asio::async_read_until

The async_read_until function is a composed asynchronous operation that reads data into a dynamic buffer sequence, or into a streambuf, until it contains a delimiter, matches a regular expression, or a function object indicates a match. More...

Functions
template<typename AsyncReadStream , typename DynamicBuffer_v1 , ASIO_COMPLETION_TOKEN_FOR(void(asio::error_code, std::size_t)) ReadHandler ASIO_DEFAULT_COMPLETION_TOKEN_TYPE( typename AsyncReadStream::executor_type) >
char ASIO_MOVE_ARG(ReadHandler) handler ASIO_DEFAULT_COMPLETION_TOKEN(typename AsyncReadStream	asio::ASIO_INITFN_AUTO_RESULT_TYPE (ReadHandler, void(asio::error_code, std::size_t)) async_read_until(AsyncReadStream &s
	Start an asynchronous operation to read data into a dynamic buffer sequence until it contains a specified delimiter. More...
template<typename AsyncReadStream , typename DynamicBuffer_v1 , typename MatchCondition , ASIO_COMPLETION_TOKEN_FOR(void(asio::error_code, std::size_t)) ReadHandler ASIO_DEFAULT_COMPLETION_TOKEN_TYPE( typename AsyncReadStream::executor_type) >
char ASIO_MOVE_ARG(ReadHandler) handler ASIO_DEFAULT_COMPLETION_TOKEN(typename AsyncReadStream ASIO_STRING_VIEW_PARAM ASIO_MOVE_ARG(ReadHandler) handler ASIO_DEFAULT_COMPLETION_TOKEN(typename AsyncReadStream	asio::ASIO_INITFN_AUTO_RESULT_TYPE (ReadHandler, void(asio::error_code, std::size_t)) async_read_until(AsyncReadStream &s
	Start an asynchronous operation to read data into a dynamic buffer sequence until a function object indicates a match. More...

Variables
char	asio::delim
MatchCondition	asio::match_condition

Detailed Description

The async_read_until function is a composed asynchronous operation that reads data into a dynamic buffer sequence, or into a streambuf, until it contains a delimiter, matches a regular expression, or a function object indicates a match.

Function Documentation

ASIO_INITFN_AUTO_RESULT_TYPE() [1/2]

template<typename AsyncReadStream , typename DynamicBuffer_v1 , ASIO_COMPLETION_TOKEN_FOR(void(asio::error_code, std::size_t)) ReadHandler ASIO_DEFAULT_COMPLETION_TOKEN_TYPE( typename AsyncReadStream::executor_type) >

char ASIO_MOVE_ARG (ReadHandler) handler ASIO_DEFAULT_COMPLETION_TOKEN( typename AsyncReadStream asio::ASIO_INITFN_AUTO_RESULT_TYPE	(	ReadHandler	,
		void(asio::error_code, std::size_t)
	)		&

Start an asynchronous operation to read data into a dynamic buffer sequence until it contains a specified delimiter.

This function is used to asynchronously read data into the specified dynamic buffer sequence until the dynamic buffer sequence's get area contains the specified delimiter. The function call always returns immediately. The asynchronous operation will continue until one of the following conditions is true:

• The get area of the dynamic buffer sequence contains the specified delimiter.

• An error occurred.

This operation is implemented in terms of zero or more calls to the stream's async_read_some function, and is known as a composed operation. If the dynamic buffer sequence's get area already contains the delimiter, this asynchronous operation completes immediately. The program must ensure that the stream performs no other read operations (such as async_read, async_read_until, the stream's async_read_some function, or any other composed operations that perform reads) until this operation completes.

Parameters

s	The stream from which the data is to be read. The type must support the AsyncReadStream concept.
buffers	The dynamic buffer sequence into which the data will be read. Although the buffers object may be copied as necessary, ownership of the underlying memory blocks is retained by the caller, which must guarantee that they remain valid until the handler is called.
delim	The delimiter string.
handler	The handler to be called when the read operation completes. Copies will be made of the handler as required. The function signature of the handler must be: void handler( // Result of operation. const asio::error_code& error, // The number of bytes in the dynamic buffer sequence's // get area up to and including the delimiter. // 0 if an error occurred. std::size_t bytes_transferred ); Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. On immediate completion, invocation of the handler will be performed in a manner equivalent to using asio::post().

Note

After a successful async_read_until operation, the dynamic buffer sequence may contain additional data beyond the delimiter. An application will typically leave that data in the dynamic buffer sequence for a subsequent async_read_until operation to examine.

Example

To asynchronously read data into a std::string until a CR-LF sequence is encountered:

 std::string data;
...
void handler(const asio::error_code& e, std::size_t size)
{
  if (!e)
  {
    std::string line = data.substr(0, n);
    data.erase(0, n);
    ...
  }
}
...
asio::async_read_until(s, data, "\r\n", handler); 

After the async_read_until operation completes successfully, the string data contains the delimiter:

{ 'a', 'b', ..., 'c', '\r', '\n', 'd', 'e', ... } 

The call to substr then extracts the data up to and including the delimiter, so that the string line contains:

{ 'a', 'b', ..., 'c', '\r', '\n' } 

After the call to erase, the remaining data is left in the string data as follows:

{ 'd', 'e', ... } 

This data may be the start of a new line, to be extracted by a subsequent async_read_until operation.

ASIO_INITFN_AUTO_RESULT_TYPE() [2/2]

template<typename AsyncReadStream , typename DynamicBuffer_v1 , typename MatchCondition , ASIO_COMPLETION_TOKEN_FOR(void(asio::error_code, std::size_t)) ReadHandler ASIO_DEFAULT_COMPLETION_TOKEN_TYPE( typename AsyncReadStream::executor_type) >

char ASIO_MOVE_ARG (ReadHandler) handler ASIO_DEFAULT_COMPLETION_TOKEN( typename AsyncReadStream ASIO_STRING_VIEW_PARAM ASIO_MOVE_ARG (ReadHandler) handler ASIO_DEFAULT_COMPLETION_TOKEN( typename AsyncReadStream asio::ASIO_INITFN_AUTO_RESULT_TYPE	(	ReadHandler	,
		void(asio::error_code, std::size_t)
	)		&

Start an asynchronous operation to read data into a dynamic buffer sequence until a function object indicates a match.

This function is used to asynchronously read data into the specified dynamic buffer sequence until a user-defined match condition function object, when applied to the data contained in the dynamic buffer sequence, indicates a successful match. The function call always returns immediately. The asynchronous operation will continue until one of the following conditions is true:

• The match condition function object returns a std::pair where the second element evaluates to true.

• An error occurred.

This operation is implemented in terms of zero or more calls to the stream's async_read_some function, and is known as a composed operation. If the match condition function object already indicates a match, this asynchronous operation completes immediately. The program must ensure that the stream performs no other read operations (such as async_read, async_read_until, the stream's async_read_some function, or any other composed operations that perform reads) until this operation completes.

Parameters

s	The stream from which the data is to be read. The type must support the AsyncReadStream concept.
buffers	The dynamic buffer sequence into which the data will be read. Although the buffers object may be copied as necessary, ownership of the underlying memory blocks is retained by the caller, which must guarantee that they remain valid until the handler is called.
match_condition	The function object to be called to determine whether a match exists. The signature of the function object must be: pair<iterator, bool> match_condition(iterator begin, iterator end); where iterator represents the type: buffers_iterator<typename DynamicBuffer_v1::const_buffers_type> The iterator parameters begin and end define the range of bytes to be scanned to determine whether there is a match. The first member of the return value is an iterator marking one-past-the-end of the bytes that have been consumed by the match function. This iterator is used to calculate the begin parameter for any subsequent invocation of the match condition. The second member of the return value is true if a match has been found, false otherwise.
handler	The handler to be called when the read operation completes. Copies will be made of the handler as required. The function signature of the handler must be: void handler( // Result of operation. const asio::error_code& error, // The number of bytes in the dynamic buffer sequence's // get area that have been fully consumed by the match // function. O if an error occurred. std::size_t bytes_transferred ); Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. On immediate completion, invocation of the handler will be performed in a manner equivalent to using asio::post().

Note

After a successful async_read_until operation, the dynamic buffer sequence may contain additional data beyond that which matched the function object. An application will typically leave that data in the dynamic buffer sequence for a subsequent async_read_until operation to examine.

The default implementation of the is_match_condition type trait evaluates to true for function pointers and function objects with a result_type typedef. It must be specialised for other user-defined function objects.

Examples

To asynchronously read data into a std::string until whitespace is encountered:

 typedef asio::buffers_iterator<
    asio::const_buffers_1> iterator;

std::pair<iterator, bool>
match_whitespace(iterator begin, iterator end)
{
  iterator i = begin;
  while (i != end)
    if (std::isspace(*i++))
      return std::make_pair(i, true);
  return std::make_pair(i, false);
}
...
void handler(const asio::error_code& e, std::size_t size);
...
std::string data;
asio::async_read_until(s, data, match_whitespace, handler);

To asynchronously read data into a std::string until a matching character is found:

 class match_char
{
public:
  explicit match_char(char c) : c_(c) {}

  template <typename Iterator>
  std::pair<Iterator, bool> operator()(
      Iterator begin, Iterator end) const
  {
    Iterator i = begin;
    while (i != end)
      if (c_ == *i++)
        return std::make_pair(i, true);
    return std::make_pair(i, false);
  }

private:
  char c_;
};

namespace asio {
  template <> struct is_match_condition<match_char>
    : public boost::true_type {};
} // namespace asio
...
void handler(const asio::error_code& e, std::size_t size);
...
std::string data;
asio::async_read_until(s, data, match_char('a'), handler);