1# buf\_re(a)dux
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6
7Drop-in replacements for buffered I/O types in `std::io`.
8
9These replacements retain the method names/signatures and implemented traits of their stdlib
10counterparts, making replacement as simple as swapping the import of the type.
11
12### More Direct Control
13
14All replacement types provide methods to:
15* Increase the capacity of the buffer
16* Get the number of available bytes as well as the total capacity of the buffer
17* Consume the wrapper without losing data
18
19`BufReader` provides methods to:
20* Access the buffer through an `&`-reference without performing I/O
21* Force unconditional reads into the buffer
22* Get a `Read` adapter which empties the buffer and then pulls from the inner reader directly
23* Shuffle bytes down to the beginning of the buffer to make room for more reading
24* Get inner reader and trimmed buffer with the remaining data
25
26`BufWriter` and `LineWriter` provide methods to:
27* Flush the buffer and unwrap the inner writer unconditionally.
28
29### More Sensible and Customizable Buffering Behavior
30Tune the behavior of the buffer to your specific use-case using the types in the
31`policy` module:
32
33* Refine `BufReader`'s behavior by implementing the `ReaderPolicy` trait or use
34an existing implementation like `MinBuffered` to ensure the buffer always contains
35a minimum number of bytes (until the underlying reader is empty).
36
37* Refine `BufWriter`'s behavior by implementing the `WriterPolicy` trait
38or use an existing implementation like `FlushOn` to flush when a particular byte
39appears in the buffer (used to implement `LineWriter`).
40
41
42## Usage
43
44#### [Documentation](http://docs.rs/buf_redux/)
45
46`Cargo.toml`:
47```toml
48[dependencies]
49buf_redux = "0.2"
50```
51
52`lib.rs` or `main.rs`:
53```rust
54extern crate buf_redux;
55```
56
57And then simply swap the import of the types you want to replace:
58
59#### `BufReader`:
60```
61- use std::io::BufReader;
62+ use buf_redux::BufReader;
63```
64#### `BufWriter`:
65```
66- use std::io::BufWriter;
67+ use buf_redux::BufWriter;
68```
69
70#### `LineWriter`:
71```
72- use std::io::LineWriter;
73+ use buf_redux::LineWriter;
74```
75
76### Using `MinBuffered`
77The new `policy::MinBuffered` reader-policy can be used to ensure that `BufReader` always has at least a
78certain number of bytes in its buffer. This can be useful for parsing applications that require a
79certain amount of lookahead.
80
81```rust
82use buf_redux::BufReader;
83use buf_redux::policy::MinBuffered;
84use std::io::{BufRead, Cursor};
85
86let data = (1 .. 16).collect::<Vec<u8>>();
87
88// normally you should use `BufReader::new()` or give a capacity of several KiB or more
89let mut reader = BufReader::with_capacity(8, Cursor::new(data))
90    // always at least 4 bytes in the buffer (or until the source is empty)
91    .set_policy(MinBuffered(4)); // always at least 4 bytes in the buffer
92
93// first buffer fill, same as `std::io::BufReader`
94assert_eq!(reader.fill_buf().unwrap(), &[1, 2, 3, 4, 5, 6, 7, 8]);
95reader.consume(3);
96
97// enough data in the buffer, another read isn't done yet
98assert_eq!(reader.fill_buf().unwrap(), &[4, 5, 6, 7, 8]);
99reader.consume(4);
100
101// `std::io::BufReader` would return `&[8]`
102assert_eq!(reader.fill_buf().unwrap(), &[8, 9, 10, 11, 12, 13, 14, 15]);
103reader.consume(5);
104
105// no data left in the reader
106assert_eq!(reader.fill_buf().unwrap(), &[13, 14, 15]);
107```
108
109### Note: Making Room / Ringbuffers / `slice-deque` Feature
110With policies like `MinBuffered`, that will read into the buffer and consume bytes from it without completely
111emptying it, normal buffer handling can run out of room to read/write into as all the free space is at the
112head of the buffer. If the amount of data in the buffer is small, you can call `.make_room()` on the buffered
113type to make more room for reading. `MinBuffered` will do this automatically.
114
115Instead of this, with the `slice-deque` feature, you can instead have your buffered type allocate a *ringbuffer*,
116simply by using the `::new_ringbuf()` or `::with_capacity_ringbuf()` constructors instead of
117`::new()` or `with_capacity()`, respectively. With a ringbuffer, consuming/flushing bytes
118from a buffer instantly makes room for more reading/writing at the end.
119However, this has some caveats:
120
121* It is only available on target platforms with virtual memory support, namely fully fledged
122OSes such as Windows and Unix-derivative platforms like Linux, OS X, BSD variants, etc.
123
124* The default capacity varies based on platform, and custom capacities are rounded up to a
125multiple of their minimum size, typically the page size of the platform.
126Windows' minimum size is comparably quite large (**64 KiB**) due to some legacy reasons,
127so this may be less optimal than the default capacity for a normal buffer (8 KiB) for some
128use-cases.
129
130* Due to the nature of the virtual-memory trick, the virtual address space the buffer
131allocates will be double its capacity. This means that your program will *appear* to use more
132memory than it would if it was using a normal buffer of the same capacity. The physical memory
133usage will be the same in both cases, but if address space is at a premium in your application
134(32-bit targets) then this may be a concern.
135
136It is up to you to decide if the benefits outweigh the costs. With a policy like `MinBuffered`,
137it could significantly improve performance.
138
139## License
140
141Licensed under either of
142
143 * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
144 * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
145
146at your option.
147
148### Contribution
149
150Unless you explicitly state otherwise, any contribution intentionally submitted
151for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any
152additional terms or conditions.
153