Remove BodyReader::is_deferred (API Change):

The is_deferred nested type is removed from the BodyReader
requirements.

Performance for sending messages with `file_body` was cut
almost in half with is_deferred as `std::true_type` since
it caused double the number of socket writes. If the
deferred behavior is absolutely necessary, callers can get
the same effect by manually sending the headers first.

Actions Required:

* Callers who need the behavior of is_deferred as `std::true_type`
  should manually construct a serializer and serialize the header
  first, followed by the body.

test/exemplars.cpp

@@ -48,14 +48,6 @@ struct Body_BodyReader {
 struct BodyReader
 {
 public:
-    /** Controls when the implementation requests buffers.
-
-        If false, the implementation will request the first buffer
-        immediately and try to serialize both the header and some
-        or all of the body in a single buffer.
-    */
-    using is_deferred = std::false_type;
-
     /// The type of buffer returned by `get`.
     using const_buffers_type = boost::asio::const_buffers_1;
 

test/http/write.cpp

@@ -42,8 +42,6 @@ public:
             value_type const& body_;
 
         public:
-            using is_deferred = std::false_type;
-
             using const_buffers_type =
                 boost::asio::const_buffers_1;
 
@@ -67,7 +65,6 @@ public:
     };
 
     template<
-        bool isDeferred,
         bool isSplit,
         bool isFinalEmpty
     >
@@ -85,9 +82,6 @@ public:
             value_type const& body_;
 
         public:
-            using is_deferred =
-                std::integral_constant<bool, isDeferred>;
-
             using const_buffers_type =
                 boost::asio::const_buffers_1;
 
@@ -220,8 +214,6 @@ public:
             value_type const& body_;
 
         public:
-            using is_deferred = std::false_type;
-
             using const_buffers_type =
                 boost::asio::const_buffers_1;
 
@@ -844,14 +836,10 @@ public:
         yield_to(
             [&](yield_context yield)
             {
-                testWriteStream<test_body<false, false, false>>(yield);
-                testWriteStream<test_body<false, false,  true>>(yield);
-                testWriteStream<test_body<false,  true, false>>(yield);
-                testWriteStream<test_body<false,  true,  true>>(yield);
-                testWriteStream<test_body< true, false, false>>(yield);
-                testWriteStream<test_body< true, false,  true>>(yield);
-                testWriteStream<test_body< true,  true, false>>(yield);
-                testWriteStream<test_body< true,  true,  true>>(yield);
+                testWriteStream<test_body<false, false>>(yield);
+                testWriteStream<test_body<false,  true>>(yield);
+                testWriteStream<test_body< true, false>>(yield);
+                testWriteStream<test_body< true,  true>>(yield);
             });
     }
 };