1use super::{BorrowedBuf, BufReader, BufWriter, DEFAULT_BUF_SIZE, Read, Result, Write};
2use crate::alloc::Allocator;
3use crate::cmp;
4use crate::collections::VecDeque;
5use crate::io::IoSlice;
6use crate::mem::MaybeUninit;
7
8#[cfg(test)]
9mod tests;
10
11/// Copies the entire contents of a reader into a writer.
12///
13/// This function will continuously read data from `reader` and then
14/// write it into `writer` in a streaming fashion until `reader`
15/// returns EOF.
16///
17/// On success, the total number of bytes that were copied from
18/// `reader` to `writer` is returned.
19///
20/// If you want to copy the contents of one file to another and you’re
21/// working with filesystem paths, see the [`fs::copy`] function.
22///
23/// [`fs::copy`]: crate::fs::copy
24///
25/// # Errors
26///
27/// This function will return an error immediately if any call to [`read`] or
28/// [`write`] returns an error. All instances of [`ErrorKind::Interrupted`] are
29/// handled by this function and the underlying operation is retried.
30///
31/// [`read`]: Read::read
32/// [`write`]: Write::write
33/// [`ErrorKind::Interrupted`]: crate::io::ErrorKind::Interrupted
34///
35/// # Examples
36///
37/// ```
38/// use std::io;
39///
40/// fn main() -> io::Result<()> {
41/// let mut reader: &[u8] = b"hello";
42/// let mut writer: Vec<u8> = vec![];
43///
44/// io::copy(&mut reader, &mut writer)?;
45///
46/// assert_eq!(&b"hello"[..], &writer[..]);
47/// Ok(())
48/// }
49/// ```
50///
51/// # Platform-specific behavior
52///
53/// On Linux (including Android), this function uses `copy_file_range(2)`,
54/// `sendfile(2)` or `splice(2)` syscalls to move data directly between file
55/// descriptors if possible.
56///
57/// Note that platform-specific behavior [may change in the future][changes].
58///
59/// [changes]: crate::io#platform-specific-behavior
60#[stable(feature = "rust1", since = "1.0.0")]
61pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> Result<u64>
62where
63 R: Read,
64 W: Write,
65{
66 cfg_if::cfg_if! {
67 if #[cfg(any(target_os = "linux", target_os = "android"))] {
68 crate::sys::kernel_copy::copy_spec(reader, writer)
69 } else {
70 generic_copy(reader, writer)
71 }
72 }
73}
74
75/// The userspace read-write-loop implementation of `io::copy` that is used when
76/// OS-specific specializations for copy offloading are not available or not applicable.
77pub(crate) fn generic_copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> Result<u64>
78where
79 R: Read,
80 W: Write,
81{
82 let read_buf: usize = BufferedReaderSpec::buffer_size(self:reader);
83 let write_buf: usize = BufferedWriterSpec::buffer_size(self:writer);
84
85 if read_buf >= DEFAULT_BUF_SIZE && read_buf >= write_buf {
86 return BufferedReaderSpec::copy_to(self:reader, to:writer);
87 }
88
89 BufferedWriterSpec::copy_from(self:writer, reader)
90}
91
92/// Specialization of the read-write loop that reuses the internal
93/// buffer of a BufReader. If there's no buffer then the writer side
94/// should be used instead.
95trait BufferedReaderSpec {
96 fn buffer_size(&self) -> usize;
97
98 fn copy_to(&mut self, to: &mut (impl Write + ?Sized)) -> Result<u64>;
99}
100
101impl<T> BufferedReaderSpec for T
102where
103 Self: Read,
104 T: ?Sized,
105{
106 #[inline]
107 default fn buffer_size(&self) -> usize {
108 0
109 }
110
111 default fn copy_to(&mut self, _to: &mut (impl Write + ?Sized)) -> Result<u64> {
112 unreachable!("only called from specializations")
113 }
114}
115
116impl BufferedReaderSpec for &[u8] {
117 fn buffer_size(&self) -> usize {
118 // prefer this specialization since the source "buffer" is all we'll ever need,
119 // even if it's small
120 usize::MAX
121 }
122
123 fn copy_to(&mut self, to: &mut (impl Write + ?Sized)) -> Result<u64> {
124 let len: usize = self.len();
125 to.write_all(self)?;
126 *self = &self[len..];
127 Ok(len as u64)
128 }
129}
130
131impl<A: Allocator> BufferedReaderSpec for VecDeque<u8, A> {
132 fn buffer_size(&self) -> usize {
133 // prefer this specialization since the source "buffer" is all we'll ever need,
134 // even if it's small
135 usize::MAX
136 }
137
138 fn copy_to(&mut self, to: &mut (impl Write + ?Sized)) -> Result<u64> {
139 let len: usize = self.len();
140 let (front: &[u8], back: &[u8]) = self.as_slices();
141 let bufs: &mut [IoSlice<'_>; 2] = &mut [IoSlice::new(buf:front), IoSlice::new(buf:back)];
142 to.write_all_vectored(bufs)?;
143 self.clear();
144 Ok(len as u64)
145 }
146}
147
148impl<I> BufferedReaderSpec for BufReader<I>
149where
150 Self: Read,
151 I: ?Sized,
152{
153 fn buffer_size(&self) -> usize {
154 self.capacity()
155 }
156
157 fn copy_to(&mut self, to: &mut (impl Write + ?Sized)) -> Result<u64> {
158 let mut len = 0;
159
160 loop {
161 // Hack: this relies on `impl Read for BufReader` always calling fill_buf
162 // if the buffer is empty, even for empty slices.
163 // It can't be called directly here since specialization prevents us
164 // from adding I: Read
165 match self.read(&mut []) {
166 Ok(_) => {}
167 Err(e) if e.is_interrupted() => continue,
168 Err(e) => return Err(e),
169 }
170 let buf = self.buffer();
171 if self.buffer().len() == 0 {
172 return Ok(len);
173 }
174
175 // In case the writer side is a BufWriter then its write_all
176 // implements an optimization that passes through large
177 // buffers to the underlying writer. That code path is #[cold]
178 // but we're still avoiding redundant memcopies when doing
179 // a copy between buffered inputs and outputs.
180 to.write_all(buf)?;
181 len += buf.len() as u64;
182 self.discard_buffer();
183 }
184 }
185}
186
187/// Specialization of the read-write loop that either uses a stack buffer
188/// or reuses the internal buffer of a BufWriter
189trait BufferedWriterSpec: Write {
190 fn buffer_size(&self) -> usize;
191
192 fn copy_from<R: Read + ?Sized>(&mut self, reader: &mut R) -> Result<u64>;
193}
194
195impl<W: Write + ?Sized> BufferedWriterSpec for W {
196 #[inline]
197 default fn buffer_size(&self) -> usize {
198 0
199 }
200
201 default fn copy_from<R: Read + ?Sized>(&mut self, reader: &mut R) -> Result<u64> {
202 stack_buffer_copy(reader, self)
203 }
204}
205
206impl<I: Write + ?Sized> BufferedWriterSpec for BufWriter<I> {
207 fn buffer_size(&self) -> usize {
208 self.capacity()
209 }
210
211 fn copy_from<R: Read + ?Sized>(&mut self, reader: &mut R) -> Result<u64> {
212 if self.capacity() < DEFAULT_BUF_SIZE {
213 return stack_buffer_copy(reader, self);
214 }
215
216 let mut len = 0;
217 let mut init = 0;
218
219 loop {
220 let buf = self.buffer_mut();
221 let mut read_buf: BorrowedBuf<'_> = buf.spare_capacity_mut().into();
222
223 unsafe {
224 // SAFETY: init is either 0 or the init_len from the previous iteration.
225 read_buf.set_init(init);
226 }
227
228 if read_buf.capacity() >= DEFAULT_BUF_SIZE {
229 let mut cursor = read_buf.unfilled();
230 match reader.read_buf(cursor.reborrow()) {
231 Ok(()) => {
232 let bytes_read = cursor.written();
233
234 if bytes_read == 0 {
235 return Ok(len);
236 }
237
238 init = read_buf.init_len() - bytes_read;
239 len += bytes_read as u64;
240
241 // SAFETY: BorrowedBuf guarantees all of its filled bytes are init
242 unsafe { buf.set_len(buf.len() + bytes_read) };
243
244 // Read again if the buffer still has enough capacity, as BufWriter itself would do
245 // This will occur if the reader returns short reads
246 }
247 Err(ref e) if e.is_interrupted() => {}
248 Err(e) => return Err(e),
249 }
250 } else {
251 // All the bytes that were already in the buffer are initialized,
252 // treat them as such when the buffer is flushed.
253 init += buf.len();
254
255 self.flush_buf()?;
256 }
257 }
258 }
259}
260
261impl BufferedWriterSpec for Vec<u8> {
262 fn buffer_size(&self) -> usize {
263 cmp::max(DEFAULT_BUF_SIZE, self.capacity() - self.len())
264 }
265
266 fn copy_from<R: Read + ?Sized>(&mut self, reader: &mut R) -> Result<u64> {
267 reader.read_to_end(self).map(|bytes: usize| u64::try_from(bytes).expect(msg:"usize overflowed u64"))
268 }
269}
270
271pub fn stack_buffer_copy<R: Read + ?Sized, W: Write + ?Sized>(
272 reader: &mut R,
273 writer: &mut W,
274) -> Result<u64> {
275 let buf: &mut [_] = &mut [MaybeUninit::uninit(); DEFAULT_BUF_SIZE];
276 let mut buf: BorrowedBuf<'_> = buf.into();
277
278 let mut len: u64 = 0;
279
280 loop {
281 match reader.read_buf(buf.unfilled()) {
282 Ok(()) => {}
283 Err(e: Error) if e.is_interrupted() => continue,
284 Err(e: Error) => return Err(e),
285 };
286
287 if buf.filled().is_empty() {
288 break;
289 }
290
291 len += buf.filled().len() as u64;
292 writer.write_all(buf.filled())?;
293 buf.clear();
294 }
295
296 Ok(len)
297}
298