Add http::message_generator

doc/qbk/07_concepts/BuffersGenerator.qbk

@@ -16,6 +16,11 @@ The generator will be asked to produce buffers. The consuming code will signal
 how much of the data has been consumed, and repeatedly query for buffers until
 no more data is available, or the generator indicates an error condition.
 
+In this way, serializers can be adapted as [*BuffersGenerator], for example
+[link beast.ref.boost__beast__http__message_generator
+`http::message_generator`] which provides a type-erased interface for a variety
+of concrete http message types.
+
 Overloads of [link beast.ref.boost__beast__write `write`] and [link
 beast.ref.boost__beast__async_write `async_write`] operations are provided as
 free functions. These operations will consume the output of a
@@ -33,6 +38,7 @@ In this table:
 
 * `G` denotes a type meeting the requirements of [*BuffersGenerator].
 * `g` denotes a value of type `G`.
+* `c` denotes a possibly-const value of type `G`.
 * `n` is a value of type `std::size_t`.
 * `ec` is a value of type [link beast.ref.boost__beast__error_code `error_code&`].
 
@@ -46,7 +52,7 @@ In this table:
         This is the type of buffer returned by `g.prepare(ec)`.
     ]
 ][
-    [`g.is_done()`]
+    [`c.is_done()`]
     [`bool`]
     [
         Called to ask the generator for its completion status.
@@ -56,8 +62,6 @@ In this table:
 
         [*Note:] The result of invoking `prepare` on `g` once it has completed
         is unspecified.
-
-        This member function does not alter the state of the generator.
     ]
 ][
     [`g.prepare(ec)`]
@@ -106,7 +110,7 @@ In this table:
     ]
 ][
     [`is_buffers_generator<G>`]
-    [`std::true_type`]
+    [`std::bool_constant`]
     [
         An alias for `std::true_type` for `G`, otherwise an alias
         for `std::false_type`.
@@ -121,7 +125,7 @@ In this table:
     {
         using const_buffers_type = net::const_buffer;
 
-        bool is_done();
+        bool is_done() const;
         const_buffers_type prepare( error_code& ec );
         void consume( std::size_t n );
     };
@@ -132,6 +136,8 @@ In this table:
 
 [heading Models]
 
+* [link beast.ref.boost__beast__http__message_generator `http::message_generator`]
+
 [heading Algorithms]
 
 * [link beast.ref.boost__beast__async_write `async_write`]

doc/qbk/quickref.xml

@@ -205,6 +205,7 @@
           <member><link linkend="beast.ref.boost__beast__http__file_body">file_body</link></member>
           <member><link linkend="beast.ref.boost__beast__http__header">header</link></member>
           <member><link linkend="beast.ref.boost__beast__http__message">message</link></member>
+          <member><link linkend="beast.ref.boost__beast__http__message_generator">message_generator</link></member>
           <member><link linkend="beast.ref.boost__beast__http__parser">parser</link></member>
           <member><link linkend="beast.ref.boost__beast__http__request">request</link></member>
           <member><link linkend="beast.ref.boost__beast__http__request_header">request_header</link></member>

include/boost/beast/core/buffers_generator.hpp

@@ -11,11 +11,9 @@
 #define BOOST_BEAST_CORE_BUFFERS_GENERATOR_HPP
 
 #include <boost/beast/core/detail/config.hpp>
-
 #include <boost/beast/core/detail/type_traits.hpp>
 #include <boost/beast/core/error.hpp>
 #include <boost/asio/async_result.hpp>
-
 #include <type_traits>
 
 namespace boost {
@@ -63,7 +61,7 @@ struct is_buffers_generator<
     by a caller-provided BuffersGenerator to a stream. The call
     will block until one of the following conditions is true:
 
-    @li The generator returns an empty buffers sequence.
+    @li A call to the generator's `is_done` returns `false`.
 
     @li An error occurs.
 
@@ -85,8 +83,7 @@ template<
     class SyncWriteStream,
     class BuffersGenerator
 #if ! BOOST_BEAST_DOXYGEN
-    ,
+    , typename std::enable_if<is_buffers_generator<
-    typename std::enable_if<is_buffers_generator<
         typename std::decay<BuffersGenerator>::
             type>::value>::type* = nullptr
 #endif
@@ -103,7 +100,7 @@ write(
     by a caller-provided BuffersGenerator to a stream. The call
     will block until one of the following conditions is true:
 
-    @li The generator returns an empty buffers sequence.
+    @li A call to the generator's `is_done` returns `false`.
 
     @li An error occurs.
 
@@ -125,8 +122,7 @@ template<
     class SyncWriteStream,
     class BuffersGenerator
 #if ! BOOST_BEAST_DOXYGEN
-    ,
+    , typename std::enable_if<is_buffers_generator<
-    typename std::enable_if<is_buffers_generator<
         typename std::decay<BuffersGenerator>::
             type>::value>::type* = nullptr
 #endif
@@ -145,7 +141,7 @@ write(
     operation will continue until one of the following
     conditions is true:
 
-    @li The generator returns an empty buffers sequence.
+    @li A call to the generator's `is_done` returns `false`.
 
     @li An error occurs.
 
@@ -182,8 +178,7 @@ template<
     class BuffersGenerator,
     class CompletionToken
 #if !BOOST_BEAST_DOXYGEN
-    ,
+    , typename std::enable_if<is_buffers_generator<
-    typename std::enable_if<is_buffers_generator<
         BuffersGenerator>::value>::type* = nullptr
 #endif
     >
@@ -191,16 +186,15 @@ auto
 async_write(
     AsyncWriteStream& stream,
     BuffersGenerator generator,
-    CompletionToken&& token) //
+    CompletionToken&& token) ->
-    -> typename net::async_result<
+        typename net::async_result<
             typename std::decay<
                 CompletionToken>::type,
-        void(error_code, std::size_t)>::
+            void(error_code, std::size_t)>::return_type;
-        return_type;
 
-} // namespace beast
+} // beast
-} // namespace boost
+} // boost
 
-#include <include/boost/beast/core/impl/buffers_generator.hpp>
+#include <boost/beast/core/impl/buffers_generator.hpp>
 
 #endif

include/boost/beast/http.hpp

@@ -23,6 +23,7 @@
 #include <boost/beast/http/field.hpp>
 #include <boost/beast/http/fields.hpp>
 #include <boost/beast/http/file_body.hpp>
+#include <boost/beast/http/message_generator.hpp>
 #include <boost/beast/http/message.hpp>
 #include <boost/beast/http/parser.hpp>
 #include <boost/beast/http/read.hpp>

include/boost/beast/http/impl/message_generator.hpp

@@ -0,0 +1,104 @@
+//
+// Copyright (c) 2022 Seth Heeren (sgheeren 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)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+#ifndef BOOST_BEAST_HTTP_IMPL_MESSAGE_GENERATOR_HPP
+#define BOOST_BEAST_HTTP_IMPL_MESSAGE_GENERATOR_HPP
+
+#include <boost/beast/http/message_generator.hpp>
+#include <boost/smart_ptr/make_unique.hpp>
+#include <boost/beast/core/buffers_generator.hpp>
+
+namespace boost {
+namespace beast {
+namespace http {
+
+template <bool isRequest, class Body, class Fields>
+message_generator::message_generator(
+    http::message<isRequest, Body, Fields>&& m)
+    : impl_(boost::make_unique<
+            generator_impl<isRequest, Body, Fields>>(
+          std::move(m)))
+{
+}
+
+template <bool isRequest, class Body, class Fields>
+struct message_generator::generator_impl
+    : message_generator::impl_base
+{
+    explicit generator_impl(
+        http::message<isRequest, Body, Fields>&& m)
+        : m_(std::move(m))
+        , sr_(m_)
+    {
+    }
+
+    bool
+    is_done() override
+    {
+        return sr_.is_done();
+    }
+
+    const_buffers_type
+    prepare(error_code& ec) override
+    {
+        sr_.next(ec, visit{*this});
+        return current_;
+    }
+
+    void
+    consume(std::size_t n) override
+    {
+        sr_.consume((std::min)(n, beast::buffer_bytes(current_)));
+    }
+
+    bool
+    keep_alive() const noexcept override
+    {
+        return m_.keep_alive();
+    }
+
+private:
+    static constexpr unsigned max_fixed_bufs = 12;
+
+    http::message<isRequest, Body, Fields> m_;
+    http::serializer<isRequest, Body, Fields> sr_;
+
+    std::array<net::const_buffer, max_fixed_bufs> bs_;
+    const_buffers_type current_ = bs_; // subspan
+
+    struct visit
+    {
+        generator_impl& self_;
+
+        template<class ConstBufferSequence>
+        void
+        operator()(error_code&, ConstBufferSequence const& buffers)
+        {
+            auto& s = self_.bs_;
+            auto& cur = self_.current_;
+
+            auto it = net::buffer_sequence_begin(buffers);
+
+            std::size_t n =
+                std::distance(it, net::buffer_sequence_end(buffers));
+
+            n = (std::min)(s.size(), n);
+
+            cur = { s.data(), n };
+            std::copy_n(it, n, cur.begin());
+        }
+    };
+
+};
+
+} // namespace http
+} // namespace beast
+} // namespace boost
+
+#endif

include/boost/beast/http/message_generator.hpp

@@ -0,0 +1,99 @@
+//
+// Copyright (c) 2022 Seth Heeren (sgheeren 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)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+#ifndef BOOST_BEAST_HTTP_MESSAGE_GENERATOR_HPP
+#define BOOST_BEAST_HTTP_MESSAGE_GENERATOR_HPP
+
+#include <boost/beast/core/span.hpp>
+#include <boost/beast/http/message.hpp>
+#include <boost/beast/http/serializer.hpp>
+#include <memory>
+
+namespace boost {
+namespace beast {
+namespace http {
+
+/** Type-erased buffers generator for @ref http::message
+   
+    Implements the BuffersGenerator concept for any concrete instance of the
+    @ref http::message template.
+   
+    @ref http::message_generator takes ownership of a message on construction,
+    erasing the concrete type from the interface.
+   
+    This makes it practical for use in server applications to implement request
+    handling:
+   
+    @code
+    template <class Body, class Fields>
+    http::message_generator handle_request(
+        string_view doc_root,
+        http::request<Body, Fields>&& request);
+    @endcode
+   
+    The @ref beast::write and @ref beast::async_write operations are provided
+    for BuffersGenerator. The @ref http::message::keep_alive property is made
+    available for use after writing the message.
+*/
+class message_generator
+{
+public:
+    using const_buffers_type = span<net::const_buffer>;
+
+    template <bool isRequest, class Body, class Fields>
+    message_generator(http::message<isRequest, Body, Fields>&&);
+
+    /// @ref BuffersGenerator
+    bool is_done() const {
+        return impl_->is_done();
+    }
+
+    /// @ref BuffersGenerator
+    const_buffers_type
+    prepare(error_code& ec)
+    {
+        return impl_->prepare(ec);
+    }
+
+    /// @ref BuffersGenerator
+    void
+    consume(std::size_t n)
+    {
+        impl_->consume(n);
+    }
+
+    /// Returns the result of `m.keep_alive()` on the underlying message
+    bool
+    keep_alive() const noexcept
+    {
+        return impl_->keep_alive();
+    }
+
+private:
+    struct impl_base
+    {
+        virtual ~impl_base() = default;
+        virtual bool is_done() = 0;
+        virtual const_buffers_type prepare(error_code& ec) = 0;
+        virtual void consume(std::size_t n) = 0;
+        virtual bool keep_alive() const noexcept = 0;
+    };
+
+    std::unique_ptr<impl_base> impl_;
+
+    template <bool isRequest, class Body, class Fields>
+    struct generator_impl;
+};
+
+} // namespace http
+} // namespace beast
+} // namespace boost
+
+#include <boost/beast/http/impl/message_generator.hpp>
+
+#endif

test/beast/core/buffers_generator.cpp

@@ -27,7 +27,8 @@ namespace beast {
 
 namespace detail {
 
-struct test_buffers_generator {
+struct test_buffers_generator
+{
     using underlying_buffer_sequence = std::array<net::const_buffer, 2>;
     using const_buffers_type = buffers_suffix<underlying_buffer_sequence>;
     std::size_t iterations_ = 5;
@@ -212,7 +213,8 @@ public:
             BEAST_EXPECT(30 == in.nwrite_bytes());
             BEAST_EXPECT(
                 "abcde12345abcd1234abc123ab12a1" == in.str());
-        } else
+        }
+        else
         {
             BEAST_EXPECT(1 == out.nwrite());
             BEAST_EXPECT(10 == in.nwrite_bytes());
@@ -254,7 +256,8 @@ public:
             BEAST_EXPECT(30 == in.nwrite_bytes());
             BEAST_EXPECT(
                 "abcde12345abcd1234abc123ab12a1" == in.str());
-        } else
+        }
+        else
         {
             BEAST_EXPECT(1 == out.nwrite());
             BEAST_EXPECT(10 == in.nwrite_bytes());

test/beast/http/CMakeLists.txt

@@ -29,6 +29,7 @@ add_executable (tests-beast-http
     field_compiles.cpp
     fields.cpp
     file_body.cpp
+    message_generator.cpp
     message.cpp
     parser.cpp
     read.cpp

test/beast/http/Jamfile

@@ -19,6 +19,7 @@ local SOURCES =
     field_compiles.cpp
     fields.cpp
     file_body.cpp
+    message_generator.cpp
     message.cpp
     parser.cpp
     read.cpp

test/beast/http/message_generator.cpp

@@ -0,0 +1,315 @@
+//
+// Copyright (c) 2022 Seth Heeren (sgheeren 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)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+// Test that header file is self-contained.
+#include <boost/beast/http/message_generator.hpp>
+
+#include <boost/beast/http/message.hpp>
+#include <boost/beast/http/string_body.hpp>
+#include <boost/beast/http/write.hpp> //for operator<<
+
+#include <boost/beast/core/buffers_to_string.hpp>
+#include <boost/beast/core/multi_buffer.hpp>
+#include <boost/beast/core/buffers_generator.hpp> // for is_buffers_generator and [async_]write overloads
+#include <boost/beast/_experimental/test/stream.hpp>
+
+#include <boost/beast/_experimental/unit_test/suite.hpp>
+
+#include <iostream>
+#include <iomanip>
+
+namespace boost {
+namespace beast {
+namespace http {
+
+namespace detail {
+
+// Degenerate body generator to trigger dynamic generator buffer
+// allocation
+//
+// Warning: magic numbers ahead
+//
+// Arbitrarily decided on 65 buffers of which two are "some" and "body", the
+// other bufs are chosen by the "seed fragment"
+struct fragmented_test_body
+{
+    using value_type = net::const_buffer;
+
+    static std::uint64_t
+    size(net::const_buffer fragment)
+    {
+        return 8 + 63 * fragment.size();
+    }
+
+    struct writer
+    {
+        using const_buffers_type = std::array<net::const_buffer, 65>;
+
+        bool done_ = false;
+        net::const_buffer seed_fragment_;
+
+        template<typename Fields>
+        writer(Fields const&, net::const_buffer fragment)
+            : seed_fragment_(fragment)
+        {
+        }
+
+        void
+        init(beast::error_code&) const
+        {
+        }
+
+        boost::optional<std::pair<const_buffers_type, bool>>
+        get(beast::error_code&)
+        {
+            const_buffers_type cb;
+            std::fill(begin(cb), end(cb), seed_fragment_);
+            cb.at(7) = { "some", 4 };
+            cb.at(27) = { "body", 4 };
+            return std::make_pair(cb, exchange(done_, true));
+        }
+    };
+};
+}
+
+namespace detail {
+template<>
+struct is_body_sized<detail::fragmented_test_body>
+    : std::true_type
+{
+};
+} // namespace detail
+
+class message_generator_test : public beast::unit_test::suite
+{
+    static_assert(
+        is_buffers_generator<message_generator>::value,
+        "buffers_generator not modeled");
+    BOOST_STATIC_ASSERT(
+        std::is_constructible<
+            message_generator,
+            message<true, string_body>&&>::value);
+    BOOST_STATIC_ASSERT(
+        std::is_constructible<
+            message_generator,
+            message<false, string_body>&&>::value);
+
+    // only rvalue refs
+    BOOST_STATIC_ASSERT(
+        not std::is_constructible<
+            message_generator,
+            message<true, string_body>&>::value);
+    BOOST_STATIC_ASSERT(
+        not std::is_constructible<
+            message_generator,
+            message<true, string_body> const&>::value);
+
+    static request<string_body> make_get() {
+        return request<string_body>{
+            verb::get, "/path/query?1", 11,
+            "Serializable but ignored on GET"
+        };
+    }
+
+    static http::response<detail::fragmented_test_body>
+    make_fragmented_body_response(net::const_buffer seed_fragment)
+    {
+        http::response<detail::fragmented_test_body> msg(
+            http::status::ok, 11, seed_fragment);
+        msg.prepare_payload();
+
+        BEAST_EXPECT(msg.has_content_length());
+        BEAST_EXPECT(
+            msg.at(http::field::content_length) ==
+            std::to_string(8 + 63 * seed_fragment.size()));
+        return msg;
+    }
+
+public:
+    void
+    testGenerate()
+    {
+        message_generator gen(make_get());
+        error_code ec;
+
+        std::string received;
+
+        while(! gen.is_done())
+        {
+            message_generator::const_buffers_type b = gen.prepare(ec);
+            BEAST_EXPECT(! ec);
+            received += buffers_to_string(b);
+
+            gen.consume(buffer_bytes(b));
+        }
+
+        BEAST_EXPECT(received ==
+                     "GET /path/query?1 HTTP/1.1\r\n\r\n"
+                     "Serializable but ignored on GET");
+    }
+
+    void
+    testGenerateSlowConsumer()
+    {
+        message_generator gen(make_get());
+        error_code ec;
+
+        std::vector<std::string> received;
+
+        while(! gen.is_done())
+        {
+            message_generator::const_buffers_type b = gen.prepare(ec);
+            BEAST_EXPECT(! ec);
+            received.push_back(buffers_to_string(b).substr(0, 3));
+
+            gen.consume(3); // allowed > buffer_bytes(b)
+        }
+
+        BEAST_EXPECT(
+            (received ==
+             std::vector<std::string>{
+                 "GET", " /p", "ath", "/qu", "ery",
+                 "?1 ", "HTT", "P/1", ".1\r", "\n\r\n",
+                 "Ser", "ial", "iza", "ble", " bu",
+                 "t i", "gno", "red", " on", " GE",
+                 "T",
+             }));
+    }
+
+    void
+    testAsyncWrite()
+    {
+        net::io_context ioc;
+        test::stream out(ioc), in(ioc);
+        {
+            test::connect(out, in);
+
+            message_generator gen(make_get());
+
+            beast::async_write(out, std::move(gen),
+                        [&](error_code ec, size_t total) {
+                            BEAST_EXPECT(total == 61);
+                            BEAST_EXPECT(!ec.failed());
+                        });
+
+            ioc.run();
+        }
+
+        BEAST_EXPECT(61 == in.nwrite_bytes());
+        BEAST_EXPECT(in.str() ==
+                     "GET /path/query?1 HTTP/1.1\r\n\r\n"
+                     "Serializable but ignored on GET");
+    }
+
+    void
+    testWrite()
+    {
+        net::io_context ioc;
+        test::stream out(ioc), in(ioc);
+        test::connect(out, in);
+
+        {
+            message_generator gen(make_get());
+
+            error_code ec;
+            std::size_t total = beast::write(out, gen, ec);
+
+            BEAST_EXPECT(total == 61);
+            BEAST_EXPECT(!ec.failed());
+
+            BEAST_EXPECT(61 == in.nwrite_bytes());
+            BEAST_EXPECT(in.str() ==
+                    "GET /path/query?1 HTTP/1.1\r\n\r\n"
+                    "Serializable but ignored on GET");
+        }
+
+        in.clear();
+
+        {
+            // rvalue accepted
+            std::size_t total =
+                beast::write(out, message_generator{ make_get() });
+            BEAST_EXPECT(total == 61);
+            BEAST_EXPECT(in.str() ==
+                    "GET /path/query?1 HTTP/1.1\r\n\r\n"
+                    "Serializable but ignored on GET");
+        }
+    }
+
+    void
+    testFragmentedBody()
+    {
+        net::io_context ioc;
+        test::stream out(ioc), in(ioc);
+        test::connect(out, in);
+
+        {
+            message_generator gen(make_fragmented_body_response(net::buffer("", 0)));
+
+            error_code ec;
+            std::size_t total = beast::write(out, gen, ec);
+
+            BEAST_EXPECT(total == 46);
+            BEAST_EXPECT(! ec.failed());
+
+            BEAST_EXPECT(
+                in.str() ==
+                "HTTP/1.1 200 OK\r\n"
+                "Content-Length: 8\r\n\r\nsomebody");
+        }
+
+        in.clear();
+
+        {
+            message_generator gen(make_fragmented_body_response(net::buffer("x", 1)));
+
+            error_code ec;
+            std::size_t total = beast::write(out, gen, ec);
+
+            BEAST_EXPECT(total == 47 + 63);
+            BEAST_EXPECT(! ec.failed());
+
+            BEAST_EXPECT(
+                in.str() ==
+                "HTTP/1.1 200 OK\r\n"
+                "Content-Length: 71\r\n\r\nxxxxxxxsomexxxxxxxxxxxxxxxxxxxbodyxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx");
+        }
+    }
+
+    void
+    testKeepAlive()
+    {
+        auto request = [](int version)
+        {
+            return http::request<http::string_body>(
+                http::verb::post, "/", version);
+        };
+        BEAST_EXPECT(
+            ! http::message_generator(request(10)).keep_alive());
+        BEAST_EXPECT(
+            http::message_generator(request(11)).keep_alive());
+    }
+
+    void
+    run() override
+    {
+        testGenerate();
+        testGenerateSlowConsumer();
+        testAsyncWrite();
+        testWrite();
+        testFragmentedBody();
+        testKeepAlive();
+    }
+};
+
+BEAST_DEFINE_TESTSUITE(beast,http,message_generator);
+
+} // http
+} // beast
+} // boost