asio/src/doc/requirements/CompletionCondition.qbk

[/
 / Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
 /
 / Distributed under the Boost Software License, Version 1.0. (See accompanying
 / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 /]

[section:CompletionCondition Completion condition requirements]

A ['completion condition] is a function object that is used with the algorithms
[link asio.reference.read `read`], [link asio.reference.async_read
`async_read`], [link asio.reference.write `write`], and [link
asio.reference.async_write `async_write`] to determine when the algorithm has
completed transferring data.

A type `X` meets the `CompletionCondition` requirements if it satisfies the
requirements of `Destructible` (C++Std [destructible]) and
`MoveConstructible` (C++Std [moveconstructible]), as well as the additional
requirements listed below.

In the table below, `x` denotes a value of type `X`, `ec` denotes a (possibly
const) value of type `error_code`, and `n` denotes a (possibly const) value of
type `size_t`.

[table CompletionCondition requirements
  [[expression] [return type] [assertion/note[br]pre/post-condition]]
  [
    [`x(ec, n)`]
    [`size_t`]
    [
      Let `n` be the total number of bytes transferred by the read or write
      algorithm so far.[br]
      [br]
      Returns the maximum number of bytes to be transferred on the next
      `read_some`, `async_read_some`, `write_some`, or `async_write_some`
      operation performed by the algorithm. Returns `0` to indicate that the
      algorithm is complete.
    ]
  ]
]

[endsect]