder.create(PIPE_NAME)?;
    /// # Ok(()) }
    /// ```
    ///
    /// [`create`]: ServerOptions::create
    /// [`FILE_FLAG_FIRST_PIPE_INSTANCE`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea#pipe_first_pipe_instance
    pub fn first_pipe_instance(&mut self, first: bool) -> &mut Self {
        bool_flag!(
            self.open_mode,
            first,
            winbase::FILE_FLAG_FIRST_PIPE_INSTANCE
        );
        self
    }

    /// Indicates whether this server can accept remote clients or not. Remote
    /// clients are disabled by default.
    ///
    /// This corresponds to setting [`PIPE_REJECT_REMOTE_CLIENTS`].
    ///
    /// [`PIPE_REJECT_REMOTE_CLIENTS`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea#pipe_reject_remote_clients
    pub fn reject_remote_clients(&mut self, reject: bool) -> &mut Self {
        bool_flag!(self.pipe_mode, reject, winbase::PIPE_REJECT_REMOTE_CLIENTS);
        self
    }

    /// The maximum number of instances that can be created for this pipe. The
    /// first instance of the pipe can specify this value; the same number must
    /// be specified for other instances of the pipe. Acceptable values are in
    /// the range 1 through 254. The default value is unlimited.
    ///
    /// This corresponds to specifying [`nMaxInstances`].
    ///
    /// [`nMaxInstances`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
    ///
    /// # Errors
    ///
    /// The same numbers of `max_instances` have to be used by all servers. Any
    /// additional servers trying to be built which uses a mismatching value
    /// might error.
    ///
    /// ```
    /// use std::io;
    /// use tokio::net::windows::named_pipe::{ServerOptions, ClientOptions};
    /// use winapi::shared::winerror;
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-max-instances";
    ///
    /// # #[tokio::main] async fn main() -> io::Result<()> {
    /// let mut server = ServerOptions::new();
    /// server.max_instances(2);
    ///
    /// let s1 = server.create(PIPE_NAME)?;
    /// let c1 = ClientOptions::new().open(PIPE_NAME);
    ///
    /// let s2 = server.create(PIPE_NAME)?;
    /// let c2 = ClientOptions::new().open(PIPE_NAME);
    ///
    /// // Too many servers!
    /// let e = server.create(PIPE_NAME).unwrap_err();
    /// assert_eq!(e.raw_os_error(), Some(winerror::ERROR_PIPE_BUSY as i32));
    ///
    /// // Still too many servers even if we specify a higher value!
    /// let e = server.max_instances(100).create(PIPE_NAME).unwrap_err();
    /// assert_eq!(e.raw_os_error(), Some(winerror::ERROR_PIPE_BUSY as i32));
    /// # Ok(()) }
    /// ```
    ///
    /// # Panics
    ///
    /// This function will panic if more than 254 instances are specified. If
    /// you do not wish to set an instance limit, leave it unspecified.
    ///
    /// ```should_panic
    /// use tokio::net::windows::named_pipe::ServerOptions;
    ///
    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
    /// let builder = ServerOptions::new().max_instances(255);
    /// # Ok(()) }
    /// ```
    pub fn max_instances(&mut self, instances: usize) -> &mut Self {
        assert!(instances < 255, "cannot specify more than 254 instances");
        self.max_instances = instances as DWORD;
        self
    }

    /// The number of bytes to reserve for the output buffer.
    ///
    /// This corresponds to specifying [`nOutBufferSize`].
    ///
    /// [`nOutBufferSize`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
    pub fn out_buffer_size(&mut self, buffer: u32) -> &mut Self {
        self.out_buffer_size = buffer as DWORD;
        self
    }

    /// The number of bytes to reserve for the input buffer.
    ///
    /// This corresponds to specifying [`nInBufferSize`].
    ///
    /// [`nInBufferSize`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
    pub fn in_buffer_size(&mut self, buffer: u32) -> &mut Self {
        self.in_buffer_size = buffer as DWORD;
        self
    }

    /// Create the named pipe identified by `addr` for use as a server.
    ///
    /// This uses the [`CreateNamedPipe`] function.
    ///
    /// [`CreateNamedPipe`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
    ///
    /// # Errors
    ///
    /// This errors if called outside of a [Tokio Runtime], or in a runtime that
    /// has not [enabled I/O], or if any OS-specific I/O errors occur.
    ///
    /// [Tokio Runtime]: crate::runtime::Runtime
    /// [enabled I/O]: crate::runtime::Builder::enable_io
    ///
    /// # Examples
    ///
    /// ```
    /// use tokio::net::windows::named_pipe::ServerOptions;
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-create";
    ///
    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
    /// let server = ServerOptions::new().create(PIPE_NAME)?;
    /// # Ok(()) }
    /// ```
    pub fn create(&self, addr: impl AsRef<OsStr>) -> io::Result<NamedPipeServer> {
        // Safety: We're calling create_with_security_attributes_raw w/ a null
        // pointer which disables it.
        unsafe { self.create_with_security_attributes_raw(addr, ptr::null_mut()) }
    }

    /// Create the named pipe identified by `addr` for use as a server.
    ///
    /// This is the same as [`create`] except that it supports providing the raw
    /// pointer to a structure of [`SECURITY_ATTRIBUTES`] which will be passed
    /// as the `lpSecurityAttributes` argument to [`CreateFile`].
    ///
    /// # Errors
    ///
    /// This errors if called outside of a [Tokio Runtime], or in a runtime that
    /// has not [enabled I/O], or if any OS-specific I/O errors occur.
    ///
    /// [Tokio Runtime]: crate::runtime::Runtime
    /// [enabled I/O]: crate::runtime::Builder::enable_io
    ///
    /// # Safety
    ///
    /// The `attrs` argument must either be null or point at a valid instance of
    /// the [`SECURITY_ATTRIBUTES`] structure. If the argument is null, the
    /// behavior is identical to calling the [`create`] method.
    ///
    /// [`create`]: ServerOptions::create
    /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilew
    /// [`SECURITY_ATTRIBUTES`]: crate::winapi::um::minwinbase::SECURITY_ATTRIBUTES
    pub unsafe fn create_with_security_attributes_raw(
        &self,
        addr: impl AsRef<OsStr>,
        attrs: *mut c_void,
    ) -> io::Result<NamedPipeServer> {
        let addr = encode_addr(addr);

        let h = namedpipeapi::CreateNamedPipeW(
            addr.as_ptr(),
            self.open_mode,
            self.pipe_mode,
            self.max_instances,
            self.out_buffer_size,
            self.in_buffer_size,
            self.default_timeout,
            attrs as *mut _,
        );

        if h == handleapi::INVALID_HANDLE_VALUE {
            return Err(io::Error::last_os_error());
        }

        NamedPipeServer::from_raw_handle(h)
    }
}

/// A builder suitable for building and interacting with named pipes from the
/// client side.
///
/// See [`ClientOptions::open`].
#[derive(Debug, Clone)]
pub struct ClientOptions {
    desired_access: DWORD,
    security_qos_flags: DWORD,
}

impl ClientOptions {
    /// Creates a new named pipe builder with the default settings.
    ///
    /// ```
    /// use tokio::net::windows::named_pipe::{ServerOptions, ClientOptions};
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-client-new";
    ///
    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
    /// // Server must be created in order for the client creation to succeed.
    /// let server = ServerOptions::new().create(PIPE_NAME)?;
    /// let client = ClientOptions::new().open(PIPE_NAME)?;
    /// # Ok(()) }
    /// ```
    pub fn new() -> Self {
        Self {
            desired_access: winnt::GENERIC_READ | winnt::GENERIC_WRITE,
            security_qos_flags: winbase::SECURITY_IDENTIFICATION | winbase::SECURITY_SQOS_PRESENT,
        }
    }

    /// If the client supports reading data. This is enabled by default.
    ///
    /// This corresponds to setting [`GENERIC_READ`] in the call to [`CreateFile`].
    ///
    /// [`GENERIC_READ`]: https://docs.microsoft.com/en-us/windows/win32/secauthz/generic-access-rights
    /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilew
    pub fn read(&mut self, allowed: bool) -> &mut Self {
        bool_flag!(self.desired_access, allowed, winnt::GENERIC_READ);
        self
    }

    /// If the created pipe supports writing data. This is enabled by default.
    ///
    /// This corresponds to setting [`GENERIC_WRITE`] in the call to [`CreateFile`].
    ///
    /// [`GENERIC_WRITE`]: https://docs.microsoft.com/en-us/windows/win32/secauthz/generic-access-rights
    /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilew
    pub fn write(&mut self, allowed: bool) -> &mut Self {
        bool_flag!(self.desired_access, allowed, winnt::GENERIC_WRITE);
        self
    }

    /// Sets qos flags which are combined with other flags and attributes in the
    /// call to [`CreateFile`].
    ///
    /// By default `security_qos_flags` is set to [`SECURITY_IDENTIFICATION`],
    /// calling this function would override that value completely with the
    /// argument specified.
    ///
    /// When `security_qos_flags` is not set, a malicious program can gain the
    /// elevated privileges of a privileged Rust process when it allows opening
    /// user-specified paths, by tricking it into opening a named pipe. So
    /// arguably `security_qos_flags` should also be set when opening arbitrary
    /// paths. However the bits can then conflict with other flags, specifically
    /// `FILE_FLAG_OPEN_NO_RECALL`.
    ///
    /// For information about possible values, see [Impersonation Levels] on the
    /// Windows Dev Center site. The `SECURITY_SQOS_PRESENT` flag is set
    /// automatically when using this method.
    ///
    /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
    /// [`SECURITY_IDENTIFICATION`]: crate::winapi::um::winbase::SECURITY_IDENTIFICATION
    /// [Impersonation Levels]: https://docs.microsoft.com/en-us/windows/win32/api/winnt/ne-winnt-security_impersonation_level
    pub fn security_qos_flags(&mut self, flags: u32) -> &mut Self {
        // See: https://github.com/rust-lang/rust/pull/58216
        self.security_qos_flags = flags | winbase::SECURITY_SQOS_PRESENT;
        self
    }

    /// Open the named pipe identified by `addr`.
    ///
    /// This opens the client using [`CreateFile`] with the
    /// `dwCreationDisposition` option set to `OPEN_EXISTING`.
    ///
    /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
    ///
    /// # Errors
    ///
    /// This errors if called outside of a [Tokio Runtime], or in a runtime that
    /// has not [enabled I/O], or if any OS-specific I/O errors occur.
    ///
    /// There are a few errors you need to take into account when creating a
    /// named pipe on the client side:
    ///
    /// * [`std::io::ErrorKind::NotFound`] - This indicates that the named pipe
    ///   does not exist. Presumably the server is not up.
    /// * [`ERROR_PIPE_BUSY`] - This error is raised when the named pipe exists,
    ///   but the server is not currently waiting for a connection. Please see the
    ///   examples for how to check for this error.
    ///
    /// [`ERROR_PIPE_BUSY`]: crate::winapi::shared::winerror::ERROR_PIPE_BUSY
    /// [`winapi`]: crate::winapi
    /// [enabled I/O]: crate::runtime::Builder::enable_io
    /// [Tokio Runtime]: crate::runtime::Runtime
    ///
    /// A connect loop that waits until a socket becomes available looks like
    /// this:
    ///
    /// ```no_run
    /// use std::time::Duration;
    /// use tokio::net::windows::named_pipe::ClientOptions;
    /// use tokio::time;
    /// use winapi::shared::winerror;
    ///
    /// const PIPE_NAME: &str = r"\\.\pipe\mynamedpipe";
    ///
    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
    /// let client = loop {
    ///     match ClientOptions::new().open(PIPE_NAME) {
    ///         Ok(client) => break client,
    ///         Err(e) if e.raw_os_error() == Some(winerror::ERROR_PIPE_BUSY as i32) => (),
    ///         Err(e) => return Err(e),
    ///     }
    ///
    ///     time::sleep(Duration::from_millis(50)).await;
    /// };
    ///
    /// // use the connected client.
    /// # Ok(()) }
    /// ```
    pub fn open(&self, addr: impl AsRef<OsStr>) -> io::Result<NamedPipeClient> {
        // Safety: We're calling open_with_security_attributes_raw w/ a null
        // pointer which disables it.
        unsafe { self.open_with_security_attributes_raw(addr, ptr::null_mut()) }
    }

    /// Open the named pipe identified by `addr`.
    ///
    /// This is the same as [`open`] except that it supports providing the raw
    /// pointer to a structure of [`SECURITY_ATTRIBUTES`] which will be passed
    /// as the `lpSecurityAttributes` argument to [`CreateFile`].
    ///
    /// # Safety
    ///
    /// The `attrs` argument must either be null or point at a valid instance of
    /// the [`SECURITY_ATTRIBUTES`] structure. If the argument is null, the
    /// behavior is identical to calling the [`open`] method.
    ///
    /// [`open`]: ClientOptions::open
    /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilew
    /// [`SECURITY_ATTRIBUTES`]: crate::winapi::um::minwinbase::SECURITY_ATTRIBUTES
    pub unsafe fn open_with_security_attributes_raw(
        &self,
        addr: impl AsRef<OsStr>,
        attrs: *mut c_void,
    ) -> io::Result<NamedPipeClient> {
        let addr = encode_addr(addr);

        // NB: We could use a platform specialized `OpenOptions` here, but since
        // we have access to winapi it ultimately doesn't hurt to use
        // `CreateFile` explicitly since it allows the use of our already
        // well-structured wide `addr` to pass into CreateFileW.
        let h = fileapi::CreateFileW(
            addr.as_ptr(),
            self.desired_access,
            0,
            attrs as *mut _,
            fileapi::OPEN_EXISTING,
            self.get_flags(),
            ptr::null_mut(),
        );

        if h == handleapi::INVALID_HANDLE_VALUE {
            return Err(io::Error::last_os_error());
        }

        NamedPipeClient::from_raw_handle(h)
    }

    fn get_flags(&self) -> u32 {
        self.security_qos_flags | winbase::FILE_FLAG_OVERLAPPED
    }
}

/// The pipe mode of a named pipe.
///
/// Set through [`ServerOptions::pipe_mode`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
#[non_exhaustive]
pub enum PipeMode {
    /// Data is written to the pipe as a stream of bytes. The pipe does not
    /// distinguish bytes written during different write operations.
    ///
    /// Corresponds to [`PIPE_TYPE_BYTE`][crate::winapi::um::winbase::PIPE_TYPE_BYTE].
    Byte,
    /// Data is written to the pipe as a stream of messages. The pipe treats the
    /// bytes written during each write operation as a message unit. Any reading
    /// on a named pipe returns [`ERROR_MORE_DATA`] when a message is not read
    /// completely.
    ///
    /// Corresponds to [`PIPE_TYPE_MESSAGE`][crate::winapi::um::winbase::PIPE_TYPE_MESSAGE].
    ///
    /// [`ERROR_MORE_DATA`]: crate::winapi::shared::winerror::ERROR_MORE_DATA
    Message,
}

/// Indicates the end of a named pipe.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
#[non_exhaustive]
pub enum PipeEnd {
    /// The named pipe refers to the client end of a named pipe instance.
    ///
    /// Corresponds to [`PIPE_CLIENT_END`][crate::winapi::um::winbase::PIPE_CLIENT_END].
    Client,
    /// The named pipe refers to the server end of a named pipe instance.
    ///
    /// Corresponds to [`PIPE_SERVER_END`][crate::winapi::um::winbase::PIPE_SERVER_END].
    Server,
}

/// Information about a named pipe.
///
/// Constructed through [`NamedPipeServer::info`] or [`NamedPipeClient::info`].
#[derive(Debug)]
#[non_exhaustive]
pub struct PipeInfo {
    /// Indicates the mode of a named pipe.
    pub mode: PipeMode,
    /// Indicates the end of a named pipe.
    pub end: PipeEnd,
    /// The maximum number of instances that can be created for this pipe.
    pub max_instances: u32,
    /// The number of bytes to reserve for the output buffer.
    pub out_buffer_size: u32,
    /// The number of bytes to reserve for the input buffer.
    pub in_buffer_size: u32,
}

/// Encode an address so that it is a null-terminated wide string.
fn encode_addr(addr: impl AsRef<OsStr>) -> Box<[u16]> {
    let len = addr.as_ref().encode_wide().count();
    let mut vec = Vec::with_capacity(len + 1);
    vec.extend(addr.as_ref().encode_wide());
    vec.push(0);
    vec.into_boxed_slice()
}

/// Internal function to get the info out of a raw named pipe.
unsafe fn named_pipe_info(handle: RawHandle) -> io::Result<PipeInfo> {
    let mut flags = 0;
    let mut out_buffer_size = 0;
    let mut in_buffer_size = 0;
    let mut max_instances = 0;

    let result = namedpipeapi::GetNamedPipeInfo(
        handle,
        &mut flags,
        &mut out_buffer_size,
        &mut in_buffer_size,
        &mut max_instances,
    );

    if result == FALSE {
        return Err(io::Error::last_os_error());
    }

    let mut end = PipeEnd::Client;
    let mut mode = PipeMode::Byte;

    if flags & winbase::PIPE_SERVER_END != 0 {
        end = PipeEnd::Server;
    }

    if flags & winbase::PIPE_TYPE_MESSAGE != 0 {
        mode = PipeMode::Message;
    }

    Ok(PipeInfo {
        end,
        mode,
        out_buffer_size,
        in_buffer_size,
        max_instances,
    })
}