1 //! Buffering wrappers for I/O traits
3 use crate::io::prelude::*;
9 self, Error, ErrorKind, Initializer, IoSlice, IoSliceMut, SeekFrom, DEFAULT_BUF_SIZE,
13 /// The `BufReader<R>` struct adds buffering to any reader.
15 /// It can be excessively inefficient to work directly with a [`Read`] instance.
16 /// For example, every call to [`read`][`TcpStream::read`] on [`TcpStream`]
17 /// results in a system call. A `BufReader<R>` performs large, infrequent reads on
18 /// the underlying [`Read`] and maintains an in-memory buffer of the results.
20 /// `BufReader<R>` can improve the speed of programs that make *small* and
21 /// *repeated* read calls to the same file or network socket. It does not
22 /// help when reading very large amounts at once, or reading just one or a few
23 /// times. It also provides no advantage when reading from a source that is
24 /// already in memory, like a `Vec<u8>`.
26 /// When the `BufReader<R>` is dropped, the contents of its buffer will be
27 /// discarded. Creating multiple instances of a `BufReader<R>` on the same
28 /// stream can cause data loss. Reading from the underlying reader after
29 /// unwrapping the `BufReader<R>` with `BufReader::into_inner` can also cause
32 /// [`Read`]: ../../std/io/trait.Read.html
33 /// [`TcpStream::read`]: ../../std/net/struct.TcpStream.html#method.read
34 /// [`TcpStream`]: ../../std/net/struct.TcpStream.html
39 /// use std::io::prelude::*;
40 /// use std::io::BufReader;
41 /// use std::fs::File;
43 /// fn main() -> std::io::Result<()> {
44 /// let f = File::open("log.txt")?;
45 /// let mut reader = BufReader::new(f);
47 /// let mut line = String::new();
48 /// let len = reader.read_line(&mut line)?;
49 /// println!("First line is {} bytes long", len);
53 #[stable(feature = "rust1", since = "1.0.0")]
54 pub struct BufReader<R> {
61 impl<R: Read> BufReader<R> {
62 /// Creates a new `BufReader<R>` with a default buffer capacity. The default is currently 8 KB,
63 /// but may change in the future.
68 /// use std::io::BufReader;
69 /// use std::fs::File;
71 /// fn main() -> std::io::Result<()> {
72 /// let f = File::open("log.txt")?;
73 /// let reader = BufReader::new(f);
77 #[stable(feature = "rust1", since = "1.0.0")]
78 pub fn new(inner: R) -> BufReader<R> {
79 BufReader::with_capacity(DEFAULT_BUF_SIZE, inner)
82 /// Creates a new `BufReader<R>` with the specified buffer capacity.
86 /// Creating a buffer with ten bytes of capacity:
89 /// use std::io::BufReader;
90 /// use std::fs::File;
92 /// fn main() -> std::io::Result<()> {
93 /// let f = File::open("log.txt")?;
94 /// let reader = BufReader::with_capacity(10, f);
98 #[stable(feature = "rust1", since = "1.0.0")]
99 pub fn with_capacity(capacity: usize, inner: R) -> BufReader<R> {
101 let mut buffer = Vec::with_capacity(capacity);
102 buffer.set_len(capacity);
103 inner.initializer().initialize(&mut buffer);
104 BufReader { inner, buf: buffer.into_boxed_slice(), pos: 0, cap: 0 }
109 impl<R> BufReader<R> {
110 /// Gets a reference to the underlying reader.
112 /// It is inadvisable to directly read from the underlying reader.
117 /// use std::io::BufReader;
118 /// use std::fs::File;
120 /// fn main() -> std::io::Result<()> {
121 /// let f1 = File::open("log.txt")?;
122 /// let reader = BufReader::new(f1);
124 /// let f2 = reader.get_ref();
128 #[stable(feature = "rust1", since = "1.0.0")]
129 pub fn get_ref(&self) -> &R {
133 /// Gets a mutable reference to the underlying reader.
135 /// It is inadvisable to directly read from the underlying reader.
140 /// use std::io::BufReader;
141 /// use std::fs::File;
143 /// fn main() -> std::io::Result<()> {
144 /// let f1 = File::open("log.txt")?;
145 /// let mut reader = BufReader::new(f1);
147 /// let f2 = reader.get_mut();
151 #[stable(feature = "rust1", since = "1.0.0")]
152 pub fn get_mut(&mut self) -> &mut R {
156 /// Returns a reference to the internally buffered data.
158 /// Unlike `fill_buf`, this will not attempt to fill the buffer if it is empty.
163 /// use std::io::{BufReader, BufRead};
164 /// use std::fs::File;
166 /// fn main() -> std::io::Result<()> {
167 /// let f = File::open("log.txt")?;
168 /// let mut reader = BufReader::new(f);
169 /// assert!(reader.buffer().is_empty());
171 /// if reader.fill_buf()?.len() > 0 {
172 /// assert!(!reader.buffer().is_empty());
177 #[stable(feature = "bufreader_buffer", since = "1.37.0")]
178 pub fn buffer(&self) -> &[u8] {
179 &self.buf[self.pos..self.cap]
182 /// Unwraps this `BufReader<R>`, returning the underlying reader.
184 /// Note that any leftover data in the internal buffer is lost. Therefore,
185 /// a following read from the underlying reader may lead to data loss.
190 /// use std::io::BufReader;
191 /// use std::fs::File;
193 /// fn main() -> std::io::Result<()> {
194 /// let f1 = File::open("log.txt")?;
195 /// let reader = BufReader::new(f1);
197 /// let f2 = reader.into_inner();
201 #[stable(feature = "rust1", since = "1.0.0")]
202 pub fn into_inner(self) -> R {
206 /// Invalidates all data in the internal buffer.
208 fn discard_buffer(&mut self) {
214 impl<R: Seek> BufReader<R> {
215 /// Seeks relative to the current position. If the new position lies within the buffer,
216 /// the buffer will not be flushed, allowing for more efficient seeks.
217 /// This method does not return the location of the underlying reader, so the caller
218 /// must track this information themselves if it is required.
219 #[unstable(feature = "bufreader_seek_relative", issue = "31100")]
220 pub fn seek_relative(&mut self, offset: i64) -> io::Result<()> {
221 let pos = self.pos as u64;
223 if let Some(new_pos) = pos.checked_sub((-offset) as u64) {
224 self.pos = new_pos as usize;
228 if let Some(new_pos) = pos.checked_add(offset as u64) {
229 if new_pos <= self.cap as u64 {
230 self.pos = new_pos as usize;
235 self.seek(SeekFrom::Current(offset)).map(drop)
239 #[stable(feature = "rust1", since = "1.0.0")]
240 impl<R: Read> Read for BufReader<R> {
241 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
242 // If we don't have any buffered data and we're doing a massive read
243 // (larger than our internal buffer), bypass our internal buffer
245 if self.pos == self.cap && buf.len() >= self.buf.len() {
246 self.discard_buffer();
247 return self.inner.read(buf);
250 let mut rem = self.fill_buf()?;
257 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
258 let total_len = bufs.iter().map(|b| b.len()).sum::<usize>();
259 if self.pos == self.cap && total_len >= self.buf.len() {
260 self.discard_buffer();
261 return self.inner.read_vectored(bufs);
264 let mut rem = self.fill_buf()?;
265 rem.read_vectored(bufs)?
271 // we can't skip unconditionally because of the large buffer case in read.
272 unsafe fn initializer(&self) -> Initializer {
273 self.inner.initializer()
277 #[stable(feature = "rust1", since = "1.0.0")]
278 impl<R: Read> BufRead for BufReader<R> {
279 fn fill_buf(&mut self) -> io::Result<&[u8]> {
280 // If we've reached the end of our internal buffer then we need to fetch
281 // some more data from the underlying reader.
282 // Branch using `>=` instead of the more correct `==`
283 // to tell the compiler that the pos..cap slice is always valid.
284 if self.pos >= self.cap {
285 debug_assert!(self.pos == self.cap);
286 self.cap = self.inner.read(&mut self.buf)?;
289 Ok(&self.buf[self.pos..self.cap])
292 fn consume(&mut self, amt: usize) {
293 self.pos = cmp::min(self.pos + amt, self.cap);
297 #[stable(feature = "rust1", since = "1.0.0")]
298 impl<R> fmt::Debug for BufReader<R>
302 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
303 fmt.debug_struct("BufReader")
304 .field("reader", &self.inner)
305 .field("buffer", &format_args!("{}/{}", self.cap - self.pos, self.buf.len()))
310 #[stable(feature = "rust1", since = "1.0.0")]
311 impl<R: Seek> Seek for BufReader<R> {
312 /// Seek to an offset, in bytes, in the underlying reader.
314 /// The position used for seeking with `SeekFrom::Current(_)` is the
315 /// position the underlying reader would be at if the `BufReader<R>` had no
318 /// Seeking always discards the internal buffer, even if the seek position
319 /// would otherwise fall within it. This guarantees that calling
320 /// `.into_inner()` immediately after a seek yields the underlying reader
321 /// at the same position.
323 /// To seek without discarding the internal buffer, use [`BufReader::seek_relative`].
325 /// See [`std::io::Seek`] for more details.
327 /// Note: In the edge case where you're seeking with `SeekFrom::Current(n)`
328 /// where `n` minus the internal buffer length overflows an `i64`, two
329 /// seeks will be performed instead of one. If the second seek returns
330 /// `Err`, the underlying reader will be left at the same position it would
331 /// have if you called `seek` with `SeekFrom::Current(0)`.
333 /// [`BufReader::seek_relative`]: struct.BufReader.html#method.seek_relative
334 /// [`std::io::Seek`]: trait.Seek.html
335 fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
337 if let SeekFrom::Current(n) = pos {
338 let remainder = (self.cap - self.pos) as i64;
339 // it should be safe to assume that remainder fits within an i64 as the alternative
340 // means we managed to allocate 8 exbibytes and that's absurd.
341 // But it's not out of the realm of possibility for some weird underlying reader to
342 // support seeking by i64::min_value() so we need to handle underflow when subtracting
344 if let Some(offset) = n.checked_sub(remainder) {
345 result = self.inner.seek(SeekFrom::Current(offset))?;
347 // seek backwards by our remainder, and then by the offset
348 self.inner.seek(SeekFrom::Current(-remainder))?;
349 self.discard_buffer();
350 result = self.inner.seek(SeekFrom::Current(n))?;
353 // Seeking with Start/End doesn't care about our buffer length.
354 result = self.inner.seek(pos)?;
356 self.discard_buffer();
361 /// Wraps a writer and buffers its output.
363 /// It can be excessively inefficient to work directly with something that
364 /// implements [`Write`]. For example, every call to
365 /// [`write`][`TcpStream::write`] on [`TcpStream`] results in a system call. A
366 /// `BufWriter<W>` keeps an in-memory buffer of data and writes it to an underlying
367 /// writer in large, infrequent batches.
369 /// `BufWriter<W>` can improve the speed of programs that make *small* and
370 /// *repeated* write calls to the same file or network socket. It does not
371 /// help when writing very large amounts at once, or writing just one or a few
372 /// times. It also provides no advantage when writing to a destination that is
373 /// in memory, like a `Vec<u8>`.
375 /// It is critical to call [`flush`] before `BufWriter<W>` is dropped. Though
376 /// dropping will attempt to flush the the contents of the buffer, any errors
377 /// that happen in the process of dropping will be ignored. Calling [`flush`]
378 /// ensures that the buffer is empty and thus dropping will not even attempt
383 /// Let's write the numbers one through ten to a [`TcpStream`]:
386 /// use std::io::prelude::*;
387 /// use std::net::TcpStream;
389 /// let mut stream = TcpStream::connect("127.0.0.1:34254").unwrap();
392 /// stream.write(&[i+1]).unwrap();
396 /// Because we're not buffering, we write each one in turn, incurring the
397 /// overhead of a system call per byte written. We can fix this with a
401 /// use std::io::prelude::*;
402 /// use std::io::BufWriter;
403 /// use std::net::TcpStream;
405 /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
408 /// stream.write(&[i+1]).unwrap();
410 /// stream.flush().unwrap();
413 /// By wrapping the stream with a `BufWriter<W>`, these ten writes are all grouped
414 /// together by the buffer and will all be written out in one system call when
415 /// the `stream` is flushed.
417 /// [`Write`]: ../../std/io/trait.Write.html
418 /// [`TcpStream::write`]: ../../std/net/struct.TcpStream.html#method.write
419 /// [`TcpStream`]: ../../std/net/struct.TcpStream.html
420 /// [`flush`]: #method.flush
421 #[stable(feature = "rust1", since = "1.0.0")]
422 pub struct BufWriter<W: Write> {
425 // #30888: If the inner writer panics in a call to write, we don't want to
426 // write the buffered data a second time in BufWriter's destructor. This
427 // flag tells the Drop impl if it should skip the flush.
431 /// An error returned by `into_inner` which combines an error that
432 /// happened while writing out the buffer, and the buffered writer object
433 /// which may be used to recover from the condition.
438 /// use std::io::BufWriter;
439 /// use std::net::TcpStream;
441 /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
443 /// // do stuff with the stream
445 /// // we want to get our `TcpStream` back, so let's try:
447 /// let stream = match stream.into_inner() {
450 /// // Here, e is an IntoInnerError
451 /// panic!("An error occurred");
456 #[stable(feature = "rust1", since = "1.0.0")]
457 pub struct IntoInnerError<W>(W, Error);
459 impl<W: Write> BufWriter<W> {
460 /// Creates a new `BufWriter<W>` with a default buffer capacity. The default is currently 8 KB,
461 /// but may change in the future.
466 /// use std::io::BufWriter;
467 /// use std::net::TcpStream;
469 /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
471 #[stable(feature = "rust1", since = "1.0.0")]
472 pub fn new(inner: W) -> BufWriter<W> {
473 BufWriter::with_capacity(DEFAULT_BUF_SIZE, inner)
476 /// Creates a new `BufWriter<W>` with the specified buffer capacity.
480 /// Creating a buffer with a buffer of a hundred bytes.
483 /// use std::io::BufWriter;
484 /// use std::net::TcpStream;
486 /// let stream = TcpStream::connect("127.0.0.1:34254").unwrap();
487 /// let mut buffer = BufWriter::with_capacity(100, stream);
489 #[stable(feature = "rust1", since = "1.0.0")]
490 pub fn with_capacity(capacity: usize, inner: W) -> BufWriter<W> {
491 BufWriter { inner: Some(inner), buf: Vec::with_capacity(capacity), panicked: false }
494 fn flush_buf(&mut self) -> io::Result<()> {
496 let len = self.buf.len();
497 let mut ret = Ok(());
498 while written < len {
499 self.panicked = true;
500 let r = self.inner.as_mut().unwrap().write(&self.buf[written..]);
501 self.panicked = false;
506 Err(Error::new(ErrorKind::WriteZero, "failed to write the buffered data"));
509 Ok(n) => written += n,
510 Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
518 self.buf.drain(..written);
523 /// Gets a reference to the underlying writer.
528 /// use std::io::BufWriter;
529 /// use std::net::TcpStream;
531 /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
533 /// // we can use reference just like buffer
534 /// let reference = buffer.get_ref();
536 #[stable(feature = "rust1", since = "1.0.0")]
537 pub fn get_ref(&self) -> &W {
538 self.inner.as_ref().unwrap()
541 /// Gets a mutable reference to the underlying writer.
543 /// It is inadvisable to directly write to the underlying writer.
548 /// use std::io::BufWriter;
549 /// use std::net::TcpStream;
551 /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
553 /// // we can use reference just like buffer
554 /// let reference = buffer.get_mut();
556 #[stable(feature = "rust1", since = "1.0.0")]
557 pub fn get_mut(&mut self) -> &mut W {
558 self.inner.as_mut().unwrap()
561 /// Returns a reference to the internally buffered data.
566 /// use std::io::BufWriter;
567 /// use std::net::TcpStream;
569 /// let buf_writer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
571 /// // See how many bytes are currently buffered
572 /// let bytes_buffered = buf_writer.buffer().len();
574 #[stable(feature = "bufreader_buffer", since = "1.37.0")]
575 pub fn buffer(&self) -> &[u8] {
579 /// Unwraps this `BufWriter<W>`, returning the underlying writer.
581 /// The buffer is written out before returning the writer.
585 /// An `Err` will be returned if an error occurs while flushing the buffer.
590 /// use std::io::BufWriter;
591 /// use std::net::TcpStream;
593 /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
595 /// // unwrap the TcpStream and flush the buffer
596 /// let stream = buffer.into_inner().unwrap();
598 #[stable(feature = "rust1", since = "1.0.0")]
599 pub fn into_inner(mut self) -> Result<W, IntoInnerError<BufWriter<W>>> {
600 match self.flush_buf() {
601 Err(e) => Err(IntoInnerError(self, e)),
602 Ok(()) => Ok(self.inner.take().unwrap()),
607 #[stable(feature = "rust1", since = "1.0.0")]
608 impl<W: Write> Write for BufWriter<W> {
609 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
610 if self.buf.len() + buf.len() > self.buf.capacity() {
613 if buf.len() >= self.buf.capacity() {
614 self.panicked = true;
615 let r = self.get_mut().write(buf);
616 self.panicked = false;
623 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
624 let total_len = bufs.iter().map(|b| b.len()).sum::<usize>();
625 if self.buf.len() + total_len > self.buf.capacity() {
628 if total_len >= self.buf.capacity() {
629 self.panicked = true;
630 let r = self.get_mut().write_vectored(bufs);
631 self.panicked = false;
634 self.buf.write_vectored(bufs)
638 fn flush(&mut self) -> io::Result<()> {
639 self.flush_buf().and_then(|()| self.get_mut().flush())
643 #[stable(feature = "rust1", since = "1.0.0")]
644 impl<W: Write> fmt::Debug for BufWriter<W>
648 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
649 fmt.debug_struct("BufWriter")
650 .field("writer", &self.inner.as_ref().unwrap())
651 .field("buffer", &format_args!("{}/{}", self.buf.len(), self.buf.capacity()))
656 #[stable(feature = "rust1", since = "1.0.0")]
657 impl<W: Write + Seek> Seek for BufWriter<W> {
658 /// Seek to the offset, in bytes, in the underlying writer.
660 /// Seeking always writes out the internal buffer before seeking.
661 fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
662 self.flush_buf().and_then(|_| self.get_mut().seek(pos))
666 #[stable(feature = "rust1", since = "1.0.0")]
667 impl<W: Write> Drop for BufWriter<W> {
669 if self.inner.is_some() && !self.panicked {
670 // dtors should not panic, so we ignore a failed flush
671 let _r = self.flush_buf();
676 impl<W> IntoInnerError<W> {
677 /// Returns the error which caused the call to `into_inner()` to fail.
679 /// This error was returned when attempting to write the internal buffer.
684 /// use std::io::BufWriter;
685 /// use std::net::TcpStream;
687 /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
689 /// // do stuff with the stream
691 /// // we want to get our `TcpStream` back, so let's try:
693 /// let stream = match stream.into_inner() {
696 /// // Here, e is an IntoInnerError, let's log the inner error.
698 /// // We'll just 'log' to stdout for this example.
699 /// println!("{}", e.error());
701 /// panic!("An unexpected error occurred.");
705 #[stable(feature = "rust1", since = "1.0.0")]
706 pub fn error(&self) -> &Error {
710 /// Returns the buffered writer instance which generated the error.
712 /// The returned object can be used for error recovery, such as
713 /// re-inspecting the buffer.
718 /// use std::io::BufWriter;
719 /// use std::net::TcpStream;
721 /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
723 /// // do stuff with the stream
725 /// // we want to get our `TcpStream` back, so let's try:
727 /// let stream = match stream.into_inner() {
730 /// // Here, e is an IntoInnerError, let's re-examine the buffer:
731 /// let buffer = e.into_inner();
733 /// // do stuff to try to recover
735 /// // afterwards, let's just return the stream
736 /// buffer.into_inner().unwrap()
740 #[stable(feature = "rust1", since = "1.0.0")]
741 pub fn into_inner(self) -> W {
746 #[stable(feature = "rust1", since = "1.0.0")]
747 impl<W> From<IntoInnerError<W>> for Error {
748 fn from(iie: IntoInnerError<W>) -> Error {
753 #[stable(feature = "rust1", since = "1.0.0")]
754 impl<W: Send + fmt::Debug> error::Error for IntoInnerError<W> {
755 #[allow(deprecated, deprecated_in_future)]
756 fn description(&self) -> &str {
757 error::Error::description(self.error())
761 #[stable(feature = "rust1", since = "1.0.0")]
762 impl<W> fmt::Display for IntoInnerError<W> {
763 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
768 /// Wraps a writer and buffers output to it, flushing whenever a newline
769 /// (`0x0a`, `'\n'`) is detected.
771 /// The [`BufWriter`][bufwriter] struct wraps a writer and buffers its output.
772 /// But it only does this batched write when it goes out of scope, or when the
773 /// internal buffer is full. Sometimes, you'd prefer to write each line as it's
774 /// completed, rather than the entire buffer at once. Enter `LineWriter`. It
775 /// does exactly that.
777 /// Like [`BufWriter`][bufwriter], a `LineWriter`’s buffer will also be flushed when the
778 /// `LineWriter` goes out of scope or when its internal buffer is full.
780 /// [bufwriter]: struct.BufWriter.html
782 /// If there's still a partial line in the buffer when the `LineWriter` is
783 /// dropped, it will flush those contents.
787 /// We can use `LineWriter` to write one line at a time, significantly
788 /// reducing the number of actual writes to the file.
791 /// use std::fs::{self, File};
792 /// use std::io::prelude::*;
793 /// use std::io::LineWriter;
795 /// fn main() -> std::io::Result<()> {
796 /// let road_not_taken = b"I shall be telling this with a sigh
797 /// Somewhere ages and ages hence:
798 /// Two roads diverged in a wood, and I -
799 /// I took the one less traveled by,
800 /// And that has made all the difference.";
802 /// let file = File::create("poem.txt")?;
803 /// let mut file = LineWriter::new(file);
805 /// file.write_all(b"I shall be telling this with a sigh")?;
807 /// // No bytes are written until a newline is encountered (or
808 /// // the internal buffer is filled).
809 /// assert_eq!(fs::read_to_string("poem.txt")?, "");
810 /// file.write_all(b"\n")?;
812 /// fs::read_to_string("poem.txt")?,
813 /// "I shall be telling this with a sigh\n",
816 /// // Write the rest of the poem.
817 /// file.write_all(b"Somewhere ages and ages hence:
818 /// Two roads diverged in a wood, and I -
819 /// I took the one less traveled by,
820 /// And that has made all the difference.")?;
822 /// // The last line of the poem doesn't end in a newline, so
823 /// // we have to flush or drop the `LineWriter` to finish
827 /// // Confirm the whole poem was written.
828 /// assert_eq!(fs::read("poem.txt")?, &road_not_taken[..]);
832 #[stable(feature = "rust1", since = "1.0.0")]
833 pub struct LineWriter<W: Write> {
838 impl<W: Write> LineWriter<W> {
839 /// Creates a new `LineWriter`.
844 /// use std::fs::File;
845 /// use std::io::LineWriter;
847 /// fn main() -> std::io::Result<()> {
848 /// let file = File::create("poem.txt")?;
849 /// let file = LineWriter::new(file);
853 #[stable(feature = "rust1", since = "1.0.0")]
854 pub fn new(inner: W) -> LineWriter<W> {
855 // Lines typically aren't that long, don't use a giant buffer
856 LineWriter::with_capacity(1024, inner)
859 /// Creates a new `LineWriter` with a specified capacity for the internal
865 /// use std::fs::File;
866 /// use std::io::LineWriter;
868 /// fn main() -> std::io::Result<()> {
869 /// let file = File::create("poem.txt")?;
870 /// let file = LineWriter::with_capacity(100, file);
874 #[stable(feature = "rust1", since = "1.0.0")]
875 pub fn with_capacity(capacity: usize, inner: W) -> LineWriter<W> {
876 LineWriter { inner: BufWriter::with_capacity(capacity, inner), need_flush: false }
879 /// Gets a reference to the underlying writer.
884 /// use std::fs::File;
885 /// use std::io::LineWriter;
887 /// fn main() -> std::io::Result<()> {
888 /// let file = File::create("poem.txt")?;
889 /// let file = LineWriter::new(file);
891 /// let reference = file.get_ref();
895 #[stable(feature = "rust1", since = "1.0.0")]
896 pub fn get_ref(&self) -> &W {
900 /// Gets a mutable reference to the underlying writer.
902 /// Caution must be taken when calling methods on the mutable reference
903 /// returned as extra writes could corrupt the output stream.
908 /// use std::fs::File;
909 /// use std::io::LineWriter;
911 /// fn main() -> std::io::Result<()> {
912 /// let file = File::create("poem.txt")?;
913 /// let mut file = LineWriter::new(file);
915 /// // we can use reference just like file
916 /// let reference = file.get_mut();
920 #[stable(feature = "rust1", since = "1.0.0")]
921 pub fn get_mut(&mut self) -> &mut W {
925 /// Unwraps this `LineWriter`, returning the underlying writer.
927 /// The internal buffer is written out before returning the writer.
931 /// An `Err` will be returned if an error occurs while flushing the buffer.
936 /// use std::fs::File;
937 /// use std::io::LineWriter;
939 /// fn main() -> std::io::Result<()> {
940 /// let file = File::create("poem.txt")?;
942 /// let writer: LineWriter<File> = LineWriter::new(file);
944 /// let file: File = writer.into_inner()?;
948 #[stable(feature = "rust1", since = "1.0.0")]
949 pub fn into_inner(self) -> Result<W, IntoInnerError<LineWriter<W>>> {
950 self.inner.into_inner().map_err(|IntoInnerError(buf, e)| {
951 IntoInnerError(LineWriter { inner: buf, need_flush: false }, e)
956 #[stable(feature = "rust1", since = "1.0.0")]
957 impl<W: Write> Write for LineWriter<W> {
958 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
963 // Find the last newline character in the buffer provided. If found then
964 // we're going to write all the data up to that point and then flush,
965 // otherwise we just write the whole block to the underlying writer.
966 let i = match memchr::memrchr(b'\n', buf) {
968 None => return self.inner.write(buf),
971 // Ok, we're going to write a partial amount of the data given first
972 // followed by flushing the newline. After we've successfully written
973 // some data then we *must* report that we wrote that data, so future
974 // errors are ignored. We set our internal `need_flush` flag, though, in
975 // case flushing fails and we need to try it first next time.
976 let n = self.inner.write(&buf[..=i])?;
977 self.need_flush = true;
978 if self.flush().is_err() || n != i + 1 {
982 // At this point we successfully wrote `i + 1` bytes and flushed it out,
983 // meaning that the entire line is now flushed out on the screen. While
984 // we can attempt to finish writing the rest of the data provided.
985 // Remember though that we ignore errors here as we've successfully
986 // written data, so we need to report that.
987 match self.inner.write(&buf[i + 1..]) {
993 // Vectored writes are very similar to the writes above, but adjusted for
994 // the list of buffers that we have to write.
995 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
1000 // Find the last newline, and failing that write the whole buffer
1001 let last_newline = bufs
1005 .filter_map(|(i, buf)| {
1006 let pos = memchr::memrchr(b'\n', buf)?;
1010 let (i, j) = match last_newline {
1012 None => return self.inner.write_vectored(bufs),
1014 let (prefix, suffix) = bufs.split_at(i);
1015 let (buf, suffix) = suffix.split_at(1);
1018 // Write everything up to the last newline, flushing afterwards. Note
1019 // that only if we finished our entire `write_vectored` do we try the
1023 let prefix_amt = prefix.iter().map(|i| i.len()).sum();
1025 n += self.inner.write_vectored(prefix)?;
1026 self.need_flush = true;
1028 if n == prefix_amt {
1029 match self.inner.write(&buf[..=j]) {
1031 Err(e) if n == 0 => return Err(e),
1032 Err(_) => return Ok(n),
1034 self.need_flush = true;
1036 if self.flush().is_err() || n != j + 1 + prefix_amt {
1040 // ... and now write out everything remaining
1041 match self.inner.write(&buf[j + 1..]) {
1043 Err(_) => return Ok(n),
1046 if suffix.iter().map(|s| s.len()).sum::<usize>() == 0 {
1049 match self.inner.write_vectored(suffix) {
1055 fn flush(&mut self) -> io::Result<()> {
1056 self.inner.flush()?;
1057 self.need_flush = false;
1062 #[stable(feature = "rust1", since = "1.0.0")]
1063 impl<W: Write> fmt::Debug for LineWriter<W>
1067 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
1068 fmt.debug_struct("LineWriter")
1069 .field("writer", &self.inner.inner)
1072 &format_args!("{}/{}", self.inner.buf.len(), self.inner.buf.capacity()),
1080 use crate::io::prelude::*;
1081 use crate::io::{self, BufReader, BufWriter, IoSlice, LineWriter, SeekFrom};
1082 use crate::sync::atomic::{AtomicUsize, Ordering};
1085 /// A dummy reader intended at testing short-reads propagation.
1086 pub struct ShortReader {
1087 lengths: Vec<usize>,
1090 impl Read for ShortReader {
1091 fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
1092 if self.lengths.is_empty() { Ok(0) } else { Ok(self.lengths.remove(0)) }
1097 fn test_buffered_reader() {
1098 let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
1099 let mut reader = BufReader::with_capacity(2, inner);
1101 let mut buf = [0, 0, 0];
1102 let nread = reader.read(&mut buf);
1103 assert_eq!(nread.unwrap(), 3);
1104 assert_eq!(buf, [5, 6, 7]);
1105 assert_eq!(reader.buffer(), []);
1107 let mut buf = [0, 0];
1108 let nread = reader.read(&mut buf);
1109 assert_eq!(nread.unwrap(), 2);
1110 assert_eq!(buf, [0, 1]);
1111 assert_eq!(reader.buffer(), []);
1114 let nread = reader.read(&mut buf);
1115 assert_eq!(nread.unwrap(), 1);
1116 assert_eq!(buf, [2]);
1117 assert_eq!(reader.buffer(), [3]);
1119 let mut buf = [0, 0, 0];
1120 let nread = reader.read(&mut buf);
1121 assert_eq!(nread.unwrap(), 1);
1122 assert_eq!(buf, [3, 0, 0]);
1123 assert_eq!(reader.buffer(), []);
1125 let nread = reader.read(&mut buf);
1126 assert_eq!(nread.unwrap(), 1);
1127 assert_eq!(buf, [4, 0, 0]);
1128 assert_eq!(reader.buffer(), []);
1130 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1134 fn test_buffered_reader_seek() {
1135 let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
1136 let mut reader = BufReader::with_capacity(2, io::Cursor::new(inner));
1138 assert_eq!(reader.seek(SeekFrom::Start(3)).ok(), Some(3));
1139 assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
1140 assert_eq!(reader.seek(SeekFrom::Current(0)).ok(), Some(3));
1141 assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
1142 assert_eq!(reader.seek(SeekFrom::Current(1)).ok(), Some(4));
1143 assert_eq!(reader.fill_buf().ok(), Some(&[1, 2][..]));
1145 assert_eq!(reader.seek(SeekFrom::Current(-2)).ok(), Some(3));
1149 fn test_buffered_reader_seek_relative() {
1150 let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
1151 let mut reader = BufReader::with_capacity(2, io::Cursor::new(inner));
1153 assert!(reader.seek_relative(3).is_ok());
1154 assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
1155 assert!(reader.seek_relative(0).is_ok());
1156 assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
1157 assert!(reader.seek_relative(1).is_ok());
1158 assert_eq!(reader.fill_buf().ok(), Some(&[1][..]));
1159 assert!(reader.seek_relative(-1).is_ok());
1160 assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
1161 assert!(reader.seek_relative(2).is_ok());
1162 assert_eq!(reader.fill_buf().ok(), Some(&[2, 3][..]));
1166 fn test_buffered_reader_invalidated_after_read() {
1167 let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
1168 let mut reader = BufReader::with_capacity(3, io::Cursor::new(inner));
1170 assert_eq!(reader.fill_buf().ok(), Some(&[5, 6, 7][..]));
1173 let mut buffer = [0, 0, 0, 0, 0];
1174 assert_eq!(reader.read(&mut buffer).ok(), Some(5));
1175 assert_eq!(buffer, [0, 1, 2, 3, 4]);
1177 assert!(reader.seek_relative(-2).is_ok());
1178 let mut buffer = [0, 0];
1179 assert_eq!(reader.read(&mut buffer).ok(), Some(2));
1180 assert_eq!(buffer, [3, 4]);
1184 fn test_buffered_reader_invalidated_after_seek() {
1185 let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
1186 let mut reader = BufReader::with_capacity(3, io::Cursor::new(inner));
1188 assert_eq!(reader.fill_buf().ok(), Some(&[5, 6, 7][..]));
1191 assert!(reader.seek(SeekFrom::Current(5)).is_ok());
1193 assert!(reader.seek_relative(-2).is_ok());
1194 let mut buffer = [0, 0];
1195 assert_eq!(reader.read(&mut buffer).ok(), Some(2));
1196 assert_eq!(buffer, [3, 4]);
1200 fn test_buffered_reader_seek_underflow() {
1201 // gimmick reader that yields its position modulo 256 for each byte
1202 struct PositionReader {
1205 impl Read for PositionReader {
1206 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
1207 let len = buf.len();
1209 *x = self.pos as u8;
1210 self.pos = self.pos.wrapping_add(1);
1215 impl Seek for PositionReader {
1216 fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
1218 SeekFrom::Start(n) => {
1221 SeekFrom::Current(n) => {
1222 self.pos = self.pos.wrapping_add(n as u64);
1224 SeekFrom::End(n) => {
1225 self.pos = u64::max_value().wrapping_add(n as u64);
1232 let mut reader = BufReader::with_capacity(5, PositionReader { pos: 0 });
1233 assert_eq!(reader.fill_buf().ok(), Some(&[0, 1, 2, 3, 4][..]));
1234 assert_eq!(reader.seek(SeekFrom::End(-5)).ok(), Some(u64::max_value() - 5));
1235 assert_eq!(reader.fill_buf().ok().map(|s| s.len()), Some(5));
1236 // the following seek will require two underlying seeks
1237 let expected = 9223372036854775802;
1238 assert_eq!(reader.seek(SeekFrom::Current(i64::min_value())).ok(), Some(expected));
1239 assert_eq!(reader.fill_buf().ok().map(|s| s.len()), Some(5));
1240 // seeking to 0 should empty the buffer.
1241 assert_eq!(reader.seek(SeekFrom::Current(0)).ok(), Some(expected));
1242 assert_eq!(reader.get_ref().pos, expected);
1246 fn test_buffered_reader_seek_underflow_discard_buffer_between_seeks() {
1247 // gimmick reader that returns Err after first seek
1248 struct ErrAfterFirstSeekReader {
1251 impl Read for ErrAfterFirstSeekReader {
1252 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
1253 for x in &mut *buf {
1259 impl Seek for ErrAfterFirstSeekReader {
1260 fn seek(&mut self, _: SeekFrom) -> io::Result<u64> {
1261 if self.first_seek {
1262 self.first_seek = false;
1265 Err(io::Error::new(io::ErrorKind::Other, "oh no!"))
1270 let mut reader = BufReader::with_capacity(5, ErrAfterFirstSeekReader { first_seek: true });
1271 assert_eq!(reader.fill_buf().ok(), Some(&[0, 0, 0, 0, 0][..]));
1273 // The following seek will require two underlying seeks. The first will
1274 // succeed but the second will fail. This should still invalidate the
1276 assert!(reader.seek(SeekFrom::Current(i64::min_value())).is_err());
1277 assert_eq!(reader.buffer().len(), 0);
1281 fn test_buffered_writer() {
1282 let inner = Vec::new();
1283 let mut writer = BufWriter::with_capacity(2, inner);
1285 writer.write(&[0, 1]).unwrap();
1286 assert_eq!(writer.buffer(), []);
1287 assert_eq!(*writer.get_ref(), [0, 1]);
1289 writer.write(&[2]).unwrap();
1290 assert_eq!(writer.buffer(), [2]);
1291 assert_eq!(*writer.get_ref(), [0, 1]);
1293 writer.write(&[3]).unwrap();
1294 assert_eq!(writer.buffer(), [2, 3]);
1295 assert_eq!(*writer.get_ref(), [0, 1]);
1297 writer.flush().unwrap();
1298 assert_eq!(writer.buffer(), []);
1299 assert_eq!(*writer.get_ref(), [0, 1, 2, 3]);
1301 writer.write(&[4]).unwrap();
1302 writer.write(&[5]).unwrap();
1303 assert_eq!(writer.buffer(), [4, 5]);
1304 assert_eq!(*writer.get_ref(), [0, 1, 2, 3]);
1306 writer.write(&[6]).unwrap();
1307 assert_eq!(writer.buffer(), [6]);
1308 assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5]);
1310 writer.write(&[7, 8]).unwrap();
1311 assert_eq!(writer.buffer(), []);
1312 assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8]);
1314 writer.write(&[9, 10, 11]).unwrap();
1315 assert_eq!(writer.buffer(), []);
1316 assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]);
1318 writer.flush().unwrap();
1319 assert_eq!(writer.buffer(), []);
1320 assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]);
1324 fn test_buffered_writer_inner_flushes() {
1325 let mut w = BufWriter::with_capacity(3, Vec::new());
1326 w.write(&[0, 1]).unwrap();
1327 assert_eq!(*w.get_ref(), []);
1328 let w = w.into_inner().unwrap();
1329 assert_eq!(w, [0, 1]);
1333 fn test_buffered_writer_seek() {
1334 let mut w = BufWriter::with_capacity(3, io::Cursor::new(Vec::new()));
1335 w.write_all(&[0, 1, 2, 3, 4, 5]).unwrap();
1336 w.write_all(&[6, 7]).unwrap();
1337 assert_eq!(w.seek(SeekFrom::Current(0)).ok(), Some(8));
1338 assert_eq!(&w.get_ref().get_ref()[..], &[0, 1, 2, 3, 4, 5, 6, 7][..]);
1339 assert_eq!(w.seek(SeekFrom::Start(2)).ok(), Some(2));
1340 w.write_all(&[8, 9]).unwrap();
1341 assert_eq!(&w.into_inner().unwrap().into_inner()[..], &[0, 1, 8, 9, 4, 5, 6, 7]);
1345 fn test_read_until() {
1346 let inner: &[u8] = &[0, 1, 2, 1, 0];
1347 let mut reader = BufReader::with_capacity(2, inner);
1348 let mut v = Vec::new();
1349 reader.read_until(0, &mut v).unwrap();
1352 reader.read_until(2, &mut v).unwrap();
1353 assert_eq!(v, [1, 2]);
1355 reader.read_until(1, &mut v).unwrap();
1358 reader.read_until(8, &mut v).unwrap();
1361 reader.read_until(9, &mut v).unwrap();
1366 fn test_line_buffer_fail_flush() {
1368 struct FailFlushWriter<'a>(&'a mut Vec<u8>);
1370 impl Write for FailFlushWriter<'_> {
1371 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
1372 self.0.extend_from_slice(buf);
1375 fn flush(&mut self) -> io::Result<()> {
1376 Err(io::Error::new(io::ErrorKind::Other, "flush failed"))
1380 let mut buf = Vec::new();
1382 let mut writer = LineWriter::new(FailFlushWriter(&mut buf));
1383 let to_write = b"abc\ndef";
1384 if let Ok(written) = writer.write(to_write) {
1385 assert!(written < to_write.len(), "didn't flush on new line");
1390 assert!(buf.is_empty(), "write returned an error but wrote data");
1394 fn test_line_buffer() {
1395 let mut writer = LineWriter::new(Vec::new());
1396 writer.write(&[0]).unwrap();
1397 assert_eq!(*writer.get_ref(), []);
1398 writer.write(&[1]).unwrap();
1399 assert_eq!(*writer.get_ref(), []);
1400 writer.flush().unwrap();
1401 assert_eq!(*writer.get_ref(), [0, 1]);
1402 writer.write(&[0, b'\n', 1, b'\n', 2]).unwrap();
1403 assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n']);
1404 writer.flush().unwrap();
1405 assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n', 2]);
1406 writer.write(&[3, b'\n']).unwrap();
1407 assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n', 2, 3, b'\n']);
1411 fn test_read_line() {
1412 let in_buf: &[u8] = b"a\nb\nc";
1413 let mut reader = BufReader::with_capacity(2, in_buf);
1414 let mut s = String::new();
1415 reader.read_line(&mut s).unwrap();
1416 assert_eq!(s, "a\n");
1418 reader.read_line(&mut s).unwrap();
1419 assert_eq!(s, "b\n");
1421 reader.read_line(&mut s).unwrap();
1424 reader.read_line(&mut s).unwrap();
1430 let in_buf: &[u8] = b"a\nb\nc";
1431 let reader = BufReader::with_capacity(2, in_buf);
1432 let mut it = reader.lines();
1433 assert_eq!(it.next().unwrap().unwrap(), "a".to_string());
1434 assert_eq!(it.next().unwrap().unwrap(), "b".to_string());
1435 assert_eq!(it.next().unwrap().unwrap(), "c".to_string());
1436 assert!(it.next().is_none());
1440 fn test_short_reads() {
1441 let inner = ShortReader { lengths: vec![0, 1, 2, 0, 1, 0] };
1442 let mut reader = BufReader::new(inner);
1443 let mut buf = [0, 0];
1444 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1445 assert_eq!(reader.read(&mut buf).unwrap(), 1);
1446 assert_eq!(reader.read(&mut buf).unwrap(), 2);
1447 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1448 assert_eq!(reader.read(&mut buf).unwrap(), 1);
1449 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1450 assert_eq!(reader.read(&mut buf).unwrap(), 0);
1455 fn dont_panic_in_drop_on_panicked_flush() {
1456 struct FailFlushWriter;
1458 impl Write for FailFlushWriter {
1459 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
1462 fn flush(&mut self) -> io::Result<()> {
1463 Err(io::Error::last_os_error())
1467 let writer = FailFlushWriter;
1468 let _writer = BufWriter::new(writer);
1470 // If writer panics *again* due to the flush error then the process will
1476 #[cfg_attr(target_os = "emscripten", ignore)]
1477 fn panic_in_write_doesnt_flush_in_drop() {
1478 static WRITES: AtomicUsize = AtomicUsize::new(0);
1482 impl Write for PanicWriter {
1483 fn write(&mut self, _: &[u8]) -> io::Result<usize> {
1484 WRITES.fetch_add(1, Ordering::SeqCst);
1487 fn flush(&mut self) -> io::Result<()> {
1493 let mut writer = BufWriter::new(PanicWriter);
1494 let _ = writer.write(b"hello world");
1495 let _ = writer.flush();
1500 assert_eq!(WRITES.load(Ordering::SeqCst), 1);
1504 fn bench_buffered_reader(b: &mut test::Bencher) {
1505 b.iter(|| BufReader::new(io::empty()));
1509 fn bench_buffered_writer(b: &mut test::Bencher) {
1510 b.iter(|| BufWriter::new(io::sink()));
1513 struct AcceptOneThenFail {
1518 impl Write for AcceptOneThenFail {
1519 fn write(&mut self, data: &[u8]) -> io::Result<usize> {
1521 assert_eq!(data, b"a\nb\n");
1522 self.written = true;
1525 Err(io::Error::new(io::ErrorKind::NotFound, "test"))
1529 fn flush(&mut self) -> io::Result<()> {
1530 assert!(self.written);
1531 assert!(!self.flushed);
1532 self.flushed = true;
1533 Err(io::Error::new(io::ErrorKind::Other, "test"))
1538 fn erroneous_flush_retried() {
1539 let a = AcceptOneThenFail { written: false, flushed: false };
1541 let mut l = LineWriter::new(a);
1542 assert_eq!(l.write(b"a\nb\na").unwrap(), 4);
1543 assert!(l.get_ref().written);
1544 assert!(l.get_ref().flushed);
1545 l.get_mut().flushed = false;
1547 assert_eq!(l.write(b"a").unwrap_err().kind(), io::ErrorKind::Other)
1551 fn line_vectored() {
1552 let mut a = LineWriter::new(Vec::new());
1556 IoSlice::new(b"\n"),
1563 assert_eq!(a.get_ref(), b"\n");
1577 assert_eq!(a.get_ref(), b"\n");
1579 assert_eq!(a.get_ref(), b"\nabac");
1580 assert_eq!(a.write_vectored(&[]).unwrap(), 0);
1591 assert_eq!(a.write_vectored(&[IoSlice::new(b"a\nb"),]).unwrap(), 3);
1592 assert_eq!(a.get_ref(), b"\nabaca\n");
1596 fn line_vectored_partial_and_errors() {
1598 Write { inputs: Vec<&'static [u8]>, output: io::Result<usize> },
1599 Flush { output: io::Result<()> },
1605 impl Write for Writer {
1606 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
1607 self.write_vectored(&[IoSlice::new(buf)])
1610 fn write_vectored(&mut self, buf: &[IoSlice<'_>]) -> io::Result<usize> {
1611 match self.calls.pop().unwrap() {
1612 Call::Write { inputs, output } => {
1613 assert_eq!(inputs, buf.iter().map(|b| &**b).collect::<Vec<_>>());
1616 _ => panic!("unexpected call to write"),
1620 fn flush(&mut self) -> io::Result<()> {
1621 match self.calls.pop().unwrap() {
1622 Call::Flush { output } => output,
1623 _ => panic!("unexpected call to flush"),
1628 impl Drop for Writer {
1629 fn drop(&mut self) {
1630 if !thread::panicking() {
1631 assert_eq!(self.calls.len(), 0);
1636 // partial writes keep going
1637 let mut a = LineWriter::new(Writer { calls: Vec::new() });
1638 a.write_vectored(&[IoSlice::new(&[]), IoSlice::new(b"abc")]).unwrap();
1639 a.get_mut().calls.push(Call::Flush { output: Ok(()) });
1640 a.get_mut().calls.push(Call::Write { inputs: vec![b"bcx\n"], output: Ok(4) });
1641 a.get_mut().calls.push(Call::Write { inputs: vec![b"abcx\n"], output: Ok(1) });
1642 a.write_vectored(&[IoSlice::new(b"x"), IoSlice::new(b"\n")]).unwrap();
1643 a.get_mut().calls.push(Call::Flush { output: Ok(()) });
1646 // erroneous writes stop and don't write more
1647 a.get_mut().calls.push(Call::Write { inputs: vec![b"x\n"], output: Err(err()) });
1648 assert_eq!(a.write_vectored(&[IoSlice::new(b"x"), IoSlice::new(b"\na")]).unwrap(), 2);
1649 a.get_mut().calls.push(Call::Flush { output: Ok(()) });
1650 a.get_mut().calls.push(Call::Write { inputs: vec![b"x\n"], output: Ok(2) });
1653 fn err() -> io::Error {
1654 io::Error::new(io::ErrorKind::Other, "x")