#### read_until (16 of 24 overloads)

Read data into a streambuf until a function object indicates a match.

    template<
        typename SyncReadStream,
        typename Allocator,
        typename MatchCondition>
    std::size_t read_until(
        SyncReadStream & s,
        asio::basic_streambuf< Allocator > & b,
        MatchCondition match_condition,
        asio::error_code & ec,
        constraint_t< is_match_condition< MatchCondition >::value >  = 0);

This function is used to read data into the specified streambuf until a user-defined match condition function object, when applied to the data contained in the streambuf, indicates a successful match. The call will block 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 read_some function. If the match condition function object already indicates a match, the function returns immediately.

###### Parameters

s

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

b

  A streambuf object into which the data will be read.

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<basic_streambuf<Allocator>::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.

ec

  Set to indicate what error occurred, if any.

###### Return Value

The number of bytes in the streambuf's get area that have been fully consumed by the match function. Returns 0 if an error occurred.

###### Remarks

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

###### Remarks

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.