Refactor header and message constructors:

fix #581

* request and response headers now have convenience
  constructors so important fields like method, target,
  result, and version may be set upon construction.

Actions Required:

* Evaluate each message constructor call site and
  adjust the constructor argument list as needed.

example/http-client/http_client.cpp

@@ -48,10 +48,7 @@ int main()
         return fail("connect", ec);
 
     // Set up an HTTP GET request message
-    http::request<http::string_body> req;
-    req.method(http::verb::get);
-    req.target("/");
-    req.version = 11;
+    http::request<http::string_body> req{http::verb::get, "/", 11};
     req.set(http::field::host, host + ":" +
         std::to_string(sock.remote_endpoint().port()));
     req.set(http::field::user_agent, BEAST_VERSION_STRING);

example/http-crawl/http_crawl.cpp

@@ -75,10 +75,7 @@ main(int, char const*[])
         }
 
         // Set up an HTTP GET request
-        http::request<http::string_body> req;
-        req.version = 11;
-        req.method(http::verb::get);
-        req.target("/");
+        http::request<http::string_body> req{http::verb::get, "/", 11};
         req.set(http::field::host, host + std::string(":") + std::to_string(ep.port()));
         req.set(http::field::user_agent, BEAST_VERSION_STRING);
 

example/http-server-threaded/http_server_threaded.cpp

@@ -60,8 +60,7 @@ private:
     http::response<http::string_view_body>
     client_error(http::status result, beast::string_view text)
     {
-        http::response<http::string_view_body> res;
-        res.result(result);
+        http::response<http::string_view_body> res{result, 11};
         res.set(http::field::server, BEAST_VERSION_STRING);
         res.set(http::field::content_type, "text/plain");
         res.set(http::field::connection, "close");
@@ -75,8 +74,7 @@ private:
     beast::http::response<beast::http::string_body>
     not_found() const
     {
-        beast::http::response<beast::http::string_body> res;
-        res.result(beast::http::status::not_found);
+        beast::http::response<beast::http::string_body> res{beast::http::status::not_found, 11};
         res.set(beast::http::field::server, BEAST_VERSION_STRING);
         res.set(beast::http::field::content_type, "text/html");
         res.set(http::field::connection, "close");
@@ -90,8 +88,7 @@ private:
     beast::http::response<beast::http::string_body>
     server_error(beast::error_code const& ec) const
     {
-        beast::http::response<beast::http::string_body> res;
-        res.result(beast::http::status::internal_server_error);
+        beast::http::response<beast::http::string_body> res{beast::http::status::internal_server_error, 11};
         res.set(beast::http::field::server, BEAST_VERSION_STRING);
         res.set(beast::http::field::content_type, "text/html");
         res.set(http::field::connection, "close");

example/server-framework/http_async_port.hpp

@@ -264,7 +264,7 @@ protected:
         // We construct the dynamic body with a 1MB limit
         // to prevent vulnerability to buffer attacks.
         //
-        parser_.emplace(1024 * 1024);
+        parser_.emplace(std::piecewise_construct, std::make_tuple(1024 * 1024));
 
         // Read just the header
         beast::http::async_read_header(

example/server-framework/http_sync_port.hpp

@@ -188,7 +188,8 @@ private:
             // We construct the dynamic body with a 1MB limit
             // to prevent vulnerability to buffer attacks.
             //
-            beast::http::request_parser<beast::http::dynamic_body> parser(1024* 1024);
+            beast::http::request_parser<beast::http::dynamic_body> parser(
+                std::piecewise_construct, std::make_tuple(1024* 1024));
 
             // Read the header first
             beast::http::read_header(impl().stream(), buffer_, parser, ec);