New flat_stream example class:

fix #1108

The `flat_stream` is a stream wrapper designed to overcome a
performance limitation of the `boost::asio::ssl::stream`
implementation. Specifically, when writing buffer sequences having
length greater than one, the `ssl::stream` implementation does
not use scatter-gather I/O and instead performs a kernel transition
for every buffer in the sequence.

The wrapper addresses this problem by allocating memory and
presenting the buffer sequence into a single buffer, using
some logic to determine when this allocation is advantageous
versus simply passing the buffers through as-is.

See Also:
https://github.com/boostorg/asio/issues/100
https://stackoverflow.com/questions/50026167/performance-drop-on-port-from-beast-1-0-0-b66-to-boost-1-67-0-beast

test/example/common/CMakeLists.txt

@@ -16,13 +16,15 @@ GroupSources(test/example/common "/")
 add_executable (tests-example-common
     ${BOOST_BEAST_FILES}
     ${COMMON_FILES}
+    ${EXTRAS_FILES}
+    ${TEST_MAIN}
     Jamfile
     detect_ssl.cpp
+    flat_stream.cpp
     root_certificates.cpp
     server_certificate.cpp
     session_alloc.cpp
     ssl_stream.cpp
-    main.cpp
 )
 
 set_property(TARGET tests-example-common PROPERTY FOLDER "tests")

test/example/common/Jamfile

@@ -9,6 +9,7 @@
 
 local SOURCES =
     detect_ssl.cpp
+    flat_stream.cpp
     root_certificates.cpp
     server_certificate.cpp
     session_alloc.cpp

test/example/common/flat_stream.cpp

@@ -0,0 +1,109 @@
+//
+// Copyright (c) 2016-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+// Test that header file is self-contained.
+#include <example/common/flat_stream.hpp>
+
+#include <boost/beast/test/websocket.hpp>
+#include <boost/beast/test/yield_to.hpp>
+#include <boost/beast/unit_test/suite.hpp>
+#include <initializer_list>
+#include <vector>
+
+namespace boost {
+namespace beast {
+
+class flat_stream_test
+    : public unit_test::suite
+    , public test::enable_yield_to
+{
+public:
+    void
+    testSplit()
+    {
+        auto const check =
+            [&](
+                std::initializer_list<int> v0,
+                std::size_t limit,
+                unsigned long count,
+                bool copy)
+            {
+                std::vector<boost::asio::const_buffer> v;
+                v.reserve(v0.size());
+                for(auto const n : v0)
+                    v.emplace_back("", n);
+                auto const result =
+                    ::detail::flat_stream_base::coalesce(v, limit);
+                BEAST_EXPECT(result.first == count);
+                BEAST_EXPECT(result.second == copy);
+                return result;
+            };
+        check({},           1,    0, false);
+        check({1,2},        1,    1, false);
+        check({1,2},        2,    1, false);
+        check({1,2},        3,    3, true);
+        check({1,2},        4,    3, true);
+        check({1,2,3},      1,    1, false);
+        check({1,2,3},      2,    1, false);
+        check({1,2,3},      3,    3, true);
+        check({1,2,3},      4,    3, true);
+        check({1,2,3},      7,    6, true);
+        check({1,2,3,4},    3,    3, true);
+    }
+
+    void
+    testHttp()
+    {
+        pass();
+    }
+
+    void
+    testWebsocket()
+    {
+        {
+            error_code ec;
+            test::ws_echo_server es{log};
+            boost::asio::io_context ioc;
+            websocket::stream<flat_stream<test::stream>> ws{ioc};
+            ws.next_layer().next_layer().connect(es.stream());
+            ws.handshake("localhost", "/", ec);
+            BEAST_EXPECTS(! ec, ec.message());
+            ws.close({}, ec);
+            BEAST_EXPECTS(! ec, ec.message());
+        }
+        {
+            test::ws_echo_server es{log};
+            boost::asio::io_context ioc;
+            websocket::stream<flat_stream<test::stream>> ws{ioc};
+            ws.next_layer().next_layer().connect(es.stream());
+            ws.async_handshake("localhost", "/",
+                [&](error_code)
+                {
+                    ws.async_close({},
+                        [&](error_code)
+                        {
+                        });
+                });
+            ioc.run();
+        }
+    }
+
+    void
+    run() override
+    {
+        testSplit();
+        testHttp();
+        testWebsocket();
+    }
+};
+
+BEAST_DEFINE_TESTSUITE(beast,example,flat_stream);
+
+} // beast
+} // boost

test/example/common/main.cpp

@@ -1,12 +0,0 @@
-//
-// Copyright (c) 2016-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
-//
-// Distributed under the Boost Software License, Version 1.0. (See accompanying
-// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-//
-// Official repository: https://github.com/boostorg/beast
-//
-
-int main()
-{
-}