boost_beast/include/beast/http/serializer.hpp

//
// Copyright (c) 2013-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef BEAST_HTTP_SERIALIZER_HPP
#define BEAST_HTTP_SERIALIZER_HPP

#include <beast/config.hpp>
#include <beast/core/async_result.hpp>
#include <beast/core/buffer_cat.hpp>
#include <beast/core/consuming_buffers.hpp>
#include <beast/core/multi_buffer.hpp>
#include <beast/core/string_view.hpp>
#include <beast/core/type_traits.hpp>
#include <beast/http/message.hpp>
#include <beast/http/detail/chunk_encode.hpp>
#include <boost/asio/buffer.hpp>
#include <boost/optional.hpp>
#include <boost/variant.hpp>
#include <memory>

namespace beast {
namespace http {

/** A chunk decorator which does nothing.

    When selected as a chunk decorator, objects of this type
    affect the output of messages specifying chunked
    transfer encodings as follows:

    @li chunk headers will have empty chunk extensions, and

    @li final chunks will have an empty set of trailers.

    @see @ref serializer
*/
struct empty_decorator
{
    template<class ConstBufferSequence>
    string_view
    operator()(ConstBufferSequence const&) const
    {
        return {"\r\n"};
    }

    string_view
    operator()(boost::asio::null_buffers) const
    {
        return {};
    }
};

/** Provides buffer oriented HTTP message serialization functionality.

    An object of this type is used to serialize a complete
    HTTP message into a seriest of octets. To use this class,
    construct an instance with the message to be serialized.
    To make it easier to declare the type, the helper function
    @ref make_serializer is provided.

    The implementation will automatically perform chunk encoding
    if the contents of the message indicate that chunk encoding
    is required. If the semantics of the message indicate that
    the connection should be closed after the message is sent, the
    function @ref needs_close will return `true`.

    Upon construction, an optional chunk decorator may be
    specified. This decorator is a function object called with
    each buffer sequence of the body when the chunked transfer
    encoding is indicate in the message header. The decorator
    will be called with an empty buffer sequence (actually
    the type `boost::asio::null_buffers`) to indicate the
    final chunk. The decorator may return a string which forms
    the chunk extension for chunks, and the field trailers
    for the final chunk.

    In C++11 the decorator must be declared as a class or
    struct with a templated operator() thusly:

    @code
        // The implementation guarantees that operator()
        // will be called only after the view returned by
        // any previous calls to operator() are no longer
        // needed. The decorator instance is intended to
        // manage the lifetime of the storage for all returned
        // views.
        //
        struct decorator
        {
            // Returns the chunk-extension for each chunk.
            // The buffer returned must include a trailing "\r\n",
            // and the leading semicolon (";") if one or more
            // chunk extensions are specified.
            //
            template<class ConstBufferSequence>
            string_view
            operator()(ConstBufferSequence const&) const;

            // Returns a set of field trailers for the final chunk.
            // Each field should be formatted according to rfc7230
            // including the trailing "\r\n" for each field. If
            // no trailers are indicated, an empty string is returned.
            //
            string_view
            operator()(boost::asio::null_buffers) const;
        };
    @endcode

    @tparam isRequest `true` if the message is a request.

    @tparam Body The body type of the message.

    @tparam Fields The type of fields in the message.

    @tparam Decorator The type of chunk decorator to use.

    @tparam Allocator The type of allocator to use.

    @see @ref make_serializer
*/
template<
    bool isRequest, class Body, class Fields,
    class Decorator = empty_decorator,
    class Allocator = std::allocator<char>
>
class serializer
{
    static_assert(is_body<Body>::value,
        "Body requirements not met");
    static_assert(is_body_reader<Body>::value,
        "BodyReader requirements not met");

    enum
    {
        do_init             =   0,
        do_header_only      =  10,
        do_header           =  20,
        do_body             =  40,
        
        do_init_c           =  50,
        do_header_only_c    =  60,
        do_header_c         =  70,
        do_body_c           =  90,
        do_final_c          = 100,

        do_complete         = 110
    };

    void split(bool, std::true_type) {}
    void split(bool v, std::false_type) { split_ = v; }

    using buffer_type =
        basic_multi_buffer<Allocator>;

    using reader = typename Body::reader;

    using is_deferred =
        typename reader::is_deferred;

    using cb0_t = consuming_buffers<buffers_view<
        typename buffer_type::const_buffers_type,   // header
        typename reader::const_buffers_type>>;      // body

    using cb1_t = consuming_buffers<
        typename reader::const_buffers_type>;       // body

    using ch0_t = consuming_buffers<buffers_view<
        typename buffer_type::const_buffers_type,   // header
        detail::chunk_header,                       // chunk-header
        boost::asio::const_buffers_1,               // chunk-ext+\r\n
        typename reader::const_buffers_type,        // body
        boost::asio::const_buffers_1>>;             // crlf
    
    using ch1_t = consuming_buffers<buffers_view<
        detail::chunk_header,                       // chunk-header
        boost::asio::const_buffers_1,               // chunk-ext+\r\n
        typename reader::const_buffers_type,        // body
        boost::asio::const_buffers_1>>;             // crlf

    using ch2_t = consuming_buffers<buffers_view<
        boost::asio::const_buffers_1,               // chunk-final
        boost::asio::const_buffers_1,               // trailers 
        boost::asio::const_buffers_1>>;             // crlf

    message<isRequest, Body, Fields> const& m_;
    Decorator d_;
    boost::optional<reader> rd_;
    buffer_type b_;
    boost::variant<boost::blank,
        cb0_t, cb1_t, ch0_t, ch1_t, ch2_t> v_;
    int s_;
    bool split_ = is_deferred::value;
    bool header_done_ = false;
    bool chunked_;
    bool close_;
    bool more_;

public:
    /** Constructor

        @param msg The message to serialize. The message object
        must remain valid for the lifetime of the write stream.

        @param decorator An optional decorator to use.

        @param alloc An optional allocator to use.
    */
    explicit
    serializer(message<isRequest, Body, Fields> const& msg,
        Decorator const& decorator = Decorator{},
            Allocator const& alloc = Allocator{});

    /** Returns `true` if we will pause after writing the header.
    */
    bool
    split() const
    {
        return split_;
    }

    /** Set whether the header and body are written separately.

        When the split feature is enabled, the implementation will
        write only the octets corresponding to the serialized header
        first. If the header has already been written, this function
        will have no effect on output. This function should be called
        before any writes take place, otherwise the behavior is
        undefined.
    */
    void
    split(bool v)
    {
        split(v, is_deferred{});
    }

    /** Return `true` if serialization of the header is complete.

        This function indicates whether or not all octets
        corresponding to the serialized representation of the
        header have been successfully delivered to the stream.
    */
    bool
    is_header_done() const
    {
        return header_done_;
    }

    /** Return `true` if serialization is complete

        The operation is complete when all octets corresponding
        to the serialized representation of the message have been
        successfully delivered to the stream.
    */
    bool
    is_done() const
    {
        return s_ == do_complete;
    }

    /** Return `true` if Connection: close semantic is indicated.

        After serialization is complete, if there is an
        underlying network connection then it should be closed if
        this function returns `true`.
    */
    bool
    needs_close() const
    {
        return close_;
    }

    /** Returns the next set of buffers in the serialization.

        This function will attempt to call the `visit` function
        object with a @b ConstBufferSequence of unspecified type
        representing the next set of buffers in the serialization
        of the message represented by this object. 

        If there are no more buffers in the serialization, the
        visit function will not be called. In this case, no error
        will be indicated, and the function @ref is_done will
        return `true`.

        @param ec Set to the error, if any occurred.

        @param visit The function to call. The equivalent function
        signature of this object must be:
        @code template<class ConstBufferSequence>
            void visit(error_code&, ConstBufferSequence const&);
        @endcode
        The function is not copied, if no error occurs it will be
        invoked before the call to @ref get returns.

    */
    template<class Visit>
    void
    get(error_code& ec, Visit&& visit);

    /** Consume buffer octets in the serialization.

        This function should be called after one or more octets
        contained in the buffers provided in the prior call
        to @ref get have been used.

        After a call to @ref consume, callers should check the
        return value of @ref is_done to determine if the entire
        message has been serialized.

        @param n The number of octets to consume. This number must
        be greater than zero and no greater than the number of
        octets in the buffers provided in the prior call to @ref get.
    */
    void
    consume(std::size_t n);
};

/** Return a stateful object to serialize an HTTP message.

    This convenience function makes it easier to declare
    the variable for a given message.

    @see @ref serializer
*/
template<
    bool isRequest, class Body, class Fields,
    class Decorator = empty_decorator,
    class Allocator = std::allocator<char>>
inline
serializer<isRequest, Body, Fields,
    typename std::decay<Decorator>::type,
    typename std::decay<Allocator>::type>
make_serializer(message<isRequest, Body, Fields> const& m,
    Decorator const& decorator = Decorator{},
        Allocator const& allocator = Allocator{})
{
    return serializer<isRequest, Body, Fields,
        typename std::decay<Decorator>::type,
        typename std::decay<Allocator>::type>{
            m, decorator, allocator};
}

} // http
} // beast

#include <beast/http/impl/serializer.ipp>

#endif