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Custom Body Types

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User-defined types are possible for the message body, where the type meets the __Body__ requirements. This simplified class declaration shows the customization points available to user-defined body types: ``` /// Defines a Body type struct body {

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} ```

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The meaning of the nested types is as follows

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Body Type Members

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Name

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Description

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`value_type`

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Determines the type of the [link beast.ref.boost__beast__http__message.body `message::body`] member.

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`reader`

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An optional nested type meeting the requirements of __BodyReader__, which provides the algorithm for storing a forward range of buffer sequences in the body representation. If present, this body type may be used with a __parser__.

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`writer`

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An optional nested type meeting the requirements of __BodyWriter__, which provides the algorithm for converting the body representation to a forward range of buffer sequences. If present this body type may be used with a __serializer__.

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Value Type

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The `value_type` nested type allows the body to define the declaration of the body type as it appears in the message. This can be any type. For example, a body's value type may specify `std::vector<char>` or `std::list<std::string>`. A custom body may even set the value type to something that is not a container for body octets, such as a [@boost:/libs/filesystem/doc/reference.html#class-path `boost::filesystem::path`]. Or, a more structured container may be chosen. This declares a body's value type as a JSON tree structure produced from a [@boost:/doc/html/json/input_output.html#json.input_output.parsing.streaming_parser `boost::json::stream_parser`]: ``` #include <boost/json/stream_parser.hpp>

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struct Body {

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}; ```

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As long as a suitable reader or writer is available to provide the algorithm for transferring buffers in and out of the value type, those bodies may be parsed or serialized.

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File Body __example__

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Use of the flexible __Body__ concept customization point enables authors to preserve the self-contained nature of the __message__ object while allowing domain specific behaviors. Common operations for HTTP servers include sending responses which deliver file contents, and allowing for file uploads. In this example we build the [link beast.ref.boost__beast__http__basic_file_body `basic_file_body`] type which supports both reading and writing to a file on the file system. The interface is a class templated on the type of file used to access the file system, which must meet the requirements of __File__.