// Copyright 2024 The NativeLink Authors. All rights reserved.

//

// Licensed under the Functional Source License, Version 1.1, Apache 2.0 Future License (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

//    See LICENSE file for details

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

use core::pin::Pin;

use core::sync::atomic::{AtomicUsize, Ordering};

use core::task::{Context, Poll};

use std::fs::{Metadata, Permissions};

use std::io::{self, IoSlice, Seek};

#[cfg(target_os = "linux")]

use std::os::unix::io::AsRawFd;

use std::path::{Path, PathBuf};

use nativelink_error::{Code, Error, ResultExt, make_err};

use rlimit::increase_nofile_limit;

/// We wrap all `tokio::fs` items in our own wrapper so we can limit the number of outstanding

/// open files at any given time. This will greatly reduce the chance we'll hit open file limit

/// issues.

pub use tokio::fs::DirEntry;

use tokio::io::{AsyncRead, AsyncReadExt, AsyncSeek, AsyncWrite, ReadBuf, SeekFrom, Take};

use tokio::sync::{Semaphore, SemaphorePermit};

use tracing::{error, info, trace, warn};

use crate::spawn_blocking;

/// Default read buffer size when reading to/from disk.

pub const DEFAULT_READ_BUFF_SIZE: usize = 0x4000;

#[derive(Debug)]

pub struct FileSlot {

    // We hold the permit because once it is dropped it goes back into the queue.

    _permit: SemaphorePermit<'static>,

    inner: tokio::fs::File,

}

impl FileSlot {

    /// Advise the kernel to drop page cache for this file's contents.

    /// Only available on Linux;

    #[cfg(target_os = "linux")]

    pub fn advise_dontneed(&self) {

        let fd = self.inner.as_raw_fd();

        let ret = unsafe { libc::posix_fadvise(fd, 0, 0, libc::POSIX_FADV_DONTNEED) };

        if ret != 0 {

            tracing::debug!(

                fd,

                ret,

                "posix_fadvise(DONTNEED) returned non-zero (best-effort, ignoring)",

            );

        }

    }

    #[cfg(not(target_os = "linux"))]

    pub const fn advise_dontneed(&self) {

        // No-op: posix_fadvise is not available on Mac or Windows.

    }

}

/// Enable [`IP_FREEBIND`](`libc::IP_FREEBIND`) before binding a socket.

#[cfg(target_os = "linux")]

pub fn set_freebind<F: AsRawFd>(socket: &F) -> Result<(), io::Error> {

    let enable = 1;

    let optlen = libc::socklen_t::try_from(size_of::<libc::c_int>())

        .expect("size of c_int always fits in socklen_t");

    // SAFETY: we pass in a valid fd, initialized optval, and matching optlen.

    let ret = unsafe {

        libc::setsockopt(

            socket.as_raw_fd(),

            libc::IPPROTO_IP,

            libc::IP_FREEBIND,

            core::ptr::addr_of!(enable).cast(),

            optlen,

        )

    };

    if ret == 0 {

        Ok(())

    } else {

        Err(io::Error::last_os_error())

    }

}

#[cfg(not(target_os = "linux"))]

pub const fn set_freebind<F>(_socket: &F) -> Result<(), io::Error> {

    Ok(())

}

impl AsRef<tokio::fs::File> for FileSlot {

    fn as_ref(&self) -> &tokio::fs::File {

        &self.inner

    }

}

impl AsMut<tokio::fs::File> for FileSlot {

    fn as_mut(&mut self) -> &mut tokio::fs::File {

        &mut self.inner

    }

}

impl AsyncRead for FileSlot {

    fn poll_read(

        mut self: Pin<&mut Self>,

        cx: &mut Context<'_>,

        buf: &mut ReadBuf<'_>,

    ) -> Poll<Result<(), tokio::io::Error>> {

        Pin::new(&mut self.inner).poll_read(cx, buf)

    }

}

impl AsyncSeek for FileSlot {

    fn start_seek(mut self: Pin<&mut Self>, position: SeekFrom) -> Result<(), tokio::io::Error> {

        Pin::new(&mut self.inner).start_seek(position)

    }

    fn poll_complete(

        mut self: Pin<&mut Self>,

        cx: &mut Context<'_>,

    ) -> Poll<Result<u64, tokio::io::Error>> {

        Pin::new(&mut self.inner).poll_complete(cx)

    }

}

impl AsyncWrite for FileSlot {

    fn poll_write(

        mut self: Pin<&mut Self>,

        cx: &mut Context<'_>,

        buf: &[u8],

    ) -> Poll<Result<usize, tokio::io::Error>> {

        Pin::new(&mut self.inner).poll_write(cx, buf)

    }

    fn poll_flush(

        mut self: Pin<&mut Self>,

        cx: &mut Context<'_>,

    ) -> Poll<Result<(), tokio::io::Error>> {

        Pin::new(&mut self.inner).poll_flush(cx)

    }

    fn poll_shutdown(

        mut self: Pin<&mut Self>,

        cx: &mut Context<'_>,

    ) -> Poll<Result<(), tokio::io::Error>> {

        Pin::new(&mut self.inner).poll_shutdown(cx)

    }

    fn poll_write_vectored(

        mut self: Pin<&mut Self>,

        cx: &mut Context<'_>,

        bufs: &[IoSlice<'_>],

    ) -> Poll<Result<usize, tokio::io::Error>> {

        Pin::new(&mut self.inner).poll_write_vectored(cx, bufs)

    }

    fn is_write_vectored(&self) -> bool {

        self.inner.is_write_vectored()

    }

}

// Note: If the default changes make sure you update the documentation in

// `config/cas_server.rs`.

pub const DEFAULT_OPEN_FILE_LIMIT: usize = 24 * 1024; // 24k.

static OPEN_FILE_LIMIT: AtomicUsize = AtomicUsize::new(DEFAULT_OPEN_FILE_LIMIT);

pub static OPEN_FILE_SEMAPHORE: Semaphore = Semaphore::const_new(DEFAULT_OPEN_FILE_LIMIT);

/// Try to acquire a permit from the open file semaphore.

#[inline]

pub async fn get_permit() -> Result<SemaphorePermit<'static>, Error> {

    trace!(

        available_permits = OPEN_FILE_SEMAPHORE.available_permits(),

        "getting FS permit"

    );

    OPEN_FILE_SEMAPHORE

        .acquire()

        .await

        .map_err(|e| 
make_err!0
(
Code::Internal0
, "Open file semaphore closed {:?}", e))

}

/// Acquire a permit from the open file semaphore and call a raw function.

#[inline]

pub async fn call_with_permit<F, T>(f: F) -> Result<T, Error>

where

    F: FnOnce(SemaphorePermit<'static>) -> Result<T, Error> + Send + 'static,

    T: Send + 'static,

{

    let permit = get_permit().await
?0
;

    spawn_blocking!("fs_call_with_permit", move || 
f5.90k
(
permit5.90k
))

        .await

        .unwrap_or_else(|e| 
{0

            Err(Error::from_std_err(Code::Internal, &e).append("background task failed"))

        })

}

/// Sets the soft nofile limit to `desired_open_file_limit` and adjusts

/// `OPEN_FILE_SEMAPHORE` accordingly.

///

/// # Panics

///

/// If any type conversion fails. This can't happen if `usize` is smaller than

/// `u64`.

pub fn set_open_file_limit(desired_open_file_limit: usize) {

    // Tokio semaphores have a max of 2^61 - 1 permits. On some platforms

    // (e.g. macOS) the kernel reports an "unlimited" file limit that exceeds

    // this, causing a panic when we try to add permits. Cap at a generous but

    // safe value.

    const MAX_SAFE_LIMIT: usize = 1 << 30; // ~1 billion

    let new_open_file_limit = {

        match increase_nofile_limit(

            u64::try_from(desired_open_file_limit)

                .expect("desired_open_file_limit is too large to convert to u64."),

        ) {

            Ok(open_file_limit) => {

                info!("set_open_file_limit() assigns new open file limit {open_file_limit}.",);

                usize::try_from(open_file_limit)

                    .expect("open_file_limit is too large to convert to usize.")

                    .min(MAX_SAFE_LIMIT)

            }

            Err(e) => {

                error!(

                    "set_open_file_limit() failed to assign open file limit. Maybe system does not have ulimits, continuing anyway. - {e:?}",

                );

                DEFAULT_OPEN_FILE_LIMIT

            }

        }

    };

    // TODO(jaroeichler): Can we give a better estimate?

    if new_open_file_limit < DEFAULT_OPEN_FILE_LIMIT {

        warn!(

            "The new open file limit ({new_open_file_limit}) is below the recommended value of {DEFAULT_OPEN_FILE_LIMIT}. Consider raising max_open_files.",

        );

    }

    // Use only 80% of the open file limit for permits from OPEN_FILE_SEMAPHORE

    // to give extra room for other file descriptors like sockets, pipes, and

    // other things.

    let reduced_open_file_limit = new_open_file_limit.saturating_sub(new_open_file_limit / 5);

    let previous_open_file_limit = OPEN_FILE_LIMIT.load(Ordering::Acquire);

    // No permit should be acquired yet, so this warning should not occur.

    if (OPEN_FILE_SEMAPHORE.available_permits() + reduced_open_file_limit)

        < previous_open_file_limit

    {

        warn!(

            "There are not enough available permits to remove {previous_open_file_limit} - {reduced_open_file_limit} permits.",

        );

    }

    if previous_open_file_limit <= reduced_open_file_limit {

        OPEN_FILE_LIMIT.fetch_add(

            reduced_open_file_limit - previous_open_file_limit,

            Ordering::Release,

        );

        OPEN_FILE_SEMAPHORE.add_permits(reduced_open_file_limit - previous_open_file_limit);

    } else {

        OPEN_FILE_LIMIT.fetch_sub(

            previous_open_file_limit - reduced_open_file_limit,

            Ordering::Release,

        );

        OPEN_FILE_SEMAPHORE.forget_permits(previous_open_file_limit - reduced_open_file_limit);

    }

}

pub fn get_open_files_for_test() -> usize {

    OPEN_FILE_LIMIT.load(Ordering::Acquire) - OPEN_FILE_SEMAPHORE.available_permits()

}

pub async fn open_file(

    path: impl AsRef<Path>,

    start: u64,

    limit: u64,

) -> Result<Take<FileSlot>, Error> {

    let path = path.as_ref().to_owned();

    let (
permit613
, 
os_file613
) = call_with_permit(move |permit| {

        let mut os_file =

            std::fs::File::open(&path).err_tip(|| 
format!3
("Could not open {}", 
path.display()3
))
?3
;

        if start > 0 {

            os_file

                .seek(SeekFrom::Start(start))

                .err_tip(|| format!("Could not seek to {start} in {}", path.display()))?;

        }

        Ok((permit, os_file))

    })

    .await
?3
;

    Ok(FileSlot {

        _permit: permit,

        inner: tokio::fs::File::from_std(os_file),

    }

    .take(limit))

}

pub async fn create_file(path: impl AsRef<Path>) -> Result<FileSlot, Error> {

    let path = path.as_ref().to_owned();

    let (permit, os_file) = call_with_permit(move |permit| {

        Ok((

            permit,

            std::fs::File::options()

                .read(true)

                .write(true)

                .create(true)

                .truncate(true)

                .open(&path)

                .err_tip(|| 
format!0
("Could not open {}", 
path.display()0
))
?0
,

        ))

    })

    .await
?0
;

    Ok(FileSlot {

        _permit: permit,

        inner: tokio::fs::File::from_std(os_file),

    })

}

pub async fn hard_link(src: impl AsRef<Path>, dst: impl AsRef<Path>) -> Result<(), Error> {

    let src = src.as_ref().to_owned();

    let dst = dst.as_ref().to_owned();

    call_with_permit(move |_| std::fs::hard_link(src, dst).map_err(Into::<Error>::into)).await

}

/// Hardlinks many files under a single permit and a single `spawn_blocking`

/// dispatch, returning one result per input in the same order.

///

/// [`hard_link`] pays a semaphore acquire plus a `spawn_blocking` hop per call,

/// and both dwarf the `hard_link(2)` syscall itself, which is a few microseconds

/// on tmpfs. Staging an input tree of thousands of small files therefore spends

/// most of its wall time in the tokio scheduler rather than in the kernel.

/// Batching amortizes the acquire and the dispatch over the whole batch.

///

/// A single permit covers the batch because `hard_link(2)` is a metadata

/// operation that never leaves a file descriptor open, so it does not consume

/// the open-file budget [`OPEN_FILE_SEMAPHORE`] exists to protect.

///

/// This does change the backpressure profile; the permit no longer paces

/// individual syscalls, only whole batches, and one blocking thread is held for

/// the length of a batch rather than for one syscall. On Linux and tmpfs, where

/// this was measured, that trades well because the per-call dispatch was the

/// cost. A filesystem that serializes metadata operations internally, as APFS

/// does on a per-volume lock, gets a different bargain: less parallel

/// contention, but a long batch occupies its thread throughout. Size batches

/// accordingly.

pub async fn hard_link_many(

    links: Vec<(PathBuf, PathBuf)>,

) -> Result<Vec<Result<(), Error>>, Error> {

    call_with_permit(move |_| {

        Ok(links

            .into_iter()

            .map(|(src, dst)| 
std::fs::hard_link15
(
src15
, 
dst15
).
map_err15
(Into::<Error>::into))

            .collect())

    })

    .await

}

pub async fn set_permissions(src: impl AsRef<Path>, perm: Permissions) -> Result<(), Error> {

    let src = src.as_ref().to_owned();

    call_with_permit(move |_| std::fs::set_permissions(src, perm).map_err(Into::<Error>::into))

        .await

}

/// Creates many directories under a single permit and a single `spawn_blocking`

/// dispatch, each parent before its children.

///

/// An existing directory is an error, exactly as [`create_dir`] reports it.

///

/// See [`hard_link_many`] for why batching matters here: the `mkdir(2)` syscall

/// is dwarfed by the semaphore acquire and `spawn_blocking` hop, and an input

/// tree contributes hundreds of directories.

pub async fn create_dir_many(mut dirs: Vec<PathBuf>) -> Result<(), Error>0
 {

    // Sorting puts every parent ahead of its children, since a parent's path is

    // a prefix of theirs. We do this instead of using `create_dir_all` below

    // because we want to fail on existing directories: on case-insensitive

    // filesystems, that will ensure that we don't silently merge two trees in

    // the event of a different-in-case-only collision.

    dirs.sort_unstable();

    call_with_permit(move |_| {

        for 
dir16
 in dirs {

            std::fs::create_dir(&dir).map_err(|e| 
{2

                Error::from(e).append(format!("Could not create directory {}", dir.display()))

            })?;

        }

        Ok(())

    })

    .await

}

pub async fn create_dir(path: impl AsRef<Path>) -> Result<(), Error> {

    let path = path.as_ref().to_owned();

    call_with_permit(move |_| std::fs::create_dir(path).map_err(Into::<Error>::into)).await

}

pub async fn create_dir_all(path: impl AsRef<Path>) -> Result<(), Error> {

    let path = path.as_ref().to_owned();

    call_with_permit(move |_| std::fs::create_dir_all(path).map_err(Into::<Error>::into)).await

}

#[cfg(target_family = "unix")]

pub async fn symlink(src: impl AsRef<Path>, dst: impl AsRef<Path>) -> Result<(), Error> {

    // TODO: add a test for #2051: deadlock with large number of files

    let _permit = get_permit().await
?0
;

    tokio::fs::symlink(src, dst).await.map_err(Into::into)

}

pub async fn read_link(path: impl AsRef<Path>) -> Result<PathBuf, Error> {

    let path = path.as_ref().to_owned();

    call_with_permit(move |_| std::fs::read_link(path).map_err(Into::<Error>::into)).await

}

#[derive(Debug)]

pub struct ReadDir {

    // We hold the permit because once it is dropped it goes back into the queue.

    permit: SemaphorePermit<'static>,

    inner: tokio::fs::ReadDir,

}

impl ReadDir {

    pub fn into_inner(self) -> (SemaphorePermit<'static>, tokio::fs::ReadDir) {

        (self.permit, self.inner)

    }

}

impl AsRef<tokio::fs::ReadDir> for ReadDir {

    fn as_ref(&self) -> &tokio::fs::ReadDir {

        &self.inner

    }

}

impl AsMut<tokio::fs::ReadDir> for ReadDir {

    fn as_mut(&mut self) -> &mut tokio::fs::ReadDir {

        &mut self.inner

    }

}

pub async fn read_dir(path: impl AsRef<Path>) -> Result<ReadDir, Error> {

    let path = path.as_ref().to_owned();

    let (permit, inner) = call_with_permit(move |permit| {

        Ok((

            permit,

            tokio::runtime::Handle::current()

                .block_on(tokio::fs::read_dir(path))

                .map_err(Into::<Error>::into)
?0
,

        ))

    })

    .await
?0
;

    Ok(ReadDir { permit, inner })

}

pub async fn rename(from: impl AsRef<Path>, to: impl AsRef<Path>) -> Result<(), Error> {

    let from = from.as_ref().to_owned();

    let to = to.as_ref().to_owned();

    call_with_permit(move |_| std::fs::rename(from, to).map_err(Into::<Error>::into)).await

}

pub async fn remove_file(path: impl AsRef<Path>) -> Result<(), Error> {

    let path = path.as_ref().to_owned();

    call_with_permit(move |_| 
std::fs::remove_file40
(
path40
).
map_err40
(Into::<Error>::into)).await

}

/// Removes an empty directory. Errors if the directory is not empty; use

/// [`remove_dir_all`] when the contents should be removed too.

pub async fn remove_dir(path: impl AsRef<Path>) -> Result<(), Error> {

    let path = path.as_ref().to_owned();

    call_with_permit(move |_| std::fs::remove_dir(path).map_err(Into::<Error>::into)).await

}

pub async fn canonicalize(path: impl AsRef<Path>) -> Result<PathBuf, Error> {

    let path = path.as_ref().to_owned();

    call_with_permit(move |_| std::fs::canonicalize(path).map_err(Into::<Error>::into)).await

}

pub async fn metadata(path: impl AsRef<Path>) -> Result<Metadata, Error> {

    let path = path.as_ref().to_owned();

    call_with_permit(move |_| std::fs::metadata(path).map_err(Into::<Error>::into)).await

}

/// Tests many paths for existence under a single permit and a single

/// `spawn_blocking` dispatch, returning one answer per input in the same order.

///

/// A `stat(2)` on a warm tmpfs costs far less than the permit acquisition and

/// thread hop needed to dispatch it, so callers checking a whole input tree pay

/// almost entirely dispatch overhead when they ask one path at a time.

///

/// Any error is reported as `false`, since every failure mode (absent,

/// dangling, unreadable parent) answers "can I use this path" the same way.

pub async fn exists_many(paths: Vec<PathBuf>) -> Result<Vec<bool>, Error>0
 {

    call_with_permit(move |_| {

        Ok(paths

            .into_iter()

            .map(|path| 
std::fs::metadata(path)6
.
is_ok6
())

            .collect())

    })

    .await

}

pub async fn read(path: impl AsRef<Path>) -> Result<Vec<u8>, Error> {

    let path = path.as_ref().to_owned();

    call_with_permit(move |_| std::fs::read(path).map_err(Into::<Error>::into)).await

}

pub async fn symlink_metadata(path: impl AsRef<Path>) -> Result<Metadata, Error> {

    let path = path.as_ref().to_owned();

    call_with_permit(move |_| std::fs::symlink_metadata(path).map_err(Into::<Error>::into)).await

}

// We can't just use the stock remove_dir_all as it falls over if someone's set readonly

// permissions. This version walks the directories and fixes the permissions where needed

// before deleting everything.

#[cfg(not(target_family = "windows"))]

fn internal_remove_dir_all(path: impl AsRef<Path>) -> Result<(), Error> {

    // Because otherwise Windows builds complain about these things not being used

    use std::io::ErrorKind;

    use std::os::unix::fs::PermissionsExt;

    use tracing::debug;

    use walkdir::WalkDir;

    for entry in 
WalkDir::new238
(
&path238
) {

        let Ok(
entry236
) = &entry else {

            debug!(?entry, "Can't get entry, assuming already deleted");

            continue;

        };

        let metadata = entry.metadata()
?0
;

        if metadata.is_dir() {

            match std::fs::remove_dir_all(entry.path()) {

                Ok(()) => {}

                Err(e) if e.kind() == ErrorKind::PermissionDenied => {

                    std::fs::set_permissions(entry.path(), Permissions::from_mode(0o700)).err_tip(

                        || format!("Setting permissions for {}", entry.path().display()),

                    )?;

                }

                e @ Err(_) => e.err_tip(|| format!("Removing {}", entry.path().display()))?,

            }

        } else if metadata.is_file() {

            std::fs::set_permissions(entry.path(), Permissions::from_mode(0o600))

                .err_tip(|| format!("Setting permissions for {}", entry.path().display()))?;

        }

    }

    // should now be safe to delete after we fixed all the permissions in the walk loop

    match std::fs::remove_dir_all(&path) {

        Ok(()) => {}

        Err(e) if e.kind() == ErrorKind::NotFound => {}

        e @ Err(_) => e.err_tip(|| {

            format!(

                "Removing {} after permissions fixes",

                path.as_ref().display()

            )

        })?,

    }

    Ok(())

}

// We can't set the permissions easily in Windows, so just fallback to

// the stock Rust remove_dir_all

#[cfg(target_family = "windows")]

fn internal_remove_dir_all(path: impl AsRef<Path>) -> Result<(), Error> {

    std::fs::remove_dir_all(&path)?;

    Ok(())

}

pub async fn remove_dir_all(path: impl AsRef<Path>) -> Result<(), Error> {

    let path = path.as_ref().to_owned();

    call_with_permit(move |_| internal_remove_dir_all(path)).await

}