diff --git a/CHANGELOG.md b/CHANGELOG.md
index ed253bc0..1f8c7572 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@ API Changes:
 
 * Remove header_parser
 * Add verb to on_request for parsers
+* Refactor prepare
 
 --------------------------------------------------------------------------------
 
diff --git a/doc/4_02_message.qbk b/doc/4_02_message.qbk
index c8ddd429..4bcb1a26 100644
--- a/doc/4_02_message.qbk
+++ b/doc/4_02_message.qbk
@@ -154,7 +154,7 @@ objects:
 ```
 ][
 ```
-    200 OK HTTP/1.1\r\n
+    HTTP/1.1 200 OK\r\n
     Server: Beast\r\n
     Content-Length: 13\r\n
     \r\n
diff --git a/doc/quickref.xml b/doc/quickref.xml
index 3a290303..9d70480f 100644
--- a/doc/quickref.xml
+++ b/doc/quickref.xml
@@ -62,7 +62,6 @@
             <member><link linkend="beast.ref.http__make_serializer">make_serializer</link></member>
             <member><link linkend="beast.ref.http__obsolete_reason">obsolete_reason</link></member>
             <member><link linkend="beast.ref.http__operator_ls_">operator&lt;&lt;</link></member>
-            <member><link linkend="beast.ref.http__prepare">prepare</link></member>
             <member><link linkend="beast.ref.http__read">read</link></member>
             <member><link linkend="beast.ref.http__read_header">read_header</link></member>
             <member><link linkend="beast.ref.http__read_some">read_some</link></member>
diff --git a/examples/doc_http_samples.hpp b/examples/doc_http_samples.hpp
index af6c9315..c319cf3e 100644
--- a/examples/doc_http_samples.hpp
+++ b/examples/doc_http_samples.hpp
@@ -449,9 +449,10 @@ do_head_request(
     @param transform The header transformation to apply. The function will
     be called with this signature:
     @code
-        void transform(
-            header<isRequest, Fields>&,     // The header to transform
-            error_code&);                   // Set to the error, if any
+        template<class Body>
+        void transform(message<
+            isRequest, Body, Fields>&,  // The message to transform
+            error_code&);               // Set to the error, if any
     @endcode
 
     @param ec Set to the error if any occurred.
@@ -496,8 +497,7 @@ relay(
         return;
 
     // Apply the caller's header tranformation
-    // base() returns a reference to the header portion of the message.
-    transform(p.get().base(), ec);
+    transform(p.get(), ec);
     if(ec)
         return;
 
diff --git a/examples/file_body.hpp b/examples/file_body.hpp
index c130a03a..7a9d7eb5 100644
--- a/examples/file_body.hpp
+++ b/examples/file_body.hpp
@@ -24,6 +24,16 @@ struct file_body
 {
     using value_type = std::string;
 
+    /// Returns the content length of the body in a message.
+    template<bool isRequest, class Fields>
+    static
+    std::uint64_t
+    size(
+        message<isRequest, file_body, Fields> const& m)
+    {
+        return boost::filesystem::file_size(m.body.c_str());
+    }
+
     class reader
     {
         std::uint64_t size_ = 0;
@@ -67,12 +77,6 @@ struct file_body
                 size_ = boost::filesystem::file_size(path_);
         }
 
-        std::uint64_t
-        content_length() const
-        {
-            return size_;
-        }
-
         boost::optional<std::pair<const_buffers_type, bool>>
         get(error_code& ec)
         {
diff --git a/examples/http_async_server.hpp b/examples/http_async_server.hpp
index a1af3133..ac29b129 100644
--- a/examples/http_async_server.hpp
+++ b/examples/http_async_server.hpp
@@ -239,7 +239,7 @@ private:
                 res.insert("Server", "http_async_server");
                 res.insert("Content-Type", "text/html");
                 res.body = "The file '" + path + "' was not found";
-                prepare(res);
+                res.prepare();
                 async_write(sock_, std::move(res),
                     std::bind(&peer::on_write, shared_from_this(),
                         std::placeholders::_1));
@@ -253,7 +253,7 @@ private:
                 res.insert("Server", "http_async_server");
                 res.insert("Content-Type", mime_type(path));
                 res.body = path;
-                prepare(res);
+                res.prepare();
                 async_write(sock_, std::move(res),
                     std::bind(&peer::on_write, shared_from_this(),
                         std::placeholders::_1));
@@ -267,7 +267,7 @@ private:
                 res.insert("Content-Type", "text/html");
                 res.body =
                     std::string{"An internal error occurred"} + e.what();
-                prepare(res);
+                res.prepare();
                 async_write(sock_, std::move(res),
                     std::bind(&peer::on_write, shared_from_this(),
                         std::placeholders::_1));
diff --git a/examples/http_crawl.cpp b/examples/http_crawl.cpp
index 85fa39b8..0df6884b 100644
--- a/examples/http_crawl.cpp
+++ b/examples/http_crawl.cpp
@@ -38,12 +38,12 @@ int main(int, char const*[])
             auto ep = sock.remote_endpoint();
             request<string_body> req;
             req.method(verb::get);
-            req.target("/");
             req.version = 11;
+            req.target("/");
             req.insert("Host", host + std::string(":") +
                 boost::lexical_cast<std::string>(ep.port()));
             req.insert("User-Agent", "beast/http");
-            prepare(req);
+            req.prepare();
             write(sock, req);
             response<string_body> res;
             beast::multi_buffer b;
diff --git a/examples/http_example.cpp b/examples/http_example.cpp
index 4be99e3d..a190bd7a 100644
--- a/examples/http_example.cpp
+++ b/examples/http_example.cpp
@@ -32,7 +32,7 @@ int main()
     req.replace("Host", host + ":" +
         boost::lexical_cast<std::string>(sock.remote_endpoint().port()));
     req.replace("User-Agent", "Beast");
-    beast::http::prepare(req);
+    req.prepare();
     beast::http::write(sock, req);
 
     // Receive and print HTTP response using beast
diff --git a/examples/http_sync_server.hpp b/examples/http_sync_server.hpp
index 7c175f0a..98f8bfaa 100644
--- a/examples/http_sync_server.hpp
+++ b/examples/http_sync_server.hpp
@@ -169,7 +169,7 @@ private:
                 res.insert("Server", "http_sync_server");
                 res.insert("Content-Type", "text/html");
                 res.body = "The file '" + path + "' was not found";
-                prepare(res);
+                res.prepare();
                 write(sock, res, ec);
                 if(ec)
                     break;
@@ -184,7 +184,7 @@ private:
                 res.insert("Server", "http_sync_server");
                 res.insert("Content-Type", mime_type(path));
                 res.body = path;
-                prepare(res);
+                res.prepare();
                 write(sock, res, ec);
                 if(ec)
                     break;
@@ -199,7 +199,7 @@ private:
                 res.insert("Content-Type", "text/html");
                 res.body =
                     std::string{"An internal error occurred: "} + e.what();
-                prepare(res);
+                res.prepare();
                 write(sock, res, ec);
                 if(ec)
                     break;
diff --git a/examples/ssl/http_ssl_example.cpp b/examples/ssl/http_ssl_example.cpp
index 0dc40d0f..9a3749c4 100644
--- a/examples/ssl/http_ssl_example.cpp
+++ b/examples/ssl/http_ssl_example.cpp
@@ -41,7 +41,7 @@ int main()
     req.insert("Host", host + ":" +
         boost::lexical_cast<std::string>(sock.remote_endpoint().port()));
     req.insert("User-Agent", "Beast");
-    beast::http::prepare(req);
+    req.prepare();
     beast::http::write(stream, req);
 
     // Receive and print HTTP response using Beast
diff --git a/include/beast/http.hpp b/include/beast/http.hpp
index 87c92258..6f6063c5 100644
--- a/include/beast/http.hpp
+++ b/include/beast/http.hpp
@@ -12,9 +12,11 @@
 
 #include <beast/http/basic_parser.hpp>
 #include <beast/http/buffer_body.hpp>
+#include <beast/http/connection.hpp>
 #include <beast/http/dynamic_body.hpp>
 #include <beast/http/empty_body.hpp>
 #include <beast/http/error.hpp>
+#include <beast/http/field.hpp>
 #include <beast/http/fields.hpp>
 #include <beast/http/message.hpp>
 #include <beast/http/parser.hpp>
diff --git a/include/beast/http/connection.hpp b/include/beast/http/connection.hpp
new file mode 100644
index 00000000..68a9e291
--- /dev/null
+++ b/include/beast/http/connection.hpp
@@ -0,0 +1,88 @@
+//
+// Copyright (c) 2013-2017 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)
+//
+
+#ifndef BEAST_HTTP_CONNECTION_HPP
+#define BEAST_HTTP_CONNECTION_HPP
+
+#include <beast/config.hpp>
+
+namespace beast {
+namespace http {
+
+/// The type of @ref connection::close
+struct close_t {};
+
+/// The type of @ref connection::upgrade
+struct upgrade_t {};
+
+/// The type of @ref connection::keep_alive
+struct keep_alive_t {};
+
+namespace detail {
+
+template<class = void>
+struct connection_impl
+{
+    static close_t constexpr close{};
+    static keep_alive_t constexpr keep_alive{};
+    static upgrade_t constexpr upgrade{};
+};
+
+template<class _>
+constexpr
+close_t
+connection_impl<_>::close;
+
+template<class _>
+constexpr
+keep_alive_t
+connection_impl<_>::keep_alive;
+
+template<class _>
+constexpr
+upgrade_t
+connection_impl<_>::upgrade;
+
+} // detail
+
+/** HTTP/1 Connection prepare options.
+
+    Each value is an individual settings, they can be combined.
+    
+    @par Example
+    @code
+    request<empty_body> req;
+    req.version = 11;
+    req.method(verb::upgrade);
+    req.target("/");
+    req.insert("User-Agent", "Beast");
+    req.prepare(connection::close, connection::upgrade);
+    @endcode
+
+    @note These values are used with @ref message::prepare.
+*/
+struct connection
+#if ! BEAST_DOXYGEN
+    : detail::connection_impl<>
+#endif
+{
+#if BEAST_DOXYGEN
+    /// Specify connection close semantics.
+    static close_t constexpr close;
+
+    /// Specify connection keep-alive semantics.
+    static keep_alive_t constexpr keep_alive;
+
+    /// Specify Connection: upgrade.
+    static upgrade_t constexpr upgrade;
+#endif
+};
+
+} // http
+} // beast
+
+#endif
diff --git a/include/beast/http/detail/type_traits.hpp b/include/beast/http/detail/type_traits.hpp
index 6c9b62cc..4479f2ae 100644
--- a/include/beast/http/detail/type_traits.hpp
+++ b/include/beast/http/detail/type_traits.hpp
@@ -59,19 +59,21 @@ struct has_value_type<T, beast::detail::void_t<
     typename T::value_type
         > > : std::true_type {};
 
-template<class T, class = beast::detail::void_t<>>
-struct has_content_length : std::false_type {};
+/** Determine if a @b Body type has a size
 
-template<class T>
-struct has_content_length<T, beast::detail::void_t<decltype(
-    std::declval<T>().content_length()
-        )> > : std::true_type
-{
-    static_assert(std::is_convertible<
-        decltype(std::declval<T>().content_length()),
-            std::uint64_t>::value,
-        "Writer::content_length requirements not met");
-};
+    This metafunction is equivalent to `std::true_type` if
+    Body contains a static member function called `content_lengeth`.
+*/
+template<class T, class M, class = void>
+struct is_body_sized : std::false_type {};
+
+template<class T, class M>
+struct is_body_sized<T, M, beast::detail::void_t<
+    typename T::value_type,
+        decltype(
+    std::declval<std::uint64_t&>() =
+        T::size(std::declval<M const&>()),
+    (void)0)>> : std::true_type {};
 
 } // detail
 } // http
diff --git a/include/beast/http/dynamic_body.hpp b/include/beast/http/dynamic_body.hpp
index 09f38ab9..ffaddebb 100644
--- a/include/beast/http/dynamic_body.hpp
+++ b/include/beast/http/dynamic_body.hpp
@@ -28,6 +28,16 @@ struct basic_dynamic_body
     /// The type of the body member when used in a message.
     using value_type = DynamicBuffer;
 
+    /// Returns the content length of this body in a message.
+    template<bool isRequest, class Fields>
+    static
+    std::uint64_t
+    size(message<isRequest,
+        basic_dynamic_body, Fields> const& m)
+    {
+        return m.body.size();
+    }
+
 #if BEAST_DOXYGEN
     /// The algorithm to obtain buffers representing the body
     using reader = implementation_defined;
@@ -55,12 +65,6 @@ struct basic_dynamic_body
         {
         }
 
-        std::uint64_t
-        content_length() const
-        {
-            return body_.size();
-        }
-
         boost::optional<std::pair<const_buffers_type, bool>>
         get(error_code& ec)
         {
diff --git a/include/beast/http/empty_body.hpp b/include/beast/http/empty_body.hpp
index 71c1bf72..60575b17 100644
--- a/include/beast/http/empty_body.hpp
+++ b/include/beast/http/empty_body.hpp
@@ -35,6 +35,15 @@ struct empty_body
         //        for the content length here, set on init()
     };
 
+    /// Returns the content length of the body in a message.
+    template<bool isRequest, class Fields>
+    static
+    std::uint64_t
+    size(message<isRequest, empty_body, Fields> const& m)
+    {
+        return 0;
+    }
+
 #if BEAST_DOXYGEN
     /// The algorithm to obtain buffers representing the body
     using reader = implementation_defined;
@@ -58,12 +67,6 @@ struct empty_body
         {
         }
 
-        std::uint64_t
-        content_length() const
-        {
-            return 0;
-        }
-
         boost::optional<std::pair<const_buffers_type, bool>>
         get(error_code& ec)
         {
diff --git a/include/beast/http/fields.hpp b/include/beast/http/fields.hpp
index 0eb52850..ee55df27 100644
--- a/include/beast/http/fields.hpp
+++ b/include/beast/http/fields.hpp
@@ -11,6 +11,7 @@
 #include <beast/config.hpp>
 #include <beast/core/string_view.hpp>
 #include <beast/core/detail/ci_char_traits.hpp>
+#include <beast/http/connection.hpp>
 #include <boost/lexical_cast.hpp>
 #include <boost/intrusive/list.hpp>
 #include <boost/intrusive/set.hpp>
@@ -276,6 +277,11 @@ protected:
     void method_impl(string_view s);
     void target_impl(string_view s);
     void reason_impl(string_view s);
+    void content_length_impl(std::uint64_t n);
+    void connection_impl(close_t);
+    void connection_impl(keep_alive_t);
+    void connection_impl(upgrade_t);
+    void chunked_impl();
 
 private:
     struct element
diff --git a/include/beast/http/impl/fields.ipp b/include/beast/http/impl/fields.ipp
index 703f0ed3..267773b4 100644
--- a/include/beast/http/impl/fields.ipp
+++ b/include/beast/http/impl/fields.ipp
@@ -8,6 +8,7 @@
 #ifndef BEAST_HTTP_IMPL_FIELDS_IPP
 #define BEAST_HTTP_IMPL_FIELDS_IPP
 
+#include <beast/core/static_string.hpp>
 #include <beast/http/detail/rfc7230.hpp>
 #include <boost/throw_exception.hpp>
 #include <algorithm>
@@ -74,7 +75,7 @@ target_impl(string_view s)
     if(s.empty())
         this->erase(":target");
     else
-        return this->replace(":target", s);
+        this->replace(":target", s);
 }
 
 template<class Allocator>
@@ -89,6 +90,73 @@ reason_impl(string_view s)
         this->replace(":reason", s);
 }
 
+template<class Allocator>
+inline
+void
+basic_fields<Allocator>::
+content_length_impl(std::uint64_t n)
+{
+    this->erase("Content-Length");
+    this->insert("Content-Length",
+        to_static_string(n));
+}
+
+template<class Allocator>
+inline
+void
+basic_fields<Allocator>::
+connection_impl(close_t)
+{
+    auto it = find("Connection");
+    if(it == end())
+        this->insert("Connection", "close");
+    else
+        this->replace("Connection",
+            it->value().to_string() + ", close");
+}
+
+template<class Allocator>
+inline
+void
+basic_fields<Allocator>::
+connection_impl(keep_alive_t)
+{
+    auto it = find("Connection");
+    if(it == end())
+        this->insert("Connection", "keep-alive");
+    else
+        this->replace("Connection",
+            it->value().to_string() + ", keep-alive");
+}
+
+template<class Allocator>
+inline
+void
+basic_fields<Allocator>::
+connection_impl(upgrade_t)
+{
+    auto it = find("Connection");
+    if(it == end())
+        this->insert("Connection", "upgrade");
+    else
+        this->replace("Connection",
+            it->value().to_string() + ", upgrade");
+}
+
+template<class Allocator>
+inline
+void
+basic_fields<Allocator>::
+chunked_impl()
+{
+    auto it = find("Transfer-Encoding");
+    if(it == end())
+        this->insert("Transfer-Encoding", "chunked");
+    else
+        this->replace("Transfer-Encoding",
+            it->value().to_string() + ", chunked");
+}
+
 //------------------------------------------------------------------------------
 
 template<class Allocator>
diff --git a/include/beast/http/impl/message.ipp b/include/beast/http/impl/message.ipp
index 0710dd16..12600c50 100644
--- a/include/beast/http/impl/message.ipp
+++ b/include/beast/http/impl/message.ipp
@@ -9,14 +9,10 @@
 #define BEAST_HTTP_IMPL_MESSAGE_IPP
 
 #include <beast/core/error.hpp>
-#include <beast/core/string_view.hpp>
-#include <beast/http/type_traits.hpp>
 #include <beast/http/rfc7230.hpp>
 #include <beast/core/detail/ci_char_traits.hpp>
 #include <beast/core/detail/type_traits.hpp>
 #include <boost/assert.hpp>
-#include <boost/optional.hpp>
-#include <boost/throw_exception.hpp>
 #include <stdexcept>
 
 namespace beast {
@@ -71,6 +67,170 @@ get_reason() const
     return obsolete_reason(result_);
 }
 
+//------------------------------------------------------------------------------
+
+namespace detail {
+
+} // detail
+
+template<bool isRequest, class Body, class Fields>
+bool
+message<isRequest, Body, Fields>::
+chunked() const
+{
+    auto const it0 = this->find("Transfer-Encoding");
+    if(it0 == this->end())
+        return false;
+    token_list value{*it0};
+    for(auto it = value.begin(); it != value.end();)
+    {
+        auto cur = it++;
+        if(it == value.end())
+            return *cur == "chunked";
+    }
+    return false;
+}
+
+template<bool isRequest, class Body, class Fields>
+boost::optional<std::uint64_t>
+message<isRequest, Body, Fields>::
+size() const
+{
+    static_assert(is_body_reader<Body>::value,
+        "BodyReader requirements not met");
+
+    return size(detail::is_body_sized<
+        Body, decltype(*this)>{});
+}
+
+template<bool isRequest, class Body, class Fields>
+template<class... Args>
+void
+message<isRequest, Body, Fields>::
+prepare(Args const&... args)
+{
+    static_assert(is_body_reader<Body>::value,
+        "BodyReader requirements not met");
+
+    unsigned f = 0;
+    prepare_opt(f, args...);
+
+    if(f & 1)
+    {
+        if(this->version > 10)
+            this->connection_impl(connection::close);
+    }
+
+    if(f & 2)
+    {
+        if(this->version < 11)
+            this->connection_impl(connection::keep_alive);
+    }
+
+    if(f & 4)
+    {
+        if(this->version < 11)
+            BOOST_THROW_EXCEPTION(std::invalid_argument{
+                "invalid connection upgrade"});
+        this->connection_impl(connection::upgrade);
+    }
+
+    prepare_payload(typename header<
+        isRequest, Fields>::is_request{});
+}
+
+template<bool isRequest, class Body, class Fields>
+template<class Arg, class... Args>
+inline
+void
+message<isRequest, Body, Fields>::
+prepare_opt(unsigned& f,
+    Arg const& arg, Args const&... args)
+{
+    prepare_opt(f, arg);
+    prepare_opt(f, args...);
+}
+
+template<bool isRequest, class Body, class Fields>
+inline
+void
+message<isRequest, Body, Fields>::
+prepare_opt(unsigned& f, close_t)
+{
+    f |= 1;
+}
+
+template<bool isRequest, class Body, class Fields>
+inline
+void
+message<isRequest, Body, Fields>::
+prepare_opt(unsigned& f, keep_alive_t)
+{
+    f |= 2;
+}
+
+template<bool isRequest, class Body, class Fields>
+inline
+void
+message<isRequest, Body, Fields>::
+prepare_opt(unsigned& f, upgrade_t)
+{
+    f |= 4;
+}
+
+template<bool isRequest, class Body, class Fields>
+inline
+void
+message<isRequest, Body, Fields>::
+prepare_payload(std::true_type)
+{
+    auto const n = size();
+    if(this->method_ == verb::trace &&
+            (! n || *n > 0))
+        BOOST_THROW_EXCEPTION(std::invalid_argument{
+            "invalid request body"});
+    if(n)
+    {
+        if(*n > 0 ||
+            this->method_ == verb::options ||
+            this->method_ == verb::put ||
+            this->method_ == verb::post
+            )
+        {
+            this->content_length_impl(*n);
+        }
+    }
+    else if(this->version >= 11)
+    {
+        this->chunked_impl();
+    }
+}
+
+template<bool isRequest, class Body, class Fields>
+inline
+void
+message<isRequest, Body, Fields>::
+prepare_payload(std::false_type)
+{
+    auto const n = size();
+    if((status_class(this->result_) ==
+            status_class::informational ||
+        this->result_ == status::no_content ||
+        this->result_ == status::not_modified))
+    {
+        if(! n || *n > 0)
+            // The response body MUST BE empty for this case
+            BOOST_THROW_EXCEPTION(std::invalid_argument{
+                "invalid response body"});
+    }
+    if(n)
+        this->content_length_impl(*n);
+    else if(this->version >= 11)
+        this->chunked_impl();
+}
+
+//------------------------------------------------------------------------------
+
 template<class Fields>
 void
 swap(
@@ -106,7 +266,9 @@ swap(
     message<isRequest, Body, Fields>& m2)
 {
     using std::swap;
-    swap(m1.base(), m2.base());
+    swap(
+        static_cast<header<isRequest, Fields>&>(m1),
+        static_cast<header<isRequest, Fields>&>(m2));
     swap(m1.body, m2.body);
 }
 
@@ -138,176 +300,6 @@ is_upgrade(header<isRequest, Fields> const& msg)
     return false;
 }
 
-namespace detail {
-
-struct prepare_info
-{
-    boost::optional<connection> connection_value;
-    boost::optional<std::uint64_t> content_length;
-};
-
-template<bool isRequest, class Body, class Fields>
-inline
-void
-prepare_options(prepare_info& pi,
-    message<isRequest, Body, Fields>& msg)
-{
-    beast::detail::ignore_unused(pi, msg);
-}
-
-template<bool isRequest, class Body, class Fields>
-void
-prepare_option(prepare_info& pi,
-    message<isRequest, Body, Fields>& msg,
-        connection value)
-{
-    beast::detail::ignore_unused(msg);
-    pi.connection_value = value;
-}
-
-template<
-    bool isRequest, class Body, class Fields,
-    class Opt, class... Opts>
-void
-prepare_options(prepare_info& pi,
-    message<isRequest, Body, Fields>& msg,
-        Opt&& opt, Opts&&... opts)
-{
-    prepare_option(pi, msg, opt);
-    prepare_options(pi, msg,
-        std::forward<Opts>(opts)...);
-}
-
-template<bool isRequest, class Body, class Fields>
-void
-prepare_content_length(prepare_info& pi,
-    message<isRequest, Body, Fields> const& msg,
-        std::true_type)
-{
-    typename Body::reader w{msg};
-    // VFALCO This is a design problem!
-    error_code ec;
-    w.init(ec);
-    if(ec)
-        BOOST_THROW_EXCEPTION(system_error{ec});
-    pi.content_length = w.content_length();
-}
-
-template<bool isRequest, class Body, class Fields>
-void
-prepare_content_length(prepare_info& pi,
-    message<isRequest, Body, Fields> const& msg,
-        std::false_type)
-{
-    beast::detail::ignore_unused(msg);
-    pi.content_length = boost::none;
-}
-
-} // detail
-
-template<
-    bool isRequest, class Body, class Fields,
-    class... Options>
-void
-prepare(message<isRequest, Body, Fields>& msg,
-    Options&&... options)
-{
-    // VFALCO TODO
-    static_assert(is_body<Body>::value,
-        "Body requirements not met");
-    static_assert(is_body_reader<Body>::value,
-        "BodyReader requirements not met");
-    detail::prepare_info pi;
-    detail::prepare_content_length(pi, msg,
-        detail::has_content_length<typename Body::reader>{});
-    detail::prepare_options(pi, msg,
-        std::forward<Options>(options)...);
-
-    if(msg.exists("Connection"))
-        BOOST_THROW_EXCEPTION(std::invalid_argument{
-            "prepare called with Connection field set"});
-
-    if(msg.exists("Content-Length"))
-        BOOST_THROW_EXCEPTION(std::invalid_argument{
-            "prepare called with Content-Length field set"});
-
-    if(token_list{msg["Transfer-Encoding"]}.exists("chunked"))
-        BOOST_THROW_EXCEPTION(std::invalid_argument{
-            "prepare called with Transfer-Encoding: chunked set"});
-
-    if(pi.connection_value != connection::upgrade)
-    {
-        if(pi.content_length)
-        {
-            struct set_field
-            {
-                void
-                operator()(message<true, Body, Fields>& msg,
-                    detail::prepare_info const& pi) const
-                {
-                    using beast::detail::ci_equal;
-                    if(*pi.content_length > 0 ||
-                        msg.method() == verb::post)
-                    {
-                        msg.insert(
-                            "Content-Length", *pi.content_length);
-                    }
-                }
-
-                void
-                operator()(message<false, Body, Fields>& msg,
-                    detail::prepare_info const& pi) const
-                {
-                    if(to_status_class(msg.result()) != status_class::informational &&
-                        msg.result() != status::no_content &&
-                        msg.result() != status::not_modified)
-                    {
-                        msg.insert(
-                            "Content-Length", *pi.content_length);
-                    }
-                }
-            };
-            set_field{}(msg, pi);
-        }
-        else if(msg.version >= 11)
-        {
-            msg.insert("Transfer-Encoding", "chunked");
-        }
-    }
-
-    auto const content_length =
-        msg.exists("Content-Length");
-
-    if(pi.connection_value)
-    {
-        switch(*pi.connection_value)
-        {
-        case connection::upgrade:
-            msg.insert("Connection", "upgrade");
-            break;
-
-        case connection::keep_alive:
-            if(msg.version < 11)
-            {
-                if(content_length)
-                    msg.insert("Connection", "keep-alive");
-            }
-            break;
-
-        case connection::close:
-            if(msg.version >= 11)
-                msg.insert("Connection", "close");
-            break;
-        }
-    }
-
-    // rfc7230 6.7.
-    if(msg.version < 11 && token_list{
-            msg["Connection"]}.exists("upgrade"))
-        BOOST_THROW_EXCEPTION(std::invalid_argument{
-            "invalid version for Connection: upgrade"});
-}
-
 } // http
 } // beast
 
diff --git a/include/beast/http/impl/parser.ipp b/include/beast/http/impl/parser.ipp
index 90f4abbc..ca14e493 100644
--- a/include/beast/http/impl/parser.ipp
+++ b/include/beast/http/impl/parser.ipp
@@ -29,8 +29,7 @@ parser<isRequest, Body, Fields>::
 parser(parser<isRequest, OtherBody, Fields>&& parser,
         Args&&... args)
     : base_type(std::move(parser))
-    , m_(parser.release().base(),
-        std::forward<Args>(args)...)
+    , m_(parser.release(), std::forward<Args>(args)...)
 {
     if(parser.wr_)
         BOOST_THROW_EXCEPTION(std::invalid_argument{
diff --git a/include/beast/http/message.hpp b/include/beast/http/message.hpp
index 33f02bc0..b94f8b38 100644
--- a/include/beast/http/message.hpp
+++ b/include/beast/http/message.hpp
@@ -9,11 +9,14 @@
 #define BEAST_HTTP_MESSAGE_HPP
 
 #include <beast/config.hpp>
+#include <beast/http/connection.hpp>
 #include <beast/http/fields.hpp>
 #include <beast/http/verb.hpp>
 #include <beast/http/status.hpp>
+#include <beast/http/type_traits.hpp>
 #include <beast/core/string_view.hpp>
 #include <beast/core/detail/integer_sequence.hpp>
+#include <boost/optional.hpp>
 #include <boost/throw_exception.hpp>
 #include <memory>
 #include <stdexcept>
@@ -49,12 +52,7 @@ struct header<true, Fields> : Fields
 #endif
 {
     /// Indicates if the header is a request or response.
-#if BEAST_DOXYGEN
-    static bool constexpr is_request = isRequest;
-
-#else
-    static bool constexpr is_request = true;
-#endif
+    using is_request = std::true_type;
 
     /// The type representing the fields.
     using fields_type = Fields;
@@ -194,6 +192,9 @@ struct header<true, Fields> : Fields
     }
 
 private:
+    template<bool, class, class>
+    friend struct message;
+
     template<class T>
     friend
     void
@@ -230,7 +231,7 @@ template<class Fields>
 struct header<false, Fields> : Fields
 {
     /// Indicates if the header is a request or response.
-    static bool constexpr is_request = false;
+    using is_request = std::false_type;
 
     /// The type representing the fields.
     using fields_type = Fields;
@@ -377,6 +378,9 @@ struct header<false, Fields> : Fields
     }
    
 private:
+    template<bool, class, class>
+    friend struct message;
+
     template<class T>
     friend
     void
@@ -412,7 +416,7 @@ template<bool isRequest, class Body, class Fields = fields>
 struct message : header<isRequest, Fields>
 {
     /// The base class used to hold the header portion of the message.
-    using base_type = header<isRequest, Fields>;
+    using header_type = header<isRequest, Fields>;
 
     /** The type providing the body traits.
 
@@ -445,8 +449,8 @@ struct message : header<isRequest, Fields>
     */
     template<class... Args>
     explicit
-    message(base_type&& base, Args&&... args)
-        : base_type(std::move(base))
+    message(header_type&& base, Args&&... args)
+        : header_type(std::move(base))
         , body(std::forward<Args>(args)...)
     {
     }
@@ -458,8 +462,8 @@ struct message : header<isRequest, Fields>
     */
     template<class... Args>
     explicit
-    message(base_type const& base, Args&&... args)
-        : base_type(base)
+    message(header_type const& base, Args&&... args)
+        : header_type(base)
         , body(std::forward<Args>(args)...)
     {
     }
@@ -469,13 +473,13 @@ struct message : header<isRequest, Fields>
         @param u An argument forwarded to the body constructor.
 
         @note This constructor participates in overload resolution
-        only if `u` is not convertible to `base_type`.
+        only if `u` is not convertible to `header_type`.
     */
     template<class U
 #if ! BEAST_DOXYGEN
         , class = typename std::enable_if<
             ! std::is_convertible<typename
-                std::decay<U>::type, base_type>::value>::type
+                std::decay<U>::type, header_type>::value>::type
 #endif
     >
     explicit
@@ -491,16 +495,16 @@ struct message : header<isRequest, Fields>
         @param v An argument forwarded to the fields constructor.
 
         @note This constructor participates in overload resolution
-        only if `u` is not convertible to `base_type`.
+        only if `u` is not convertible to `header_type`.
     */
     template<class U, class V
 #if ! BEAST_DOXYGEN
         ,class = typename std::enable_if<! std::is_convertible<
-            typename std::decay<U>::type, base_type>::value>::type
+            typename std::decay<U>::type, header_type>::value>::type
 #endif
     >
     message(U&& u, V&& v)
-        : base_type(std::forward<V>(v))
+        : header_type(std::forward<V>(v))
         , body(std::forward<U>(u))
     {
     }
@@ -531,24 +535,71 @@ struct message : header<isRequest, Fields>
     {
     }
 
-    /// Returns the header portion of the message
-    base_type&
-    base()
-    {
-        return *this;
-    }
+    /** Returns `true` if Transfer-Encoding is present, and chunked appears last.
+    */
+    bool
+    chunked() const;
 
-    /// Returns the header portion of the message
-    base_type const&
-    base() const
-    {
-        return *this;
-    }
+    /** Returns the payload size of the body in octets if possible.
+
+        This function invokes the @b Body algorithm to measure
+        the number of octets in the serialized body container. If
+        there is no body, this will return zero. Otherwise, if the
+        body exists but is not known ahead of time, `boost::none`
+        is returned (usually indicating that a chunked Transfer-Encoding
+        will be used).
+
+        @note The value of the Content-Length field in the message
+        is not inspected.
+    */
+    boost::optional<std::uint64_t>
+    size() const;
+
+    /** Set the Content-Length field.
+
+        The value of the Content-Length field will be unconditionally
+        set to the specified number of octets.
+    */
+    void
+    content_length(std::uint64_t n);
+
+    /** Prepare some fields automatically.
+
+        This function will adjust the Connection, Content-Length
+        and Transfer-Encoding, fields of the message based on the
+        properties of the body and the options passed in.
+
+        @par Example
+        @code
+        request<empty_body> req;
+        req.version = 11;
+        req.method(verb::upgrade);
+        req.target("/");
+        req.insert("User-Agent", "Beast");
+        req.prepare(connection::close, connection::upgrade);
+        @endcode
+
+        @param args An list of zero or more options to use.
+
+        @throw std::invalid_argument if the values of certain
+        fields detectably violate the semantic requirements of HTTP.
+
+        @note Undefined behavior if called more than once.
+
+        @see @ref connection
+    */
+    template<class... Args>
+    void
+    prepare(Args const&... args);
 
 private:
+    static_assert(is_body<Body>::value,
+        "Body requirements not met");
+
     template<class... Un, size_t... IUn>
     message(std::piecewise_construct_t,
-            std::tuple<Un...>& tu, beast::detail::index_sequence<IUn...>)
+        std::tuple<Un...>& tu,
+            beast::detail::index_sequence<IUn...>)
         : body(std::forward<Un>(std::get<IUn>(tu))...)
     {
     }
@@ -559,10 +610,46 @@ private:
             std::tuple<Un...>& tu, std::tuple<Vn...>& tv,
                 beast::detail::index_sequence<IUn...>,
                     beast::detail::index_sequence<IVn...>)
-        : base_type(std::forward<Vn>(std::get<IVn>(tv))...)
+        : header_type(std::forward<Vn>(std::get<IVn>(tv))...)
         , body(std::forward<Un>(std::get<IUn>(tu))...)
     {
     }
+
+    boost::optional<std::uint64_t>
+    size(std::true_type) const
+    {
+        return Body::size(*this);
+    }
+
+    boost::optional<std::uint64_t>
+    size(std::false_type) const
+    {
+        return boost::none;
+    }
+
+    template<class Arg, class... Args>
+    void
+    prepare_opt(unsigned&, Arg const&, Args const&...);
+
+    void
+    prepare_opt(unsigned&)
+    {
+    }
+
+    void
+    prepare_opt(unsigned&, close_t);
+
+    void
+    prepare_opt(unsigned&, keep_alive_t);
+
+    void
+    prepare_opt(unsigned&, upgrade_t);
+
+    void
+    prepare_payload(std::true_type);
+
+    void
+    prepare_payload(std::false_type);
 };
 
 /// A typical HTTP request
@@ -617,39 +704,6 @@ template<bool isRequest, class Fields>
 bool
 is_upgrade(header<isRequest, Fields> const& msg);
 
-/** HTTP/1 connection prepare options.
-
-    @note These values are used with @ref prepare.
-*/
-enum class connection
-{
-    /// Specify Connection: close.
-    close,
-
-    /// Specify Connection: keep-alive where possible.
-    keep_alive,
-
-    /// Specify Connection: upgrade.
-    upgrade
-};
-
-/** Prepare an HTTP message.
-
-    This function will adjust the Content-Length, Transfer-Encoding,
-    and Connection fields of the message based on the properties of
-    the body and the options passed in.
-
-    @param msg The message to prepare. The fields may be modified.
-
-    @param options A list of prepare options.
-*/
-template<
-    bool isRequest, class Body, class Fields,
-    class... Options>
-void
-prepare(message<isRequest, Body, Fields>& msg,
-    Options&&... options);
-
 } // http
 } // beast
 
diff --git a/include/beast/http/string_body.hpp b/include/beast/http/string_body.hpp
index ab8f026b..a960ee58 100644
--- a/include/beast/http/string_body.hpp
+++ b/include/beast/http/string_body.hpp
@@ -30,6 +30,16 @@ struct string_body
     /// The type of the body member when used in a message.
     using value_type = std::string;
 
+    /// Returns the content length of the body in a message.
+    template<bool isRequest, class Fields>
+    static
+    std::uint64_t
+    size(
+        message<isRequest, string_body, Fields> const& m)
+    {
+        return m.body.size();
+    }
+
 #if BEAST_DOXYGEN
     /// The algorithm to obtain buffers representing the body
     using reader = implementation_defined;
@@ -53,19 +63,12 @@ struct string_body
         }
 
         void
-        init(error_code& ec)
+        init(error_code&)
         {
-            beast::detail::ignore_unused(ec);
-        }
-
-        std::uint64_t
-        content_length() const
-        {
-            return body_.size();
         }
 
         boost::optional<std::pair<const_buffers_type, bool>>
-        get(error_code& ec)
+        get(error_code&)
         {
             return {{const_buffers_type{
                 body_.data(), body_.size()}, false}};
diff --git a/include/beast/http/type_traits.hpp b/include/beast/http/type_traits.hpp
index 20a74930..7ae997a1 100644
--- a/include/beast/http/type_traits.hpp
+++ b/include/beast/http/type_traits.hpp
@@ -21,6 +21,9 @@
 namespace beast {
 namespace http {
 
+template<bool, class, class>
+struct message;
+
 /** Determine if `T` meets the requirements of @b Body.
 
     This metafunction is equivalent to `std::true_type`
diff --git a/include/beast/websocket/impl/stream.ipp b/include/beast/websocket/impl/stream.ipp
index 75adb35f..9d9cc9f1 100644
--- a/include/beast/websocket/impl/stream.ipp
+++ b/include/beast/websocket/impl/stream.ipp
@@ -213,10 +213,10 @@ build_response(http::header<true, Fields> const& req,
         [&](std::string const& text)
         {
             response_type res;
-            res.result(http::status::bad_request);
             res.version = req.version;
+            res.result(http::status::bad_request);
             res.body = text;
-            prepare(res);
+            res.prepare();
             decorate(res);
             return res;
         };
@@ -246,7 +246,7 @@ build_response(http::header<true, Fields> const& req,
             res.result(http::status::upgrade_required);
             res.version = req.version;
             res.insert("Sec-WebSocket-Version", "13");
-            prepare(res);
+            res.prepare();
             decorate(res);
             return res;
         }
diff --git a/test/http/doc_http_samples.cpp b/test/http/doc_http_samples.cpp
index 0f557494..6afab8e6 100644
--- a/test/http/doc_http_samples.cpp
+++ b/test/http/doc_http_samples.cpp
@@ -72,7 +72,7 @@ public:
                 req.target("/");
                 req.insert("User-Agent", "test");
                 req.body = "Hello, world!";
-                prepare(req);
+                req.prepare();
 
                 error_code ec;
                 send_expect_100_continue(
@@ -105,7 +105,7 @@ public:
         req.target("/");
         req.insert("User-Agent", "test");
         req.body = "Hello, world!";
-        prepare(req);
+        req.prepare();
 
         test::pipe downstream{ios_};
         downstream.server.read_size(3);
diff --git a/test/http/message.cpp b/test/http/message.cpp
index 23a0bb5e..17bb1273 100644
--- a/test/http/message.cpp
+++ b/test/http/message.cpp
@@ -205,7 +205,7 @@ public:
             m.insert("Upgrade", "test");
             BEAST_EXPECT(! is_upgrade(m));
 
-            prepare(m, connection::upgrade);
+            m.prepare(connection::upgrade);
             BEAST_EXPECT(is_upgrade(m));
             BEAST_EXPECT(m["Connection"] == "upgrade");
 
@@ -214,49 +214,6 @@ public:
         }
     }
 
-    void
-    testPrepare()
-    {
-        request<string_body> m;
-        m.version = 10;
-        BEAST_EXPECT(! is_upgrade(m));
-        m.insert("Transfer-Encoding", "chunked");
-        try
-        {
-            prepare(m);
-            fail();
-        }
-        catch(std::exception const&)
-        {
-        }
-        m.erase("Transfer-Encoding");
-        m.insert("Content-Length", "0");
-        try
-        {
-            prepare(m);
-            fail();
-        }
-        catch(std::exception const&)
-        {
-            pass();
-        }
-        m.erase("Content-Length");
-        m.insert("Connection", "keep-alive");
-        try
-        {
-            prepare(m);
-            fail();
-        }
-        catch(std::exception const&)
-        {
-            pass();
-        }
-        m.version = 11;
-        m.erase("Connection");
-        m.insert("Connection", "close");
-        BEAST_EXPECT(! is_keep_alive(m));
-    }
-
     void
     testSwap()
     {
@@ -357,7 +314,6 @@ public:
         testMessage();
         testHeaders();
         testFreeFunctions();
-        testPrepare();
         testSwap();
         testSpecialMembers();
         testMethod();
diff --git a/test/http/write.cpp b/test/http/write.cpp
index a9a7441e..1119df31 100644
--- a/test/http/write.cpp
+++ b/test/http/write.cpp
@@ -55,9 +55,8 @@ public:
             }
 
             void
-            init(error_code& ec)
+            init(error_code&)
             {
-                beast::detail::ignore_unused(ec);
             }
             
             boost::optional<std::pair<const_buffers_type, bool>>
@@ -502,7 +501,7 @@ public:
             m.version = 10;
             m.insert("User-Agent", "test");
             m.body = "*";
-            prepare(m);
+            m.prepare();
             BEAST_EXPECT(str(m) ==
                 "GET / HTTP/1.0\r\n"
                 "User-Agent: test\r\n"
@@ -519,12 +518,12 @@ public:
             m.version = 10;
             m.insert("User-Agent", "test");
             m.body = "*";
-            prepare(m, connection::keep_alive);
+            m.prepare(connection::keep_alive);
             BEAST_EXPECT(str(m) ==
                 "GET / HTTP/1.0\r\n"
                 "User-Agent: test\r\n"
-                "Content-Length: 1\r\n"
                 "Connection: keep-alive\r\n"
+                "Content-Length: 1\r\n"
                 "\r\n"
                 "*"
             );
@@ -539,7 +538,7 @@ public:
             m.body = "*";
             try
             {
-                prepare(m, connection::upgrade);
+                m.prepare( connection::upgrade);
                 fail();
             }
             catch(std::exception const&)
@@ -555,7 +554,7 @@ public:
             m.version = 10;
             m.insert("User-Agent", "test");
             m.body = "*";
-            prepare(m);
+            m.prepare();
             test::string_ostream ss(ios_);
             error_code ec;
             write(ss, m, ec);
@@ -575,7 +574,7 @@ public:
             m.version = 11;
             m.insert("User-Agent", "test");
             m.body = "*";
-            prepare(m);
+            m.prepare();
             BEAST_EXPECT(str(m) ==
                 "GET / HTTP/1.1\r\n"
                 "User-Agent: test\r\n"
@@ -592,7 +591,7 @@ public:
             m.version = 11;
             m.insert("User-Agent", "test");
             m.body = "*";
-            prepare(m, connection::close);
+            m.prepare(connection::close);
             test::string_ostream ss(ios_);
             error_code ec;
             write(ss, m, ec);
@@ -600,8 +599,8 @@ public:
             BEAST_EXPECT(ss.str ==
                 "GET / HTTP/1.1\r\n"
                 "User-Agent: test\r\n"
-                "Content-Length: 1\r\n"
                 "Connection: close\r\n"
+                "Content-Length: 1\r\n"
                 "\r\n"
                 "*"
             );
@@ -613,7 +612,7 @@ public:
             m.target("/");
             m.version = 11;
             m.insert("User-Agent", "test");
-            prepare(m, connection::upgrade);
+            m.prepare(connection::upgrade);
             BEAST_EXPECT(str(m) ==
                 "GET / HTTP/1.1\r\n"
                 "User-Agent: test\r\n"
@@ -629,7 +628,7 @@ public:
             m.version = 11;
             m.insert("User-Agent", "test");
             m.body = "*";
-            prepare(m);
+            m.prepare();
             test::string_ostream ss(ios_);
             error_code ec;
             write(ss, m, ec);
@@ -656,8 +655,6 @@ public:
         m.body = "*";
         BEAST_EXPECT(boost::lexical_cast<std::string>(m) ==
             "GET / HTTP/1.1\r\nUser-Agent: test\r\n\r\n*");
-        BEAST_EXPECT(boost::lexical_cast<std::string>(m.base()) ==
-            "GET / HTTP/1.1\r\nUser-Agent: test\r\n\r\n");
     }
 
     // Ensure completion handlers are not leaked