Exit Zen
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* The [*Body] customization point constrains user defined types to
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This representation addresses a narrow range of use cases. It has limited potential for customization and performance. It is more difficult to use because it excludes the start line fields from the model.
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C++ REST SDK (cpprestsdk)
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is a Microsoft project which ['"...aims to help C++ developers connect to and interact with services"]. It offers the most functionality of the libraries reviewed here, including support for Websocket services using its websocket++ dependency. It can use native APIs such as HTTP.SYS when building Windows based applications, and it can use Boost.Asio. The WebSocket module uses Boost.Asio exclusively.
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As cpprestsdk is developed by a large corporation, it contains quite a bit of functionality and necessarily has more interfaces. We will break down the interfaces used to model messages into more manageable pieces. This is the container used to store the HTTP header fields: ``` class http_headers { public:
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private:
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}; ```
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This declaration is quite bare-bones. We note the typical problems of most field containers:
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* The container may only be default-constructed.
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* No support for allocators, stateful or otherwise.
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* There are no customization points at all.
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Now we analyze the structure of the larger message container. The library uses a handle/body idiom. There are two public message container interfaces, one for requests (`http_request`) and one for responses (`http_response`). Each interface maintains a private shared pointer to an implementation class. Public member function calls are routed to the internal implementation. This is the first implementation class, which forms the base class for both the request and response implementations: ``` namespace details {
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class http_msg_base { public:
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protected:
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}; ```
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To understand these declarations we need to first understand that cpprestsdk uses the asynchronous model defined by Microsoft's [@https://msdn.microsoft.com/en-us/library/dd504870.aspx [*Concurrency Runtime]]. Identifiers from the [@https://msdn.microsoft.com/en-us/library/jj987780.aspx [*`pplx` namespace]] define common asynchronous patterns such as tasks and events. The `concurrency::streams::istream` parameter and `m_data_available` data member indicates a lack of separation of concerns. The representation of HTTP messages should not be conflated with the asynchronous model used to serialize or parse those messages in the message declarations.
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The next declaration forms the complete implementation class referenced by the handle in the public interface (which follows after): ``` /// Internal representation of an HTTP request message. class _http_request final : public http::details::http_msg_base, public std::enable_shared_from_this<_http_request> { public:
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private:
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};
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} // namespace details ```
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