Don't use async_write_msg in examples

fix #746

example/http/server/flex/http_server_flex.cpp

@@ -15,7 +15,6 @@
 
 #include "example/common/detect_ssl.hpp"
 #include "example/common/server_certificate.hpp"
-#include "example/common/write_msg.hpp"
 
 #include <boost/beast/core.hpp>
 #include <boost/beast/http.hpp>
@@ -242,12 +241,20 @@ class session
         void
         operator()(http::message<isRequest, Body, Fields>&& msg) const
         {
-            // This function takes ownership of the message by moving
-            // it into a temporary buffer, otherwise we would have
-            // to manage the lifetime of the message and serializer.
-            async_write_msg(
+            // 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(),
-                std::move(msg),
+                *sp,
                 self_.strand_.wrap(std::bind(
                     &session::on_write,
                     self_.derived().shared_from_this(),
@@ -257,6 +264,7 @@ class session
 
     std::string const& doc_root_;
     http::request<http::string_body> req_;
+    std::shared_ptr<void> res_;
     send_lambda lambda_;
 
 protected:
@@ -318,6 +326,9 @@ public:
         if(ec)
             return fail(ec, "write");
 
+        // We're done with the response so delete it
+        res_ = nullptr;
+
         // Read another request
         do_read();
     }