Examples use http::message_generator

example/advanced/server-flex/advanced_server_flex.cpp

@@ -23,7 +23,6 @@
 #include <boost/asio/bind_executor.hpp>
 #include <boost/asio/dispatch.hpp>
 #include <boost/asio/signal_set.hpp>
-#include <boost/asio/steady_timer.hpp>
 #include <boost/asio/strand.hpp>
 #include <boost/make_unique.hpp>
 #include <boost/optional.hpp>
@@ -106,18 +105,15 @@ path_cat(
     return result;
 }
 
-// This function produces an HTTP response for the given
+// Return a response for the given request.
-// request. The type of the response object depends on the
+//
-// contents of the request, so the interface requires the
+// The concrete type of the response message (which depends on the
-// caller to pass a generic lambda for receiving the response.
+// request), is type-erased in message_generator.
-template<
+template<class Body, class Allocator>
-    class Body, class Allocator,
+http::message_generator
-    class Send>
-void
 handle_request(
     beast::string_view doc_root,
-    http::request<Body, http::basic_fields<Allocator>>&& req,
+    http::request<Body, http::basic_fields<Allocator>>&& req)
-    Send&& send)
 {
     // Returns a bad request response
     auto const bad_request =
@@ -161,13 +157,13 @@ handle_request(
     // Make sure we can handle the method
     if( req.method() != http::verb::get &&
         req.method() != http::verb::head)
-        return send(bad_request("Unknown HTTP-method"));
+        return bad_request("Unknown HTTP-method");
 
     // Request path must be absolute and not contain "..".
     if( req.target().empty() ||
         req.target()[0] != '/' ||
         req.target().find("..") != beast::string_view::npos)
-        return send(bad_request("Illegal request-target"));
+        return bad_request("Illegal request-target");
 
     // Build the path to the requested file
     std::string path = path_cat(doc_root, req.target());
@@ -181,11 +177,11 @@ handle_request(
 
     // Handle the case where the file doesn't exist
     if(ec == beast::errc::no_such_file_or_directory)
-        return send(not_found(req.target()));
+        return not_found(req.target());
 
     // Handle an unknown error
     if(ec)
-        return send(server_error(ec.message()));
+        return server_error(ec.message());
 
     // Cache the size since we need it after the move
     auto const size = body.size();
@@ -198,7 +194,7 @@ handle_request(
         res.set(http::field::content_type, mime_type(path));
         res.content_length(size);
         res.keep_alive(req.keep_alive());
-        return send(std::move(res));
+        return res;
     }
 
     // Respond to GET request
@@ -210,7 +206,7 @@ handle_request(
     res.set(http::field::content_type, mime_type(path));
     res.content_length(size);
     res.keep_alive(req.keep_alive());
-    return send(std::move(res));
+    return res;
 }
 
 //------------------------------------------------------------------------------
@@ -288,6 +284,7 @@ class websocket_session
                 derived().shared_from_this()));
     }
 
+private:
     void
     on_accept(beast::error_code ec)
     {
@@ -444,6 +441,8 @@ make_websocket_session(
 template<class Derived>
 class http_session
 {
+    std::shared_ptr<std::string const> doc_root_;
+
     // Access the derived class, this is part of
     // the Curiously Recurring Template Pattern idiom.
     Derived&
@@ -452,98 +451,8 @@ class http_session
         return static_cast<Derived&>(*this);
     }
 
-    // This queue is used for HTTP pipelining.
+    static constexpr std::size_t queue_limit = 8; // max responses
-    class queue
+    std::vector<http::message_generator> response_queue_;
-    {
-        enum
-        {
-            // Maximum number of responses we will queue
-            limit = 8
-        };
-
-        // The type-erased, saved work item
-        struct work
-        {
-            virtual ~work() = default;
-            virtual void operator()() = 0;
-        };
-
-        http_session& self_;
-        std::vector<std::unique_ptr<work>> items_;
-
-    public:
-        explicit
-        queue(http_session& self)
-            : self_(self)
-        {
-            static_assert(limit > 0, "queue limit must be positive");
-            items_.reserve(limit);
-        }
-
-        // Returns `true` if we have reached the queue limit
-        bool
-        is_full() const
-        {
-            return items_.size() >= limit;
-        }
-
-        // Called when a message finishes sending
-        // Returns `true` if the caller should initiate a read
-        bool
-        on_write()
-        {
-            BOOST_ASSERT(! items_.empty());
-            auto const was_full = is_full();
-            items_.erase(items_.begin());
-            if(! items_.empty())
-                (*items_.front())();
-            return was_full;
-        }
-
-        // Called by the HTTP handler to send a response.
-        template<bool isRequest, class Body, class Fields>
-        void
-        operator()(http::message<isRequest, Body, Fields>&& msg)
-        {
-            // This holds a work item
-            struct work_impl : work
-            {
-                http_session& self_;
-                http::message<isRequest, Body, Fields> msg_;
-
-                work_impl(
-                    http_session& self,
-                    http::message<isRequest, Body, Fields>&& msg)
-                    : self_(self)
-                    , msg_(std::move(msg))
-                {
-                }
-
-                void
-                operator()()
-                {
-                    http::async_write(
-                        self_.derived().stream(),
-                        msg_,
-                        beast::bind_front_handler(
-                            &http_session::on_write,
-                            self_.derived().shared_from_this(),
-                            msg_.need_eof()));
-                }
-            };
-
-            // Allocate and store the work
-            items_.push_back(
-                boost::make_unique<work_impl>(self_, std::move(msg)));
-
-            // If there was no previous work, start this one
-            if(items_.size() == 1)
-                (*items_.front())();
-        }
-    };
-
-    std::shared_ptr<std::string const> doc_root_;
-    queue queue_;
 
     // The parser is stored in an optional container so we can
     // construct it from scratch it at the beginning of each new message.
@@ -558,7 +467,6 @@ public:
         beast::flat_buffer buffer,
         std::shared_ptr<std::string const> const& doc_root)
         : doc_root_(doc_root)
-        , queue_(*this)
         , buffer_(std::move(buffer))
     {
     }
@@ -614,22 +522,67 @@ public:
         }
 
         // Send the response
-        handle_request(*doc_root_, parser_->release(), queue_);
+        queue_write(handle_request(*doc_root_, parser_->release()));
 
         // If we aren't at the queue limit, try to pipeline another request
-        if(! queue_.is_full())
+        if (response_queue_.size() < queue_limit)
             do_read();
     }
 
     void
-    on_write(bool close, beast::error_code ec, std::size_t bytes_transferred)
+    queue_write(http::message_generator response)
+    {
+        // Allocate and store the work
+        response_queue_.push_back(std::move(response));
+
+        // If there was no previous work, start the write
+        // loop
+        if (response_queue_.size() == 1)
+            do_write();
+    }
+
+    // Called to start/continue the write-loop. Should not be called when
+    // write_loop is already active.
+    //
+    // Returns `true` if the caller may initiate a new read
+    bool
+    do_write()
+    {
+        bool const was_full =
+            response_queue_.size() == queue_limit;
+
+        if(! response_queue_.empty())
+        {
+            http::message_generator msg =
+                std::move(response_queue_.front());
+            response_queue_.erase(response_queue_.begin());
+
+            bool keep_alive = msg.keep_alive();
+
+            beast::async_write(
+                derived().stream(),
+                std::move(msg),
+                beast::bind_front_handler(
+                    &http_session::on_write,
+                    derived().shared_from_this(),
+                    keep_alive));
+        }
+
+        return was_full;
+    }
+
+    void
+    on_write(
+        bool keep_alive,
+        beast::error_code ec,
+        std::size_t bytes_transferred)
     {
         boost::ignore_unused(bytes_transferred);
 
         if(ec)
             return fail(ec, "write");
 
-        if(close)
+        if(! keep_alive)
         {
             // This means we should close the connection, usually because
             // the response indicated the "Connection: close" semantic.
@@ -637,7 +590,7 @@ public:
         }
 
         // Inform the queue that a write completed
-        if(queue_.on_write())
+        if(do_write())
         {
             // Read another request
             do_read();

example/advanced/server/advanced_server.cpp

@@ -101,18 +101,15 @@ path_cat(
     return result;
 }
 
-// This function produces an HTTP response for the given
+// Return a response for the given request.
-// request. The type of the response object depends on the
+//
-// contents of the request, so the interface requires the
+// The concrete type of the response message (which depends on the
-// caller to pass a generic lambda for receiving the response.
+// request), is type-erased in message_generator.
-template<
+template <class Body, class Allocator>
-    class Body, class Allocator,
+http::message_generator
-    class Send>
-void
 handle_request(
     beast::string_view doc_root,
-    http::request<Body, http::basic_fields<Allocator>>&& req,
+    http::request<Body, http::basic_fields<Allocator>>&& req)
-    Send&& send)
 {
     // Returns a bad request response
     auto const bad_request =
@@ -156,13 +153,13 @@ handle_request(
     // Make sure we can handle the method
     if( req.method() != http::verb::get &&
         req.method() != http::verb::head)
-        return send(bad_request("Unknown HTTP-method"));
+        return bad_request("Unknown HTTP-method");
 
     // Request path must be absolute and not contain "..".
     if( req.target().empty() ||
         req.target()[0] != '/' ||
         req.target().find("..") != beast::string_view::npos)
-        return send(bad_request("Illegal request-target"));
+        return bad_request("Illegal request-target");
 
     // Build the path to the requested file
     std::string path = path_cat(doc_root, req.target());
@@ -176,11 +173,11 @@ handle_request(
 
     // Handle the case where the file doesn't exist
     if(ec == beast::errc::no_such_file_or_directory)
-        return send(not_found(req.target()));
+        return not_found(req.target());
 
     // Handle an unknown error
     if(ec)
-        return send(server_error(ec.message()));
+        return server_error(ec.message());
 
     // Cache the size since we need it after the move
     auto const size = body.size();
@@ -193,7 +190,7 @@ handle_request(
         res.set(http::field::content_type, mime_type(path));
         res.content_length(size);
         res.keep_alive(req.keep_alive());
-        return send(std::move(res));
+        return res;
     }
 
     // Respond to GET request
@@ -205,7 +202,7 @@ handle_request(
     res.set(http::field::content_type, mime_type(path));
     res.content_length(size);
     res.keep_alive(req.keep_alive());
-    return send(std::move(res));
+    return res;
 }
 
 //------------------------------------------------------------------------------
@@ -326,100 +323,12 @@ private:
 // Handles an HTTP server connection
 class http_session : public std::enable_shared_from_this<http_session>
 {
-    // This queue is used for HTTP pipelining.
-    class queue
-    {
-        enum
-        {
-            // Maximum number of responses we will queue
-            limit = 8
-        };
-
-        // The type-erased, saved work item
-        struct work
-        {
-            virtual ~work() = default;
-            virtual void operator()() = 0;
-        };
-
-        http_session& self_;
-        std::vector<std::unique_ptr<work>> items_;
-
-    public:
-        explicit
-        queue(http_session& self)
-            : self_(self)
-        {
-            static_assert(limit > 0, "queue limit must be positive");
-            items_.reserve(limit);
-        }
-
-        // Returns `true` if we have reached the queue limit
-        bool
-        is_full() const
-        {
-            return items_.size() >= limit;
-        }
-
-        // Called when a message finishes sending
-        // Returns `true` if the caller should initiate a read
-        bool
-        on_write()
-        {
-            BOOST_ASSERT(! items_.empty());
-            auto const was_full = is_full();
-            items_.erase(items_.begin());
-            if(! items_.empty())
-                (*items_.front())();
-            return was_full;
-        }
-
-        // Called by the HTTP handler to send a response.
-        template<bool isRequest, class Body, class Fields>
-        void
-        operator()(http::message<isRequest, Body, Fields>&& msg)
-        {
-            // This holds a work item
-            struct work_impl : work
-            {
-                http_session& self_;
-                http::message<isRequest, Body, Fields> msg_;
-
-                work_impl(
-                    http_session& self,
-                    http::message<isRequest, Body, Fields>&& msg)
-                    : self_(self)
-                    , msg_(std::move(msg))
-                {
-                }
-
-                void
-                operator()()
-                {
-                    http::async_write(
-                        self_.stream_,
-                        msg_,
-                        beast::bind_front_handler(
-                            &http_session::on_write,
-                            self_.shared_from_this(),
-                            msg_.need_eof()));
-                }
-            };
-
-            // Allocate and store the work
-            items_.push_back(
-                boost::make_unique<work_impl>(self_, std::move(msg)));
-
-            // If there was no previous work, start this one
-            if(items_.size() == 1)
-                (*items_.front())();
-        }
-    };
-
     beast::tcp_stream stream_;
     beast::flat_buffer buffer_;
     std::shared_ptr<std::string const> doc_root_;
-    queue queue_;
+
+    static constexpr std::size_t queue_limit = 8; // max responses
+    std::vector<http::message_generator> response_queue_;
 
     // The parser is stored in an optional container so we can
     // construct it from scratch it at the beginning of each new message.
@@ -432,8 +341,10 @@ public:
         std::shared_ptr<std::string const> const& doc_root)
         : stream_(std::move(socket))
         , doc_root_(doc_root)
-        , queue_(*this)
     {
+        static_assert(queue_limit > 0,
+                      "queue limit must be positive");
+        response_queue_.reserve(queue_limit);
     }
 
     // Start the session
@@ -451,7 +362,6 @@ public:
                 this->shared_from_this()));
     }
 
-
 private:
     void
     do_read()
@@ -499,22 +409,67 @@ private:
         }
 
         // Send the response
-        handle_request(*doc_root_, parser_->release(), queue_);
+        queue_write(handle_request(*doc_root_, parser_->release()));
 
         // If we aren't at the queue limit, try to pipeline another request
-        if(! queue_.is_full())
+        if (response_queue_.size() < queue_limit)
             do_read();
     }
 
     void
-    on_write(bool close, beast::error_code ec, std::size_t bytes_transferred)
+    queue_write(http::message_generator response)
+    {
+        // Allocate and store the work
+        response_queue_.push_back(std::move(response));
+
+        // If there was no previous work, start the write
+        // loop
+        if (response_queue_.size() == 1)
+            do_write();
+    }
+
+    // Called to start/continue the write-loop. Should not be called when
+    // write_loop is already active.
+    //
+    // Returns `true` if the caller may initiate a new read
+    bool
+    do_write()
+    {
+        bool const was_full =
+            response_queue_.size() == queue_limit;
+
+        if(! response_queue_.empty())
+        {
+            http::message_generator msg =
+                std::move(response_queue_.front());
+            response_queue_.erase(response_queue_.begin());
+
+            bool keep_alive = msg.keep_alive();
+
+            beast::async_write(
+                stream_,
+                std::move(msg),
+                beast::bind_front_handler(
+                    &http_session::on_write,
+                    shared_from_this(),
+                    keep_alive));
+        }
+
+        return was_full;
+    }
+
+    void
+    on_write(
+        bool keep_alive,
+        beast::error_code ec,
+        std::size_t bytes_transferred)
     {
         boost::ignore_unused(bytes_transferred);
 
         if(ec)
             return fail(ec, "write");
 
-        if(close)
+        if(! keep_alive)
         {
             // This means we should close the connection, usually because
             // the response indicated the "Connection: close" semantic.
@@ -522,7 +477,7 @@ private:
         }
 
         // Inform the queue that a write completed
-        if(queue_.on_write())
+        if(do_write())
         {
             // Read another request
             do_read();

example/http/server/async-ssl/http_server_async_ssl.cpp

@@ -100,18 +100,15 @@ path_cat(
     return result;
 }
 
-// This function produces an HTTP response for the given
+// Return a response for the given request.
-// request. The type of the response object depends on the
+//
-// contents of the request, so the interface requires the
+// The concrete type of the response message (which depends on the
-// caller to pass a generic lambda for receiving the response.
+// request), is type-erased in message_generator.
-template<
+template <class Body, class Allocator>
-    class Body, class Allocator,
+http::message_generator
-    class Send>
-void
 handle_request(
     beast::string_view doc_root,
-    http::request<Body, http::basic_fields<Allocator>>&& req,
+    http::request<Body, http::basic_fields<Allocator>>&& req)
-    Send&& send)
 {
     // Returns a bad request response
     auto const bad_request =
@@ -155,13 +152,13 @@ handle_request(
     // Make sure we can handle the method
     if( req.method() != http::verb::get &&
         req.method() != http::verb::head)
-        return send(bad_request("Unknown HTTP-method"));
+        return bad_request("Unknown HTTP-method");
 
     // Request path must be absolute and not contain "..".
     if( req.target().empty() ||
         req.target()[0] != '/' ||
         req.target().find("..") != beast::string_view::npos)
-        return send(bad_request("Illegal request-target"));
+        return bad_request("Illegal request-target");
 
     // Build the path to the requested file
     std::string path = path_cat(doc_root, req.target());
@@ -175,11 +172,11 @@ handle_request(
 
     // Handle the case where the file doesn't exist
     if(ec == beast::errc::no_such_file_or_directory)
-        return send(not_found(req.target()));
+        return not_found(req.target());
 
     // Handle an unknown error
     if(ec)
-        return send(server_error(ec.message()));
+        return server_error(ec.message());
 
     // Cache the size since we need it after the move
     auto const size = body.size();
@@ -192,7 +189,7 @@ handle_request(
         res.set(http::field::content_type, mime_type(path));
         res.content_length(size);
         res.keep_alive(req.keep_alive());
-        return send(std::move(res));
+        return res;
     }
 
     // Respond to GET request
@@ -204,7 +201,7 @@ handle_request(
     res.set(http::field::content_type, mime_type(path));
     res.content_length(size);
     res.keep_alive(req.keep_alive());
-    return send(std::move(res));
+    return res;
 }
 
 //------------------------------------------------------------------------------
@@ -239,49 +236,10 @@ fail(beast::error_code ec, char const* what)
 // Handles an HTTP server connection
 class session : public std::enable_shared_from_this<session>
 {
-    // This is the C++11 equivalent of a generic lambda.
-    // The function object is used to send an HTTP message.
-    struct send_lambda
-    {
-        session& self_;
-
-        explicit
-        send_lambda(session& self)
-            : self_(self)
-        {
-        }
-
-        template<bool isRequest, class Body, class Fields>
-        void
-        operator()(http::message<isRequest, Body, Fields>&& msg) const
-        {
-            // The lifetime of the message has to extend
-            // for the duration of the async operation so
-            // we use a shared_ptr to manage it.
-            auto sp = std::make_shared<
-                http::message<isRequest, Body, Fields>>(std::move(msg));
-
-            // Store a type-erased version of the shared
-            // pointer in the class to keep it alive.
-            self_.res_ = sp;
-
-            // Write the response
-            http::async_write(
-                self_.stream_,
-                *sp,
-                beast::bind_front_handler(
-                    &session::on_write,
-                    self_.shared_from_this(),
-                    sp->need_eof()));
-        }
-    };
-
     beast::ssl_stream<beast::tcp_stream> stream_;
     beast::flat_buffer buffer_;
     std::shared_ptr<std::string const> doc_root_;
     http::request<http::string_body> req_;
-    std::shared_ptr<void> res_;
-    send_lambda lambda_;
 
 public:
     // Take ownership of the socket
@@ -292,7 +250,6 @@ public:
         std::shared_ptr<std::string const> const& doc_root)
         : stream_(std::move(socket), ctx)
         , doc_root_(doc_root)
-        , lambda_(*this)
     {
     }
 
@@ -367,12 +324,28 @@ public:
             return fail(ec, "read");
 
         // Send the response
-        handle_request(*doc_root_, std::move(req_), lambda_);
+        send_response(
+            handle_request(*doc_root_, std::move(req_)));
+    }
+
+    void
+    send_response(http::message_generator&& msg)
+    {
+        bool keep_alive = msg.keep_alive();
+
+        // Write the response
+        beast::async_write(
+            stream_,
+            std::move(msg),
+            beast::bind_front_handler(
+                &session::on_write,
+                this->shared_from_this(),
+                keep_alive));
     }
 
     void
     on_write(
-        bool close,
+        bool keep_alive,
         beast::error_code ec,
         std::size_t bytes_transferred)
     {
@@ -381,16 +354,13 @@ public:
         if(ec)
             return fail(ec, "write");
 
-        if(close)
+        if(! keep_alive)
         {
             // This means we should close the connection, usually because
             // the response indicated the "Connection: close" semantic.
             return do_close();
         }
 
-        // We're done with the response so delete it
-        res_ = nullptr;
-
         // Read another request
         do_read();
     }

example/http/server/async/http_server_async.cpp

@@ -96,18 +96,15 @@ path_cat(
     return result;
 }
 
-// This function produces an HTTP response for the given
+// Return a response for the given request.
-// request. The type of the response object depends on the
+//
-// contents of the request, so the interface requires the
+// The concrete type of the response message (which depends on the
-// caller to pass a generic lambda for receiving the response.
+// request), is type-erased in message_generator.
-template<
+template <class Body, class Allocator>
-    class Body, class Allocator,
+http::message_generator
-    class Send>
-void
 handle_request(
     beast::string_view doc_root,
-    http::request<Body, http::basic_fields<Allocator>>&& req,
+    http::request<Body, http::basic_fields<Allocator>>&& req)
-    Send&& send)
 {
     // Returns a bad request response
     auto const bad_request =
@@ -151,13 +148,13 @@ handle_request(
     // Make sure we can handle the method
     if( req.method() != http::verb::get &&
         req.method() != http::verb::head)
-        return send(bad_request("Unknown HTTP-method"));
+        return bad_request("Unknown HTTP-method");
 
     // Request path must be absolute and not contain "..".
     if( req.target().empty() ||
         req.target()[0] != '/' ||
         req.target().find("..") != beast::string_view::npos)
-        return send(bad_request("Illegal request-target"));
+        return bad_request("Illegal request-target");
 
     // Build the path to the requested file
     std::string path = path_cat(doc_root, req.target());
@@ -171,11 +168,11 @@ handle_request(
 
     // Handle the case where the file doesn't exist
     if(ec == beast::errc::no_such_file_or_directory)
-        return send(not_found(req.target()));
+        return not_found(req.target());
 
     // Handle an unknown error
     if(ec)
-        return send(server_error(ec.message()));
+        return server_error(ec.message());
 
     // Cache the size since we need it after the move
     auto const size = body.size();
@@ -188,7 +185,7 @@ handle_request(
         res.set(http::field::content_type, mime_type(path));
         res.content_length(size);
         res.keep_alive(req.keep_alive());
-        return send(std::move(res));
+        return res;
     }
 
     // Respond to GET request
@@ -200,7 +197,7 @@ handle_request(
     res.set(http::field::content_type, mime_type(path));
     res.content_length(size);
     res.keep_alive(req.keep_alive());
-    return send(std::move(res));
+    return res;
 }
 
 //------------------------------------------------------------------------------
@@ -215,49 +212,10 @@ fail(beast::error_code ec, char const* what)
 // Handles an HTTP server connection
 class session : public std::enable_shared_from_this<session>
 {
-    // This is the C++11 equivalent of a generic lambda.
-    // The function object is used to send an HTTP message.
-    struct send_lambda
-    {
-        session& self_;
-
-        explicit
-        send_lambda(session& self)
-            : self_(self)
-        {
-        }
-
-        template<bool isRequest, class Body, class Fields>
-        void
-        operator()(http::message<isRequest, Body, Fields>&& msg) const
-        {
-            // The lifetime of the message has to extend
-            // for the duration of the async operation so
-            // we use a shared_ptr to manage it.
-            auto sp = std::make_shared<
-                http::message<isRequest, Body, Fields>>(std::move(msg));
-
-            // Store a type-erased version of the shared
-            // pointer in the class to keep it alive.
-            self_.res_ = sp;
-
-            // Write the response
-            http::async_write(
-                self_.stream_,
-                *sp,
-                beast::bind_front_handler(
-                    &session::on_write,
-                    self_.shared_from_this(),
-                    sp->need_eof()));
-        }
-    };
-
     beast::tcp_stream stream_;
     beast::flat_buffer buffer_;
     std::shared_ptr<std::string const> doc_root_;
     http::request<http::string_body> req_;
-    std::shared_ptr<void> res_;
-    send_lambda lambda_;
 
 public:
     // Take ownership of the stream
@@ -266,7 +224,6 @@ public:
         std::shared_ptr<std::string const> const& doc_root)
         : stream_(std::move(socket))
         , doc_root_(doc_root)
-        , lambda_(*this)
     {
     }
 
@@ -316,12 +273,26 @@ public:
             return fail(ec, "read");
 
         // Send the response
-        handle_request(*doc_root_, std::move(req_), lambda_);
+        send_response(
+            handle_request(*doc_root_, std::move(req_)));
+    }
+
+    void
+    send_response(http::message_generator&& msg)
+    {
+        bool keep_alive = msg.keep_alive();
+
+        // Write the response
+        beast::async_write(
+            stream_,
+            std::move(msg),
+            beast::bind_front_handler(
+                &session::on_write, shared_from_this(), keep_alive));
     }
 
     void
     on_write(
-        bool close,
+        bool keep_alive,
         beast::error_code ec,
         std::size_t bytes_transferred)
     {
@@ -330,16 +301,13 @@ public:
         if(ec)
             return fail(ec, "write");
 
-        if(close)
+        if(! keep_alive)
         {
             // This means we should close the connection, usually because
             // the response indicated the "Connection: close" semantic.
             return do_close();
         }
 
-        // We're done with the response so delete it
-        res_ = nullptr;
-
         // Read another request
         do_read();
     }

example/http/server/coro-ssl/http_server_coro_ssl.cpp

@@ -98,18 +98,15 @@ path_cat(
     return result;
 }
 
-// This function produces an HTTP response for the given
+// Return a response for the given request.
-// request. The type of the response object depends on the
+//
-// contents of the request, so the interface requires the
+// The concrete type of the response message (which depends on the
-// caller to pass a generic lambda for receiving the response.
+// request), is type-erased in message_generator.
-template<
+template <class Body, class Allocator>
-    class Body, class Allocator,
+http::message_generator
-    class Send>
-void
 handle_request(
     beast::string_view doc_root,
-    http::request<Body, http::basic_fields<Allocator>>&& req,
+    http::request<Body, http::basic_fields<Allocator>>&& req)
-    Send&& send)
 {
     // Returns a bad request response
     auto const bad_request =
@@ -153,13 +150,13 @@ handle_request(
     // Make sure we can handle the method
     if( req.method() != http::verb::get &&
         req.method() != http::verb::head)
-        return send(bad_request("Unknown HTTP-method"));
+        return bad_request("Unknown HTTP-method");
 
     // Request path must be absolute and not contain "..".
     if( req.target().empty() ||
         req.target()[0] != '/' ||
         req.target().find("..") != beast::string_view::npos)
-        return send(bad_request("Illegal request-target"));
+        return bad_request("Illegal request-target");
 
     // Build the path to the requested file
     std::string path = path_cat(doc_root, req.target());
@@ -173,11 +170,11 @@ handle_request(
 
     // Handle the case where the file doesn't exist
     if(ec == beast::errc::no_such_file_or_directory)
-        return send(not_found(req.target()));
+        return not_found(req.target());
 
     // Handle an unknown error
     if(ec)
-        return send(server_error(ec.message()));
+        return server_error(ec.message());
 
     // Cache the size since we need it after the move
     auto const size = body.size();
@@ -190,7 +187,7 @@ handle_request(
         res.set(http::field::content_type, mime_type(path));
         res.content_length(size);
         res.keep_alive(req.keep_alive());
-        return send(std::move(res));
+        return res;
     }
 
     // Respond to GET request
@@ -202,7 +199,7 @@ handle_request(
     res.set(http::field::content_type, mime_type(path));
     res.content_length(size);
     res.keep_alive(req.keep_alive());
-    return send(std::move(res));
+    return res;
 }
 
 //------------------------------------------------------------------------------
@@ -234,42 +231,6 @@ fail(beast::error_code ec, char const* what)
     std::cerr << what << ": " << ec.message() << "\n";
 }
 
-// This is the C++11 equivalent of a generic lambda.
-// The function object is used to send an HTTP message.
-struct send_lambda
-{
-    beast::ssl_stream<beast::tcp_stream>& stream_;
-    bool& close_;
-    beast::error_code& ec_;
-    net::yield_context yield_;
-
-    send_lambda(
-        beast::ssl_stream<beast::tcp_stream>& stream,
-        bool& close,
-        beast::error_code& ec,
-        net::yield_context yield)
-        : stream_(stream)
-        , close_(close)
-        , ec_(ec)
-        , yield_(yield)
-    {
-    }
-
-    template<bool isRequest, class Body, class Fields>
-    void
-    operator()(http::message<isRequest, Body, Fields>&& msg) const
-    {
-        // Determine if we should close the connection after
-        close_ = msg.need_eof();
-
-        // We need the serializer here because the serializer requires
-        // a non-const file_body, and the message oriented version of
-        // http::write only works with const messages.
-        http::serializer<isRequest, Body, Fields> sr{msg};
-        http::async_write(stream_, sr, yield_[ec_]);
-    }
-};
-
 // Handles an HTTP server connection
 void
 do_session(
@@ -277,7 +238,7 @@ do_session(
     std::shared_ptr<std::string const> const& doc_root,
     net::yield_context yield)
 {
-    bool close = false;
+    bool keep_alive = true;
     beast::error_code ec;
 
     // Set the timeout.
@@ -291,9 +252,6 @@ do_session(
     // This buffer is required to persist across reads
     beast::flat_buffer buffer;
 
-    // This lambda is used to send messages
-    send_lambda lambda{stream, close, ec, yield};
-
     for(;;)
     {
         // Set the timeout.
@@ -307,11 +265,19 @@ do_session(
         if(ec)
             return fail(ec, "read");
 
+        // Handle the request
+        http::message_generator res =
+            handle_request(*doc_root, std::move(req));
+
+        // Determine if we should close the connection
+        keep_alive = res.keep_alive();
+
         // Send the response
-        handle_request(*doc_root, std::move(req), lambda);
+        beast::async_write(stream, std::move(res), yield[ec]);
+
         if(ec)
             return fail(ec, "write");
-        if(close)
+        if(! keep_alive)
         {
             // This means we should close the connection, usually because
             // the response indicated the "Connection: close" semantic.

example/http/server/coro/http_server_coro.cpp

@@ -95,18 +95,15 @@ path_cat(
     return result;
 }
 
-// This function produces an HTTP response for the given
+// Return a response for the given request.
-// request. The type of the response object depends on the
+//
-// contents of the request, so the interface requires the
+// The concrete type of the response message (which depends on the
-// caller to pass a generic lambda for receiving the response.
+// request), is type-erased in message_generator.
-template<
+template <class Body, class Allocator>
-    class Body, class Allocator,
+http::message_generator
-    class Send>
-void
 handle_request(
     beast::string_view doc_root,
-    http::request<Body, http::basic_fields<Allocator>>&& req,
+    http::request<Body, http::basic_fields<Allocator>>&& req)
-    Send&& send)
 {
     // Returns a bad request response
     auto const bad_request =
@@ -150,13 +147,13 @@ handle_request(
     // Make sure we can handle the method
     if( req.method() != http::verb::get &&
         req.method() != http::verb::head)
-        return send(bad_request("Unknown HTTP-method"));
+        return bad_request("Unknown HTTP-method");
 
     // Request path must be absolute and not contain "..".
     if( req.target().empty() ||
         req.target()[0] != '/' ||
         req.target().find("..") != beast::string_view::npos)
-        return send(bad_request("Illegal request-target"));
+        return bad_request("Illegal request-target");
 
     // Build the path to the requested file
     std::string path = path_cat(doc_root, req.target());
@@ -170,11 +167,11 @@ handle_request(
 
     // Handle the case where the file doesn't exist
     if(ec == beast::errc::no_such_file_or_directory)
-        return send(not_found(req.target()));
+        return not_found(req.target());
 
     // Handle an unknown error
     if(ec)
-        return send(server_error(ec.message()));
+        return server_error(ec.message());
 
     // Cache the size since we need it after the move
     auto const size = body.size();
@@ -187,7 +184,7 @@ handle_request(
         res.set(http::field::content_type, mime_type(path));
         res.content_length(size);
         res.keep_alive(req.keep_alive());
-        return send(std::move(res));
+        return res;
     }
 
     // Respond to GET request
@@ -199,7 +196,7 @@ handle_request(
     res.set(http::field::content_type, mime_type(path));
     res.content_length(size);
     res.keep_alive(req.keep_alive());
-    return send(std::move(res));
+    return res;
 }
 
 //------------------------------------------------------------------------------
@@ -211,41 +208,6 @@ fail(beast::error_code ec, char const* what)
     std::cerr << what << ": " << ec.message() << "\n";
 }
 
-// This is the C++11 equivalent of a generic lambda.
-// The function object is used to send an HTTP message.
-struct send_lambda
-{
-    beast::tcp_stream& stream_;
-    bool& close_;
-    beast::error_code& ec_;
-    net::yield_context yield_;
-
-    send_lambda(
-        beast::tcp_stream& stream,
-        bool& close,
-        beast::error_code& ec,
-        net::yield_context yield)
-        : stream_(stream)
-        , close_(close)
-        , ec_(ec)
-        , yield_(yield)
-    {
-    }
-
-    template<bool isRequest, class Body, class Fields>
-    void
-    operator()(http::message<isRequest, Body, Fields>&& msg) const
-    {
-        // Determine if we should close the connection after
-        close_ = msg.need_eof();
-
-        // We need the serializer here because the serializer requires
-        // a non-const file_body, and the message oriented version of
-        // http::write only works with const messages.
-        http::serializer<isRequest, Body, Fields> sr{msg};
-        http::async_write(stream_, sr, yield_[ec_]);
-    }
-};
 
 // Handles an HTTP server connection
 void
@@ -254,15 +216,12 @@ do_session(
     std::shared_ptr<std::string const> const& doc_root,
     net::yield_context yield)
 {
-    bool close = false;
     beast::error_code ec;
 
     // This buffer is required to persist across reads
     beast::flat_buffer buffer;
 
     // This lambda is used to send messages
-    send_lambda lambda{stream, close, ec, yield};
-
     for(;;)
     {
         // Set the timeout.
@@ -276,11 +235,20 @@ do_session(
         if(ec)
             return fail(ec, "read");
 
+        // Handle the request
+        http::message_generator msg =
+            handle_request(*doc_root, std::move(req));
+
+        // Determine if we should close the connection
+        bool keep_alive = msg.keep_alive();
+
         // Send the response
-        handle_request(*doc_root, std::move(req), lambda);
+        beast::async_write(stream, std::move(msg), yield[ec]);
+
         if(ec)
             return fail(ec, "write");
-        if(close)
+
+        if(! keep_alive)
         {
             // This means we should close the connection, usually because
             // the response indicated the "Connection: close" semantic.

example/http/server/flex/http_server_flex.cpp

@@ -99,18 +99,15 @@ path_cat(
     return result;
 }
 
-// This function produces an HTTP response for the given
+// Return a response for the given request.
-// request. The type of the response object depends on the
+//
-// contents of the request, so the interface requires the
+// The concrete type of the response message (which depends on the
-// caller to pass a generic lambda for receiving the response.
+// request), is type-erased in message_generator.
-template<
+template <class Body, class Allocator>
-    class Body, class Allocator,
+http::message_generator
-    class Send>
-void
 handle_request(
     beast::string_view doc_root,
-    http::request<Body, http::basic_fields<Allocator>>&& req,
+    http::request<Body, http::basic_fields<Allocator>>&& req)
-    Send&& send)
 {
     // Returns a bad request response
     auto const bad_request =
@@ -154,13 +151,13 @@ handle_request(
     // Make sure we can handle the method
     if( req.method() != http::verb::get &&
         req.method() != http::verb::head)
-        return send(bad_request("Unknown HTTP-method"));
+        return bad_request("Unknown HTTP-method");
 
     // Request path must be absolute and not contain "..".
     if( req.target().empty() ||
         req.target()[0] != '/' ||
         req.target().find("..") != beast::string_view::npos)
-        return send(bad_request("Illegal request-target"));
+        return bad_request("Illegal request-target");
 
     // Build the path to the requested file
     std::string path = path_cat(doc_root, req.target());
@@ -174,11 +171,11 @@ handle_request(
 
     // Handle the case where the file doesn't exist
     if(ec == beast::errc::no_such_file_or_directory)
-        return send(not_found(req.target()));
+        return not_found(req.target());
 
     // Handle an unknown error
     if(ec)
-        return send(server_error(ec.message()));
+        return server_error(ec.message());
 
     // Cache the size since we need it after the move
     auto const size = body.size();
@@ -191,7 +188,7 @@ handle_request(
         res.set(http::field::content_type, mime_type(path));
         res.content_length(size);
         res.keep_alive(req.keep_alive());
-        return send(std::move(res));
+        return res;
     }
 
     // Respond to GET request
@@ -203,7 +200,7 @@ handle_request(
     res.set(http::field::content_type, mime_type(path));
     res.content_length(size);
     res.keep_alive(req.keep_alive());
-    return send(std::move(res));
+    return res;
 }
 
 //------------------------------------------------------------------------------
@@ -249,47 +246,8 @@ class session
         return static_cast<Derived&>(*this);
     }
 
-    // This is the C++11 equivalent of a generic lambda.
-    // The function object is used to send an HTTP message.
-    struct send_lambda
-    {
-        session& self_;
-
-        explicit
-        send_lambda(session& self)
-            : self_(self)
-        {
-        }
-
-        template<bool isRequest, class Body, class Fields>
-        void
-        operator()(http::message<isRequest, Body, Fields>&& msg) const
-        {
-            // The lifetime of the message has to extend
-            // for the duration of the async operation so
-            // we use a shared_ptr to manage it.
-            auto sp = std::make_shared<
-                http::message<isRequest, Body, Fields>>(std::move(msg));
-
-            // Store a type-erased version of the shared
-            // pointer in the class to keep it alive.
-            self_.res_ = sp;
-
-            // Write the response
-            http::async_write(
-                self_.derived().stream(),
-                *sp,
-                beast::bind_front_handler(
-                    &session::on_write,
-                    self_.derived().shared_from_this(),
-                    sp->need_eof()));
-        }
-    };
-
     std::shared_ptr<std::string const> doc_root_;
     http::request<http::string_body> req_;
-    std::shared_ptr<void> res_;
-    send_lambda lambda_;
 
 protected:
     beast::flat_buffer buffer_;
@@ -300,7 +258,6 @@ public:
         beast::flat_buffer buffer,
         std::shared_ptr<std::string const> const& doc_root)
         : doc_root_(doc_root)
-        , lambda_(*this)
         , buffer_(std::move(buffer))
     {
     }
@@ -337,12 +294,28 @@ public:
             return fail(ec, "read");
 
         // Send the response
-        handle_request(*doc_root_, std::move(req_), lambda_);
+        send_response(
+            handle_request(*doc_root_, std::move(req_)));
+    }
+
+    void
+    send_response(http::message_generator&& msg)
+    {
+        bool keep_alive = msg.keep_alive();
+
+        // Write the response
+        beast::async_write(
+            derived().stream(),
+            std::move(msg),
+            beast::bind_front_handler(
+                &session::on_write,
+                derived().shared_from_this(),
+                keep_alive));
     }
 
     void
     on_write(
-        bool close,
+        bool keep_alive,
         beast::error_code ec,
         std::size_t bytes_transferred)
     {
@@ -351,16 +324,13 @@ public:
         if(ec)
             return fail(ec, "write");
 
-        if(close)
+        if(! keep_alive)
         {
             // This means we should close the connection, usually because
             // the response indicated the "Connection: close" semantic.
             return derived().do_eof();
         }
 
-        // We're done with the response so delete it
-        res_ = nullptr;
-
         // Read another request
         do_read();
     }

example/http/server/stackless-ssl/http_server_stackless_ssl.cpp

@@ -101,18 +101,15 @@ path_cat(
     return result;
 }
 
-// This function produces an HTTP response for the given
+// Return a response for the given request.
-// request. The type of the response object depends on the
+//
-// contents of the request, so the interface requires the
+// The concrete type of the response message (which depends on the
-// caller to pass a generic lambda for receiving the response.
+// request), is type-erased in message_generator.
-template<
+template <class Body, class Allocator>
-    class Body, class Allocator,
+http::message_generator
-    class Send>
-void
 handle_request(
     beast::string_view doc_root,
-    http::request<Body, http::basic_fields<Allocator>>&& req,
+    http::request<Body, http::basic_fields<Allocator>>&& req)
-    Send&& send)
 {
     // Returns a bad request response
     auto const bad_request =
@@ -156,13 +153,13 @@ handle_request(
     // Make sure we can handle the method
     if( req.method() != http::verb::get &&
         req.method() != http::verb::head)
-        return send(bad_request("Unknown HTTP-method"));
+        return bad_request("Unknown HTTP-method");
 
     // Request path must be absolute and not contain "..".
     if( req.target().empty() ||
         req.target()[0] != '/' ||
         req.target().find("..") != beast::string_view::npos)
-        return send(bad_request("Illegal request-target"));
+        return bad_request("Illegal request-target");
 
     // Build the path to the requested file
     std::string path = path_cat(doc_root, req.target());
@@ -176,11 +173,11 @@ handle_request(
 
     // Handle the case where the file doesn't exist
     if(ec == beast::errc::no_such_file_or_directory)
-        return send(not_found(req.target()));
+        return not_found(req.target());
 
     // Handle an unknown error
     if(ec)
-        return send(server_error(ec.message()));
+        return server_error(ec.message());
 
     // Cache the size since we need it after the move
     auto const size = body.size();
@@ -193,7 +190,7 @@ handle_request(
         res.set(http::field::content_type, mime_type(path));
         res.content_length(size);
         res.keep_alive(req.keep_alive());
-        return send(std::move(res));
+        return res;
     }
 
     // Respond to GET request
@@ -205,7 +202,7 @@ handle_request(
     res.set(http::field::content_type, mime_type(path));
     res.content_length(size);
     res.keep_alive(req.keep_alive());
-    return send(std::move(res));
+    return res;
 }
 
 //------------------------------------------------------------------------------
@@ -242,51 +239,11 @@ class session
     : public boost::asio::coroutine
     , public std::enable_shared_from_this<session>
 {
-    // This is the C++11 equivalent of a generic lambda.
-    // The function object is used to send an HTTP message.
-    struct send_lambda
-    {
-        session& self_;
-
-        explicit
-        send_lambda(session& self)
-            : self_(self)
-        {
-        }
-
-        template<bool isRequest, class Body, class Fields>
-        void
-        operator()(http::message<isRequest, Body, Fields>&& msg) const
-        {
-            // The lifetime of the message has to extend
-            // for the duration of the async operation so
-            // we use a shared_ptr to manage it.
-            auto sp = std::make_shared<
-                http::message<isRequest, Body, Fields>>(std::move(msg));
-
-            // Store a type-erased version of the shared
-            // pointer in the class to keep it alive.
-            self_.res_ = sp;
-
-            // Write the response
-            http::async_write(
-                self_.stream_,
-                *sp,
-                std::bind(
-                    &session::loop,
-                    self_.shared_from_this(),
-                    std::placeholders::_1,
-                    std::placeholders::_2,
-                    sp->need_eof()));
-        }
-    };
-
     beast::ssl_stream<beast::tcp_stream> stream_;
     beast::flat_buffer buffer_;
     std::shared_ptr<std::string const> doc_root_;
     http::request<http::string_body> req_;
-    std::shared_ptr<void> res_;
+    bool keep_alive_ = true;
-    send_lambda lambda_;
 
 public:
     // Take ownership of the socket
@@ -297,7 +254,6 @@ public:
         std::shared_ptr<std::string const> const& doc_root)
         : stream_(std::move(socket), ctx)
         , doc_root_(doc_root)
-        , lambda_(*this)
     {
     }
 
@@ -313,17 +269,13 @@ public:
                       beast::bind_front_handler(&session::loop,
                                                 shared_from_this(),
                                                 beast::error_code{},
-                                                0,
+                                                0));
-                                                false));
     }
 
     #include <boost/asio/yield.hpp>
 
     void
-    loop(
+    loop(beast::error_code ec, std::size_t bytes_transferred)
-        beast::error_code ec,
-        std::size_t bytes_transferred,
-        bool close)
     {
         boost::ignore_unused(bytes_transferred);
         reenter(*this)
@@ -335,11 +287,8 @@ public:
             yield stream_.async_handshake(
                 ssl::stream_base::server,
                 std::bind(
-                    &session::loop,
+                    &session::loop, shared_from_this(),
-                    shared_from_this(),
+                    std::placeholders::_1, 0));
-                    std::placeholders::_1,
-                    0,
-                    false));
             if(ec)
                 return fail(ec, "handshake");
 
@@ -353,34 +302,41 @@ public:
                 req_ = {};
 
                 // Read a request
-                yield http::async_read(stream_, buffer_, req_,
+                yield http::async_read(
-                    std::bind(
+                    stream_, buffer_, req_,
-                        &session::loop,
+                    beast::bind_front_handler(
-                        shared_from_this(),
+                        &session::loop, shared_from_this()));
-                        std::placeholders::_1,
+
-                        std::placeholders::_2,
+                if (ec == http::error::end_of_stream) {
-                        false));
-                if(ec == http::error::end_of_stream)
-                {
                     // The remote host closed the connection
                     break;
                 }
                 if(ec)
                     return fail(ec, "read");
 
+                yield {
+                    // Handle request
+                    http::message_generator msg =
+                        handle_request(*doc_root_, std::move(req_));
+
+                    // Determine if we should close the connection
+                    keep_alive_ = msg.keep_alive();
+
                     // Send the response
-                yield handle_request(*doc_root_, std::move(req_), lambda_);
+                    beast::async_write(
+                        stream_, std::move(msg),
+                        beast::bind_front_handler(
+                            &session::loop, shared_from_this()));
+                }
+
                 if(ec)
                     return fail(ec, "write");
-                if(close)
+                if(! keep_alive_)
                 {
                     // This means we should close the connection, usually because
                     // the response indicated the "Connection: close" semantic.
                     break;
                 }
-
-                // We're done with the response so delete it
-                res_ = nullptr;
             }
 
             // Set the timeout.
@@ -392,8 +348,7 @@ public:
                     &session::loop,
                     shared_from_this(),
                     std::placeholders::_1,
-                    0,
+                    0));
-                    false));
             if(ec)
                 return fail(ec, "shutdown");
 

example/http/server/stackless/http_server_stackless.cpp

@@ -97,18 +97,15 @@ path_cat(
     return result;
 }
 
-// This function produces an HTTP response for the given
+// Return a response for the given request.
-// request. The type of the response object depends on the
+//
-// contents of the request, so the interface requires the
+// The concrete type of the response message (which depends on the
-// caller to pass a generic lambda for receiving the response.
+// request), is type-erased in message_generator.
-template<
+template <class Body, class Allocator>
-    class Body, class Allocator,
+http::message_generator
-    class Send>
-void
 handle_request(
     beast::string_view doc_root,
-    http::request<Body, http::basic_fields<Allocator>>&& req,
+    http::request<Body, http::basic_fields<Allocator>>&& req)
-    Send&& send)
 {
     // Returns a bad request response
     auto const bad_request =
@@ -152,13 +149,13 @@ handle_request(
     // Make sure we can handle the method
     if( req.method() != http::verb::get &&
         req.method() != http::verb::head)
-        return send(bad_request("Unknown HTTP-method"));
+        return bad_request("Unknown HTTP-method");
 
     // Request path must be absolute and not contain "..".
     if( req.target().empty() ||
         req.target()[0] != '/' ||
         req.target().find("..") != beast::string_view::npos)
-        return send(bad_request("Illegal request-target"));
+        return bad_request("Illegal request-target");
 
     // Build the path to the requested file
     std::string path = path_cat(doc_root, req.target());
@@ -172,11 +169,11 @@ handle_request(
 
     // Handle the case where the file doesn't exist
     if(ec == beast::errc::no_such_file_or_directory)
-        return send(not_found(req.target()));
+        return not_found(req.target());
 
     // Handle an unknown error
     if(ec)
-        return send(server_error(ec.message()));
+        return server_error(ec.message());
 
     // Cache the size since we need it after the move
     auto const size = body.size();
@@ -189,7 +186,7 @@ handle_request(
         res.set(http::field::content_type, mime_type(path));
         res.content_length(size);
         res.keep_alive(req.keep_alive());
-        return send(std::move(res));
+        return res;
     }
 
     // Respond to GET request
@@ -201,7 +198,7 @@ handle_request(
     res.set(http::field::content_type, mime_type(path));
     res.content_length(size);
     res.keep_alive(req.keep_alive());
-    return send(std::move(res));
+    return res;
 }
 
 //------------------------------------------------------------------------------
@@ -218,50 +215,11 @@ class session
     : public boost::asio::coroutine
     , public std::enable_shared_from_this<session>
 {
-    // This is the C++11 equivalent of a generic lambda.
-    // The function object is used to send an HTTP message.
-    struct send_lambda
-    {
-        session& self_;
-        std::shared_ptr<void> res_;
-
-        explicit
-        send_lambda(session& self)
-            : self_(self)
-        {
-        }
-
-        template<bool isRequest, class Body, class Fields>
-        void
-        operator()(http::message<isRequest, Body, Fields>&& msg) const
-        {
-            // The lifetime of the message has to extend
-            // for the duration of the async operation so
-            // we use a shared_ptr to manage it.
-            auto sp = std::make_shared<
-                http::message<isRequest, Body, Fields>>(std::move(msg));
-
-            // Store a type-erased version of the shared
-            // pointer in the class to keep it alive.
-            self_.res_ = sp;
-
-            // Write the response
-            http::async_write(
-                self_.stream_,
-                *sp,
-                beast::bind_front_handler(
-                    &session::loop,
-                    self_.shared_from_this(),
-                    sp->need_eof()));
-        }
-    };
-
     beast::tcp_stream stream_;
     beast::flat_buffer buffer_;
     std::shared_ptr<std::string const> doc_root_;
     http::request<http::string_body> req_;
-    std::shared_ptr<void> res_;
+    bool keep_alive_ = true;
-    send_lambda lambda_;
 
 public:
     // Take ownership of the socket
@@ -271,7 +229,6 @@ public:
         std::shared_ptr<std::string const> const& doc_root)
         : stream_(std::move(socket))
         , doc_root_(doc_root)
-        , lambda_(*this)
     {
     }
 
@@ -286,7 +243,6 @@ public:
         net::dispatch(stream_.get_executor(),
                       beast::bind_front_handler(&session::loop,
                                                 shared_from_this(),
-                                                false,
                                                 beast::error_code{},
                                                 0));
     }
@@ -294,10 +250,7 @@ public:
     #include <boost/asio/yield.hpp>
 
     void
-    loop(
+    loop(beast::error_code ec, std::size_t bytes_transferred)
-        bool close,
-        beast::error_code ec,
-        std::size_t bytes_transferred)
     {
         boost::ignore_unused(bytes_transferred);
         reenter(*this)
@@ -315,8 +268,8 @@ public:
                 yield http::async_read(stream_, buffer_, req_,
                     beast::bind_front_handler(
                         &session::loop,
-                        shared_from_this(),
+                        shared_from_this()));
-                        false));
+
                 if(ec == http::error::end_of_stream)
                 {
                     // The remote host closed the connection
@@ -325,19 +278,30 @@ public:
                 if(ec)
                     return fail(ec, "read");
 
+                yield {
+                    // Handle request
+                    http::message_generator msg =
+                        handle_request(*doc_root_, std::move(req_));
+
+                    // Determine if we should close the connection
+                    keep_alive_ = msg.keep_alive();
+
                     // Send the response
-                yield handle_request(*doc_root_, std::move(req_), lambda_);
+                    beast::async_write(
+                        stream_,
+                        std::move(msg),
+                        beast::bind_front_handler(
+                            &session::loop, shared_from_this()));
+                }
+
                 if(ec)
                     return fail(ec, "write");
-                if(close)
+                if(! keep_alive_)
                 {
                     // This means we should close the connection, usually because
                     // the response indicated the "Connection: close" semantic.
                     break;
                 }
-
-                // We're done with the response so delete it
-                res_ = nullptr;
             }
 
             // Send a TCP shutdown

example/http/server/sync-ssl/http_server_sync_ssl.cpp

@@ -97,18 +97,15 @@ path_cat(
     return result;
 }
 
-// This function produces an HTTP response for the given
+// Return a response for the given request.
-// request. The type of the response object depends on the
+//
-// contents of the request, so the interface requires the
+// The concrete type of the response message (which depends on the
-// caller to pass a generic lambda for receiving the response.
+// request), is type-erased in message_generator.
-template<
+template <class Body, class Allocator>
-    class Body, class Allocator,
+http::message_generator
-    class Send>
-void
 handle_request(
     beast::string_view doc_root,
-    http::request<Body, http::basic_fields<Allocator>>&& req,
+    http::request<Body, http::basic_fields<Allocator>>&& req)
-    Send&& send)
 {
     // Returns a bad request response
     auto const bad_request =
@@ -152,13 +149,13 @@ handle_request(
     // Make sure we can handle the method
     if( req.method() != http::verb::get &&
         req.method() != http::verb::head)
-        return send(bad_request("Unknown HTTP-method"));
+        return bad_request("Unknown HTTP-method");
 
     // Request path must be absolute and not contain "..".
     if( req.target().empty() ||
         req.target()[0] != '/' ||
         req.target().find("..") != beast::string_view::npos)
-        return send(bad_request("Illegal request-target"));
+        return bad_request("Illegal request-target");
 
     // Build the path to the requested file
     std::string path = path_cat(doc_root, req.target());
@@ -172,11 +169,11 @@ handle_request(
 
     // Handle the case where the file doesn't exist
     if(ec == beast::errc::no_such_file_or_directory)
-        return send(not_found(req.target()));
+        return not_found(req.target());
 
     // Handle an unknown error
     if(ec)
-        return send(server_error(ec.message()));
+        return server_error(ec.message());
 
     // Cache the size since we need it after the move
     auto const size = body.size();
@@ -189,7 +186,7 @@ handle_request(
         res.set(http::field::content_type, mime_type(path));
         res.content_length(size);
         res.keep_alive(req.keep_alive());
-        return send(std::move(res));
+        return res;
     }
 
     // Respond to GET request
@@ -201,7 +198,7 @@ handle_request(
     res.set(http::field::content_type, mime_type(path));
     res.content_length(size);
     res.keep_alive(req.keep_alive());
-    return send(std::move(res));
+    return res;
 }
 
 //------------------------------------------------------------------------------
@@ -213,41 +210,6 @@ fail(beast::error_code ec, char const* what)
     std::cerr << what << ": " << ec.message() << "\n";
 }
 
-// This is the C++11 equivalent of a generic lambda.
-// The function object is used to send an HTTP message.
-template<class Stream>
-struct send_lambda
-{
-    Stream& stream_;
-    bool& close_;
-    beast::error_code& ec_;
-
-    explicit
-    send_lambda(
-        Stream& stream,
-        bool& close,
-        beast::error_code& ec)
-        : stream_(stream)
-        , close_(close)
-        , ec_(ec)
-    {
-    }
-
-    template<bool isRequest, class Body, class Fields>
-    void
-    operator()(http::message<isRequest, Body, Fields>&& msg) const
-    {
-        // Determine if we should close the connection after
-        close_ = msg.need_eof();
-
-        // We need the serializer here because the serializer requires
-        // a non-const file_body, and the message oriented version of
-        // http::write only works with const messages.
-        http::serializer<isRequest, Body, Fields> sr{msg};
-        http::write(stream_, sr, ec_);
-    }
-};
-
 // Handles an HTTP server connection
 void
 do_session(
@@ -255,7 +217,6 @@ do_session(
     ssl::context& ctx,
     std::shared_ptr<std::string const> const& doc_root)
 {
-    bool close = false;
     beast::error_code ec;
 
     // Construct the stream around the socket
@@ -269,9 +230,6 @@ do_session(
     // This buffer is required to persist across reads
     beast::flat_buffer buffer;
 
-    // This lambda is used to send messages
-    send_lambda<beast::ssl_stream<tcp::socket&>> lambda{stream, close, ec};
-
     for(;;)
     {
         // Read a request
@@ -282,11 +240,20 @@ do_session(
         if(ec)
             return fail(ec, "read");
 
+        // Handle request
+        http::message_generator msg =
+            handle_request(*doc_root, std::move(req));
+
+        // Determine if we should close the connection
+        bool keep_alive = msg.keep_alive();
+
         // Send the response
-        handle_request(*doc_root, std::move(req), lambda);
+        beast::write(stream, std::move(msg), ec);
+
         if(ec)
             return fail(ec, "write");
-        if(close)
+
+        if(! keep_alive)
         {
             // This means we should close the connection, usually because
             // the response indicated the "Connection: close" semantic.

example/http/server/sync/http_server_sync.cpp

@@ -94,18 +94,15 @@ path_cat(
     return result;
 }
 
-// This function produces an HTTP response for the given
+// Return a response for the given request.
-// request. The type of the response object depends on the
+//
-// contents of the request, so the interface requires the
+// The concrete type of the response message (which depends on the
-// caller to pass a generic lambda for receiving the response.
+// request), is type-erased in message_generator.
-template<
+template <class Body, class Allocator>
-    class Body, class Allocator,
+http::message_generator
-    class Send>
-void
 handle_request(
     beast::string_view doc_root,
-    http::request<Body, http::basic_fields<Allocator>>&& req,
+    http::request<Body, http::basic_fields<Allocator>>&& req)
-    Send&& send)
 {
     // Returns a bad request response
     auto const bad_request =
@@ -149,13 +146,13 @@ handle_request(
     // Make sure we can handle the method
     if( req.method() != http::verb::get &&
         req.method() != http::verb::head)
-        return send(bad_request("Unknown HTTP-method"));
+        return bad_request("Unknown HTTP-method");
 
     // Request path must be absolute and not contain "..".
     if( req.target().empty() ||
         req.target()[0] != '/' ||
         req.target().find("..") != beast::string_view::npos)
-        return send(bad_request("Illegal request-target"));
+        return bad_request("Illegal request-target");
 
     // Build the path to the requested file
     std::string path = path_cat(doc_root, req.target());
@@ -169,11 +166,11 @@ handle_request(
 
     // Handle the case where the file doesn't exist
     if(ec == beast::errc::no_such_file_or_directory)
-        return send(not_found(req.target()));
+        return not_found(req.target());
 
     // Handle an unknown error
     if(ec)
-        return send(server_error(ec.message()));
+        return server_error(ec.message());
 
     // Cache the size since we need it after the move
     auto const size = body.size();
@@ -186,7 +183,7 @@ handle_request(
         res.set(http::field::content_type, mime_type(path));
         res.content_length(size);
         res.keep_alive(req.keep_alive());
-        return send(std::move(res));
+        return res;
     }
 
     // Respond to GET request
@@ -198,7 +195,7 @@ handle_request(
     res.set(http::field::content_type, mime_type(path));
     res.content_length(size);
     res.keep_alive(req.keep_alive());
-    return send(std::move(res));
+    return res;
 }
 
 //------------------------------------------------------------------------------
@@ -210,56 +207,17 @@ fail(beast::error_code ec, char const* what)
     std::cerr << what << ": " << ec.message() << "\n";
 }
 
-// This is the C++11 equivalent of a generic lambda.
-// The function object is used to send an HTTP message.
-template<class Stream>
-struct send_lambda
-{
-    Stream& stream_;
-    bool& close_;
-    beast::error_code& ec_;
-
-    explicit
-    send_lambda(
-        Stream& stream,
-        bool& close,
-        beast::error_code& ec)
-        : stream_(stream)
-        , close_(close)
-        , ec_(ec)
-    {
-    }
-
-    template<bool isRequest, class Body, class Fields>
-    void
-    operator()(http::message<isRequest, Body, Fields>&& msg) const
-    {
-        // Determine if we should close the connection after
-        close_ = msg.need_eof();
-
-        // We need the serializer here because the serializer requires
-        // a non-const file_body, and the message oriented version of
-        // http::write only works with const messages.
-        http::serializer<isRequest, Body, Fields> sr{msg};
-        http::write(stream_, sr, ec_);
-    }
-};
-
 // Handles an HTTP server connection
 void
 do_session(
     tcp::socket& socket,
     std::shared_ptr<std::string const> const& doc_root)
 {
-    bool close = false;
     beast::error_code ec;
 
     // This buffer is required to persist across reads
     beast::flat_buffer buffer;
 
-    // This lambda is used to send messages
-    send_lambda<tcp::socket> lambda{socket, close, ec};
-
     for(;;)
     {
         // Read a request
@@ -270,11 +228,19 @@ do_session(
         if(ec)
             return fail(ec, "read");
 
+        // Handle request
+        http::message_generator msg =
+            handle_request(*doc_root, std::move(req));
+
+        // Determine if we should close the connection
+        bool keep_alive = msg.keep_alive();
+
         // Send the response
-        handle_request(*doc_root, std::move(req), lambda);
+        beast::write(socket, std::move(msg), ec);
+
         if(ec)
             return fail(ec, "write");
-        if(close)
+        if(! keep_alive)
         {
             // This means we should close the connection, usually because
             // the response indicated the "Connection: close" semantic.

example/websocket/server/chat-multi/http_session.cpp

@@ -12,8 +12,6 @@
 #include <boost/config.hpp>
 #include <iostream>
 
-#define BOOST_NO_CXX14_GENERIC_LAMBDAS
-
 //------------------------------------------------------------------------------
 
 // Return a reasonable mime type based on the extension of a file.
@@ -79,18 +77,15 @@ path_cat(
     return result;
 }
 
-// This function produces an HTTP response for the given
+// Return a response for the given request.
-// request. The type of the response object depends on the
+//
-// contents of the request, so the interface requires the
+// The concrete type of the response message (which depends on the
-// caller to pass a generic lambda for receiving the response.
+// request), is type-erased in message_generator.
-template<
+template <class Body, class Allocator>
-    class Body, class Allocator,
+http::message_generator
-    class Send>
-void
 handle_request(
     beast::string_view doc_root,
-    http::request<Body, http::basic_fields<Allocator>>&& req,
+    http::request<Body, http::basic_fields<Allocator>>&& req)
-    Send&& send)
 {
     // Returns a bad request response
     auto const bad_request =
@@ -134,13 +129,13 @@ handle_request(
     // Make sure we can handle the method
     if( req.method() != http::verb::get &&
         req.method() != http::verb::head)
-        return send(bad_request("Unknown HTTP-method"));
+        return bad_request("Unknown HTTP-method");
 
     // Request path must be absolute and not contain "..".
     if( req.target().empty() ||
         req.target()[0] != '/' ||
         req.target().find("..") != beast::string_view::npos)
-        return send(bad_request("Illegal request-target"));
+        return bad_request("Illegal request-target");
 
     // Build the path to the requested file
     std::string path = path_cat(doc_root, req.target());
@@ -154,11 +149,11 @@ handle_request(
 
     // Handle the case where the file doesn't exist
     if(ec == boost::system::errc::no_such_file_or_directory)
-        return send(not_found(req.target()));
+        return not_found(req.target());
 
     // Handle an unknown error
     if(ec)
-        return send(server_error(ec.message()));
+        return server_error(ec.message());
 
     // Cache the size since we need it after the move
     auto const size = body.size();
@@ -171,7 +166,7 @@ handle_request(
         res.set(http::field::content_type, mime_type(path));
         res.content_length(size);
         res.keep_alive(req.keep_alive());
-        return send(std::move(res));
+        return res;
     }
 
     // Respond to GET request
@@ -183,45 +178,11 @@ handle_request(
     res.set(http::field::content_type, mime_type(path));
     res.content_length(size);
     res.keep_alive(req.keep_alive());
-    return send(std::move(res));
+    return res;
 }
 
 //------------------------------------------------------------------------------
 
-struct http_session::send_lambda
-{
-    http_session& self_;
-
-    explicit
-    send_lambda(http_session& self)
-        : self_(self)
-    {
-    }
-
-    template<bool isRequest, class Body, class Fields>
-    void
-    operator()(http::message<isRequest, Body, Fields>&& msg) const
-    {
-        // The lifetime of the message has to extend
-        // for the duration of the async operation so
-        // we use a shared_ptr to manage it.
-        auto sp = boost::make_shared<
-            http::message<isRequest, Body, Fields>>(std::move(msg));
-
-        // Write the response
-        auto self = self_.shared_from_this();
-        http::async_write(
-            self_.stream_,
-            *sp,
-            [self, sp](beast::error_code ec, std::size_t bytes)
-            {
-                self->on_write(ec, bytes, sp->need_eof());
-            });
-    }
-};
-
-//------------------------------------------------------------------------------
-
 http_session::
 http_session(
     tcp::socket&& socket,
@@ -300,65 +261,33 @@ on_read(beast::error_code ec, std::size_t)
         return;
     }
 
-    // Send the response
+    // Handle request
-#ifndef BOOST_NO_CXX14_GENERIC_LAMBDAS
+    http::message_generator msg =
-    //
+        handle_request(state_->doc_root(), parser_->release());
-    // The following code requires generic
+
-    // lambdas, available in C++14 and later.
+    // Determine if we should close the connection
-    //
+    bool keep_alive = msg.keep_alive();
-    handle_request(
-        state_->doc_root(),
-        std::move(req_),
-        [this](auto&& response)
-        {
-            // The lifetime of the message has to extend
-            // for the duration of the async operation so
-            // we use a shared_ptr to manage it.
-            using response_type = typename std::decay<decltype(response)>::type;
-            auto sp = boost::make_shared<response_type>(std::forward<decltype(response)>(response));
 
-        #if 0
-            // NOTE This causes an ICE in gcc 7.3
-            // Write the response
-            http::async_write(this->stream_, *sp,
-                [self = shared_from_this(), sp](
-                    beast::error_code ec, std::size_t bytes)
-                {
-                    self->on_write(ec, bytes, sp->need_eof()); 
-                });
-        #else
-            // Write the response
     auto self = shared_from_this();
-            http::async_write(stream_, *sp,
-                [self, sp](
-                    beast::error_code ec, std::size_t bytes)
-                {
-                    self->on_write(ec, bytes, sp->need_eof()); 
-                });
-        #endif
-        });
-#else
-    //
-    // This code uses the function object type send_lambda in
-    // place of a generic lambda which is not available in C++11
-    //
-    handle_request(
-        state_->doc_root(),
-        parser_->release(),
-        send_lambda(*this));
 
-#endif
+    // Send the response
+    beast::async_write(
+        stream_, std::move(msg),
+        [self, keep_alive](beast::error_code ec, std::size_t bytes)
+        {
+            self->on_write(ec, bytes, keep_alive);
+        });
 }
 
 void
 http_session::
-on_write(beast::error_code ec, std::size_t, bool close)
+on_write(beast::error_code ec, std::size_t, bool keep_alive)
 {
     // Handle the error, if any
     if(ec)
         return fail(ec, "write");
 
-    if(close)
+    if(! keep_alive)
     {
         // This means we should close the connection, usually because
         // the response indicated the "Connection: close" semantic.