


async_read_until (10 of 12 overloads)

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

    typename AsyncReadStream,
    typename DynamicBuffer_v2,
    typename ReadHandler = DEFAULT>
DEDUCED async_read_until(
    AsyncReadStream & s,
    DynamicBuffer_v2 buffers,
    string_view delim,
    ReadHandler && handler = DEFAULT,
    typename constraint< is_dynamic_buffer_v2< DynamicBuffer_v2 >::value >::type  = 0);

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:

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.



The stream from which the data is to be read. The type must support the AsyncReadStream concept.




The delimiter string.



void handler(
  // Result of operation.
  const boost::system::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



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.


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

std::string data;
void handler(const boost::system::error_code& e, std::size_t size)
  if (!e)
    std::string line = data.substr(0, n);
    data.erase(0, n);
boost::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:


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.

Per-Operation Cancellation

This asynchronous operation supports cancellation for the following cancellation_type values:

if they are also supported by the AsyncReadStream type's async_read_some operation.