1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Buffering wrappers for I/O traits
18 use io::{self, DEFAULT_BUF_SIZE, Error, ErrorKind, SeekFrom};
21 /// The `BufReader` struct adds buffering to any reader.
23 /// It can be excessively inefficient to work directly with a [`Read`] instance.
24 /// For example, every call to [`read`] on [`TcpStream`] results in a system call.
25 /// A `BufReader` performs large, infrequent reads on the underlying [`Read`]
26 /// and maintains an in-memory buffer of the results.
28 /// [`Read`]: ../../std/io/trait.Read.html
29 /// [`read`]: ../../std/net/struct.TcpStream.html#method.read
30 /// [`TcpStream`]: ../../std/net/struct.TcpStream.html
35 /// use std::io::prelude::*;
36 /// use std::io::BufReader;
37 /// use std::fs::File;
39 /// # fn foo() -> std::io::Result<()> {
40 /// let mut f = try!(File::open("log.txt"));
41 /// let mut reader = BufReader::new(f);
43 /// let mut line = String::new();
44 /// let len = try!(reader.read_line(&mut line));
45 /// println!("First line is {} bytes long", len);
49 #[stable(feature = "rust1", since = "1.0.0")]
50 pub struct BufReader<R> {
57 impl<R: Read> BufReader<R> {
58 /// Creates a new `BufReader` with a default buffer capacity.
63 /// use std::io::BufReader;
64 /// use std::fs::File;
66 /// # fn foo() -> std::io::Result<()> {
67 /// let mut f = try!(File::open("log.txt"));
68 /// let mut reader = BufReader::new(f);
72 #[stable(feature = "rust1", since = "1.0.0")]
73 pub fn new(inner: R) -> BufReader<R> {
74 BufReader::with_capacity(DEFAULT_BUF_SIZE, inner)
77 /// Creates a new `BufReader` with the specified buffer capacity.
81 /// Creating a buffer with ten bytes of capacity:
84 /// use std::io::BufReader;
85 /// use std::fs::File;
87 /// # fn foo() -> std::io::Result<()> {
88 /// let mut f = try!(File::open("log.txt"));
89 /// let mut reader = BufReader::with_capacity(10, f);
93 #[stable(feature = "rust1", since = "1.0.0")]
94 pub fn with_capacity(cap: usize, inner: R) -> BufReader<R> {
97 buf: vec![0; cap].into_boxed_slice(),
103 /// Gets a reference to the underlying reader.
105 /// It is inadvisable to directly read from the underlying reader.
110 /// use std::io::BufReader;
111 /// use std::fs::File;
113 /// # fn foo() -> std::io::Result<()> {
114 /// let mut f1 = try!(File::open("log.txt"));
115 /// let mut reader = BufReader::new(f1);
117 /// let f2 = reader.get_ref();
121 #[stable(feature = "rust1", since = "1.0.0")]
122 pub fn get_ref(&self) -> &R { &self.inner }
124 /// Gets a mutable reference to the underlying reader.
126 /// It is inadvisable to directly read from the underlying reader.
131 /// use std::io::BufReader;
132 /// use std::fs::File;
134 /// # fn foo() -> std::io::Result<()> {
135 /// let mut f1 = try!(File::open("log.txt"));
136 /// let mut reader = BufReader::new(f1);
138 /// let f2 = reader.get_mut();
142 #[stable(feature = "rust1", since = "1.0.0")]
143 pub fn get_mut(&mut self) -> &mut R { &mut self.inner }
145 /// Unwraps this `BufReader`, returning the underlying reader.
147 /// Note that any leftover data in the internal buffer is lost.
152 /// use std::io::BufReader;
153 /// use std::fs::File;
155 /// # fn foo() -> std::io::Result<()> {
156 /// let mut f1 = try!(File::open("log.txt"));
157 /// let mut reader = BufReader::new(f1);
159 /// let f2 = reader.into_inner();
163 #[stable(feature = "rust1", since = "1.0.0")]
164 pub fn into_inner(self) -> R { self.inner }
167 #[stable(feature = "rust1", since = "1.0.0")]
168 impl<R: Read> Read for BufReader<R> {
169 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
170 // If we don't have any buffered data and we're doing a massive read
171 // (larger than our internal buffer), bypass our internal buffer
173 if self.pos == self.cap && buf.len() >= self.buf.len() {
174 return self.inner.read(buf);
177 let mut rem = self.fill_buf()?;
185 #[stable(feature = "rust1", since = "1.0.0")]
186 impl<R: Read> BufRead for BufReader<R> {
187 fn fill_buf(&mut self) -> io::Result<&[u8]> {
188 // If we've reached the end of our internal buffer then we need to fetch
189 // some more data from the underlying reader.
190 // Branch using `>=` instead of the more correct `==`
191 // to tell the compiler that the pos..cap slice is always valid.
192 if self.pos >= self.cap {
193 debug_assert!(self.pos == self.cap);
194 self.cap = self.inner.read(&mut self.buf)?;
197 Ok(&self.buf[self.pos..self.cap])
200 fn consume(&mut self, amt: usize) {
201 self.pos = cmp::min(self.pos + amt, self.cap);
205 #[stable(feature = "rust1", since = "1.0.0")]
206 impl<R> fmt::Debug for BufReader<R> where R: fmt::Debug {
207 fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
208 fmt.debug_struct("BufReader")
209 .field("reader", &self.inner)
210 .field("buffer", &format_args!("{}/{}", self.cap - self.pos, self.buf.len()))
215 #[stable(feature = "rust1", since = "1.0.0")]
216 impl<R: Seek> Seek for BufReader<R> {
217 /// Seek to an offset, in bytes, in the underlying reader.
219 /// The position used for seeking with `SeekFrom::Current(_)` is the
220 /// position the underlying reader would be at if the `BufReader` had no
223 /// Seeking always discards the internal buffer, even if the seek position
224 /// would otherwise fall within it. This guarantees that calling
225 /// `.into_inner()` immediately after a seek yields the underlying reader
226 /// at the same position.
228 /// See `std::io::Seek` for more details.
230 /// Note: In the edge case where you're seeking with `SeekFrom::Current(n)`
231 /// where `n` minus the internal buffer length underflows an `i64`, two
232 /// seeks will be performed instead of one. If the second seek returns
233 /// `Err`, the underlying reader will be left at the same position it would
234 /// have if you seeked to `SeekFrom::Current(0)`.
235 fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
237 if let SeekFrom::Current(n) = pos {
238 let remainder = (self.cap - self.pos) as i64;
239 // it should be safe to assume that remainder fits within an i64 as the alternative
240 // means we managed to allocate 8 exbibytes and that's absurd.
241 // But it's not out of the realm of possibility for some weird underlying reader to
242 // support seeking by i64::min_value() so we need to handle underflow when subtracting
244 if let Some(offset) = n.checked_sub(remainder) {
245 result = self.inner.seek(SeekFrom::Current(offset))?;
247 // seek backwards by our remainder, and then by the offset
248 self.inner.seek(SeekFrom::Current(-remainder))?;
249 self.pos = self.cap; // empty the buffer
250 result = self.inner.seek(SeekFrom::Current(n))?;
253 // Seeking with Start/End doesn't care about our buffer length.
254 result = self.inner.seek(pos)?;
256 self.pos = self.cap; // empty the buffer
261 /// Wraps a writer and buffers its output.
263 /// It can be excessively inefficient to work directly with something that
264 /// implements [`Write`]. For example, every call to [`write`] on [`TcpStream`]
265 /// results in a system call. A `BufWriter` keeps an in-memory buffer of data
266 /// and writes it to an underlying writer in large, infrequent batches.
268 /// The buffer will be written out when the writer is dropped.
272 /// Let's write the numbers one through ten to a [`TcpStream`]:
275 /// use std::io::prelude::*;
276 /// use std::net::TcpStream;
278 /// let mut stream = TcpStream::connect("127.0.0.1:34254").unwrap();
281 /// stream.write(&[i]).unwrap();
285 /// Because we're not buffering, we write each one in turn, incurring the
286 /// overhead of a system call per byte written. We can fix this with a
290 /// use std::io::prelude::*;
291 /// use std::io::BufWriter;
292 /// use std::net::TcpStream;
294 /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
297 /// stream.write(&[i]).unwrap();
301 /// By wrapping the stream with a `BufWriter`, these ten writes are all grouped
302 /// together by the buffer, and will all be written out in one system call when
303 /// the `stream` is dropped.
305 /// [`Write`]: ../../std/io/trait.Write.html
306 /// [`write`]: ../../std/net/struct.TcpStream.html#method.write
307 /// [`TcpStream`]: ../../std/net/struct.TcpStream.html
308 #[stable(feature = "rust1", since = "1.0.0")]
309 pub struct BufWriter<W: Write> {
312 // #30888: If the inner writer panics in a call to write, we don't want to
313 // write the buffered data a second time in BufWriter's destructor. This
314 // flag tells the Drop impl if it should skip the flush.
318 /// An error returned by `into_inner` which combines an error that
319 /// happened while writing out the buffer, and the buffered writer object
320 /// which may be used to recover from the condition.
325 /// use std::io::BufWriter;
326 /// use std::net::TcpStream;
328 /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
330 /// // do stuff with the stream
332 /// // we want to get our `TcpStream` back, so let's try:
334 /// let stream = match stream.into_inner() {
337 /// // Here, e is an IntoInnerError
338 /// panic!("An error occurred");
343 #[stable(feature = "rust1", since = "1.0.0")]
344 pub struct IntoInnerError<W>(W, Error);
346 impl<W: Write> BufWriter<W> {
347 /// Creates a new `BufWriter` with a default buffer capacity.
352 /// use std::io::BufWriter;
353 /// use std::net::TcpStream;
355 /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
357 #[stable(feature = "rust1", since = "1.0.0")]
358 pub fn new(inner: W) -> BufWriter<W> {
359 BufWriter::with_capacity(DEFAULT_BUF_SIZE, inner)
362 /// Creates a new `BufWriter` with the specified buffer capacity.
366 /// Creating a buffer with a buffer of a hundred bytes.
369 /// use std::io::BufWriter;
370 /// use std::net::TcpStream;
372 /// let stream = TcpStream::connect("127.0.0.1:34254").unwrap();
373 /// let mut buffer = BufWriter::with_capacity(100, stream);
375 #[stable(feature = "rust1", since = "1.0.0")]
376 pub fn with_capacity(cap: usize, inner: W) -> BufWriter<W> {
379 buf: Vec::with_capacity(cap),
384 fn flush_buf(&mut self) -> io::Result<()> {
386 let len = self.buf.len();
387 let mut ret = Ok(());
388 while written < len {
389 self.panicked = true;
390 let r = self.inner.as_mut().unwrap().write(&self.buf[written..]);
391 self.panicked = false;
395 ret = Err(Error::new(ErrorKind::WriteZero,
396 "failed to write the buffered data"));
399 Ok(n) => written += n,
400 Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
401 Err(e) => { ret = Err(e); break }
406 self.buf.drain(..written);
411 /// Gets a reference to the underlying writer.
416 /// use std::io::BufWriter;
417 /// use std::net::TcpStream;
419 /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
421 /// // we can use reference just like buffer
422 /// let reference = buffer.get_ref();
424 #[stable(feature = "rust1", since = "1.0.0")]
425 pub fn get_ref(&self) -> &W { self.inner.as_ref().unwrap() }
427 /// Gets a mutable reference to the underlying writer.
429 /// It is inadvisable to directly write to the underlying writer.
434 /// use std::io::BufWriter;
435 /// use std::net::TcpStream;
437 /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
439 /// // we can use reference just like buffer
440 /// let reference = buffer.get_mut();
442 #[stable(feature = "rust1", since = "1.0.0")]
443 pub fn get_mut(&mut self) -> &mut W { self.inner.as_mut().unwrap() }
445 /// Unwraps this `BufWriter`, returning the underlying writer.
447 /// The buffer is written out before returning the writer.
452 /// use std::io::BufWriter;
453 /// use std::net::TcpStream;
455 /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
457 /// // unwrap the TcpStream and flush the buffer
458 /// let stream = buffer.into_inner().unwrap();
460 #[stable(feature = "rust1", since = "1.0.0")]
461 pub fn into_inner(mut self) -> Result<W, IntoInnerError<BufWriter<W>>> {
462 match self.flush_buf() {
463 Err(e) => Err(IntoInnerError(self, e)),
464 Ok(()) => Ok(self.inner.take().unwrap())
469 #[stable(feature = "rust1", since = "1.0.0")]
470 impl<W: Write> Write for BufWriter<W> {
471 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
472 if self.buf.len() + buf.len() > self.buf.capacity() {
475 if buf.len() >= self.buf.capacity() {
476 self.panicked = true;
477 let r = self.inner.as_mut().unwrap().write(buf);
478 self.panicked = false;
481 Write::write(&mut self.buf, buf)
484 fn flush(&mut self) -> io::Result<()> {
485 self.flush_buf().and_then(|()| self.get_mut().flush())
489 #[stable(feature = "rust1", since = "1.0.0")]
490 impl<W: Write> fmt::Debug for BufWriter<W> where W: fmt::Debug {
491 fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
492 fmt.debug_struct("BufWriter")
493 .field("writer", &self.inner.as_ref().unwrap())
494 .field("buffer", &format_args!("{}/{}", self.buf.len(), self.buf.capacity()))
499 #[stable(feature = "rust1", since = "1.0.0")]
500 impl<W: Write + Seek> Seek for BufWriter<W> {
501 /// Seek to the offset, in bytes, in the underlying writer.
503 /// Seeking always writes out the internal buffer before seeking.
504 fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
505 self.flush_buf().and_then(|_| self.get_mut().seek(pos))
509 #[stable(feature = "rust1", since = "1.0.0")]
510 impl<W: Write> Drop for BufWriter<W> {
512 if self.inner.is_some() && !self.panicked {
513 // dtors should not panic, so we ignore a failed flush
514 let _r = self.flush_buf();
519 impl<W> IntoInnerError<W> {
520 /// Returns the error which caused the call to `into_inner()` to fail.
522 /// This error was returned when attempting to write the internal buffer.
527 /// use std::io::BufWriter;
528 /// use std::net::TcpStream;
530 /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
532 /// // do stuff with the stream
534 /// // we want to get our `TcpStream` back, so let's try:
536 /// let stream = match stream.into_inner() {
539 /// // Here, e is an IntoInnerError, let's log the inner error.
541 /// // We'll just 'log' to stdout for this example.
542 /// println!("{}", e.error());
544 /// panic!("An unexpected error occurred.");
548 #[stable(feature = "rust1", since = "1.0.0")]
549 pub fn error(&self) -> &Error { &self.1 }
551 /// Returns the buffered writer instance which generated the error.
553 /// The returned object can be used for error recovery, such as
554 /// re-inspecting the buffer.
559 /// use std::io::BufWriter;
560 /// use std::net::TcpStream;
562 /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
564 /// // do stuff with the stream
566 /// // we want to get our `TcpStream` back, so let's try:
568 /// let stream = match stream.into_inner() {
571 /// // Here, e is an IntoInnerError, let's re-examine the buffer:
572 /// let buffer = e.into_inner();
574 /// // do stuff to try to recover
576 /// // afterwards, let's just return the stream
577 /// buffer.into_inner().unwrap()
581 #[stable(feature = "rust1", since = "1.0.0")]
582 pub fn into_inner(self) -> W { self.0 }
585 #[stable(feature = "rust1", since = "1.0.0")]
586 impl<W> From<IntoInnerError<W>> for Error {
587 fn from(iie: IntoInnerError<W>) -> Error { iie.1 }
590 #[stable(feature = "rust1", since = "1.0.0")]
591 impl<W: Send + fmt::Debug> error::Error for IntoInnerError<W> {
592 fn description(&self) -> &str {
593 error::Error::description(self.error())
597 #[stable(feature = "rust1", since = "1.0.0")]
598 impl<W> fmt::Display for IntoInnerError<W> {
599 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
604 /// Wraps a writer and buffers output to it, flushing whenever a newline
605 /// (`0x0a`, `'\n'`) is detected.
607 /// The [`BufWriter`][bufwriter] struct wraps a writer and buffers its output.
608 /// But it only does this batched write when it goes out of scope, or when the
609 /// internal buffer is full. Sometimes, you'd prefer to write each line as it's
610 /// completed, rather than the entire buffer at once. Enter `LineWriter`. It
611 /// does exactly that.
613 /// [bufwriter]: struct.BufWriter.html
615 /// If there's still a partial line in the buffer when the `LineWriter` is
616 /// dropped, it will flush those contents.
620 /// We can use `LineWriter` to write one line at a time, significantly
621 /// reducing the number of actual writes to the file.
624 /// use std::fs::File;
625 /// use std::io::prelude::*;
626 /// use std::io::LineWriter;
628 /// # fn foo() -> std::io::Result<()> {
629 /// let road_not_taken = b"I shall be telling this with a sigh
630 /// Somewhere ages and ages hence:
631 /// Two roads diverged in a wood, and I -
632 /// I took the one less traveled by,
633 /// And that has made all the difference.";
635 /// let file = try!(File::create("poem.txt"));
636 /// let mut file = LineWriter::new(file);
638 /// for &byte in road_not_taken.iter() {
639 /// file.write(&[byte]).unwrap();
642 /// // let's check we did the right thing.
643 /// let mut file = try!(File::open("poem.txt"));
644 /// let mut contents = String::new();
646 /// try!(file.read_to_string(&mut contents));
648 /// assert_eq!(contents.as_bytes(), &road_not_taken[..]);
652 #[stable(feature = "rust1", since = "1.0.0")]
653 pub struct LineWriter<W: Write> {
658 impl<W: Write> LineWriter<W> {
659 /// Creates a new `LineWriter`.
664 /// use std::fs::File;
665 /// use std::io::LineWriter;
667 /// # fn foo() -> std::io::Result<()> {
668 /// let file = try!(File::create("poem.txt"));
669 /// let file = LineWriter::new(file);
673 #[stable(feature = "rust1", since = "1.0.0")]
674 pub fn new(inner: W) -> LineWriter<W> {
675 // Lines typically aren't that long, don't use a giant buffer
676 LineWriter::with_capacity(1024, inner)
679 /// Creates a new `LineWriter` with a specified capacity for the internal
685 /// use std::fs::File;
686 /// use std::io::LineWriter;
688 /// # fn foo() -> std::io::Result<()> {
689 /// let file = try!(File::create("poem.txt"));
690 /// let file = LineWriter::with_capacity(100, file);
694 #[stable(feature = "rust1", since = "1.0.0")]
695 pub fn with_capacity(cap: usize, inner: W) -> LineWriter<W> {
697 inner: BufWriter::with_capacity(cap, inner),
702 /// Gets a reference to the underlying writer.
707 /// use std::fs::File;
708 /// use std::io::LineWriter;
710 /// # fn foo() -> std::io::Result<()> {
711 /// let file = try!(File::create("poem.txt"));
712 /// let file = LineWriter::new(file);
714 /// let reference = file.get_ref();
718 #[stable(feature = "rust1", since = "1.0.0")]
719 pub fn get_ref(&self) -> &W { self.inner.get_ref() }
721 /// Gets a mutable reference to the underlying writer.
723 /// Caution must be taken when calling methods on the mutable reference
724 /// returned as extra writes could corrupt the output stream.
729 /// use std::fs::File;
730 /// use std::io::LineWriter;
732 /// # fn foo() -> std::io::Result<()> {
733 /// let file = try!(File::create("poem.txt"));
734 /// let mut file = LineWriter::new(file);
736 /// // we can use reference just like file
737 /// let reference = file.get_mut();
741 #[stable(feature = "rust1", since = "1.0.0")]
742 pub fn get_mut(&mut self) -> &mut W { self.inner.get_mut() }
744 /// Unwraps this `LineWriter`, returning the underlying writer.
746 /// The internal buffer is written out before returning the writer.
751 /// use std::fs::File;
752 /// use std::io::LineWriter;
754 /// # fn foo() -> std::io::Result<()> {
755 /// let file = try!(File::create("poem.txt"));
757 /// let writer: LineWriter<File> = LineWriter::new(file);
759 /// let file: File = try!(writer.into_inner());
763 #[stable(feature = "rust1", since = "1.0.0")]
764 pub fn into_inner(self) -> Result<W, IntoInnerError<LineWriter<W>>> {
765 self.inner.into_inner().map_err(|IntoInnerError(buf, e)| {
766 IntoInnerError(LineWriter {
774 #[stable(feature = "rust1", since = "1.0.0")]
775 impl<W: Write> Write for LineWriter<W> {
776 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
781 // Find the last newline character in the buffer provided. If found then
782 // we're going to write all the data up to that point and then flush,
783 // otherewise we just write the whole block to the underlying writer.
784 let i = match memchr::memrchr(b'\n', buf) {
786 None => return self.inner.write(buf),
790 // Ok, we're going to write a partial amount of the data given first
791 // followed by flushing the newline. After we've successfully written
792 // some data then we *must* report that we wrote that data, so future
793 // errors are ignored. We set our internal `need_flush` flag, though, in
794 // case flushing fails and we need to try it first next time.
795 let n = self.inner.write(&buf[..i + 1])?;
796 self.need_flush = true;
797 if self.flush().is_err() || n != i + 1 {
801 // At this point we successfully wrote `i + 1` bytes and flushed it out,
802 // meaning that the entire line is now flushed out on the screen. While
803 // we can attempt to finish writing the rest of the data provided.
804 // Remember though that we ignore errors here as we've successfully
805 // written data, so we need to report that.
806 match self.inner.write(&buf[i + 1..]) {
812 fn flush(&mut self) -> io::Result<()> {
814 self.need_flush = false;
819 #[stable(feature = "rust1", since = "1.0.0")]
820 impl<W: Write> fmt::Debug for LineWriter<W> where W: fmt::Debug {
821 fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
822 fmt.debug_struct("LineWriter")
823 .field("writer", &self.inner.inner)
825 &format_args!("{}/{}", self.inner.buf.len(), self.inner.buf.capacity()))
833 use io::{self, BufReader, BufWriter, LineWriter, SeekFrom};
834 use sync::atomic::{AtomicUsize, Ordering};
838 /// A dummy reader intended at testing short-reads propagation.
839 pub struct ShortReader {
843 impl Read for ShortReader {
844 fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
845 if self.lengths.is_empty() {
848 Ok(self.lengths.remove(0))
854 fn test_buffered_reader() {
855 let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
856 let mut reader = BufReader::with_capacity(2, inner);
858 let mut buf = [0, 0, 0];
859 let nread = reader.read(&mut buf);
860 assert_eq!(nread.unwrap(), 3);
861 let b: &[_] = &[5, 6, 7];
864 let mut buf = [0, 0];
865 let nread = reader.read(&mut buf);
866 assert_eq!(nread.unwrap(), 2);
867 let b: &[_] = &[0, 1];
871 let nread = reader.read(&mut buf);
872 assert_eq!(nread.unwrap(), 1);
876 let mut buf = [0, 0, 0];
877 let nread = reader.read(&mut buf);
878 assert_eq!(nread.unwrap(), 1);
879 let b: &[_] = &[3, 0, 0];
882 let nread = reader.read(&mut buf);
883 assert_eq!(nread.unwrap(), 1);
884 let b: &[_] = &[4, 0, 0];
887 assert_eq!(reader.read(&mut buf).unwrap(), 0);
891 fn test_buffered_reader_seek() {
892 let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
893 let mut reader = BufReader::with_capacity(2, io::Cursor::new(inner));
895 assert_eq!(reader.seek(SeekFrom::Start(3)).ok(), Some(3));
896 assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
897 assert_eq!(reader.seek(SeekFrom::Current(0)).ok(), Some(3));
898 assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
899 assert_eq!(reader.seek(SeekFrom::Current(1)).ok(), Some(4));
900 assert_eq!(reader.fill_buf().ok(), Some(&[1, 2][..]));
902 assert_eq!(reader.seek(SeekFrom::Current(-2)).ok(), Some(3));
906 fn test_buffered_reader_seek_underflow() {
907 // gimmick reader that yields its position modulo 256 for each byte
908 struct PositionReader {
911 impl Read for PositionReader {
912 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
916 self.pos = self.pos.wrapping_add(1);
921 impl Seek for PositionReader {
922 fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
924 SeekFrom::Start(n) => {
927 SeekFrom::Current(n) => {
928 self.pos = self.pos.wrapping_add(n as u64);
930 SeekFrom::End(n) => {
931 self.pos = u64::max_value().wrapping_add(n as u64);
938 let mut reader = BufReader::with_capacity(5, PositionReader { pos: 0 });
939 assert_eq!(reader.fill_buf().ok(), Some(&[0, 1, 2, 3, 4][..]));
940 assert_eq!(reader.seek(SeekFrom::End(-5)).ok(), Some(u64::max_value()-5));
941 assert_eq!(reader.fill_buf().ok().map(|s| s.len()), Some(5));
942 // the following seek will require two underlying seeks
943 let expected = 9223372036854775802;
944 assert_eq!(reader.seek(SeekFrom::Current(i64::min_value())).ok(), Some(expected));
945 assert_eq!(reader.fill_buf().ok().map(|s| s.len()), Some(5));
946 // seeking to 0 should empty the buffer.
947 assert_eq!(reader.seek(SeekFrom::Current(0)).ok(), Some(expected));
948 assert_eq!(reader.get_ref().pos, expected);
952 fn test_buffered_writer() {
953 let inner = Vec::new();
954 let mut writer = BufWriter::with_capacity(2, inner);
956 writer.write(&[0, 1]).unwrap();
957 assert_eq!(*writer.get_ref(), [0, 1]);
959 writer.write(&[2]).unwrap();
960 assert_eq!(*writer.get_ref(), [0, 1]);
962 writer.write(&[3]).unwrap();
963 assert_eq!(*writer.get_ref(), [0, 1]);
965 writer.flush().unwrap();
966 assert_eq!(*writer.get_ref(), [0, 1, 2, 3]);
968 writer.write(&[4]).unwrap();
969 writer.write(&[5]).unwrap();
970 assert_eq!(*writer.get_ref(), [0, 1, 2, 3]);
972 writer.write(&[6]).unwrap();
973 assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5]);
975 writer.write(&[7, 8]).unwrap();
976 assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8]);
978 writer.write(&[9, 10, 11]).unwrap();
979 assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]);
981 writer.flush().unwrap();
982 assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]);
986 fn test_buffered_writer_inner_flushes() {
987 let mut w = BufWriter::with_capacity(3, Vec::new());
988 w.write(&[0, 1]).unwrap();
989 assert_eq!(*w.get_ref(), []);
990 let w = w.into_inner().unwrap();
991 assert_eq!(w, [0, 1]);
995 fn test_buffered_writer_seek() {
996 let mut w = BufWriter::with_capacity(3, io::Cursor::new(Vec::new()));
997 w.write_all(&[0, 1, 2, 3, 4, 5]).unwrap();
998 w.write_all(&[6, 7]).unwrap();
999 assert_eq!(w.seek(SeekFrom::Current(0)).ok(), Some(8));
1000 assert_eq!(&w.get_ref().get_ref()[..], &[0, 1, 2, 3, 4, 5, 6, 7][..]);
1001 assert_eq!(w.seek(SeekFrom::Start(2)).ok(), Some(2));
1002 w.write_all(&[8, 9]).unwrap();
1003 assert_eq!(&w.into_inner().unwrap().into_inner()[..], &[0, 1, 8, 9, 4, 5, 6, 7]);
1007 fn test_read_until() {
1008 let inner: &[u8] = &[0, 1, 2, 1, 0];
1009 let mut reader = BufReader::with_capacity(2, inner);
1010 let mut v = Vec::new();
1011 reader.read_until(0, &mut v).unwrap();
1014 reader.read_until(2, &mut v).unwrap();
1015 assert_eq!(v, [1, 2]);
1017 reader.read_until(1, &mut v).unwrap();
1020 reader.read_until(8, &mut v).unwrap();
1023 reader.read_until(9, &mut v).unwrap();
1028 fn test_line_buffer_fail_flush() {
1030 struct FailFlushWriter<'a>(&'a mut Vec<u8>);
1032 impl<'a> Write for FailFlushWriter<'a> {
1033 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
1034 self.0.extend_from_slice(buf);
1037 fn flush(&mut self) -> io::Result<()> {
1038 Err(io::Error::new(io::ErrorKind::Other, "flush failed"))
1042 let mut buf = Vec::new();
1044 let mut writer = LineWriter::new(FailFlushWriter(&mut buf));
1045 let to_write = b"abc\ndef";
1046 if let Ok(written) = writer.write(to_write) {
1047 assert!(written < to_write.len(), "didn't flush on new line");
1052 assert!(buf.is_empty(), "write returned an error but wrote data");
1056 fn test_line_buffer() {
1057 let mut writer = LineWriter::new(Vec::new());
1058 writer.write(&[0]).unwrap();
1059 assert_eq!(*writer.get_ref(), []);
1060 writer.write(&[1]).unwrap();
1061 assert_eq!(*writer.get_ref(), []);
1062 writer.flush().unwrap();
1063 assert_eq!(*writer.get_ref(), [0, 1]);
1064 writer.write(&[0, b'\n', 1, b'\n', 2]).unwrap();
1065 assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n']);
1066 writer.flush().unwrap();
1067 assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n', 2]);
1068 writer.write(&[3, b'\n']).unwrap();
1069 assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n', 2, 3, b'\n']);
1073 fn test_read_line() {
1074 let in_buf: &[u8] = b"a\nb\nc";
1075 let mut reader = BufReader::with_capacity(2, in_buf);
1076 let mut s = String::new();
1077 reader.read_line(&mut s).unwrap();
1078 assert_eq!(s, "a\n");
1080 reader.read_line(&mut s).unwrap();
1081 assert_eq!(s, "b\n");
1083 reader.read_line(&mut s).unwrap();
1086 reader.read_line(&mut s).unwrap();
1092 let in_buf: &[u8] = b"a\nb\nc";
1093 let reader = BufReader::with_capacity(2, in_buf);
1094 let mut it = reader.lines();
1095 assert_eq!(it.next().unwrap().unwrap(), "a".to_string());
1096 assert_eq!(it.next().unwrap().unwrap(), "b".to_string());
1097 assert_eq!(it.next().unwrap().unwrap(), "c".to_string());
1098 assert!(it.next().is_none());
1102 fn test_short_reads() {
1103 let inner = ShortReader{lengths: vec![0, 1, 2, 0, 1, 0]};
1104 let mut reader = BufReader::new(inner);
1105 let mut buf = [0, 0];
1106 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1107 assert_eq!(reader.read(&mut buf).unwrap(), 1);
1108 assert_eq!(reader.read(&mut buf).unwrap(), 2);
1109 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1110 assert_eq!(reader.read(&mut buf).unwrap(), 1);
1111 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1112 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1116 fn read_char_buffered() {
1117 let buf = [195, 159];
1118 let reader = BufReader::with_capacity(1, &buf[..]);
1119 assert_eq!(reader.chars().next().unwrap().unwrap(), 'ß');
1124 let buf = [195, 159, b'a'];
1125 let reader = BufReader::with_capacity(1, &buf[..]);
1126 let mut it = reader.chars();
1127 assert_eq!(it.next().unwrap().unwrap(), 'ß');
1128 assert_eq!(it.next().unwrap().unwrap(), 'a');
1129 assert!(it.next().is_none());
1134 fn dont_panic_in_drop_on_panicked_flush() {
1135 struct FailFlushWriter;
1137 impl Write for FailFlushWriter {
1138 fn write(&mut self, buf: &[u8]) -> io::Result<usize> { Ok(buf.len()) }
1139 fn flush(&mut self) -> io::Result<()> {
1140 Err(io::Error::last_os_error())
1144 let writer = FailFlushWriter;
1145 let _writer = BufWriter::new(writer);
1147 // If writer panics *again* due to the flush error then the process will
1153 #[cfg_attr(target_os = "emscripten", ignore)]
1154 fn panic_in_write_doesnt_flush_in_drop() {
1155 static WRITES: AtomicUsize = AtomicUsize::new(0);
1159 impl Write for PanicWriter {
1160 fn write(&mut self, _: &[u8]) -> io::Result<usize> {
1161 WRITES.fetch_add(1, Ordering::SeqCst);
1164 fn flush(&mut self) -> io::Result<()> { Ok(()) }
1168 let mut writer = BufWriter::new(PanicWriter);
1169 let _ = writer.write(b"hello world");
1170 let _ = writer.flush();
1171 }).join().unwrap_err();
1173 assert_eq!(WRITES.load(Ordering::SeqCst), 1);
1177 fn bench_buffered_reader(b: &mut test::Bencher) {
1179 BufReader::new(io::empty())
1184 fn bench_buffered_writer(b: &mut test::Bencher) {
1186 BufWriter::new(io::sink())
1190 struct AcceptOneThenFail {
1195 impl Write for AcceptOneThenFail {
1196 fn write(&mut self, data: &[u8]) -> io::Result<usize> {
1198 assert_eq!(data, b"a\nb\n");
1199 self.written = true;
1202 Err(io::Error::new(io::ErrorKind::NotFound, "test"))
1206 fn flush(&mut self) -> io::Result<()> {
1207 assert!(self.written);
1208 assert!(!self.flushed);
1209 self.flushed = true;
1210 Err(io::Error::new(io::ErrorKind::Other, "test"))
1215 fn erroneous_flush_retried() {
1216 let a = AcceptOneThenFail {
1221 let mut l = LineWriter::new(a);
1222 assert_eq!(l.write(b"a\nb\na").unwrap(), 4);
1223 assert!(l.get_ref().written);
1224 assert!(l.get_ref().flushed);
1225 l.get_mut().flushed = false;
1227 assert_eq!(l.write(b"a").unwrap_err().kind(), io::ErrorKind::Other)