#### read_until (3 of 24 overloads)

Read data into a dynamic buffer sequence until it contains a specified delimiter.

    template<
        typename SyncReadStream,
        typename DynamicBuffer_v1>
    std::size_t read_until(
        SyncReadStream & s,
        DynamicBuffer_v1 && buffers,
        string_view delim,
        constraint_t< is_dynamic_buffer_v1< decay_t< DynamicBuffer_v1 > >::value >  = 0,
        constraint_t< !is_dynamic_buffer_v2< decay_t< DynamicBuffer_v1 > >::value >  = 0);

This function is used to read data into the specified dynamic buffer sequence until the dynamic buffer sequence's get area contains the specified delimiter. The call will block 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 read_some function. If the dynamic buffer sequence's get area already contains the delimiter, the function returns immediately.

###### Parameters

s

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

buffers

  The dynamic buffer sequence into which the data will be read.

delim

  The delimiter string.

###### Return Value

The number of bytes in the dynamic buffer sequence's get area up to and including the delimiter.

###### Remarks

After a successful 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 read_until operation to examine.

###### Example

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

    std::string data;
    std::size_t n = asio::read_until(s,
        asio::dynamic_buffer(data), "\r\n");
    std::string line = data.substr(0, n);
    data.erase(0, n);

After the `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 buffer `b` as follows:

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

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