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
19 use io::{self, DEFAULT_BUF_SIZE, Error, ErrorKind, SeekFrom};
22 /// The `BufReader` struct adds buffering to any reader.
24 /// It can be excessively inefficient to work directly with a `Read` instance.
25 /// For example, every call to `read` on `TcpStream` results in a system call.
26 /// A `BufReader` performs large, infrequent reads on the underlying `Read`
27 /// and maintains an in-memory buffer of the results.
32 /// use std::io::prelude::*;
33 /// use std::io::BufReader;
34 /// use std::fs::File;
36 /// # fn foo() -> std::io::Result<()> {
37 /// let mut f = try!(File::open("log.txt"));
38 /// let mut reader = BufReader::new(f);
40 /// let mut line = String::new();
41 /// let len = try!(reader.read_line(&mut line));
42 /// println!("First line is {} bytes long", len);
46 #[stable(feature = "rust1", since = "1.0.0")]
47 pub struct BufReader<R> {
54 impl<R: Read> BufReader<R> {
55 /// Creates a new `BufReader` with a default buffer capacity.
60 /// use std::io::BufReader;
61 /// use std::fs::File;
63 /// # fn foo() -> std::io::Result<()> {
64 /// let mut f = try!(File::open("log.txt"));
65 /// let mut reader = BufReader::new(f);
69 #[stable(feature = "rust1", since = "1.0.0")]
70 pub fn new(inner: R) -> BufReader<R> {
71 BufReader::with_capacity(DEFAULT_BUF_SIZE, inner)
74 /// Creates a new `BufReader` with the specified buffer capacity.
78 /// Creating a buffer with ten bytes of capacity:
81 /// use std::io::BufReader;
82 /// use std::fs::File;
84 /// # fn foo() -> std::io::Result<()> {
85 /// let mut f = try!(File::open("log.txt"));
86 /// let mut reader = BufReader::with_capacity(10, f);
90 #[stable(feature = "rust1", since = "1.0.0")]
91 pub fn with_capacity(cap: usize, inner: R) -> BufReader<R> {
94 buf: vec![0; cap].into_boxed_slice(),
100 /// Gets a reference to the underlying reader.
102 /// It is inadvisable to directly read from the underlying reader.
107 /// use std::io::BufReader;
108 /// use std::fs::File;
110 /// # fn foo() -> std::io::Result<()> {
111 /// let mut f1 = try!(File::open("log.txt"));
112 /// let mut reader = BufReader::new(f1);
114 /// let f2 = reader.get_ref();
118 #[stable(feature = "rust1", since = "1.0.0")]
119 pub fn get_ref(&self) -> &R { &self.inner }
121 /// Gets a mutable reference to the underlying reader.
123 /// It is inadvisable to directly read from the underlying reader.
128 /// use std::io::BufReader;
129 /// use std::fs::File;
131 /// # fn foo() -> std::io::Result<()> {
132 /// let mut f1 = try!(File::open("log.txt"));
133 /// let mut reader = BufReader::new(f1);
135 /// let f2 = reader.get_mut();
139 #[stable(feature = "rust1", since = "1.0.0")]
140 pub fn get_mut(&mut self) -> &mut R { &mut self.inner }
142 /// Unwraps this `BufReader`, returning the underlying reader.
144 /// Note that any leftover data in the internal buffer is lost.
149 /// use std::io::BufReader;
150 /// use std::fs::File;
152 /// # fn foo() -> std::io::Result<()> {
153 /// let mut f1 = try!(File::open("log.txt"));
154 /// let mut reader = BufReader::new(f1);
156 /// let f2 = reader.into_inner();
160 #[stable(feature = "rust1", since = "1.0.0")]
161 pub fn into_inner(self) -> R { self.inner }
164 #[stable(feature = "rust1", since = "1.0.0")]
165 impl<R: Read> Read for BufReader<R> {
166 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
167 // If we don't have any buffered data and we're doing a massive read
168 // (larger than our internal buffer), bypass our internal buffer
170 if self.pos == self.cap && buf.len() >= self.buf.len() {
171 return self.inner.read(buf);
174 let mut rem = self.fill_buf()?;
182 #[stable(feature = "rust1", since = "1.0.0")]
183 impl<R: Read> BufRead for BufReader<R> {
184 fn fill_buf(&mut self) -> io::Result<&[u8]> {
185 // If we've reached the end of our internal buffer then we need to fetch
186 // some more data from the underlying reader.
187 if self.pos == self.cap {
188 self.cap = self.inner.read(&mut self.buf)?;
191 Ok(&self.buf[self.pos..self.cap])
194 fn consume(&mut self, amt: usize) {
195 self.pos = cmp::min(self.pos + amt, self.cap);
199 #[stable(feature = "rust1", since = "1.0.0")]
200 impl<R> fmt::Debug for BufReader<R> where R: fmt::Debug {
201 fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
202 fmt.debug_struct("BufReader")
203 .field("reader", &self.inner)
204 .field("buffer", &format_args!("{}/{}", self.cap - self.pos, self.buf.len()))
209 #[stable(feature = "rust1", since = "1.0.0")]
210 impl<R: Seek> Seek for BufReader<R> {
211 /// Seek to an offset, in bytes, in the underlying reader.
213 /// The position used for seeking with `SeekFrom::Current(_)` is the
214 /// position the underlying reader would be at if the `BufReader` had no
217 /// Seeking always discards the internal buffer, even if the seek position
218 /// would otherwise fall within it. This guarantees that calling
219 /// `.unwrap()` immediately after a seek yields the underlying reader at
220 /// the same position.
222 /// See `std::io::Seek` for more details.
224 /// Note: In the edge case where you're seeking with `SeekFrom::Current(n)`
225 /// where `n` minus the internal buffer length underflows an `i64`, two
226 /// seeks will be performed instead of one. If the second seek returns
227 /// `Err`, the underlying reader will be left at the same position it would
228 /// have if you seeked to `SeekFrom::Current(0)`.
229 fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
231 if let SeekFrom::Current(n) = pos {
232 let remainder = (self.cap - self.pos) as i64;
233 // it should be safe to assume that remainder fits within an i64 as the alternative
234 // means we managed to allocate 8 ebibytes and that's absurd.
235 // But it's not out of the realm of possibility for some weird underlying reader to
236 // support seeking by i64::min_value() so we need to handle underflow when subtracting
238 if let Some(offset) = n.checked_sub(remainder) {
239 result = self.inner.seek(SeekFrom::Current(offset))?;
241 // seek backwards by our remainder, and then by the offset
242 self.inner.seek(SeekFrom::Current(-remainder))?;
243 self.pos = self.cap; // empty the buffer
244 result = self.inner.seek(SeekFrom::Current(n))?;
247 // Seeking with Start/End doesn't care about our buffer length.
248 result = self.inner.seek(pos)?;
250 self.pos = self.cap; // empty the buffer
255 /// Wraps a writer and buffers its output.
257 /// It can be excessively inefficient to work directly with something that
258 /// implements `Write`. For example, every call to `write` on `TcpStream`
259 /// results in a system call. A `BufWriter` keeps an in-memory buffer of data
260 /// and writes it to an underlying writer in large, infrequent batches.
262 /// The buffer will be written out when the writer is dropped.
266 /// Let's write the numbers one through ten to a `TcpStream`:
269 /// use std::io::prelude::*;
270 /// use std::net::TcpStream;
272 /// let mut stream = TcpStream::connect("127.0.0.1:34254").unwrap();
275 /// stream.write(&[i]).unwrap();
279 /// Because we're not buffering, we write each one in turn, incurring the
280 /// overhead of a system call per byte written. We can fix this with a
284 /// use std::io::prelude::*;
285 /// use std::io::BufWriter;
286 /// use std::net::TcpStream;
288 /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
291 /// stream.write(&[i]).unwrap();
295 /// By wrapping the stream with a `BufWriter`, these ten writes are all grouped
296 /// together by the buffer, and will all be written out in one system call when
297 /// the `stream` is dropped.
298 #[stable(feature = "rust1", since = "1.0.0")]
299 pub struct BufWriter<W: Write> {
302 // #30888: If the inner writer panics in a call to write, we don't want to
303 // write the buffered data a second time in BufWriter's destructor. This
304 // flag tells the Drop impl if it should skip the flush.
308 /// An error returned by `into_inner` which combines an error that
309 /// happened while writing out the buffer, and the buffered writer object
310 /// which may be used to recover from the condition.
315 /// use std::io::BufWriter;
316 /// use std::net::TcpStream;
318 /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
320 /// // do stuff with the stream
322 /// // we want to get our `TcpStream` back, so let's try:
324 /// let stream = match stream.into_inner() {
327 /// // Here, e is an IntoInnerError
328 /// panic!("An error occurred");
333 #[stable(feature = "rust1", since = "1.0.0")]
334 pub struct IntoInnerError<W>(W, Error);
336 impl<W: Write> BufWriter<W> {
337 /// Creates a new `BufWriter` with a default buffer capacity.
342 /// use std::io::BufWriter;
343 /// use std::net::TcpStream;
345 /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
347 #[stable(feature = "rust1", since = "1.0.0")]
348 pub fn new(inner: W) -> BufWriter<W> {
349 BufWriter::with_capacity(DEFAULT_BUF_SIZE, inner)
352 /// Creates a new `BufWriter` with the specified buffer capacity.
356 /// Creating a buffer with a buffer of a hundred bytes.
359 /// use std::io::BufWriter;
360 /// use std::net::TcpStream;
362 /// let stream = TcpStream::connect("127.0.0.1:34254").unwrap();
363 /// let mut buffer = BufWriter::with_capacity(100, stream);
365 #[stable(feature = "rust1", since = "1.0.0")]
366 pub fn with_capacity(cap: usize, inner: W) -> BufWriter<W> {
369 buf: Vec::with_capacity(cap),
374 fn flush_buf(&mut self) -> io::Result<()> {
376 let len = self.buf.len();
377 let mut ret = Ok(());
378 while written < len {
379 self.panicked = true;
380 let r = self.inner.as_mut().unwrap().write(&self.buf[written..]);
381 self.panicked = false;
385 ret = Err(Error::new(ErrorKind::WriteZero,
386 "failed to write the buffered data"));
389 Ok(n) => written += n,
390 Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
391 Err(e) => { ret = Err(e); break }
396 self.buf.drain(..written);
401 /// Gets a reference to the underlying writer.
406 /// use std::io::BufWriter;
407 /// use std::net::TcpStream;
409 /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
411 /// // we can use reference just like buffer
412 /// let reference = buffer.get_ref();
414 #[stable(feature = "rust1", since = "1.0.0")]
415 pub fn get_ref(&self) -> &W { self.inner.as_ref().unwrap() }
417 /// Gets a mutable reference to the underlying writer.
419 /// It is inadvisable to directly write to the underlying writer.
424 /// use std::io::BufWriter;
425 /// use std::net::TcpStream;
427 /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
429 /// // we can use reference just like buffer
430 /// let reference = buffer.get_mut();
432 #[stable(feature = "rust1", since = "1.0.0")]
433 pub fn get_mut(&mut self) -> &mut W { self.inner.as_mut().unwrap() }
435 /// Unwraps this `BufWriter`, returning the underlying writer.
437 /// The buffer is written out before returning the writer.
442 /// use std::io::BufWriter;
443 /// use std::net::TcpStream;
445 /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
447 /// // unwrap the TcpStream and flush the buffer
448 /// let stream = buffer.into_inner().unwrap();
450 #[stable(feature = "rust1", since = "1.0.0")]
451 pub fn into_inner(mut self) -> Result<W, IntoInnerError<BufWriter<W>>> {
452 match self.flush_buf() {
453 Err(e) => Err(IntoInnerError(self, e)),
454 Ok(()) => Ok(self.inner.take().unwrap())
459 #[stable(feature = "rust1", since = "1.0.0")]
460 impl<W: Write> Write for BufWriter<W> {
461 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
462 if self.buf.len() + buf.len() > self.buf.capacity() {
465 if buf.len() >= self.buf.capacity() {
466 self.panicked = true;
467 let r = self.inner.as_mut().unwrap().write(buf);
468 self.panicked = false;
471 let amt = cmp::min(buf.len(), self.buf.capacity());
472 Write::write(&mut self.buf, &buf[..amt])
475 fn flush(&mut self) -> io::Result<()> {
476 self.flush_buf().and_then(|()| self.get_mut().flush())
480 #[stable(feature = "rust1", since = "1.0.0")]
481 impl<W: Write> fmt::Debug for BufWriter<W> where W: fmt::Debug {
482 fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
483 fmt.debug_struct("BufWriter")
484 .field("writer", &self.inner.as_ref().unwrap())
485 .field("buffer", &format_args!("{}/{}", self.buf.len(), self.buf.capacity()))
490 #[stable(feature = "rust1", since = "1.0.0")]
491 impl<W: Write + Seek> Seek for BufWriter<W> {
492 /// Seek to the offset, in bytes, in the underlying writer.
494 /// Seeking always writes out the internal buffer before seeking.
495 fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
496 self.flush_buf().and_then(|_| self.get_mut().seek(pos))
500 #[stable(feature = "rust1", since = "1.0.0")]
501 impl<W: Write> Drop for BufWriter<W> {
503 if self.inner.is_some() && !self.panicked {
504 // dtors should not panic, so we ignore a failed flush
505 let _r = self.flush_buf();
510 impl<W> IntoInnerError<W> {
511 /// Returns the error which caused the call to `into_inner()` to fail.
513 /// This error was returned when attempting to write the internal buffer.
518 /// use std::io::BufWriter;
519 /// use std::net::TcpStream;
521 /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
523 /// // do stuff with the stream
525 /// // we want to get our `TcpStream` back, so let's try:
527 /// let stream = match stream.into_inner() {
530 /// // Here, e is an IntoInnerError, let's log the inner error.
532 /// // We'll just 'log' to stdout for this example.
533 /// println!("{}", e.error());
535 /// panic!("An unexpected error occurred.");
539 #[stable(feature = "rust1", since = "1.0.0")]
540 pub fn error(&self) -> &Error { &self.1 }
542 /// Returns the buffered writer instance which generated the error.
544 /// The returned object can be used for error recovery, such as
545 /// re-inspecting the buffer.
550 /// use std::io::BufWriter;
551 /// use std::net::TcpStream;
553 /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
555 /// // do stuff with the stream
557 /// // we want to get our `TcpStream` back, so let's try:
559 /// let stream = match stream.into_inner() {
562 /// // Here, e is an IntoInnerError, let's re-examine the buffer:
563 /// let buffer = e.into_inner();
565 /// // do stuff to try to recover
567 /// // afterwards, let's just return the stream
568 /// buffer.into_inner().unwrap()
572 #[stable(feature = "rust1", since = "1.0.0")]
573 pub fn into_inner(self) -> W { self.0 }
576 #[stable(feature = "rust1", since = "1.0.0")]
577 impl<W> From<IntoInnerError<W>> for Error {
578 fn from(iie: IntoInnerError<W>) -> Error { iie.1 }
581 #[stable(feature = "rust1", since = "1.0.0")]
582 impl<W: Reflect + Send + fmt::Debug> error::Error for IntoInnerError<W> {
583 fn description(&self) -> &str {
584 error::Error::description(self.error())
588 #[stable(feature = "rust1", since = "1.0.0")]
589 impl<W> fmt::Display for IntoInnerError<W> {
590 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
595 /// Wraps a writer and buffers output to it, flushing whenever a newline
596 /// (`0x0a`, `'\n'`) is detected.
598 /// The [`BufWriter`][bufwriter] struct wraps a writer and buffers its output.
599 /// But it only does this batched write when it goes out of scope, or when the
600 /// internal buffer is full. Sometimes, you'd prefer to write each line as it's
601 /// completed, rather than the entire buffer at once. Enter `LineWriter`. It
602 /// does exactly that.
604 /// [bufwriter]: struct.BufWriter.html
606 /// If there's still a partial line in the buffer when the `LineWriter` is
607 /// dropped, it will flush those contents.
611 /// We can use `LineWriter` to write one line at a time, significantly
612 /// reducing the number of actual writes to the file.
615 /// use std::fs::File;
616 /// use std::io::prelude::*;
617 /// use std::io::LineWriter;
619 /// # fn foo() -> std::io::Result<()> {
620 /// let road_not_taken = b"I shall be telling this with a sigh
621 /// Somewhere ages and ages hence:
622 /// Two roads diverged in a wood, and I -
623 /// I took the one less traveled by,
624 /// And that has made all the difference.";
626 /// let file = try!(File::create("poem.txt"));
627 /// let mut file = LineWriter::new(file);
629 /// for &byte in road_not_taken.iter() {
630 /// file.write(&[byte]).unwrap();
633 /// // let's check we did the right thing.
634 /// let mut file = try!(File::open("poem.txt"));
635 /// let mut contents = String::new();
637 /// try!(file.read_to_string(&mut contents));
639 /// assert_eq!(contents.as_bytes(), &road_not_taken[..]);
643 #[stable(feature = "rust1", since = "1.0.0")]
644 pub struct LineWriter<W: Write> {
648 impl<W: Write> LineWriter<W> {
649 /// Creates a new `LineWriter`.
654 /// use std::fs::File;
655 /// use std::io::LineWriter;
657 /// # fn foo() -> std::io::Result<()> {
658 /// let file = try!(File::create("poem.txt"));
659 /// let file = LineWriter::new(file);
663 #[stable(feature = "rust1", since = "1.0.0")]
664 pub fn new(inner: W) -> LineWriter<W> {
665 // Lines typically aren't that long, don't use a giant buffer
666 LineWriter::with_capacity(1024, inner)
669 /// Creates a new `LineWriter` with a specified capacity for the internal
675 /// use std::fs::File;
676 /// use std::io::LineWriter;
678 /// # fn foo() -> std::io::Result<()> {
679 /// let file = try!(File::create("poem.txt"));
680 /// let file = LineWriter::with_capacity(100, file);
684 #[stable(feature = "rust1", since = "1.0.0")]
685 pub fn with_capacity(cap: usize, inner: W) -> LineWriter<W> {
686 LineWriter { inner: BufWriter::with_capacity(cap, inner) }
689 /// Gets a reference to the underlying writer.
694 /// use std::fs::File;
695 /// use std::io::LineWriter;
697 /// # fn foo() -> std::io::Result<()> {
698 /// let file = try!(File::create("poem.txt"));
699 /// let file = LineWriter::new(file);
701 /// let reference = file.get_ref();
705 #[stable(feature = "rust1", since = "1.0.0")]
706 pub fn get_ref(&self) -> &W { self.inner.get_ref() }
708 /// Gets a mutable reference to the underlying writer.
710 /// Caution must be taken when calling methods on the mutable reference
711 /// returned as extra writes could corrupt the output stream.
716 /// use std::fs::File;
717 /// use std::io::LineWriter;
719 /// # fn foo() -> std::io::Result<()> {
720 /// let file = try!(File::create("poem.txt"));
721 /// let mut file = LineWriter::new(file);
723 /// // we can use reference just like file
724 /// let reference = file.get_mut();
728 #[stable(feature = "rust1", since = "1.0.0")]
729 pub fn get_mut(&mut self) -> &mut W { self.inner.get_mut() }
731 /// Unwraps this `LineWriter`, returning the underlying writer.
733 /// The internal buffer is written out before returning the writer.
738 /// use std::fs::File;
739 /// use std::io::LineWriter;
741 /// # fn foo() -> std::io::Result<()> {
742 /// let file = try!(File::create("poem.txt"));
744 /// let writer: LineWriter<File> = LineWriter::new(file);
746 /// let file: File = try!(writer.into_inner());
750 #[stable(feature = "rust1", since = "1.0.0")]
751 pub fn into_inner(self) -> Result<W, IntoInnerError<LineWriter<W>>> {
752 self.inner.into_inner().map_err(|IntoInnerError(buf, e)| {
753 IntoInnerError(LineWriter { inner: buf }, e)
758 #[stable(feature = "rust1", since = "1.0.0")]
759 impl<W: Write> Write for LineWriter<W> {
760 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
761 match memchr::memrchr(b'\n', buf) {
763 let n = self.inner.write(&buf[..i + 1])?;
764 if n != i + 1 || self.inner.flush().is_err() {
765 // Do not return errors on partial writes.
768 self.inner.write(&buf[i + 1..]).map(|i| n + i)
770 None => self.inner.write(buf),
774 fn flush(&mut self) -> io::Result<()> { self.inner.flush() }
777 #[stable(feature = "rust1", since = "1.0.0")]
778 impl<W: Write> fmt::Debug for LineWriter<W> where W: fmt::Debug {
779 fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
780 fmt.debug_struct("LineWriter")
781 .field("writer", &self.inner.inner)
783 &format_args!("{}/{}", self.inner.buf.len(), self.inner.buf.capacity()))
791 use io::{self, BufReader, BufWriter, LineWriter, SeekFrom};
792 use sync::atomic::{AtomicUsize, Ordering};
796 /// A dummy reader intended at testing short-reads propagation.
797 pub struct ShortReader {
801 impl Read for ShortReader {
802 fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
803 if self.lengths.is_empty() {
806 Ok(self.lengths.remove(0))
812 fn test_buffered_reader() {
813 let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
814 let mut reader = BufReader::with_capacity(2, inner);
816 let mut buf = [0, 0, 0];
817 let nread = reader.read(&mut buf);
818 assert_eq!(nread.unwrap(), 3);
819 let b: &[_] = &[5, 6, 7];
822 let mut buf = [0, 0];
823 let nread = reader.read(&mut buf);
824 assert_eq!(nread.unwrap(), 2);
825 let b: &[_] = &[0, 1];
829 let nread = reader.read(&mut buf);
830 assert_eq!(nread.unwrap(), 1);
834 let mut buf = [0, 0, 0];
835 let nread = reader.read(&mut buf);
836 assert_eq!(nread.unwrap(), 1);
837 let b: &[_] = &[3, 0, 0];
840 let nread = reader.read(&mut buf);
841 assert_eq!(nread.unwrap(), 1);
842 let b: &[_] = &[4, 0, 0];
845 assert_eq!(reader.read(&mut buf).unwrap(), 0);
849 fn test_buffered_reader_seek() {
850 let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
851 let mut reader = BufReader::with_capacity(2, io::Cursor::new(inner));
853 assert_eq!(reader.seek(SeekFrom::Start(3)).ok(), Some(3));
854 assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
855 assert_eq!(reader.seek(SeekFrom::Current(0)).ok(), Some(3));
856 assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
857 assert_eq!(reader.seek(SeekFrom::Current(1)).ok(), Some(4));
858 assert_eq!(reader.fill_buf().ok(), Some(&[1, 2][..]));
860 assert_eq!(reader.seek(SeekFrom::Current(-2)).ok(), Some(3));
864 fn test_buffered_reader_seek_underflow() {
865 // gimmick reader that yields its position modulo 256 for each byte
866 struct PositionReader {
869 impl Read for PositionReader {
870 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
874 self.pos = self.pos.wrapping_add(1);
879 impl Seek for PositionReader {
880 fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
882 SeekFrom::Start(n) => {
885 SeekFrom::Current(n) => {
886 self.pos = self.pos.wrapping_add(n as u64);
888 SeekFrom::End(n) => {
889 self.pos = u64::max_value().wrapping_add(n as u64);
896 let mut reader = BufReader::with_capacity(5, PositionReader { pos: 0 });
897 assert_eq!(reader.fill_buf().ok(), Some(&[0, 1, 2, 3, 4][..]));
898 assert_eq!(reader.seek(SeekFrom::End(-5)).ok(), Some(u64::max_value()-5));
899 assert_eq!(reader.fill_buf().ok().map(|s| s.len()), Some(5));
900 // the following seek will require two underlying seeks
901 let expected = 9223372036854775802;
902 assert_eq!(reader.seek(SeekFrom::Current(i64::min_value())).ok(), Some(expected));
903 assert_eq!(reader.fill_buf().ok().map(|s| s.len()), Some(5));
904 // seeking to 0 should empty the buffer.
905 assert_eq!(reader.seek(SeekFrom::Current(0)).ok(), Some(expected));
906 assert_eq!(reader.get_ref().pos, expected);
910 fn test_buffered_writer() {
911 let inner = Vec::new();
912 let mut writer = BufWriter::with_capacity(2, inner);
914 writer.write(&[0, 1]).unwrap();
915 assert_eq!(*writer.get_ref(), [0, 1]);
917 writer.write(&[2]).unwrap();
918 assert_eq!(*writer.get_ref(), [0, 1]);
920 writer.write(&[3]).unwrap();
921 assert_eq!(*writer.get_ref(), [0, 1]);
923 writer.flush().unwrap();
924 assert_eq!(*writer.get_ref(), [0, 1, 2, 3]);
926 writer.write(&[4]).unwrap();
927 writer.write(&[5]).unwrap();
928 assert_eq!(*writer.get_ref(), [0, 1, 2, 3]);
930 writer.write(&[6]).unwrap();
931 assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5]);
933 writer.write(&[7, 8]).unwrap();
934 assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8]);
936 writer.write(&[9, 10, 11]).unwrap();
937 assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]);
939 writer.flush().unwrap();
940 assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]);
944 fn test_buffered_writer_inner_flushes() {
945 let mut w = BufWriter::with_capacity(3, Vec::new());
946 w.write(&[0, 1]).unwrap();
947 assert_eq!(*w.get_ref(), []);
948 let w = w.into_inner().unwrap();
949 assert_eq!(w, [0, 1]);
953 fn test_buffered_writer_seek() {
954 let mut w = BufWriter::with_capacity(3, io::Cursor::new(Vec::new()));
955 w.write_all(&[0, 1, 2, 3, 4, 5]).unwrap();
956 w.write_all(&[6, 7]).unwrap();
957 assert_eq!(w.seek(SeekFrom::Current(0)).ok(), Some(8));
958 assert_eq!(&w.get_ref().get_ref()[..], &[0, 1, 2, 3, 4, 5, 6, 7][..]);
959 assert_eq!(w.seek(SeekFrom::Start(2)).ok(), Some(2));
960 w.write_all(&[8, 9]).unwrap();
961 assert_eq!(&w.into_inner().unwrap().into_inner()[..], &[0, 1, 8, 9, 4, 5, 6, 7]);
965 fn test_read_until() {
966 let inner: &[u8] = &[0, 1, 2, 1, 0];
967 let mut reader = BufReader::with_capacity(2, inner);
968 let mut v = Vec::new();
969 reader.read_until(0, &mut v).unwrap();
972 reader.read_until(2, &mut v).unwrap();
973 assert_eq!(v, [1, 2]);
975 reader.read_until(1, &mut v).unwrap();
978 reader.read_until(8, &mut v).unwrap();
981 reader.read_until(9, &mut v).unwrap();
986 fn test_line_buffer_fail_flush() {
988 struct FailFlushWriter<'a>(&'a mut Vec<u8>);
990 impl<'a> Write for FailFlushWriter<'a> {
991 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
992 self.0.extend_from_slice(buf);
995 fn flush(&mut self) -> io::Result<()> {
996 Err(io::Error::new(io::ErrorKind::Other, "flush failed"))
1000 let mut buf = Vec::new();
1002 let mut writer = LineWriter::new(FailFlushWriter(&mut buf));
1003 let to_write = b"abc\ndef";
1004 if let Ok(written) = writer.write(to_write) {
1005 assert!(written < to_write.len(), "didn't flush on new line");
1010 assert!(buf.is_empty(), "write returned an error but wrote data");
1014 fn test_line_buffer() {
1015 let mut writer = LineWriter::new(Vec::new());
1016 writer.write(&[0]).unwrap();
1017 assert_eq!(*writer.get_ref(), []);
1018 writer.write(&[1]).unwrap();
1019 assert_eq!(*writer.get_ref(), []);
1020 writer.flush().unwrap();
1021 assert_eq!(*writer.get_ref(), [0, 1]);
1022 writer.write(&[0, b'\n', 1, b'\n', 2]).unwrap();
1023 assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n']);
1024 writer.flush().unwrap();
1025 assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n', 2]);
1026 writer.write(&[3, b'\n']).unwrap();
1027 assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n', 2, 3, b'\n']);
1031 fn test_read_line() {
1032 let in_buf: &[u8] = b"a\nb\nc";
1033 let mut reader = BufReader::with_capacity(2, in_buf);
1034 let mut s = String::new();
1035 reader.read_line(&mut s).unwrap();
1036 assert_eq!(s, "a\n");
1038 reader.read_line(&mut s).unwrap();
1039 assert_eq!(s, "b\n");
1041 reader.read_line(&mut s).unwrap();
1044 reader.read_line(&mut s).unwrap();
1050 let in_buf: &[u8] = b"a\nb\nc";
1051 let reader = BufReader::with_capacity(2, in_buf);
1052 let mut it = reader.lines();
1053 assert_eq!(it.next().unwrap().unwrap(), "a".to_string());
1054 assert_eq!(it.next().unwrap().unwrap(), "b".to_string());
1055 assert_eq!(it.next().unwrap().unwrap(), "c".to_string());
1056 assert!(it.next().is_none());
1060 fn test_short_reads() {
1061 let inner = ShortReader{lengths: vec![0, 1, 2, 0, 1, 0]};
1062 let mut reader = BufReader::new(inner);
1063 let mut buf = [0, 0];
1064 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1065 assert_eq!(reader.read(&mut buf).unwrap(), 1);
1066 assert_eq!(reader.read(&mut buf).unwrap(), 2);
1067 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1068 assert_eq!(reader.read(&mut buf).unwrap(), 1);
1069 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1070 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1074 fn read_char_buffered() {
1075 let buf = [195, 159];
1076 let reader = BufReader::with_capacity(1, &buf[..]);
1077 assert_eq!(reader.chars().next().unwrap().unwrap(), 'ß');
1082 let buf = [195, 159, b'a'];
1083 let reader = BufReader::with_capacity(1, &buf[..]);
1084 let mut it = reader.chars();
1085 assert_eq!(it.next().unwrap().unwrap(), 'ß');
1086 assert_eq!(it.next().unwrap().unwrap(), 'a');
1087 assert!(it.next().is_none());
1092 fn dont_panic_in_drop_on_panicked_flush() {
1093 struct FailFlushWriter;
1095 impl Write for FailFlushWriter {
1096 fn write(&mut self, buf: &[u8]) -> io::Result<usize> { Ok(buf.len()) }
1097 fn flush(&mut self) -> io::Result<()> {
1098 Err(io::Error::last_os_error())
1102 let writer = FailFlushWriter;
1103 let _writer = BufWriter::new(writer);
1105 // If writer panics *again* due to the flush error then the process will
1111 fn panic_in_write_doesnt_flush_in_drop() {
1112 static WRITES: AtomicUsize = AtomicUsize::new(0);
1116 impl Write for PanicWriter {
1117 fn write(&mut self, _: &[u8]) -> io::Result<usize> {
1118 WRITES.fetch_add(1, Ordering::SeqCst);
1121 fn flush(&mut self) -> io::Result<()> { Ok(()) }
1125 let mut writer = BufWriter::new(PanicWriter);
1126 let _ = writer.write(b"hello world");
1127 let _ = writer.flush();
1128 }).join().unwrap_err();
1130 assert_eq!(WRITES.load(Ordering::SeqCst), 1);
1134 fn bench_buffered_reader(b: &mut test::Bencher) {
1136 BufReader::new(io::empty())
1141 fn bench_buffered_writer(b: &mut test::Bencher) {
1143 BufWriter::new(io::sink())