projects / ceph.git / blame
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1 | [/ |
| 2 | / Copyright (c) 2003-2016 Christopher M. Kohlhoff (chris at kohlhoff dot com) | |
| 3 | / | |
| 4 | / Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 5 | / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
| 6 | /] | |
| 7 | ||
| 8 | [section:streams Streams, Short Reads and Short Writes] | |
| 9 | ||
| 10 | Many I/O objects in Boost.Asio are stream-oriented. This means that: | |
| 11 | ||
| 12 | * There are no message boundaries. The data being transferred is a continuous | |
| 13 | sequence of bytes. | |
| 14 | ||
| 15 | * Read or write operations may transfer fewer bytes than requested. This is | |
| 16 | referred to as a short read or short write. | |
| 17 | ||
| 18 | Objects that provide stream-oriented I/O model one or more of the following | |
| 19 | type requirements: | |
| 20 | ||
| 21 | * `SyncReadStream`, where synchronous read operations are performed using a | |
| 22 | member function called `read_some()`. | |
| 23 | ||
| 24 | * `AsyncReadStream`, where asynchronous read operations are performed using a | |
| 25 | member function called `async_read_some()`. | |
| 26 | ||
| 27 | * `SyncWriteStream`, where synchronous write operations are performed using a | |
| 28 | member function called `write_some()`. | |
| 29 | ||
| 30 | * `AsyncWriteStream`, where synchronous write operations are performed using a | |
| 31 | member function called `async_write_some()`. | |
| 32 | ||
| 33 | Examples of stream-oriented I/O objects include `ip::tcp::socket`, | |
| 34 | `ssl::stream<>`, `posix::stream_descriptor`, `windows::stream_handle`, etc. | |
| 35 | ||
| 36 | Programs typically want to transfer an exact number of bytes. When a short read | |
| 37 | or short write occurs the program must restart the operation, and continue to | |
| 38 | do so until the required number of bytes has been transferred. Boost.Asio provides | |
| 39 | generic functions that do this automatically: `read()`, `async_read()`, | |
| 40 | `write()` and `async_write()`. | |
| 41 | ||
| 42 | [heading Why EOF is an Error] | |
| 43 | ||
| 44 | * The end of a stream can cause `read`, `async_read`, `read_until` or | |
| 45 | `async_read_until` functions to violate their contract. E.g. | |
| 46 | a read of N bytes may finish early due to EOF. | |
| 47 | ||
| 48 | * An EOF error may be used to distinguish the end of a stream from a successful | |
| 49 | read of size 0. | |
| 50 | ||
| 51 | [heading See Also] | |
| 52 | ||
| 53 | [link boost_asio.reference.async_read async_read()], | |
| 54 | [link boost_asio.reference.async_write async_write()], | |
| 55 | [link boost_asio.reference.read read()], | |
| 56 | [link boost_asio.reference.write write()], | |
| 57 | [link boost_asio.reference.AsyncReadStream AsyncReadStream], | |
| 58 | [link boost_asio.reference.AsyncWriteStream AsyncWriteStream], | |
| 59 | [link boost_asio.reference.SyncReadStream SyncReadStream], | |
| 60 | [link boost_asio.reference.SyncWriteStream SyncWriteStream]. | |
| 61 | ||
| 62 | [endsect] |