Add has_content_length_impl to Fields (API Change):

* The function has_content_length_impl is added to the
  requirements of Fields.

Actions Required:

* Implement has_content_length_impl for user-defined Fields

include/boost/beast/http/detail/type_traits.hpp

@@ -61,6 +61,7 @@ protected:
     string_view get_reason_impl() const;
     bool get_chunked_impl() const;
     bool get_keep_alive_impl(unsigned) const;
+    bool has_content_length_impl() const;
     void set_method_impl(string_view);
     void set_target_impl(string_view);
     void set_reason_impl(string_view);
@@ -134,54 +135,61 @@ struct is_fields_helper : T
 
     template<class U = is_fields_helper>
     static auto f6(int) -> decltype(
-        void(std::declval<U&>().set_method_impl(std::declval<string_view>())),
+        std::declval<bool&>() = std::declval<U const&>().has_content_length_impl(),
         std::true_type());
     static auto f6(...) -> std::false_type;
     using t6 = decltype(f6(0));
 
     template<class U = is_fields_helper>
     static auto f7(int) -> decltype(
-        void(std::declval<U&>().set_target_impl(std::declval<string_view>())),
+        void(std::declval<U&>().set_method_impl(std::declval<string_view>())),
         std::true_type());
     static auto f7(...) -> std::false_type;
     using t7 = decltype(f7(0));
 
     template<class U = is_fields_helper>
     static auto f8(int) -> decltype(
-        void(std::declval<U&>().set_reason_impl(std::declval<string_view>())),
+        void(std::declval<U&>().set_target_impl(std::declval<string_view>())),
         std::true_type());
     static auto f8(...) -> std::false_type;
     using t8 = decltype(f8(0));
 
     template<class U = is_fields_helper>
     static auto f9(int) -> decltype(
-        void(std::declval<U&>().set_chunked_impl(std::declval<bool>())),
+        void(std::declval<U&>().set_reason_impl(std::declval<string_view>())),
         std::true_type());
     static auto f9(...) -> std::false_type;
     using t9 = decltype(f9(0));
 
     template<class U = is_fields_helper>
     static auto f10(int) -> decltype(
-        void(std::declval<U&>().set_content_length_impl(
-            std::declval<boost::optional<std::uint64_t>>())),
+        void(std::declval<U&>().set_chunked_impl(std::declval<bool>())),
         std::true_type());
     static auto f10(...) -> std::false_type;
     using t10 = decltype(f10(0));
 
     template<class U = is_fields_helper>
     static auto f11(int) -> decltype(
+        void(std::declval<U&>().set_content_length_impl(
+            std::declval<boost::optional<std::uint64_t>>())),
+        std::true_type());
+    static auto f11(...) -> std::false_type;
+    using t11 = decltype(f11(0));
+
+    template<class U = is_fields_helper>
+    static auto f12(int) -> decltype(
         void(std::declval<U&>().set_keep_alive_impl(
             std::declval<unsigned>(),
             std::declval<bool>())),
         std::true_type());
-    static auto f11(...) -> std::false_type;
-    using t11 = decltype(f11(0));
+    static auto f12(...) -> std::false_type;
+    using t12 = decltype(f12(0));
 
     using type = std::integral_constant<bool,
          t1::value &&  t2::value && t3::value &&
          t4::value &&  t5::value && t6::value &&
          t7::value &&  t8::value && t9::value &&
-        t10::value && t11::value>;
+        t10::value && t11::value && t12::value>;
 };
 
 } // detail

include/boost/beast/http/fields.hpp

@@ -634,6 +634,11 @@ protected:
     bool
     get_keep_alive_impl(unsigned version) const;
 
+    /** Returns `true` if the Content-Length field is present.
+    */
+    bool
+    has_content_length_impl() const;
+
     /** Set or clear the method string.
 
         @note Only called for requests.

include/boost/beast/http/impl/fields.ipp

@@ -938,6 +938,14 @@ get_keep_alive_impl(unsigned version) const
         it->value()}.exists("close");
 }
 
+template<class Allocator>
+bool
+basic_fields<Allocator>::
+has_content_length_impl() const
+{
+    return count(field::content_length) > 0;
+}
+
 template<class Allocator>
 inline
 void

include/boost/beast/http/message.hpp

@@ -723,6 +723,18 @@ struct message
     void
     chunked(bool value);
 
+    /** Returns `true` if the Content-Length field is present.
+
+        This function inspects the fields and returns `true` if
+        the Content-Length field is present. The properties of the
+        body are not checked, this only looks for the field.
+    */
+    bool
+    has_content_length() const
+    {
+        return this->has_content_length_impl();
+    }
+
     /** Set or clear the Content-Length field
 
         This function adjusts the Content-Length field as follows: