1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
//! `RawDir` and `RawDirEntry`.

use core::fmt;
use core::mem::{align_of, MaybeUninit};
use linux_raw_sys::general::linux_dirent64;

use crate::backend::fs::syscalls::getdents_uninit;
use crate::fd::AsFd;
use crate::ffi::CStr;
use crate::fs::FileType;
use crate::io;

/// A directory iterator implemented with getdents.
///
/// Note: This implementation does not handle growing the buffer. If this
/// functionality is necessary, you'll need to drop the current iterator,
/// resize the buffer, and then re-create the iterator. The iterator is
/// guaranteed to continue where it left off provided the file descriptor isn't
/// changed. See the example in [`RawDir::new`].
pub struct RawDir<'buf, Fd: AsFd> {
    fd: Fd,
    buf: &'buf mut [MaybeUninit<u8>],
    initialized: usize,
    offset: usize,
}

impl<'buf, Fd: AsFd> RawDir<'buf, Fd> {
    /// Create a new iterator from the given file descriptor and buffer.
    ///
    /// Note: the buffer size may be trimmed to accommodate alignment
    /// requirements.
    ///
    /// # Examples
    ///
    /// ## Simple but non-portable
    ///
    /// These examples are non-portable, because file systems may not have a
    /// maximum file name length. If you can make assumptions that bound
    /// this length, then these examples may suffice.
    ///
    /// Using the heap:
    ///
    /// ```
    /// # use std::mem::MaybeUninit;
    /// # use rustix::fs::{CWD, Mode, OFlags, openat, RawDir};
    ///
    /// let fd = openat(
    ///     CWD,
    ///     ".",
    ///     OFlags::RDONLY | OFlags::DIRECTORY | OFlags::CLOEXEC,
    ///     Mode::empty(),
    /// )
    /// .unwrap();
    ///
    /// let mut buf = Vec::with_capacity(8192);
    /// let mut iter = RawDir::new(fd, buf.spare_capacity_mut());
    /// while let Some(entry) = iter.next() {
    ///     let entry = entry.unwrap();
    ///     dbg!(&entry);
    /// }
    /// ```
    ///
    /// Using the stack:
    ///
    /// ```
    /// # use std::mem::MaybeUninit;
    /// # use rustix::fs::{CWD, Mode, OFlags, openat, RawDir};
    ///
    /// let fd = openat(
    ///     CWD,
    ///     ".",
    ///     OFlags::RDONLY | OFlags::DIRECTORY | OFlags::CLOEXEC,
    ///     Mode::empty(),
    /// )
    /// .unwrap();
    ///
    /// let mut buf = [MaybeUninit::uninit(); 2048];
    /// let mut iter = RawDir::new(fd, &mut buf);
    /// while let Some(entry) = iter.next() {
    ///     let entry = entry.unwrap();
    ///     dbg!(&entry);
    /// }
    /// ```
    ///
    /// ## Portable
    ///
    /// Heap allocated growing buffer for supporting directory entries with
    /// arbitrarily large file names:
    ///
    /// ```notrust
    /// # // The `notrust` above can be removed when we can depend on Rust 1.65.
    /// # use std::mem::MaybeUninit;
    /// # use rustix::fs::{CWD, Mode, OFlags, openat, RawDir};
    /// # use rustix::io::Errno;
    ///
    /// let fd = openat(
    ///     CWD,
    ///     ".",
    ///     OFlags::RDONLY | OFlags::DIRECTORY | OFlags::CLOEXEC,
    ///     Mode::empty(),
    /// )
    /// .unwrap();
    ///
    /// let mut buf = Vec::with_capacity(8192);
    /// 'read: loop {
    ///     'resize: {
    ///         let mut iter = RawDir::new(&fd, buf.spare_capacity_mut());
    ///         while let Some(entry) = iter.next() {
    ///             let entry = match entry {
    ///                 Err(Errno::INVAL) => break 'resize,
    ///                 r => r.unwrap(),
    ///             };
    ///             dbg!(&entry);
    ///         }
    ///         break 'read;
    ///     }
    ///
    ///     let new_capacity = buf.capacity() * 2;
    ///     buf.reserve(new_capacity);
    /// }
    /// ```
    pub fn new(fd: Fd, buf: &'buf mut [MaybeUninit<u8>]) -> Self {
        Self {
            fd,
            buf: {
                let offset = buf.as_ptr().align_offset(align_of::<linux_dirent64>());
                if offset < buf.len() {
                    &mut buf[offset..]
                } else {
                    &mut []
                }
            },
            initialized: 0,
            offset: 0,
        }
    }
}

/// A raw directory entry, similar to [`std::fs::DirEntry`].
///
/// Unlike the std version, this may represent the `.` or `..` entries.
pub struct RawDirEntry<'a> {
    file_name: &'a CStr,
    file_type: u8,
    inode_number: u64,
    next_entry_cookie: i64,
}

impl<'a> fmt::Debug for RawDirEntry<'a> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let mut f = f.debug_struct("RawDirEntry");
        f.field("file_name", &self.file_name());
        f.field("file_type", &self.file_type());
        f.field("ino", &self.ino());
        f.field("next_entry_cookie", &self.next_entry_cookie());
        f.finish()
    }
}

impl<'a> RawDirEntry<'a> {
    /// Returns the file name of this directory entry.
    #[inline]
    pub fn file_name(&self) -> &CStr {
        self.file_name
    }

    /// Returns the type of this directory entry.
    #[inline]
    pub fn file_type(&self) -> FileType {
        FileType::from_dirent_d_type(self.file_type)
    }

    /// Returns the inode number of this directory entry.
    #[inline]
    #[doc(alias = "inode_number")]
    pub fn ino(&self) -> u64 {
        self.inode_number
    }

    /// Returns the seek cookie to the next directory entry.
    #[inline]
    #[doc(alias = "off")]
    pub fn next_entry_cookie(&self) -> u64 {
        self.next_entry_cookie as u64
    }
}

impl<'buf, Fd: AsFd> RawDir<'buf, Fd> {
    /// Identical to [`Iterator::next`] except that [`Iterator::Item`] borrows
    /// from self.
    ///
    /// Note: this interface will be broken to implement a stdlib iterator API
    /// with GAT support once one becomes available.
    #[allow(unsafe_code)]
    #[allow(clippy::should_implement_trait)]
    pub fn next(&mut self) -> Option<io::Result<RawDirEntry>> {
        if self.is_buffer_empty() {
            match getdents_uninit(self.fd.as_fd(), self.buf) {
                Ok(0) => return None,
                Ok(bytes_read) => {
                    self.initialized = bytes_read;
                    self.offset = 0;
                }
                Err(e) => return Some(Err(e)),
            }
        }

        let dirent_ptr = self.buf[self.offset..].as_ptr();
        // SAFETY:
        // - This data is initialized by the check above.
        //   - Assumption: the kernel will not give us partial structs.
        // - Assumption: the kernel uses proper alignment between structs.
        // - The starting pointer is aligned (performed in RawDir::new)
        let dirent = unsafe { &*dirent_ptr.cast::<linux_dirent64>() };

        self.offset += usize::from(dirent.d_reclen);

        Some(Ok(RawDirEntry {
            file_type: dirent.d_type,
            inode_number: dirent.d_ino.into(),
            next_entry_cookie: dirent.d_off.into(),
            // SAFETY: The kernel guarantees a NUL-terminated string.
            file_name: unsafe { CStr::from_ptr(dirent.d_name.as_ptr().cast()) },
        }))
    }

    /// Returns true if the internal buffer is empty and will be refilled when
    /// calling [`next`].
    ///
    /// [`next`]: Self::next
    pub fn is_buffer_empty(&self) -> bool {
        self.offset >= self.initialized
    }
}