Exit Zen
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"I just want to download a resource using HTTP" is a common cry from users and reviewers. Such functionality is beyond the scope of Beast. Building a full featured HTTP client is a difficult task and large enough to deserve its own library. There are many things to deal with such as the various message body encodings, complex parsing of headers, difficult header semantics such as Range and Cache-Control, redirection, Expect:100-continue, connection retrying, domain name resolution, TLS, and much, much more. It is the author's position that Boost first needs a common set of nouns and verbs for manipulating HTTP at the protocol level; Beast provides that language.
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These tasks may be performed by using the serializer stream interfaces. To use these interfaces, first construct an appropriate serializer from the message to be sent:
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* [link beast.ref.boost__beast__http__is_body_reader `is_body_reader`]
* __Body__
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[link beast.ref.boost__beast__websocket__stream_base__timeout `stream_base::timeout`]
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Calls to asynchronous initiation functions support the extensible asynchronous model developed by the Boost.Asio author, allowing for traditional completion handlers, stackful or stackless coroutines, and even futures:
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To simplify the handling of timeouts, these provided types wrap a [@boost:/doc/html/boost_asio/reference/basic_stream_socket.html `net::basic_stream_socket`] to provide additional features:
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* `S(m)` is a serialization function which produces a series of octets
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A WebSocket connection requires a stateful object, represented in Beast by a single class template [link beast.ref.boost__beast__websocket__stream `websocket::stream`]. The interface uses the layered stream model. A websocket stream object contains another stream object, called the "next layer", which it uses to perform I/O. Descriptions of each template parameter follow:
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Simple WebSocket Client __example__
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Control Callback
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Expect 100-continue (Client) __example__
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It is important to set up peer verification so that the TLS/SSL handshake fails if certificate verification is unsuccessful:
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Name
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* [*Flexibility:] Users make the important decisions such as buffer or
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There are some common mistakes that should be avoided when writing composed operations:
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BOOST_BEAST_SEPARATE_COMPILATION
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Beast comes with several layered stream wrappers, as well as facilities for authoring and working with layered streams:
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Name
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* The HTTP message doesn't contain a body, such as any response with a 1xx
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Now that we have the synchronous version, we can attempt to model the asynchronous version similarly. A function which launches an asynchronous operation is called an ['initiating function]. While the synchronous version above produces an error code through an output parameter, the asynchronous version delivers the error code to a completion handler or other custom mechanism defined by the completion token. The signature of the initiating function reflects these differences.
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