A [*BodyReader] provides an online algorithm to transfer a series of zero or more buffers containing parsed body octets into a message container. The __parser__ creates an instance of this type when needed, and calls into it zero or more times to transfer buffers. The interface of [*BodyReader] is intended to allow the conversion of buffers into these scenarios for representation:
* Storing a body in a dynamic buffer * Storing a body in a user defined container with a custom allocator * Transformation of incoming body data before storage, for example
* `a` denotes a value of type `R`. * `b` is an object whose type meets the requirements of __ConstBufferSequence__ * `h` denotes a value of type `header<isRequest, Fields>&`. * `v` denotes a value of type `Body::value_type&`. * `n` is a value of type `boost::optional<std::uint64_t>`. * `ec` is a value of type [link beast.ref.boost__beast__error_code `error_code&`].
Constructible from `h` and `v`. The lifetime of `h` and `v` is guaranteed to end no earlier than after the `R` is destroyed. The reader shall not access the contents of `h` or `v` before the first call to `init`, permitting lazy construction of the message.
Called once to fully initialize the object before any calls to `put`. The message body is valid before entering this function, and remains valid until the reader is destroyed. The value of `n` will be set to the content length of the body if known, otherwise `n` will be equal to `boost::none`. Implementations of [*BodyReader] may use this information to optimize allocation. The function will ensure that `!ec` is `true` if there was no error or set to the appropriate error code if there was one.