en	Message Containers

en	Beast provides a single class template __message__ and some aliases which model HTTP/1 and [@https://tools.ietf.org/html/rfc7540 HTTP/2] messages:

en	Message

en	Name

en	Description

en	__message__

en	/// An HTTP message template< bool isRequest, // `true` for requests, `false` for responses class Body, // Controls the container and algorithms used for the body class Fields = fields> // The type of container to store the fields class message;

en	[link beast.ref.boost__beast__http__request `request`]

en	/// A typical HTTP request template<class Body, class Fields = fields> using request = message<true, Body, Fields>;

en	[link beast.ref.boost__beast__http__response `response`]

en	/// A typical HTTP response template<class Body, class Fields = fields> using response = message<false, Body, Fields>;

en	The container offers value semantics including move and copy if supported by __Body__ and __Fields__. User defined template function parameters can accept any message, or can use partial specialization to accept just requests or responses. The default __fields__ is a provided associative container using the standard allocator and supporting modification and inspection of fields. As per __rfc7230__, a non-case-sensitive comparison is used for field names. User defined types for fields are possible. The `Body` type determines the type of the container used to represent the body as well as the algorithms for transferring buffers to and from the container. The library comes with a collection of common body types. As with fields, user defined body types are possible.

en	Sometimes it is desired to only work with a header. Beast provides a single class template __header__ and some aliases to model HTTP/1 and HTTP/2 headers:

en	Header

en	Name

en	Description

en	__header__

en	/// An HTTP header template< bool isRequest, // `true` for requests, `false` for responses class Fields = fields> // The type of container to store the fields class header;

en	[link beast.ref.boost__beast__http__request_header `request_header`]

en	/// A typical HTTP request header template<class Fields> using request_header = header<true, Fields>;

en	[link beast.ref.boost__beast__http__response_header `response_header`]

en	/// A typical HTTP response header template<class Fields> using response_header = header<false, Fields>;

en	Requests and responses share the version, fields, and body but have a few members unique to the type. This is implemented by declaring the header classes as partial specializations of `isRequest`. __message__ is derived from __header__; a message may be passed as an argument to a function taking a suitably typed header as a parameter. Additionally, `header` is publicly derived from `Fields`; a message inherits all the member functions of `Fields`. This diagram shows the inheritance relationship between header and message, along with some of the notable differences in members in each partial specialization:

en	Body Types

en	Beast defines the __Body__ concept, which determines both the type of the [link beast.ref.boost__beast__http__message.body `message::body`] member (as seen in the diagram above) and may also include algorithms for transferring buffers in and out. These algorithms are used during parsing and serialization. Users may define their own body types which meet the requirements, or use the ones that come with the library:

en	[link beast.ref.boost__beast__http__buffer_body `buffer_body`]

en	A body whose [link beast.ref.boost__beast__http__buffer_body__value_type `value_type`] holds a raw pointer and size to a caller-provided buffer. This allows for serialization of body data coming from external sources, and incremental parsing of message body content using a fixed size buffer.

en	[link beast.ref.boost__beast__http__dynamic_body `dynamic_body`] [link beast.ref.boost__beast__http__basic_dynamic_body `basic_dynamic_body`]

en	A body whose `value_type` is a __DynamicBuffer__. It inherits the insertion complexity of the underlying choice of dynamic buffer. Messages with this body type may be serialized and parsed.

en	[link beast.ref.boost__beast__http__empty_body `empty_body`]

en	A special body with an empty `value_type` indicating that the message has no body. Messages with this body may be serialized and parsed; however, body octets received while parsing a message with this body will generate a unique error.

en	[link beast.ref.boost__beast__http__file_body `file_body`] [link beast.ref.boost__beast__http__basic_file_body `basic_file_body`]

en	This body is represented by a file opened for either reading or writing. Messages with this body may be serialized and parsed. HTTP algorithms will use the open file for reading and writing, for streaming and incremental sends and receives.

en	[link beast.ref.boost__beast__http__span_body `span_body`]

en	A body whose `value_type` is a [@boost:/libs/core/doc/html/core/span.html `span`], a non-owning reference to a single linear buffer of bytes. Messages with this body type may be serialized and parsed.

en	[link beast.ref.boost__beast__http__string_body `string_body`] [link beast.ref.boost__beast__http__basic_string_body `basic_string_body`]

en	A body whose `value_type` is `std::basic_string` or `std::string`. Insertion complexity is amortized constant time, while capacity grows geometrically. Messages with this body type may be serialized and parsed. This is the type of body used in the examples.

en	[link beast.ref.boost__beast__http__vector_body `vector_body`]

en	A body whose `value_type` is `std::vector`. Insertion complexity is amortized constant time, while capacity grows geometrically. Messages with this body type may be serialized and parsed.

en	Usage

en	These examples show how to create and fill in request and response objects: Here we build an [@https://tools.ietf.org/html/rfc7231#section-4.3.1 HTTP GET] request with an empty message body:

en	Create Request

en	Statements

en	Serialized Result

en	[http_snippet_2]

en	GET /index.htm HTTP/1.1\r\n Accept: text/html\r\n User-Agent: Beast\r\n \r\n

en	In this code we create an HTTP response with a status code indicating success. This message has a body with a non-zero length. The function [link beast.ref.boost__beast__http__message.prepare_payload `message::prepare_payload`] automatically sets the Content-Length or Transfer-Encoding field depending on the content and type of the `body` member. Use of this function is optional; these fields may also be set explicitly.

en	Create Response

en	Statements

en	Serialized Result

en	[http_snippet_3]

en	HTTP/1.1 200 OK\r\n Server: Beast\r\n Content-Length: 13\r\n \r\n Hello, world!

en	The implementation will automatically fill in the obsolete [@https://tools.ietf.org/html/rfc7230#section-3.1.2 reason-phrase] from the status code when serializing a message. Or it may be set directly using [link beast.ref.boost__beast__http__header.reason.overload2 `header::reason`].