1 // Copyright 2015 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.
15 use io::{self, SeekFrom, Error, ErrorKind};
18 /// A `Cursor` wraps another type and provides it with a
19 /// [`Seek`](trait.Seek.html) implementation.
21 /// Cursors are typically used with in-memory buffers to allow them to
22 /// implement `Read` and/or `Write`, allowing these buffers to be used
23 /// anywhere you might use a reader or writer that does actual I/O.
25 /// The standard library implements some I/O traits on various types which
26 /// are commonly used as a buffer, like `Cursor<Vec<u8>>` and `Cursor<&[u8]>`.
30 /// We may want to write bytes to a [`File`][file] in our production
31 /// code, but use an in-memory buffer in our tests. We can do this with
34 /// [file]: ../fs/struct.File.html
37 /// use std::io::prelude::*;
38 /// use std::io::{self, SeekFrom};
39 /// use std::fs::File;
41 /// // a library function we've written
42 /// fn write_ten_bytes_at_end<W: Write + Seek>(writer: &mut W) -> io::Result<()> {
43 /// try!(writer.seek(SeekFrom::End(-10)));
46 /// try!(writer.write(&[i]));
53 /// # fn foo() -> io::Result<()> {
54 /// // Here's some code that uses this library function.
56 /// // We might want to use a BufReader here for efficiency, but let's
57 /// // keep this example focused.
58 /// let mut file = try!(File::create("foo.txt"));
60 /// try!(write_ten_bytes_at_end(&mut file));
64 /// // now let's write a test
66 /// fn test_writes_bytes() {
67 /// // setting up a real File is much more slow than an in-memory buffer,
68 /// // let's use a cursor instead
69 /// use std::io::Cursor;
70 /// let mut buff = Cursor::new(vec![0; 15]);
72 /// write_ten_bytes(&mut buff).unwrap();
74 /// assert_eq!(&buff.get_ref()[5..15], &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
77 #[stable(feature = "rust1", since = "1.0.0")]
78 #[derive(Clone, Debug)]
79 pub struct Cursor<T> {
85 /// Creates a new cursor wrapping the provided underlying I/O object.
90 /// use std::io::Cursor;
92 /// let buff = Cursor::new(Vec::new());
93 /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
94 /// # force_inference(&buff);
96 #[stable(feature = "rust1", since = "1.0.0")]
97 pub fn new(inner: T) -> Cursor<T> {
98 Cursor { pos: 0, inner: inner }
101 /// Consumes this cursor, returning the underlying value.
106 /// use std::io::Cursor;
108 /// let buff = Cursor::new(Vec::new());
109 /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
110 /// # force_inference(&buff);
112 /// let vec = buff.into_inner();
114 #[stable(feature = "rust1", since = "1.0.0")]
115 pub fn into_inner(self) -> T { self.inner }
117 /// Gets a reference to the underlying value in this cursor.
122 /// use std::io::Cursor;
124 /// let buff = Cursor::new(Vec::new());
125 /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
126 /// # force_inference(&buff);
128 /// let reference = buff.get_ref();
130 #[stable(feature = "rust1", since = "1.0.0")]
131 pub fn get_ref(&self) -> &T { &self.inner }
133 /// Gets a mutable reference to the underlying value in this cursor.
135 /// Care should be taken to avoid modifying the internal I/O state of the
136 /// underlying value as it may corrupt this cursor's position.
141 /// use std::io::Cursor;
143 /// let mut buff = Cursor::new(Vec::new());
144 /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
145 /// # force_inference(&buff);
147 /// let reference = buff.get_mut();
149 #[stable(feature = "rust1", since = "1.0.0")]
150 pub fn get_mut(&mut self) -> &mut T { &mut self.inner }
152 /// Returns the current position of this cursor.
157 /// use std::io::Cursor;
158 /// use std::io::prelude::*;
159 /// use std::io::SeekFrom;
161 /// let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);
163 /// assert_eq!(buff.position(), 0);
165 /// buff.seek(SeekFrom::Current(2)).unwrap();
166 /// assert_eq!(buff.position(), 2);
168 /// buff.seek(SeekFrom::Current(-1)).unwrap();
169 /// assert_eq!(buff.position(), 1);
171 #[stable(feature = "rust1", since = "1.0.0")]
172 pub fn position(&self) -> u64 { self.pos }
174 /// Sets the position of this cursor.
179 /// use std::io::Cursor;
181 /// let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);
183 /// assert_eq!(buff.position(), 0);
185 /// buff.set_position(2);
186 /// assert_eq!(buff.position(), 2);
188 /// buff.set_position(4);
189 /// assert_eq!(buff.position(), 4);
191 #[stable(feature = "rust1", since = "1.0.0")]
192 pub fn set_position(&mut self, pos: u64) { self.pos = pos; }
195 #[stable(feature = "rust1", since = "1.0.0")]
196 impl<T> io::Seek for Cursor<T> where T: AsRef<[u8]> {
197 fn seek(&mut self, style: SeekFrom) -> io::Result<u64> {
198 let pos = match style {
199 SeekFrom::Start(n) => { self.pos = n; return Ok(n) }
200 SeekFrom::End(n) => self.inner.as_ref().len() as i64 + n,
201 SeekFrom::Current(n) => self.pos as i64 + n,
205 Err(Error::new(ErrorKind::InvalidInput,
206 "invalid seek to a negative position"))
208 self.pos = pos as u64;
214 #[stable(feature = "rust1", since = "1.0.0")]
215 impl<T> Read for Cursor<T> where T: AsRef<[u8]> {
216 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
217 let n = try!(Read::read(&mut try!(self.fill_buf()), buf));
218 self.pos += n as u64;
223 #[stable(feature = "rust1", since = "1.0.0")]
224 impl<T> BufRead for Cursor<T> where T: AsRef<[u8]> {
225 fn fill_buf(&mut self) -> io::Result<&[u8]> {
226 let amt = cmp::min(self.pos, self.inner.as_ref().len() as u64);
227 Ok(&self.inner.as_ref()[(amt as usize)..])
229 fn consume(&mut self, amt: usize) { self.pos += amt as u64; }
232 #[stable(feature = "rust1", since = "1.0.0")]
233 impl<'a> Write for Cursor<&'a mut [u8]> {
234 fn write(&mut self, data: &[u8]) -> io::Result<usize> {
235 let pos = cmp::min(self.pos, self.inner.len() as u64);
236 let amt = try!((&mut self.inner[(pos as usize)..]).write(data));
237 self.pos += amt as u64;
240 fn flush(&mut self) -> io::Result<()> { Ok(()) }
243 #[stable(feature = "rust1", since = "1.0.0")]
244 impl Write for Cursor<Vec<u8>> {
245 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
246 // Make sure the internal buffer is as least as big as where we
248 let pos = self.position();
249 let amt = pos.saturating_sub(self.inner.len() as u64);
250 // use `resize` so that the zero filling is as efficient as possible
251 let len = self.inner.len();
252 self.inner.resize(len + amt as usize, 0);
254 // Figure out what bytes will be used to overwrite what's currently
255 // there (left), and what will be appended on the end (right)
256 let space = self.inner.len() - pos as usize;
257 let (left, right) = buf.split_at(cmp::min(space, buf.len()));
258 slice::bytes::copy_memory(left, &mut self.inner[(pos as usize)..]);
259 self.inner.push_all(right);
262 self.set_position(pos + buf.len() as u64);
265 fn flush(&mut self) -> io::Result<()> { Ok(()) }
272 use io::{Cursor, SeekFrom};
276 fn test_vec_writer() {
277 let mut writer = Vec::new();
278 assert_eq!(writer.write(&[0]).unwrap(), 1);
279 assert_eq!(writer.write(&[1, 2, 3]).unwrap(), 3);
280 assert_eq!(writer.write(&[4, 5, 6, 7]).unwrap(), 4);
281 let b: &[_] = &[0, 1, 2, 3, 4, 5, 6, 7];
282 assert_eq!(writer, b);
286 fn test_mem_writer() {
287 let mut writer = Cursor::new(Vec::new());
288 assert_eq!(writer.write(&[0]).unwrap(), 1);
289 assert_eq!(writer.write(&[1, 2, 3]).unwrap(), 3);
290 assert_eq!(writer.write(&[4, 5, 6, 7]).unwrap(), 4);
291 let b: &[_] = &[0, 1, 2, 3, 4, 5, 6, 7];
292 assert_eq!(&writer.get_ref()[..], b);
296 fn test_buf_writer() {
297 let mut buf = [0 as u8; 9];
299 let mut writer = Cursor::new(&mut buf[..]);
300 assert_eq!(writer.position(), 0);
301 assert_eq!(writer.write(&[0]).unwrap(), 1);
302 assert_eq!(writer.position(), 1);
303 assert_eq!(writer.write(&[1, 2, 3]).unwrap(), 3);
304 assert_eq!(writer.write(&[4, 5, 6, 7]).unwrap(), 4);
305 assert_eq!(writer.position(), 8);
306 assert_eq!(writer.write(&[]).unwrap(), 0);
307 assert_eq!(writer.position(), 8);
309 assert_eq!(writer.write(&[8, 9]).unwrap(), 1);
310 assert_eq!(writer.write(&[10]).unwrap(), 0);
312 let b: &[_] = &[0, 1, 2, 3, 4, 5, 6, 7, 8];
317 fn test_buf_writer_seek() {
318 let mut buf = [0 as u8; 8];
320 let mut writer = Cursor::new(&mut buf[..]);
321 assert_eq!(writer.position(), 0);
322 assert_eq!(writer.write(&[1]).unwrap(), 1);
323 assert_eq!(writer.position(), 1);
325 assert_eq!(writer.seek(SeekFrom::Start(2)).unwrap(), 2);
326 assert_eq!(writer.position(), 2);
327 assert_eq!(writer.write(&[2]).unwrap(), 1);
328 assert_eq!(writer.position(), 3);
330 assert_eq!(writer.seek(SeekFrom::Current(-2)).unwrap(), 1);
331 assert_eq!(writer.position(), 1);
332 assert_eq!(writer.write(&[3]).unwrap(), 1);
333 assert_eq!(writer.position(), 2);
335 assert_eq!(writer.seek(SeekFrom::End(-1)).unwrap(), 7);
336 assert_eq!(writer.position(), 7);
337 assert_eq!(writer.write(&[4]).unwrap(), 1);
338 assert_eq!(writer.position(), 8);
341 let b: &[_] = &[1, 3, 2, 0, 0, 0, 0, 4];
346 fn test_buf_writer_error() {
347 let mut buf = [0 as u8; 2];
348 let mut writer = Cursor::new(&mut buf[..]);
349 assert_eq!(writer.write(&[0]).unwrap(), 1);
350 assert_eq!(writer.write(&[0, 0]).unwrap(), 1);
351 assert_eq!(writer.write(&[0, 0]).unwrap(), 0);
355 fn test_mem_reader() {
356 let mut reader = Cursor::new(vec!(0, 1, 2, 3, 4, 5, 6, 7));
358 assert_eq!(reader.read(&mut buf).unwrap(), 0);
359 assert_eq!(reader.position(), 0);
361 assert_eq!(reader.read(&mut buf).unwrap(), 1);
362 assert_eq!(reader.position(), 1);
365 let mut buf = [0; 4];
366 assert_eq!(reader.read(&mut buf).unwrap(), 4);
367 assert_eq!(reader.position(), 5);
368 let b: &[_] = &[1, 2, 3, 4];
370 assert_eq!(reader.read(&mut buf).unwrap(), 3);
371 let b: &[_] = &[5, 6, 7];
372 assert_eq!(&buf[..3], b);
373 assert_eq!(reader.read(&mut buf).unwrap(), 0);
378 let mut reader = Cursor::new(vec!(0, 1, 2, 3, 4, 5, 6, 7));
379 let mut v = Vec::new();
380 reader.read_to_end(&mut v).unwrap();
381 assert_eq!(v, [0, 1, 2, 3, 4, 5, 6, 7]);
385 fn test_slice_reader() {
386 let in_buf = vec![0, 1, 2, 3, 4, 5, 6, 7];
387 let mut reader = &mut &in_buf[..];
389 assert_eq!(reader.read(&mut buf).unwrap(), 0);
391 assert_eq!(reader.read(&mut buf).unwrap(), 1);
392 assert_eq!(reader.len(), 7);
394 assert_eq!(&buf[..], b);
395 let mut buf = [0; 4];
396 assert_eq!(reader.read(&mut buf).unwrap(), 4);
397 assert_eq!(reader.len(), 3);
398 let b: &[_] = &[1, 2, 3, 4];
399 assert_eq!(&buf[..], b);
400 assert_eq!(reader.read(&mut buf).unwrap(), 3);
401 let b: &[_] = &[5, 6, 7];
402 assert_eq!(&buf[..3], b);
403 assert_eq!(reader.read(&mut buf).unwrap(), 0);
407 fn test_buf_reader() {
408 let in_buf = vec![0, 1, 2, 3, 4, 5, 6, 7];
409 let mut reader = Cursor::new(&in_buf[..]);
411 assert_eq!(reader.read(&mut buf).unwrap(), 0);
412 assert_eq!(reader.position(), 0);
414 assert_eq!(reader.read(&mut buf).unwrap(), 1);
415 assert_eq!(reader.position(), 1);
418 let mut buf = [0; 4];
419 assert_eq!(reader.read(&mut buf).unwrap(), 4);
420 assert_eq!(reader.position(), 5);
421 let b: &[_] = &[1, 2, 3, 4];
423 assert_eq!(reader.read(&mut buf).unwrap(), 3);
424 let b: &[_] = &[5, 6, 7];
425 assert_eq!(&buf[..3], b);
426 assert_eq!(reader.read(&mut buf).unwrap(), 0);
430 fn test_read_char() {
431 let b = &b"Vi\xE1\xBB\x87t"[..];
432 let mut c = Cursor::new(b).chars();
433 assert_eq!(c.next().unwrap().unwrap(), 'V');
434 assert_eq!(c.next().unwrap().unwrap(), 'i');
435 assert_eq!(c.next().unwrap().unwrap(), 'ệ');
436 assert_eq!(c.next().unwrap().unwrap(), 't');
437 assert!(c.next().is_none());
441 fn test_read_bad_char() {
442 let b = &b"\x80"[..];
443 let mut c = Cursor::new(b).chars();
444 assert!(c.next().unwrap().is_err());
450 let mut r = Cursor::new(&buf[..]);
451 assert_eq!(r.seek(SeekFrom::Start(10)).unwrap(), 10);
452 assert_eq!(r.read(&mut [0]).unwrap(), 0);
454 let mut r = Cursor::new(vec!(10));
455 assert_eq!(r.seek(SeekFrom::Start(10)).unwrap(), 10);
456 assert_eq!(r.read(&mut [0]).unwrap(), 0);
459 let mut r = Cursor::new(&mut buf[..]);
460 assert_eq!(r.seek(SeekFrom::Start(10)).unwrap(), 10);
461 assert_eq!(r.write(&[3]).unwrap(), 0);
467 let mut r = Cursor::new(&buf[..]);
468 assert!(r.seek(SeekFrom::End(-2)).is_err());
470 let mut r = Cursor::new(vec!(10));
471 assert!(r.seek(SeekFrom::End(-2)).is_err());
474 let mut r = Cursor::new(&mut buf[..]);
475 assert!(r.seek(SeekFrom::End(-2)).is_err());
479 fn test_seekable_mem_writer() {
480 let mut writer = Cursor::new(Vec::<u8>::new());
481 assert_eq!(writer.position(), 0);
482 assert_eq!(writer.write(&[0]).unwrap(), 1);
483 assert_eq!(writer.position(), 1);
484 assert_eq!(writer.write(&[1, 2, 3]).unwrap(), 3);
485 assert_eq!(writer.write(&[4, 5, 6, 7]).unwrap(), 4);
486 assert_eq!(writer.position(), 8);
487 let b: &[_] = &[0, 1, 2, 3, 4, 5, 6, 7];
488 assert_eq!(&writer.get_ref()[..], b);
490 assert_eq!(writer.seek(SeekFrom::Start(0)).unwrap(), 0);
491 assert_eq!(writer.position(), 0);
492 assert_eq!(writer.write(&[3, 4]).unwrap(), 2);
493 let b: &[_] = &[3, 4, 2, 3, 4, 5, 6, 7];
494 assert_eq!(&writer.get_ref()[..], b);
496 assert_eq!(writer.seek(SeekFrom::Current(1)).unwrap(), 3);
497 assert_eq!(writer.write(&[0, 1]).unwrap(), 2);
498 let b: &[_] = &[3, 4, 2, 0, 1, 5, 6, 7];
499 assert_eq!(&writer.get_ref()[..], b);
501 assert_eq!(writer.seek(SeekFrom::End(-1)).unwrap(), 7);
502 assert_eq!(writer.write(&[1, 2]).unwrap(), 2);
503 let b: &[_] = &[3, 4, 2, 0, 1, 5, 6, 1, 2];
504 assert_eq!(&writer.get_ref()[..], b);
506 assert_eq!(writer.seek(SeekFrom::End(1)).unwrap(), 10);
507 assert_eq!(writer.write(&[1]).unwrap(), 1);
508 let b: &[_] = &[3, 4, 2, 0, 1, 5, 6, 1, 2, 0, 1];
509 assert_eq!(&writer.get_ref()[..], b);
513 fn vec_seek_past_end() {
514 let mut r = Cursor::new(Vec::new());
515 assert_eq!(r.seek(SeekFrom::Start(10)).unwrap(), 10);
516 assert_eq!(r.write(&[3]).unwrap(), 1);
520 fn vec_seek_before_0() {
521 let mut r = Cursor::new(Vec::new());
522 assert!(r.seek(SeekFrom::End(-2)).is_err());