diff --git a/link/asio/async_result.hpp b/link/asio/async_result.hpp
@@ -2,7 +2,7 @@
 // async_result.hpp
 // ~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -17,109 +17,340 @@
 
 #include "asio/detail/config.hpp"
 #include "asio/detail/type_traits.hpp"
-#include "asio/handler_type.hpp"
+#include "asio/detail/variadic_templates.hpp"
 
 #include "asio/detail/push_options.hpp"
 
 namespace asio {
 
 /// An interface for customising the behaviour of an initiating function.
 /**
- * This template may be specialised for user-defined handler types.
+ * The async_result traits class is used for determining:
+ *
+ * @li the concrete completion handler type to be called at the end of the
+ * asynchronous operation;
+ *
+ * @li the initiating function return type; and
+ *
+ * @li how the return value of the initiating function is obtained.
+ *
+ * The trait allows the handler and return types to be determined at the point
+ * where the specific completion handler signature is known.
+ *
+ * This template may be specialised for user-defined completion token types.
+ * The primary template assumes that the CompletionToken is the completion
+ * handler.
  */
-template <typename Handler>
+template <typename CompletionToken, typename Signature>
 class async_result
 {
 public:
+  /// The concrete completion handler type for the specific signature.
+  typedef CompletionToken completion_handler_type;
+
   /// The return type of the initiating function.
-  typedef void type;
+  typedef void return_type;
 
   /// Construct an async result from a given handler.
   /**
    * When using a specalised async_result, the constructor has an opportunity
-   * to initialise some state associated with the handler, which is then
-   * returned from the initiating function.
+   * to initialise some state associated with the completion handler, which is
+   * then returned from the initiating function.
    */
-  explicit async_result(Handler&)
+  explicit async_result(completion_handler_type& h)
   {
+    (void)h;
   }
 
   /// Obtain the value to be returned from the initiating function.
-  type get()
+  return_type get()
+  {
+  }
+
+#if defined(ASIO_HAS_VARIADIC_TEMPLATES) \
+  || defined(GENERATING_DOCUMENTATION)
+
+  /// Initiate the asynchronous operation that will produce the result, and
+  /// obtain the value to be returned from the initiating function.
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static return_type initiate(
+      ASIO_MOVE_ARG(Initiation) initiation,
+      ASIO_MOVE_ARG(RawCompletionToken) token,
+      ASIO_MOVE_ARG(Args)... args)
   {
+    ASIO_MOVE_CAST(Initiation)(initiation)(
+        ASIO_MOVE_CAST(RawCompletionToken)(token),
+        ASIO_MOVE_CAST(Args)(args)...);
   }
+
+#else // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+      //   || defined(GENERATING_DOCUMENTATION)
+
+  template <typename Initiation, typename RawCompletionToken>
+  static return_type initiate(
+      ASIO_MOVE_ARG(Initiation) initiation,
+      ASIO_MOVE_ARG(RawCompletionToken) token)
+  {
+    ASIO_MOVE_CAST(Initiation)(initiation)(
+        ASIO_MOVE_CAST(RawCompletionToken)(token));
+  }
+
+#define ASIO_PRIVATE_INITIATE_DEF(n) \
+  template <typename Initiation, typename RawCompletionToken, \
+      ASIO_VARIADIC_TPARAMS(n)> \
+  static return_type initiate( \
+      ASIO_MOVE_ARG(Initiation) initiation, \
+      ASIO_MOVE_ARG(RawCompletionToken) token, \
+      ASIO_VARIADIC_MOVE_PARAMS(n)) \
+  { \
+    ASIO_MOVE_CAST(Initiation)(initiation)( \
+        ASIO_MOVE_CAST(RawCompletionToken)(token), \
+        ASIO_VARIADIC_MOVE_ARGS(n)); \
+  } \
+  /**/
+  ASIO_VARIADIC_GENERATE(ASIO_PRIVATE_INITIATE_DEF)
+#undef ASIO_PRIVATE_INITIATE_DEF
+
+#endif // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+       //   || defined(GENERATING_DOCUMENTATION)
+
+private:
+  async_result(const async_result&) ASIO_DELETED;
+  async_result& operator=(const async_result&) ASIO_DELETED;
 };
 
-/// Helper template to deduce the real type of a handler, capture a local copy
-/// of the handler, and then create an async_result for the handler.
-template <typename Handler, typename Signature>
+/// Helper template to deduce the handler type from a CompletionToken, capture
+/// a local copy of the handler, and then create an async_result for the
+/// handler.
+template <typename CompletionToken, typename Signature>
 struct async_completion
 {
   /// The real handler type to be used for the asynchronous operation.
-  typedef typename asio::handler_type<
-    Handler, Signature>::type handler_type;
+  typedef typename asio::async_result<
+    typename decay<CompletionToken>::type,
+      Signature>::completion_handler_type completion_handler_type;
 
+#if defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
   /// Constructor.
   /**
-   * The constructor creates the concrete handler and makes the link between
-   * the handler and the asynchronous result.
+   * The constructor creates the concrete completion handler and makes the link
+   * between the handler and the asynchronous result.
    */
-#if defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
-  explicit async_completion(
-      Handler& orig_handler)
-    : handler(static_cast<typename conditional<
-        is_same<Handler, handler_type>::value,
-        handler_type&, Handler&&>::type>(orig_handler)),
-      result(handler)
+  explicit async_completion(CompletionToken& token)
+    : completion_handler(static_cast<typename conditional<
+        is_same<CompletionToken, completion_handler_type>::value,
+        completion_handler_type&, CompletionToken&&>::type>(token)),
+      result(completion_handler)
   {
   }
 #else // defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
-  explicit async_completion(const Handler& orig_handler)
-    : handler(orig_handler),
-      result(handler)
+  explicit async_completion(typename decay<CompletionToken>::type& token)
+    : completion_handler(token),
+      result(completion_handler)
+  {
+  }
+
+  explicit async_completion(const typename decay<CompletionToken>::type& token)
+    : completion_handler(token),
+      result(completion_handler)
   {
   }
 #endif // defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
 
   /// A copy of, or reference to, a real handler object.
 #if defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
   typename conditional<
-    is_same<Handler, handler_type>::value,
-    handler_type&, handler_type>::type handler;
+    is_same<CompletionToken, completion_handler_type>::value,
+    completion_handler_type&, completion_handler_type>::type completion_handler;
 #else // defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
-  typename asio::handler_type<Handler, Signature>::type handler;
+  completion_handler_type completion_handler;
 #endif // defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
 
   /// The result of the asynchronous operation's initiating function.
-  async_result<typename asio::handler_type<
-    Handler, Signature>::type> result;
+  async_result<typename decay<CompletionToken>::type, Signature> result;
 };
 
 namespace detail {
 
-template <typename Handler, typename Signature>
-struct async_result_type_helper
+template <typename CompletionToken, typename Signature>
+struct async_result_helper
+  : async_result<typename decay<CompletionToken>::type, Signature>
 {
-  typedef typename async_result<
-      typename handler_type<Handler, Signature>::type
-    >::type type;
 };
 
-} // namespace detail
-} // namespace asio
+struct async_result_memfns_base
+{
+  void initiate();
+};
 
-#include "asio/detail/pop_options.hpp"
+template <typename T>
+struct async_result_memfns_derived
+  : T, async_result_memfns_base
+{
+};
+
+template <typename T, T>
+struct async_result_memfns_check
+{
+};
+
+template <typename>
+char (&async_result_initiate_memfn_helper(...))[2];
+
+template <typename T>
+char async_result_initiate_memfn_helper(
+    async_result_memfns_check<
+      void (async_result_memfns_base::*)(),
+      &async_result_memfns_derived<T>::initiate>*);
+
+template <typename CompletionToken, typename Signature>
+struct async_result_has_initiate_memfn
+  : integral_constant<bool, sizeof(async_result_initiate_memfn_helper<
+      async_result<typename decay<CompletionToken>::type, Signature>
+    >(0)) != 1>
+{
+};
+
+} // namespace detail
 
 #if defined(GENERATING_DOCUMENTATION)
-# define ASIO_INITFN_RESULT_TYPE(h, sig) \
+# define ASIO_INITFN_RESULT_TYPE(ct, sig) \
   void_or_deduced
 #elif defined(_MSC_VER) && (_MSC_VER < 1500)
-# define ASIO_INITFN_RESULT_TYPE(h, sig) \
-  typename ::asio::detail::async_result_type_helper<h, sig>::type
+# define ASIO_INITFN_RESULT_TYPE(ct, sig) \
+  typename ::asio::detail::async_result_helper< \
+    ct, sig>::return_type
+#define ASIO_HANDLER_TYPE(ct, sig) \
+  typename ::asio::detail::async_result_helper< \
+    ct, sig>::completion_handler_type
 #else
-# define ASIO_INITFN_RESULT_TYPE(h, sig) \
+# define ASIO_INITFN_RESULT_TYPE(ct, sig) \
+  typename ::asio::async_result< \
+    typename ::asio::decay<ct>::type, sig>::return_type
+#define ASIO_HANDLER_TYPE(ct, sig) \
   typename ::asio::async_result< \
-    typename ::asio::handler_type<h, sig>::type>::type
+    typename ::asio::decay<ct>::type, sig>::completion_handler_type
 #endif
 
+#if defined(GENERATING_DOCUMENTATION)
+
+template <typename CompletionToken, typename Signature,
+    typename Initiation, typename... Args>
+ASIO_INITFN_RESULT_TYPE(CompletionToken, Signature)
+async_initiate(ASIO_MOVE_ARG(Initiation) initiation,
+    ASIO_NONDEDUCED_MOVE_ARG(CompletionToken),
+    ASIO_MOVE_ARG(Args)... args);
+
+#elif defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename CompletionToken, typename Signature,
+    typename Initiation, typename... Args>
+inline typename enable_if<
+    detail::async_result_has_initiate_memfn<CompletionToken, Signature>::value,
+    ASIO_INITFN_RESULT_TYPE(CompletionToken, Signature)>::type
+async_initiate(ASIO_MOVE_ARG(Initiation) initiation,
+    ASIO_NONDEDUCED_MOVE_ARG(CompletionToken) token,
+    ASIO_MOVE_ARG(Args)... args)
+{
+  return async_result<typename decay<CompletionToken>::type,
+    Signature>::initiate(ASIO_MOVE_CAST(Initiation)(initiation),
+      ASIO_MOVE_CAST(CompletionToken)(token),
+      ASIO_MOVE_CAST(Args)(args)...);
+}
+
+template <typename CompletionToken, typename Signature,
+    typename Initiation, typename... Args>
+inline typename enable_if<
+    !detail::async_result_has_initiate_memfn<CompletionToken, Signature>::value,
+    ASIO_INITFN_RESULT_TYPE(CompletionToken, Signature)>::type
+async_initiate(ASIO_MOVE_ARG(Initiation) initiation,
+    ASIO_NONDEDUCED_MOVE_ARG(CompletionToken) token,
+    ASIO_MOVE_ARG(Args)... args)
+{
+  async_completion<CompletionToken, Signature> completion(token);
+
+  ASIO_MOVE_CAST(Initiation)(initiation)(
+      ASIO_MOVE_CAST(ASIO_HANDLER_TYPE(CompletionToken,
+        Signature))(completion.completion_handler),
+      ASIO_MOVE_CAST(Args)(args)...);
+
+  return completion.result.get();
+}
+
+#else // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename CompletionToken, typename Signature, typename Initiation>
+inline typename enable_if<
+    detail::async_result_has_initiate_memfn<CompletionToken, Signature>::value,
+    ASIO_INITFN_RESULT_TYPE(CompletionToken, Signature)>::type
+async_initiate(ASIO_MOVE_ARG(Initiation) initiation,
+    ASIO_NONDEDUCED_MOVE_ARG(CompletionToken) token)
+{
+  return async_result<typename decay<CompletionToken>::type,
+    Signature>::initiate(ASIO_MOVE_CAST(Initiation)(initiation),
+      ASIO_MOVE_CAST(CompletionToken)(token));
+}
+
+template <typename CompletionToken, typename Signature, typename Initiation>
+inline typename enable_if<
+    !detail::async_result_has_initiate_memfn<CompletionToken, Signature>::value,
+    ASIO_INITFN_RESULT_TYPE(CompletionToken, Signature)>::type
+async_initiate(ASIO_MOVE_ARG(Initiation) initiation,
+    ASIO_NONDEDUCED_MOVE_ARG(CompletionToken) token)
+{
+  async_completion<CompletionToken, Signature> completion(token);
+
+  ASIO_MOVE_CAST(Initiation)(initiation)(
+      ASIO_MOVE_CAST(ASIO_HANDLER_TYPE(CompletionToken,
+        Signature))(completion.completion_handler));
+
+  return completion.result.get();
+}
+
+#define ASIO_PRIVATE_INITIATE_DEF(n) \
+  template <typename CompletionToken, typename Signature, \
+      typename Initiation, ASIO_VARIADIC_TPARAMS(n)> \
+  inline typename enable_if< \
+      detail::async_result_has_initiate_memfn< \
+        CompletionToken, Signature>::value, \
+      ASIO_INITFN_RESULT_TYPE(CompletionToken, Signature)>::type \
+  async_initiate(ASIO_MOVE_ARG(Initiation) initiation, \
+      ASIO_NONDEDUCED_MOVE_ARG(CompletionToken) token, \
+      ASIO_VARIADIC_MOVE_PARAMS(n)) \
+  { \
+    return async_result<typename decay<CompletionToken>::type, \
+      Signature>::initiate(ASIO_MOVE_CAST(Initiation)(initiation), \
+        ASIO_MOVE_CAST(CompletionToken)(token), \
+        ASIO_VARIADIC_MOVE_ARGS(n)); \
+  } \
+  \
+  template <typename CompletionToken, typename Signature, \
+      typename Initiation, ASIO_VARIADIC_TPARAMS(n)> \
+  inline typename enable_if< \
+      !detail::async_result_has_initiate_memfn< \
+        CompletionToken, Signature>::value, \
+      ASIO_INITFN_RESULT_TYPE(CompletionToken, Signature)>::type \
+  async_initiate(ASIO_MOVE_ARG(Initiation) initiation, \
+      ASIO_NONDEDUCED_MOVE_ARG(CompletionToken) token, \
+      ASIO_VARIADIC_MOVE_PARAMS(n)) \
+  { \
+    async_completion<CompletionToken, Signature> completion(token); \
+  \
+    ASIO_MOVE_CAST(Initiation)(initiation)( \
+        ASIO_MOVE_CAST(ASIO_HANDLER_TYPE(CompletionToken, \
+          Signature))(completion.completion_handler), \
+        ASIO_VARIADIC_MOVE_ARGS(n)); \
+  \
+    return completion.result.get(); \
+  } \
+  /**/
+  ASIO_VARIADIC_GENERATE(ASIO_PRIVATE_INITIATE_DEF)
+#undef ASIO_PRIVATE_INITIATE_DEF
+
+#endif // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
 #endif // ASIO_ASYNC_RESULT_HPP
diff --git a/link/asio/awaitable.hpp b/link/asio/awaitable.hpp
@@ -0,0 +1,123 @@
+//
+// awaitable.hpp
+// ~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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 ASIO_AWAITABLE_HPP
+#define ASIO_AWAITABLE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if defined(ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
+
+#include <experimental/coroutine>
+#include "asio/executor.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+using std::experimental::coroutine_handle;
+using std::experimental::suspend_always;
+
+template <typename> class awaitable_thread;
+template <typename, typename> class awaitable_frame;
+
+} // namespace detail
+
+/// The return type of a coroutine or asynchronous operation.
+template <typename T, typename Executor = executor>
+class awaitable
+{
+public:
+  /// The type of the awaited value.
+  typedef T value_type;
+
+  /// The executor type that will be used for the coroutine.
+  typedef Executor executor_type;
+
+  /// Default constructor.
+  constexpr awaitable() noexcept
+    : frame_(nullptr)
+  {
+  }
+
+  /// Move constructor.
+  awaitable(awaitable&& other) noexcept
+    : frame_(std::exchange(other.frame_, nullptr))
+  {
+  }
+
+  /// Destructor
+  ~awaitable()
+  {
+    if (frame_)
+      frame_->destroy();
+  }
+
+  /// Checks if the awaitable refers to a future result.
+  bool valid() const noexcept
+  {
+    return !!frame_;
+  }
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+  // Support for co_await keyword.
+  bool await_ready() const noexcept
+  {
+    return false;
+  }
+
+  // Support for co_await keyword.
+  template <class U>
+  void await_suspend(
+      detail::coroutine_handle<detail::awaitable_frame<U, Executor>> h)
+  {
+    frame_->push_frame(&h.promise());
+  }
+
+  // Support for co_await keyword.
+  T await_resume()
+  {
+    return frame_->get();
+  }
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+private:
+  template <typename> friend class detail::awaitable_thread;
+  template <typename, typename> friend class detail::awaitable_frame;
+
+  // Not copy constructible or copy assignable.
+  awaitable(const awaitable&) = delete;
+  awaitable& operator=(const awaitable&) = delete;
+
+  // Construct the awaitable from a coroutine's frame object.
+  explicit awaitable(detail::awaitable_frame<T, Executor>* a)
+    : frame_(a)
+  {
+  }
+
+  detail::awaitable_frame<T, Executor>* frame_;
+};
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#include "asio/impl/awaitable.hpp"
+
+#endif // defined(ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
+
+#endif // ASIO_AWAITABLE_HPP
diff --git a/link/asio/basic_datagram_socket.hpp b/link/asio/basic_datagram_socket.hpp
diff --git a/link/asio/basic_deadline_timer.hpp b/link/asio/basic_deadline_timer.hpp
diff --git a/link/asio/basic_io_object.hpp b/link/asio/basic_io_object.hpp
@@ -2,7 +2,7 @@
 // basic_io_object.hpp
 // ~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -34,12 +34,13 @@ namespace detail
     typedef typename service_type::implementation_type implementation_type;
 
     template <typename T, typename U>
-    static auto eval(T* t, U* u) -> decltype(t->move_construct(*u, *u), char());
-    static char (&eval(...))[2];
+    static auto asio_service_has_move_eval(T* t, U* u)
+      -> decltype(t->move_construct(*u, *u), char());
+    static char (&asio_service_has_move_eval(...))[2];
 
   public:
     static const bool value =
-      sizeof(service_has_move::eval(
+      sizeof(asio_service_has_move_eval(
         static_cast<service_type*>(0),
         static_cast<implementation_type*>(0))) == 1;
   };
@@ -137,6 +138,11 @@ class basic_io_object
    * @note Available only for services that support movability,
    */
   basic_io_object& operator=(basic_io_object&& other);
+
+  /// Perform a converting move-construction of a basic_io_object.
+  template <typename IoObjectService1>
+  basic_io_object(IoObjectService1& other_service,
+      typename IoObjectService1::implementation_type& other_implementation);
 #endif // defined(GENERATING_DOCUMENTATION)
 
   /// Protected destructor to prevent deletion through this type.
@@ -225,6 +231,16 @@ class basic_io_object<IoObjectService, true>
     service_->move_construct(implementation_, other.implementation_);
   }
 
+  template <typename IoObjectService1>
+  basic_io_object(IoObjectService1& other_service,
+      typename IoObjectService1::implementation_type& other_implementation)
+    : service_(&asio::use_service<IoObjectService>(
+          other_service.get_io_context()))
+  {
+    service_->converting_move_construct(implementation_,
+        other_service, other_implementation);
+  }
+
   ~basic_io_object()
   {
     service_->destroy(implementation_);

diff --git a/link/asio/basic_raw_socket.hpp b/link/asio/basic_raw_socket.hpp
diff --git a/link/asio/basic_seq_packet_socket.hpp b/link/asio/basic_seq_packet_socket.hpp
diff --git a/link/asio/basic_serial_port.hpp b/link/asio/basic_serial_port.hpp
diff --git a/link/asio/basic_signal_set.hpp b/link/asio/basic_signal_set.hpp
diff --git a/link/asio/basic_socket.hpp b/link/asio/basic_socket.hpp
diff --git a/link/asio/basic_socket_acceptor.hpp b/link/asio/basic_socket_acceptor.hpp
diff --git a/link/asio/basic_socket_iostream.hpp b/link/asio/basic_socket_iostream.hpp
@@ -2,7 +2,7 @@
 // basic_socket_iostream.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -22,7 +22,6 @@
 #include <istream>
 #include <ostream>
 #include "asio/basic_socket_streambuf.hpp"
-#include "asio/stream_socket_service.hpp"
 
 #if !defined(ASIO_HAS_VARIADIC_TEMPLATES)
 
@@ -33,8 +32,7 @@
 //   explicit basic_socket_iostream(T1 x1, ..., Tn xn)
 //     : std::basic_iostream<char>(
 //         &this->detail::socket_iostream_base<
-//           Protocol, StreamSocketService, Time,
-//           TimeTraits, TimerService>::streambuf_)
+//           Protocol, Clock, WaitTraits>::streambuf_)
 //   {
 //     if (rdbuf()->connect(x1, ..., xn) == 0)
 //       this->setstate(std::ios_base::failbit);
@@ -46,8 +44,7 @@
   explicit basic_socket_iostream(ASIO_VARIADIC_BYVAL_PARAMS(n)) \
     : std::basic_iostream<char>( \
         &this->detail::socket_iostream_base< \
-          Protocol, StreamSocketService, Time, \
-          TimeTraits, TimerService>::streambuf_) \
+          Protocol, Clock, WaitTraits>::streambuf_) \
   { \
     this->setf(std::ios_base::unitbuf); \
     if (rdbuf()->connect(ASIO_VARIADIC_BYVAL_ARGS(n)) == 0) \
@@ -82,60 +79,102 @@ namespace detail {
 
 // A separate base class is used to ensure that the streambuf is initialised
 // prior to the basic_socket_iostream's basic_iostream base class.
-template <typename Protocol, typename StreamSocketService,
-    typename Time, typename TimeTraits, typename TimerService>
+template <typename Protocol, typename Clock, typename WaitTraits>
 class socket_iostream_base
 {
 protected:
-  basic_socket_streambuf<Protocol, StreamSocketService,
-    Time, TimeTraits, TimerService> streambuf_;
+  socket_iostream_base()
+  {
+  }
+
+#if defined(ASIO_HAS_MOVE)
+  socket_iostream_base(socket_iostream_base&& other)
+    : streambuf_(std::move(other.streambuf_))
+  {
+  }
+
+  socket_iostream_base(basic_stream_socket<Protocol> s)
+    : streambuf_(std::move(s))
+  {
+  }
+
+  socket_iostream_base& operator=(socket_iostream_base&& other)
+  {
+    streambuf_ = std::move(other.streambuf_);
+    return *this;
+  }
+#endif // defined(ASIO_HAS_MOVE)
+
+  basic_socket_streambuf<Protocol, Clock, WaitTraits> streambuf_;
 };
 
-}
+} // namespace detail
 
-/// Iostream interface for a socket.
+#if !defined(ASIO_BASIC_SOCKET_IOSTREAM_FWD_DECL)
+#define ASIO_BASIC_SOCKET_IOSTREAM_FWD_DECL
+
+// Forward declaration with defaulted arguments.
 template <typename Protocol,
-    typename StreamSocketService = stream_socket_service<Protocol>,
 #if defined(ASIO_HAS_BOOST_DATE_TIME) \
-  || defined(GENERATING_DOCUMENTATION)
-    typename Time = boost::posix_time::ptime,
-    typename TimeTraits = asio::time_traits<Time>,
-    typename TimerService = deadline_timer_service<Time, TimeTraits> >
-#else
-    typename Time = steady_timer::clock_type,
-    typename TimeTraits = steady_timer::traits_type,
-    typename TimerService = steady_timer::service_type>
-#endif
+  && defined(ASIO_USE_BOOST_DATE_TIME_FOR_SOCKET_IOSTREAM)
+    typename Clock = boost::posix_time::ptime,
+    typename WaitTraits = time_traits<Clock> >
+#else // defined(ASIO_HAS_BOOST_DATE_TIME)
+      // && defined(ASIO_USE_BOOST_DATE_TIME_FOR_SOCKET_IOSTREAM)
+    typename Clock = chrono::steady_clock,
+    typename WaitTraits = wait_traits<Clock> >
+#endif // defined(ASIO_HAS_BOOST_DATE_TIME)
+       // && defined(ASIO_USE_BOOST_DATE_TIME_FOR_SOCKET_IOSTREAM)
+class basic_socket_iostream;
+
+#endif // !defined(ASIO_BASIC_SOCKET_IOSTREAM_FWD_DECL)
+
+/// Iostream interface for a socket.
+#if defined(GENERATING_DOCUMENTATION)
+template <typename Protocol,
+    typename Clock = chrono::steady_clock,
+    typename WaitTraits = wait_traits<Clock> >
+#else // defined(GENERATING_DOCUMENTATION)
+template <typename Protocol, typename Clock, typename WaitTraits>
+#endif // defined(GENERATING_DOCUMENTATION)
 class basic_socket_iostream
-  : private detail::socket_iostream_base<Protocol,
-        StreamSocketService, Time, TimeTraits, TimerService>,
+  : private detail::socket_iostream_base<Protocol, Clock, WaitTraits>,
     public std::basic_iostream<char>
 {
 private:
   // These typedefs are intended keep this class's implementation independent
-  // of whether it's using Boost.DateTime, Boost.Chrono or std::chrono.
-#if defined(ASIO_HAS_BOOST_DATE_TIME)
-  typedef TimeTraits traits_helper;
-#else
-  typedef detail::chrono_time_traits<Time, TimeTraits> traits_helper;
-#endif
+  // of whether it's using Boost.DateClock, Boost.Chrono or std::chrono.
+#if defined(ASIO_HAS_BOOST_DATE_TIME) \
+  && defined(ASIO_USE_BOOST_DATE_TIME_FOR_SOCKET_IOSTREAM)
+  typedef WaitTraits traits_helper;
+#else // defined(ASIO_HAS_BOOST_DATE_TIME)
+      // && defined(ASIO_USE_BOOST_DATE_TIME_FOR_SOCKET_IOSTREAM)
+  typedef detail::chrono_time_traits<Clock, WaitTraits> traits_helper;
+#endif // defined(ASIO_HAS_BOOST_DATE_TIME)
+       // && defined(ASIO_USE_BOOST_DATE_TIME_FOR_SOCKET_IOSTREAM)
 
 public:
+  /// The protocol type.
+  typedef Protocol protocol_type;
+
   /// The endpoint type.
   typedef typename Protocol::endpoint endpoint_type;
 
+  /// The clock type.
+  typedef Clock clock_type;
+
 #if defined(GENERATING_DOCUMENTATION)
   /// (Deprecated: Use time_point.) The time type.
-  typedef typename TimeTraits::time_type time_type;
+  typedef typename WaitTraits::time_type time_type;
 
   /// The time type.
-  typedef typename TimeTraits::time_point time_point;
+  typedef typename WaitTraits::time_point time_point;
 
   /// (Deprecated: Use duration.) The duration type.
-  typedef typename TimeTraits::duration_type duration_type;
+  typedef typename WaitTraits::duration_type duration_type;
 
   /// The duration type.
-  typedef typename TimeTraits::duration duration;
+  typedef typename WaitTraits::duration duration;
 #else
 # if !defined(ASIO_NO_DEPRECATED)
   typedef typename traits_helper::time_type time_type;
@@ -149,12 +188,47 @@ class basic_socket_iostream
   basic_socket_iostream()
     : std::basic_iostream<char>(
         &this->detail::socket_iostream_base<
-          Protocol, StreamSocketService, Time,
-          TimeTraits, TimerService>::streambuf_)
+          Protocol, Clock, WaitTraits>::streambuf_)
   {
     this->setf(std::ios_base::unitbuf);
   }
 
+#if defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+  /// Construct a basic_socket_iostream from the supplied socket.
+  explicit basic_socket_iostream(basic_stream_socket<protocol_type> s)
+    : detail::socket_iostream_base<
+        Protocol, Clock, WaitTraits>(std::move(s)),
+      std::basic_iostream<char>(
+        &this->detail::socket_iostream_base<
+          Protocol, Clock, WaitTraits>::streambuf_)
+  {
+    this->setf(std::ios_base::unitbuf);
+  }
+
+#if defined(ASIO_HAS_STD_IOSTREAM_MOVE) \
+  || defined(GENERATING_DOCUMENTATION)
+  /// Move-construct a basic_socket_iostream from another.
+  basic_socket_iostream(basic_socket_iostream&& other)
+    : detail::socket_iostream_base<
+        Protocol, Clock, WaitTraits>(std::move(other)),
+      std::basic_iostream<char>(std::move(other))
+  {
+    this->set_rdbuf(&this->detail::socket_iostream_base<
+          Protocol, Clock, WaitTraits>::streambuf_);
+  }
+
+  /// Move-assign a basic_socket_iostream from another.
+  basic_socket_iostream& operator=(basic_socket_iostream&& other)
+  {
+    std::basic_iostream<char>::operator=(std::move(other));
+    detail::socket_iostream_base<
+        Protocol, Clock, WaitTraits>::operator=(std::move(other));
+    return *this;
+  }
+#endif // defined(ASIO_HAS_STD_IOSTREAM_MOVE)
+       //   || defined(GENERATING_DOCUMENTATION)
+#endif // defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+
 #if defined(GENERATING_DOCUMENTATION)
   /// Establish a connection to an endpoint corresponding to a resolver query.
   /**
@@ -169,8 +243,7 @@ class basic_socket_iostream
   explicit basic_socket_iostream(T... x)
     : std::basic_iostream<char>(
         &this->detail::socket_iostream_base<
-          Protocol, StreamSocketService, Time,
-          TimeTraits, TimerService>::streambuf_)
+          Protocol, Clock, WaitTraits>::streambuf_)
   {
     this->setf(std::ios_base::unitbuf);
     if (rdbuf()->connect(x...) == 0)
@@ -208,14 +281,17 @@ class basic_socket_iostream
   }
 
   /// Return a pointer to the underlying streambuf.
-  basic_socket_streambuf<Protocol, StreamSocketService,
-    Time, TimeTraits, TimerService>* rdbuf() const
+  basic_socket_streambuf<Protocol, Clock, WaitTraits>* rdbuf() const
   {
-    return const_cast<basic_socket_streambuf<Protocol, StreamSocketService,
-      Time, TimeTraits, TimerService>*>(
+    return const_cast<basic_socket_streambuf<Protocol, Clock, WaitTraits>*>(
         &this->detail::socket_iostream_base<
-          Protocol, StreamSocketService, Time,
-          TimeTraits, TimerService>::streambuf_);
+          Protocol, Clock, WaitTraits>::streambuf_);
+  }
+
+  /// Get a reference to the underlying socket.
+  basic_socket<Protocol>& socket()
+  {
+    return rdbuf()->socket();
   }
 
   /// Get the last error associated with the stream.
@@ -232,7 +308,7 @@ class basic_socket_iostream
    */
   const asio::error_code& error() const
   {
-    return rdbuf()->puberror();
+    return rdbuf()->error();
   }
 
 #if !defined(ASIO_NO_DEPRECATED)
@@ -309,6 +385,12 @@ class basic_socket_iostream
     rdbuf()->expires_from_now(expiry_time);
   }
 #endif // !defined(ASIO_NO_DEPRECATED)
+
+private:
+  // Disallow copying and assignment.
+  basic_socket_iostream(const basic_socket_iostream&) ASIO_DELETED;
+  basic_socket_iostream& operator=(
+      const basic_socket_iostream&) ASIO_DELETED;
 };
 
 } // namespace asio

diff --git a/link/asio/basic_socket_streambuf.hpp b/link/asio/basic_socket_streambuf.hpp
diff --git a/link/asio/basic_stream_socket.hpp b/link/asio/basic_stream_socket.hpp
diff --git a/link/asio/basic_streambuf.hpp b/link/asio/basic_streambuf.hpp
@@ -2,7 +2,7 @@
 // basic_streambuf.hpp
 // ~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -119,8 +119,8 @@ class basic_streambuf
   /// The type used to represent the output sequence as a list of buffers.
   typedef implementation_defined mutable_buffers_type;
 #else
-  typedef asio::const_buffers_1 const_buffers_type;
-  typedef asio::mutable_buffers_1 mutable_buffers_type;
+  typedef ASIO_CONST_BUFFER const_buffers_type;
+  typedef ASIO_MUTABLE_BUFFER mutable_buffers_type;
 #endif
 
   /// Construct a basic_streambuf object.
@@ -232,8 +232,7 @@ class basic_streambuf
    */
   void commit(std::size_t n)
   {
-    if (pptr() + n > epptr())
-      n = epptr() - pptr();
+    n = std::min<std::size_t>(n, epptr() - pptr());
     pbump(static_cast<int>(n));
     setg(eback(), gptr(), pptr());
   }

diff --git a/link/asio/basic_streambuf_fwd.hpp b/link/asio/basic_streambuf_fwd.hpp
@@ -2,7 +2,7 @@
 // basic_streambuf_fwd.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/basic_waitable_timer.hpp b/link/asio/basic_waitable_timer.hpp
diff --git a/link/asio/bind_executor.hpp b/link/asio/bind_executor.hpp
@@ -2,7 +2,7 @@
 // bind_executor.hpp
 // ~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -18,9 +18,11 @@
 #include "asio/detail/config.hpp"
 #include "asio/detail/type_traits.hpp"
 #include "asio/detail/variadic_templates.hpp"
+#include "asio/associated_executor.hpp"
 #include "asio/associated_allocator.hpp"
 #include "asio/async_result.hpp"
-#include "asio/handler_type.hpp"
+#include "asio/execution_context.hpp"
+#include "asio/is_executor.hpp"
 #include "asio/uses_executor.hpp"
 
 #include "asio/detail/push_options.hpp"
@@ -166,27 +168,27 @@ class executor_binder_base<T, Executor, true>
 protected:
   template <typename E, typename U>
   executor_binder_base(ASIO_MOVE_ARG(E) e, ASIO_MOVE_ARG(U) u)
-    : Executor(ASIO_MOVE_CAST(E)(e)),
-      target_(executor_arg_t(), static_cast<const Executor&>(*this),
-          ASIO_MOVE_CAST(U)(u))
+    : executor_(ASIO_MOVE_CAST(E)(e)),
+      target_(executor_arg_t(), executor_, ASIO_MOVE_CAST(U)(u))
   {
   }
 
+  Executor executor_;
   T target_;
 };
 
 template <typename T, typename Executor>
 class executor_binder_base<T, Executor, false>
-  : protected Executor
 {
 protected:
   template <typename E, typename U>
   executor_binder_base(ASIO_MOVE_ARG(E) e, ASIO_MOVE_ARG(U) u)
-    : Executor(ASIO_MOVE_CAST(E)(e)),
+    : executor_(ASIO_MOVE_CAST(E)(e)),
       target_(ASIO_MOVE_CAST(U)(u))
   {
   }
 
+  Executor executor_;
   T target_;
 };
 
@@ -393,7 +395,7 @@ class executor_binder
   /// Obtain the associated executor.
   executor_type get_executor() const ASIO_NOEXCEPT
   {
-    return static_cast<const Executor&>(*this);
+    return this->executor_;
   }
 
 #if defined(GENERATING_DOCUMENTATION)
@@ -519,30 +521,30 @@ struct uses_executor<executor_binder<T, Executor>, Executor>
   : true_type {};
 
 template <typename T, typename Executor, typename Signature>
-struct handler_type<executor_binder<T, Executor>, Signature>
+class async_result<executor_binder<T, Executor>, Signature>
 {
+public:
   typedef executor_binder<
-    typename handler_type<T, Signature>::type, Executor> type;
-};
+    typename async_result<T, Signature>::completion_handler_type, Executor>
+      completion_handler_type;
 
-template <typename T, typename Executor>
-class async_result<executor_binder<T, Executor> >
-{
-public:
-  typedef typename async_result<T>::type type;
+  typedef typename async_result<T, Signature>::return_type return_type;
 
   explicit async_result(executor_binder<T, Executor>& b)
     : target_(b.get())
   {
   }
 
-  type get()
+  return_type get()
   {
     return target_.get();
   }
 
 private:
-  async_result<T> target_;
+  async_result(const async_result&) ASIO_DELETED;
+  async_result& operator=(const async_result&) ASIO_DELETED;
+
+  async_result<T, Signature> target_;
 };
 
 template <typename T, typename Executor, typename Allocator>

diff --git a/link/asio/buffer.hpp b/link/asio/buffer.hpp
diff --git a/link/asio/buffered_read_stream.hpp b/link/asio/buffered_read_stream.hpp
@@ -2,7 +2,7 @@
 // buffered_read_stream.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -26,7 +26,6 @@
 #include "asio/detail/noncopyable.hpp"
 #include "asio/detail/type_traits.hpp"
 #include "asio/error.hpp"
-#include "asio/io_context.hpp"
 
 #include "asio/detail/push_options.hpp"
 
@@ -105,32 +104,17 @@ class buffered_read_stream
     return next_layer_.lowest_layer().get_executor();
   }
 
-#if !defined(ASIO_NO_DEPRECATED)
-  /// (Deprecated: Use get_executor().) Get the io_context associated with the
-  /// object.
-  asio::io_context& get_io_context()
-  {
-    return next_layer_.get_io_context();
-  }
-
-  /// (Deprecated: Use get_executor().) Get the io_context associated with the
-  /// object.
-  asio::io_context& get_io_service()
-  {
-    return next_layer_.get_io_service();
-  }
-#endif // !defined(ASIO_NO_DEPRECATED)
-
   /// Close the stream.
   void close()
   {
     next_layer_.close();
   }
 
   /// Close the stream.
-  asio::error_code close(asio::error_code& ec)
+  ASIO_SYNC_OP_VOID close(asio::error_code& ec)
   {
-    return next_layer_.close(ec);
+    next_layer_.close(ec);
+    ASIO_SYNC_OP_VOID_RETURN(ec);
   }
 
   /// Write the given data to the stream. Returns the number of bytes written.
@@ -158,14 +142,8 @@ class buffered_read_stream
   async_write_some(const ConstBufferSequence& buffers,
       ASIO_MOVE_ARG(WriteHandler) handler)
   {
-    async_completion<WriteHandler,
-      void (asio::error_code, std::size_t)> init(handler);
-
-    next_layer_.async_write_some(buffers,
-        ASIO_MOVE_CAST(ASIO_HANDLER_TYPE(WriteHandler,
-            void (asio::error_code, std::size_t)))(init.handler));
-
-    return init.result.get();
+    return next_layer_.async_write_some(buffers,
+        ASIO_MOVE_CAST(WriteHandler)(handler));
   }
 
   /// Fill the buffer with some data. Returns the number of bytes placed in the

diff --git a/link/asio/buffered_read_stream_fwd.hpp b/link/asio/buffered_read_stream_fwd.hpp
@@ -2,7 +2,7 @@
 // buffered_read_stream_fwd.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/buffered_stream.hpp b/link/asio/buffered_stream.hpp
@@ -2,7 +2,7 @@
 // buffered_stream.hpp
 // ~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -23,7 +23,6 @@
 #include "asio/buffered_stream_fwd.hpp"
 #include "asio/detail/noncopyable.hpp"
 #include "asio/error.hpp"
-#include "asio/io_context.hpp"
 
 #include "asio/detail/push_options.hpp"
 
@@ -96,32 +95,17 @@ class buffered_stream
     return stream_impl_.lowest_layer().get_executor();
   }
 
-#if !defined(ASIO_NO_DEPRECATED)
-  /// (Deprecated: Use get_executor().) Get the io_context associated with the
-  /// object.
-  asio::io_context& get_io_context()
-  {
-    return stream_impl_.get_io_context();
-  }
-
-  /// (Deprecated: Use get_executor().) Get the io_context associated with the
-  /// object.
-  asio::io_context& get_io_service()
-  {
-    return stream_impl_.get_io_service();
-  }
-#endif // !defined(ASIO_NO_DEPRECATED)
-
   /// Close the stream.
   void close()
   {
     stream_impl_.close();
   }
 
   /// Close the stream.
-  asio::error_code close(asio::error_code& ec)
+  ASIO_SYNC_OP_VOID close(asio::error_code& ec)
   {
-    return stream_impl_.close(ec);
+    stream_impl_.close(ec);
+    ASIO_SYNC_OP_VOID_RETURN(ec);
   }
 
   /// Flush all data from the buffer to the next layer. Returns the number of

diff --git a/link/asio/buffered_stream_fwd.hpp b/link/asio/buffered_stream_fwd.hpp
@@ -2,7 +2,7 @@
 // buffered_stream_fwd.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/buffered_write_stream.hpp b/link/asio/buffered_write_stream.hpp
@@ -2,7 +2,7 @@
 // buffered_write_stream.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -25,7 +25,6 @@
 #include "asio/detail/noncopyable.hpp"
 #include "asio/detail/type_traits.hpp"
 #include "asio/error.hpp"
-#include "asio/io_context.hpp"
 #include "asio/write.hpp"
 
 #include "asio/detail/push_options.hpp"
@@ -105,32 +104,17 @@ class buffered_write_stream
     return next_layer_.lowest_layer().get_executor();
   }
 
-#if !defined(ASIO_NO_DEPRECATED)
-  /// (Deprecated: Use get_executor().) Get the io_context associated with the
-  /// object.
-  asio::io_context& get_io_context()
-  {
-    return next_layer_.get_io_context();
-  }
-
-  /// (Deprecated: Use get_executor().) Get the io_context associated with the
-  /// object.
-  asio::io_context& get_io_service()
-  {
-    return next_layer_.get_io_service();
-  }
-#endif // !defined(ASIO_NO_DEPRECATED)
-
   /// Close the stream.
   void close()
   {
     next_layer_.close();
   }
 
   /// Close the stream.
-  asio::error_code close(asio::error_code& ec)
+  ASIO_SYNC_OP_VOID close(asio::error_code& ec)
   {
-    return next_layer_.close(ec);
+    next_layer_.close(ec);
+    ASIO_SYNC_OP_VOID_RETURN(ec);
   }
 
   /// Flush all data from the buffer to the next layer. Returns the number of
@@ -193,14 +177,8 @@ class buffered_write_stream
   async_read_some(const MutableBufferSequence& buffers,
       ASIO_MOVE_ARG(ReadHandler) handler)
   {
-    async_completion<ReadHandler,
-      void (asio::error_code, std::size_t)> init(handler);
-
-    next_layer_.async_read_some(buffers,
-        ASIO_MOVE_CAST(ASIO_HANDLER_TYPE(ReadHandler,
-            void (asio::error_code, std::size_t)))(init.handler));
-
-    return init.result.get();
+    return next_layer_.async_read_some(buffers,
+        ASIO_MOVE_CAST(ReadHandler)(handler));
   }
 
   /// Peek at the incoming data on the stream. Returns the number of bytes read.

diff --git a/link/asio/buffered_write_stream_fwd.hpp b/link/asio/buffered_write_stream_fwd.hpp
@@ -2,7 +2,7 @@
 // buffered_write_stream_fwd.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/buffers_iterator.hpp b/link/asio/buffers_iterator.hpp
@@ -2,7 +2,7 @@
 // buffers_iterator.hpp
 // ~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -65,7 +65,44 @@ namespace detail
     typedef buffers_iterator_types_helper<is_mutable> helper;
     typedef typename helper::buffer_type buffer_type;
     typedef typename helper::template byte_type<ByteType>::type byte_type;
+    typedef typename BufferSequence::const_iterator const_iterator;
   };
+
+  template <typename ByteType>
+  struct buffers_iterator_types<mutable_buffer, ByteType>
+  {
+    typedef mutable_buffer buffer_type;
+    typedef ByteType byte_type;
+    typedef const mutable_buffer* const_iterator;
+  };
+
+  template <typename ByteType>
+  struct buffers_iterator_types<const_buffer, ByteType>
+  {
+    typedef const_buffer buffer_type;
+    typedef typename add_const<ByteType>::type byte_type;
+    typedef const const_buffer* const_iterator;
+  };
+
+#if !defined(ASIO_NO_DEPRECATED)
+
+  template <typename ByteType>
+  struct buffers_iterator_types<mutable_buffers_1, ByteType>
+  {
+    typedef mutable_buffer buffer_type;
+    typedef ByteType byte_type;
+    typedef const mutable_buffer* const_iterator;
+  };
+
+  template <typename ByteType>
+  struct buffers_iterator_types<const_buffers_1, ByteType>
+  {
+    typedef const_buffer buffer_type;
+    typedef typename add_const<ByteType>::type byte_type;
+    typedef const const_buffer* const_iterator;
+  };
+
+#endif // !defined(ASIO_NO_DEPRECATED)
 }
 
 /// A random access iterator over the bytes in a buffer sequence.
@@ -76,6 +113,9 @@ class buffers_iterator
   typedef typename detail::buffers_iterator_types<
       BufferSequence, ByteType>::buffer_type buffer_type;
 
+  typedef typename detail::buffers_iterator_types<BufferSequence,
+          ByteType>::const_iterator buffer_sequence_iterator_type;
+
 public:
   /// The type used for the distance between two iterators.
   typedef std::ptrdiff_t difference_type;
@@ -130,9 +170,9 @@ class buffers_iterator
 #endif // defined(__GNUC__) && (__GNUC__ == 4) && (__GNUC_MINOR__ == 3)
   {
     buffers_iterator new_iter;
-    new_iter.begin_ = buffers.begin();
-    new_iter.current_ = buffers.begin();
-    new_iter.end_ = buffers.end();
+    new_iter.begin_ = asio::buffer_sequence_begin(buffers);
+    new_iter.current_ = asio::buffer_sequence_begin(buffers);
+    new_iter.end_ = asio::buffer_sequence_end(buffers);
     while (new_iter.current_ != new_iter.end_)
     {
       new_iter.current_buffer_ = *new_iter.current_;
@@ -150,9 +190,9 @@ class buffers_iterator
 #endif // defined(__GNUC__) && (__GNUC__ == 4) && (__GNUC_MINOR__ == 3)
   {
     buffers_iterator new_iter;
-    new_iter.begin_ = buffers.begin();
-    new_iter.current_ = buffers.begin();
-    new_iter.end_ = buffers.end();
+    new_iter.begin_ = asio::buffer_sequence_begin(buffers);
+    new_iter.current_ = asio::buffer_sequence_begin(buffers);
+    new_iter.end_ = asio::buffer_sequence_end(buffers);
     while (new_iter.current_ != new_iter.end_)
     {
       buffer_type buffer = *new_iter.current_;
@@ -347,7 +387,7 @@ class buffers_iterator
     }
 
     // Find the previous non-empty buffer.
-    typename BufferSequence::const_iterator iter = current_;
+    buffer_sequence_iterator_type iter = current_;
     while (iter != begin_)
     {
       --iter;
@@ -426,7 +466,7 @@ class buffers_iterator
         }
 
         // Find the previous non-empty buffer.
-        typename BufferSequence::const_iterator iter = current_;
+        buffer_sequence_iterator_type iter = current_;
         while (iter != begin_)
         {
           --iter;
@@ -452,9 +492,9 @@ class buffers_iterator
 
   buffer_type current_buffer_;
   std::size_t current_buffer_position_;
-  typename BufferSequence::const_iterator begin_;
-  typename BufferSequence::const_iterator current_;
-  typename BufferSequence::const_iterator end_;
+  buffer_sequence_iterator_type begin_;
+  buffer_sequence_iterator_type current_;
+  buffer_sequence_iterator_type end_;
   std::size_t position_;
 };
 

diff --git a/link/asio/co_spawn.hpp b/link/asio/co_spawn.hpp
@@ -0,0 +1,88 @@
+//
+// co_spawn.hpp
+// ~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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 ASIO_CO_SPAWN_HPP
+#define ASIO_CO_SPAWN_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if defined(ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
+
+#include "asio/awaitable.hpp"
+#include "asio/execution_context.hpp"
+#include "asio/is_executor.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+template <typename T>
+struct awaitable_signature;
+
+template <typename T, typename Executor>
+struct awaitable_signature<awaitable<T, Executor>>
+{
+  typedef void type(std::exception_ptr, T);
+};
+
+template <typename Executor>
+struct awaitable_signature<awaitable<void, Executor>>
+{
+  typedef void type(std::exception_ptr);
+};
+
+} // namespace detail
+
+/// Spawn a new thread of execution.
+/**
+ * The entry point function object @c f must have the signature:
+ *
+ * @code awaitable<void, E> f(); @endcode
+ *
+ * where @c E is convertible from @c Executor.
+ */
+template <typename Executor, typename F, typename CompletionToken>
+ASIO_INITFN_RESULT_TYPE(CompletionToken,
+    typename detail::awaitable_signature<typename result_of<F()>::type>::type)
+co_spawn(const Executor& ex, F&& f, CompletionToken&& token,
+    typename enable_if<
+      is_executor<Executor>::value
+    >::type* = 0);
+
+/// Spawn a new thread of execution.
+/**
+ * The entry point function object @c f must have the signature:
+ *
+ * @code awaitable<void, E> f(); @endcode
+ *
+ * where @c E is convertible from @c ExecutionContext::executor_type.
+ */
+template <typename ExecutionContext, typename F, typename CompletionToken>
+ASIO_INITFN_RESULT_TYPE(CompletionToken,
+    typename detail::awaitable_signature<typename result_of<F()>::type>::type)
+co_spawn(ExecutionContext& ctx, F&& f, CompletionToken&& token,
+    typename enable_if<
+      is_convertible<ExecutionContext&, execution_context&>::value
+    >::type* = 0);
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#include "asio/impl/co_spawn.hpp"
+
+#endif // defined(ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
+
+#endif // ASIO_CO_SPAWN_HPP
diff --git a/link/asio/completion_condition.hpp b/link/asio/completion_condition.hpp
@@ -2,7 +2,7 @@
 // completion_condition.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/compose.hpp b/link/asio/compose.hpp
@@ -0,0 +1,136 @@
+//
+// compose.hpp
+// ~~~~~~~~~~~
+//
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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 ASIO_COMPOSE_HPP
+#define ASIO_COMPOSE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/async_result.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+#if defined(ASIO_HAS_VARIADIC_TEMPLATES) \
+  || defined(GENERATING_DOCUMENTATION)
+
+/// Launch an asynchronous operation with a stateful implementation.
+/**
+ * The async_compose function simplifies the implementation of composed
+ * asynchronous operations automatically wrapping a stateful function object
+ * with a conforming intermediate completion handler.
+ *
+ * @param implementation A function object that contains the implementation of
+ * the composed asynchronous operation. The first argument to the function
+ * object is a non-const reference to the enclosing intermediate completion
+ * handler. The remaining arguments are any arguments that originate from the
+ * completion handlers of any asynchronous operations performed by the
+ * implementation.
+
+ * @param token The completion token.
+ *
+ * @param io_objects_or_executors Zero or more I/O objects or I/O executors for
+ * which outstanding work must be maintained.
+ *
+ * @par Example:
+ *
+ * @code struct async_echo_implementation
+ * {
+ *   tcp::socket& socket_;
+ *   asio::mutable_buffer buffer_;
+ *   enum { starting, reading, writing } state_;
+ *
+ *   template <typename Self>
+ *   void operator()(Self& self,
+ *       asio::error_code error = {},
+ *       std::size_t n = 0)
+ *   {
+ *     switch (state_)
+ *     {
+ *     case starting:
+ *       state_ = reading;
+ *       socket_.async_read_some(
+ *           buffer_, std::move(self));
+ *       break;
+ *     case reading:
+ *       if (error)
+ *       {
+ *         self.complete(error, 0);
+ *       }
+ *       else
+ *       {
+ *         state_ = writing;
+ *         asio::async_write(socket_, buffer_,
+ *             asio::transfer_exactly(n),
+ *             std::move(self));
+ *       }
+ *       break;
+ *     case writing:
+ *       self.complete(error, n);
+ *       break;
+ *     }
+ *   }
+ * };
+ *
+ * template <typename CompletionToken>
+ * auto async_echo(tcp::socket& socket,
+ *     asio::mutable_buffer buffer,
+ *     CompletionToken&& token) ->
+ *   typename asio::async_result<
+ *     typename std::decay<CompletionToken>::type,
+ *       void(asio::error_code, std::size_t)>::return_type
+ * {
+ *   return asio::async_compose<CompletionToken,
+ *     void(asio::error_code, std::size_t)>(
+ *       async_echo_implementation{socket, buffer,
+ *         async_echo_implementation::starting},
+ *       token, socket);
+ * } @endcode
+ */
+template <typename CompletionToken, typename Signature,
+    typename Implementation, typename... IoObjectsOrExecutors>
+ASIO_INITFN_RESULT_TYPE(CompletionToken, Signature)
+async_compose(ASIO_MOVE_ARG(Implementation) implementation,
+    ASIO_NONDEDUCED_MOVE_ARG(CompletionToken) token,
+    ASIO_MOVE_ARG(IoObjectsOrExecutors)... io_objects_or_executors);
+
+#else // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+      //   || defined(GENERATING_DOCUMENTATION)
+
+template <typename CompletionToken, typename Signature, typename Implementation>
+ASIO_INITFN_RESULT_TYPE(CompletionToken, Signature)
+async_compose(ASIO_MOVE_ARG(Implementation) implementation,
+    ASIO_NONDEDUCED_MOVE_ARG(CompletionToken) token);
+
+#define ASIO_PRIVATE_ASYNC_COMPOSE_DEF(n) \
+  template <typename CompletionToken, typename Signature, \
+      typename Implementation, ASIO_VARIADIC_TPARAMS(n)> \
+  ASIO_INITFN_RESULT_TYPE(CompletionToken, Signature) \
+  async_compose(ASIO_MOVE_ARG(Implementation) implementation, \
+      ASIO_NONDEDUCED_MOVE_ARG(CompletionToken) token, \
+      ASIO_VARIADIC_MOVE_PARAMS(n));
+  /**/
+  ASIO_VARIADIC_GENERATE(ASIO_PRIVATE_ASYNC_COMPOSE_DEF)
+#undef ASIO_PRIVATE_ASYNC_COMPOSE_DEF
+
+#endif // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+       //   || defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#include "asio/impl/compose.hpp"
+
+#endif // ASIO_COMPOSE_HPP
diff --git a/link/asio/connect.hpp b/link/asio/connect.hpp
diff --git a/link/asio/coroutine.hpp b/link/asio/coroutine.hpp
@@ -2,7 +2,7 @@
 // coroutine.hpp
 // ~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -205,7 +205,7 @@ class coroutine_ref;
  * {
  *   do
  *   {
- *     socket_.reset(new tcp::socket(io_context_));
+ *     socket_.reset(new tcp::socket(my_context_));
  *     yield acceptor->async_accept(*socket_, *this);
  *     fork server(*this)();
  *   } while (is_parent());
@@ -227,7 +227,7 @@ class coroutine_ref;
  * Note that @c fork doesn't do the actual forking by itself. It is the
  * application's responsibility to create a clone of the coroutine and call it.
  * The clone can be called immediately, as above, or scheduled for delayed
- * execution using something like io_context::post().
+ * execution using something like asio::post().
  *
  * @par Alternate macro names
  *
@@ -289,7 +289,7 @@ class coroutine_ref
       bail_out_of_coroutine: \
       break; \
     } \
-    else case 0:
+    else /* fall-through */ case 0:
 
 #define ASIO_CORO_YIELD_IMPL(n) \
   for (_coro_value = (n);;) \
@@ -301,12 +301,12 @@ class coroutine_ref
     else \
       switch (_coro_value ? 0 : 1) \
         for (;;) \
-          case -1: if (_coro_value) \
+          /* fall-through */ case -1: if (_coro_value) \
             goto terminate_coroutine; \
           else for (;;) \
-            case 1: if (_coro_value) \
+            /* fall-through */ case 1: if (_coro_value) \
               goto bail_out_of_coroutine; \
-            else case 0:
+            else /* fall-through */ case 0:
 
 #define ASIO_CORO_FORK_IMPL(n) \
   for (_coro_value = -(n);; _coro_value = (n)) \

diff --git a/link/asio/datagram_socket_service.hpp b/link/asio/datagram_socket_service.hpp
diff --git a/link/asio/deadline_timer.hpp b/link/asio/deadline_timer.hpp
@@ -2,7 +2,7 @@
 // deadline_timer.hpp
 // ~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/deadline_timer_service.hpp b/link/asio/deadline_timer_service.hpp
diff --git a/link/asio/defer.hpp b/link/asio/defer.hpp
@@ -2,7 +2,7 @@
 // defer.hpp
 // ~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -31,6 +31,11 @@ namespace asio {
  * executor. The function object is queued for execution, and is never called
  * from the current thread prior to returning from <tt>defer()</tt>.
  *
+ * The use of @c defer(), rather than @ref post(), indicates the caller's
+ * preference that the executor defer the queueing of the function object. This
+ * may allow the executor to optimise queueing for cases when the function
+ * object represents a continuation of the current call context.
+ *
  * This function has the following effects:
  *
  * @li Constructs a function object handler of type @c Handler, initialized
@@ -59,6 +64,11 @@ ASIO_INITFN_RESULT_TYPE(CompletionToken, void()) defer(
  * The function object is queued for execution, and is never called from the
  * current thread prior to returning from <tt>defer()</tt>.
  *
+ * The use of @c defer(), rather than @ref post(), indicates the caller's
+ * preference that the executor defer the queueing of the function object. This
+ * may allow the executor to optimise queueing for cases when the function
+ * object represents a continuation of the current call context.
+ *
  * This function has the following effects:
  *
  * @li Constructs a function object handler of type @c Handler, initialized

diff --git a/link/asio/detached.hpp b/link/asio/detached.hpp
@@ -0,0 +1,62 @@
+//
+// detached.hpp
+// ~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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 ASIO_DETACHED_HPP
+#define ASIO_DETACHED_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <memory>
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+/// Class used to specify that an asynchronous operation is detached.
+/**
+
+ * The detached_t class is used to indicate that an asynchronous operation is
+ * detached. That is, there is no completion handler waiting for the
+ * operation's result. A detached_t object may be passed as a handler to an
+ * asynchronous operation, typically using the special value
+ * @c asio::detached. For example:
+
+ * @code my_socket.async_send(my_buffer, asio::detached);
+ * @endcode
+ */
+class detached_t
+{
+public:
+  /// Constructor. 
+  ASIO_CONSTEXPR detached_t()
+  {
+  }
+};
+
+/// A special value, similar to std::nothrow.
+/**
+ * See the documentation for asio::detached_t for a usage example.
+ */
+#if defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr detached_t detached;
+#elif defined(ASIO_MSVC)
+__declspec(selectany) detached_t detached;
+#endif
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#include "asio/impl/detached.hpp"
+
+#endif // ASIO_DETACHED_HPP
diff --git a/link/asio/detail/array.hpp b/link/asio/detail/array.hpp
@@ -2,7 +2,7 @@
 // detail/array.hpp
 // ~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/detail/array_fwd.hpp b/link/asio/detail/array_fwd.hpp
@@ -2,7 +2,7 @@
 // detail/array_fwd.hpp
 // ~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/detail/assert.hpp b/link/asio/detail/assert.hpp
@@ -2,7 +2,7 @@
 // detail/assert.hpp
 // ~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/detail/atomic_count.hpp b/link/asio/detail/atomic_count.hpp
@@ -2,7 +2,7 @@
 // detail/atomic_count.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/detail/base_from_completion_cond.hpp b/link/asio/detail/base_from_completion_cond.hpp
@@ -2,7 +2,7 @@
 // detail/base_from_completion_cond.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -27,8 +27,9 @@ template <typename CompletionCondition>
 class base_from_completion_cond
 {
 protected:
-  explicit base_from_completion_cond(CompletionCondition completion_condition)
-    : completion_condition_(completion_condition)
+  explicit base_from_completion_cond(CompletionCondition& completion_condition)
+    : completion_condition_(
+        ASIO_MOVE_CAST(CompletionCondition)(completion_condition))
   {
   }
 

diff --git a/link/asio/detail/bind_handler.hpp b/link/asio/detail/bind_handler.hpp
@@ -2,7 +2,7 @@
 // detail/bind_handler.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -223,6 +223,363 @@ inline binder2<typename decay<Handler>::type, Arg1, Arg2> bind_handler(
       ASIO_MOVE_CAST(Handler)(handler), arg1, arg2);
 }
 
+template <typename Handler, typename Arg1, typename Arg2, typename Arg3>
+class binder3
+{
+public:
+  template <typename T>
+  binder3(int, ASIO_MOVE_ARG(T) handler, const Arg1& arg1,
+      const Arg2& arg2, const Arg3& arg3)
+    : handler_(ASIO_MOVE_CAST(T)(handler)),
+      arg1_(arg1),
+      arg2_(arg2),
+      arg3_(arg3)
+  {
+  }
+
+  binder3(Handler& handler, const Arg1& arg1,
+      const Arg2& arg2, const Arg3& arg3)
+    : handler_(ASIO_MOVE_CAST(Handler)(handler)),
+      arg1_(arg1),
+      arg2_(arg2),
+      arg3_(arg3)
+  {
+  }
+
+#if defined(ASIO_HAS_MOVE)
+  binder3(const binder3& other)
+    : handler_(other.handler_),
+      arg1_(other.arg1_),
+      arg2_(other.arg2_),
+      arg3_(other.arg3_)
+  {
+  }
+
+  binder3(binder3&& other)
+    : handler_(ASIO_MOVE_CAST(Handler)(other.handler_)),
+      arg1_(ASIO_MOVE_CAST(Arg1)(other.arg1_)),
+      arg2_(ASIO_MOVE_CAST(Arg2)(other.arg2_)),
+      arg3_(ASIO_MOVE_CAST(Arg3)(other.arg3_))
+  {
+  }
+#endif // defined(ASIO_HAS_MOVE)
+
+  void operator()()
+  {
+    handler_(static_cast<const Arg1&>(arg1_),
+        static_cast<const Arg2&>(arg2_), static_cast<const Arg3&>(arg3_));
+  }
+
+  void operator()() const
+  {
+    handler_(arg1_, arg2_, arg3_);
+  }
+
+//private:
+  Handler handler_;
+  Arg1 arg1_;
+  Arg2 arg2_;
+  Arg3 arg3_;
+};
+
+template <typename Handler, typename Arg1, typename Arg2, typename Arg3>
+inline void* asio_handler_allocate(std::size_t size,
+    binder3<Handler, Arg1, Arg2, Arg3>* this_handler)
+{
+  return asio_handler_alloc_helpers::allocate(
+      size, this_handler->handler_);
+}
+
+template <typename Handler, typename Arg1, typename Arg2, typename Arg3>
+inline void asio_handler_deallocate(void* pointer, std::size_t size,
+    binder3<Handler, Arg1, Arg2, Arg3>* this_handler)
+{
+  asio_handler_alloc_helpers::deallocate(
+      pointer, size, this_handler->handler_);
+}
+
+template <typename Handler, typename Arg1, typename Arg2, typename Arg3>
+inline bool asio_handler_is_continuation(
+    binder3<Handler, Arg1, Arg2, Arg3>* this_handler)
+{
+  return asio_handler_cont_helpers::is_continuation(
+      this_handler->handler_);
+}
+
+template <typename Function, typename Handler,
+    typename Arg1, typename Arg2, typename Arg3>
+inline void asio_handler_invoke(Function& function,
+    binder3<Handler, Arg1, Arg2, Arg3>* this_handler)
+{
+  asio_handler_invoke_helpers::invoke(
+      function, this_handler->handler_);
+}
+
+template <typename Function, typename Handler,
+    typename Arg1, typename Arg2, typename Arg3>
+inline void asio_handler_invoke(const Function& function,
+    binder3<Handler, Arg1, Arg2, Arg3>* this_handler)
+{
+  asio_handler_invoke_helpers::invoke(
+      function, this_handler->handler_);
+}
+
+template <typename Handler, typename Arg1, typename Arg2, typename Arg3>
+inline binder3<typename decay<Handler>::type, Arg1, Arg2, Arg3> bind_handler(
+    ASIO_MOVE_ARG(Handler) handler, const Arg1& arg1, const Arg2& arg2,
+    const Arg3& arg3)
+{
+  return binder3<typename decay<Handler>::type, Arg1, Arg2, Arg3>(0,
+      ASIO_MOVE_CAST(Handler)(handler), arg1, arg2, arg3);
+}
+
+template <typename Handler, typename Arg1,
+    typename Arg2, typename Arg3, typename Arg4>
+class binder4
+{
+public:
+  template <typename T>
+  binder4(int, ASIO_MOVE_ARG(T) handler, const Arg1& arg1,
+      const Arg2& arg2, const Arg3& arg3, const Arg4& arg4)
+    : handler_(ASIO_MOVE_CAST(T)(handler)),
+      arg1_(arg1),
+      arg2_(arg2),
+      arg3_(arg3),
+      arg4_(arg4)
+  {
+  }
+
+  binder4(Handler& handler, const Arg1& arg1,
+      const Arg2& arg2, const Arg3& arg3, const Arg4& arg4)
+    : handler_(ASIO_MOVE_CAST(Handler)(handler)),
+      arg1_(arg1),
+      arg2_(arg2),
+      arg3_(arg3),
+      arg4_(arg4)
+  {
+  }
+
+#if defined(ASIO_HAS_MOVE)
+  binder4(const binder4& other)
+    : handler_(other.handler_),
+      arg1_(other.arg1_),
+      arg2_(other.arg2_),
+      arg3_(other.arg3_),
+      arg4_(other.arg4_)
+  {
+  }
+
+  binder4(binder4&& other)
+    : handler_(ASIO_MOVE_CAST(Handler)(other.handler_)),
+      arg1_(ASIO_MOVE_CAST(Arg1)(other.arg1_)),
+      arg2_(ASIO_MOVE_CAST(Arg2)(other.arg2_)),
+      arg3_(ASIO_MOVE_CAST(Arg3)(other.arg3_)),
+      arg4_(ASIO_MOVE_CAST(Arg4)(other.arg4_))
+  {
+  }
+#endif // defined(ASIO_HAS_MOVE)
+
+  void operator()()
+  {
+    handler_(static_cast<const Arg1&>(arg1_),
+        static_cast<const Arg2&>(arg2_), static_cast<const Arg3&>(arg3_),
+        static_cast<const Arg4&>(arg4_));
+  }
+
+  void operator()() const
+  {
+    handler_(arg1_, arg2_, arg3_, arg4_);
+  }
+
+//private:
+  Handler handler_;
+  Arg1 arg1_;
+  Arg2 arg2_;
+  Arg3 arg3_;
+  Arg4 arg4_;
+};
+
+template <typename Handler, typename Arg1,
+    typename Arg2, typename Arg3, typename Arg4>
+inline void* asio_handler_allocate(std::size_t size,
+    binder4<Handler, Arg1, Arg2, Arg3, Arg4>* this_handler)
+{
+  return asio_handler_alloc_helpers::allocate(
+      size, this_handler->handler_);
+}
+
+template <typename Handler, typename Arg1,
+    typename Arg2, typename Arg3, typename Arg4>
+inline void asio_handler_deallocate(void* pointer, std::size_t size,
+    binder4<Handler, Arg1, Arg2, Arg3, Arg4>* this_handler)
+{
+  asio_handler_alloc_helpers::deallocate(
+      pointer, size, this_handler->handler_);
+}
+
+template <typename Handler, typename Arg1,
+    typename Arg2, typename Arg3, typename Arg4>
+inline bool asio_handler_is_continuation(
+    binder4<Handler, Arg1, Arg2, Arg3, Arg4>* this_handler)
+{
+  return asio_handler_cont_helpers::is_continuation(
+      this_handler->handler_);
+}
+
+template <typename Function, typename Handler, typename Arg1,
+    typename Arg2, typename Arg3, typename Arg4>
+inline void asio_handler_invoke(Function& function,
+    binder4<Handler, Arg1, Arg2, Arg3, Arg4>* this_handler)
+{
+  asio_handler_invoke_helpers::invoke(
+      function, this_handler->handler_);
+}
+
+template <typename Function, typename Handler, typename Arg1,
+    typename Arg2, typename Arg3, typename Arg4>
+inline void asio_handler_invoke(const Function& function,
+    binder4<Handler, Arg1, Arg2, Arg3, Arg4>* this_handler)
+{
+  asio_handler_invoke_helpers::invoke(
+      function, this_handler->handler_);
+}
+
+template <typename Handler, typename Arg1,
+    typename Arg2, typename Arg3, typename Arg4>
+inline binder4<typename decay<Handler>::type, Arg1, Arg2, Arg3, Arg4>
+bind_handler(ASIO_MOVE_ARG(Handler) handler, const Arg1& arg1,
+    const Arg2& arg2, const Arg3& arg3, const Arg4& arg4)
+{
+  return binder4<typename decay<Handler>::type, Arg1, Arg2, Arg3, Arg4>(0,
+      ASIO_MOVE_CAST(Handler)(handler), arg1, arg2, arg3, arg4);
+}
+
+template <typename Handler, typename Arg1, typename Arg2,
+    typename Arg3, typename Arg4, typename Arg5>
+class binder5
+{
+public:
+  template <typename T>
+  binder5(int, ASIO_MOVE_ARG(T) handler, const Arg1& arg1,
+      const Arg2& arg2, const Arg3& arg3, const Arg4& arg4, const Arg5& arg5)
+    : handler_(ASIO_MOVE_CAST(T)(handler)),
+      arg1_(arg1),
+      arg2_(arg2),
+      arg3_(arg3),
+      arg4_(arg4),
+      arg5_(arg5)
+  {
+  }
+
+  binder5(Handler& handler, const Arg1& arg1, const Arg2& arg2,
+      const Arg3& arg3, const Arg4& arg4, const Arg5& arg5)
+    : handler_(ASIO_MOVE_CAST(Handler)(handler)),
+      arg1_(arg1),
+      arg2_(arg2),
+      arg3_(arg3),
+      arg4_(arg4),
+      arg5_(arg5)
+  {
+  }
+
+#if defined(ASIO_HAS_MOVE)
+  binder5(const binder5& other)
+    : handler_(other.handler_),
+      arg1_(other.arg1_),
+      arg2_(other.arg2_),
+      arg3_(other.arg3_),
+      arg4_(other.arg4_),
+      arg5_(other.arg5_)
+  {
+  }
+
+  binder5(binder5&& other)
+    : handler_(ASIO_MOVE_CAST(Handler)(other.handler_)),
+      arg1_(ASIO_MOVE_CAST(Arg1)(other.arg1_)),
+      arg2_(ASIO_MOVE_CAST(Arg2)(other.arg2_)),
+      arg3_(ASIO_MOVE_CAST(Arg3)(other.arg3_)),
+      arg4_(ASIO_MOVE_CAST(Arg4)(other.arg4_)),
+      arg5_(ASIO_MOVE_CAST(Arg5)(other.arg5_))
+  {
+  }
+#endif // defined(ASIO_HAS_MOVE)
+
+  void operator()()
+  {
+    handler_(static_cast<const Arg1&>(arg1_),
+        static_cast<const Arg2&>(arg2_), static_cast<const Arg3&>(arg3_),
+        static_cast<const Arg4&>(arg4_), static_cast<const Arg5&>(arg5_));
+  }
+
+  void operator()() const
+  {
+    handler_(arg1_, arg2_, arg3_, arg4_, arg5_);
+  }
+
+//private:
+  Handler handler_;
+  Arg1 arg1_;
+  Arg2 arg2_;
+  Arg3 arg3_;
+  Arg4 arg4_;
+  Arg5 arg5_;
+};
+
+template <typename Handler, typename Arg1, typename Arg2,
+    typename Arg3, typename Arg4, typename Arg5>
+inline void* asio_handler_allocate(std::size_t size,
+    binder5<Handler, Arg1, Arg2, Arg3, Arg4, Arg5>* this_handler)
+{
+  return asio_handler_alloc_helpers::allocate(
+      size, this_handler->handler_);
+}
+
+template <typename Handler, typename Arg1, typename Arg2,
+    typename Arg3, typename Arg4, typename Arg5>
+inline void asio_handler_deallocate(void* pointer, std::size_t size,
+    binder5<Handler, Arg1, Arg2, Arg3, Arg4, Arg5>* this_handler)
+{
+  asio_handler_alloc_helpers::deallocate(
+      pointer, size, this_handler->handler_);
+}
+
+template <typename Handler, typename Arg1, typename Arg2,
+    typename Arg3, typename Arg4, typename Arg5>
+inline bool asio_handler_is_continuation(
+    binder5<Handler, Arg1, Arg2, Arg3, Arg4, Arg5>* this_handler)
+{
+  return asio_handler_cont_helpers::is_continuation(
+      this_handler->handler_);
+}
+
+template <typename Function, typename Handler, typename Arg1,
+    typename Arg2, typename Arg3, typename Arg4, typename Arg5>
+inline void asio_handler_invoke(Function& function,
+    binder5<Handler, Arg1, Arg2, Arg3, Arg4, Arg5>* this_handler)
+{
+  asio_handler_invoke_helpers::invoke(
+      function, this_handler->handler_);
+}
+
+template <typename Function, typename Handler, typename Arg1,
+    typename Arg2, typename Arg3, typename Arg4, typename Arg5>
+inline void asio_handler_invoke(const Function& function,
+    binder5<Handler, Arg1, Arg2, Arg3, Arg4, Arg5>* this_handler)
+{
+  asio_handler_invoke_helpers::invoke(
+      function, this_handler->handler_);
+}
+
+template <typename Handler, typename Arg1, typename Arg2,
+    typename Arg3, typename Arg4, typename Arg5>
+inline binder5<typename decay<Handler>::type, Arg1, Arg2, Arg3, Arg4, Arg5>
+bind_handler(ASIO_MOVE_ARG(Handler) handler, const Arg1& arg1,
+    const Arg2& arg2, const Arg3& arg3, const Arg4& arg4, const Arg5& arg5)
+{
+  return binder5<typename decay<Handler>::type, Arg1, Arg2, Arg3, Arg4, Arg5>(0,
+      ASIO_MOVE_CAST(Handler)(handler), arg1, arg2, arg3, arg4, arg5);
+}
+
 #if defined(ASIO_HAS_MOVE)
 
 template <typename Handler, typename Arg1>

diff --git a/link/asio/detail/buffer_resize_guard.hpp b/link/asio/detail/buffer_resize_guard.hpp
@@ -2,7 +2,7 @@
 // detail/buffer_resize_guard.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/detail/buffer_sequence_adapter.hpp b/link/asio/detail/buffer_sequence_adapter.hpp
@@ -2,7 +2,7 @@
 // detail/buffer_sequence_adapter.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -27,11 +27,12 @@ namespace detail {
 
 class buffer_sequence_adapter_base
 {
-protected:
 #if defined(ASIO_WINDOWS_RUNTIME)
+public:
   // The maximum number of buffers to support in a single operation.
   enum { max_buffers = 1 };
 
+protected:
   typedef Windows::Storage::Streams::IBuffer^ native_buffer_type;
 
   ASIO_DECL static void init_native_buffer(
@@ -42,9 +43,11 @@ class buffer_sequence_adapter_base
       native_buffer_type& buf,
       const asio::const_buffer& buffer);
 #elif defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+public:
   // The maximum number of buffers to support in a single operation.
   enum { max_buffers = 64 < max_iov_len ? 64 : max_iov_len };
 
+protected:
   typedef WSABUF native_buffer_type;
 
   static void init_native_buffer(WSABUF& buf,
@@ -61,9 +64,11 @@ class buffer_sequence_adapter_base
     buf.len = static_cast<ULONG>(buffer.size());
   }
 #else // defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+public:
   // The maximum number of buffers to support in a single operation.
   enum { max_buffers = 64 < max_iov_len ? 64 : max_iov_len };
 
+protected:
   typedef iovec native_buffer_type;
 
   static void init_iov_base(void*& base, void* addr)
@@ -102,14 +107,9 @@ class buffer_sequence_adapter
   explicit buffer_sequence_adapter(const Buffers& buffer_sequence)
     : count_(0), total_buffer_size_(0)
   {
-    typename Buffers::const_iterator iter = buffer_sequence.begin();
-    typename Buffers::const_iterator end = buffer_sequence.end();
-    for (; iter != end && count_ < max_buffers; ++iter, ++count_)
-    {
-      Buffer buffer(*iter);
-      init_native_buffer(buffers_[count_], buffer);
-      total_buffer_size_ += buffer.size();
-    }
+    buffer_sequence_adapter::init(
+        asio::buffer_sequence_begin(buffer_sequence),
+        asio::buffer_sequence_end(buffer_sequence));
   }
 
   native_buffer_type* buffers()
@@ -122,37 +122,76 @@ class buffer_sequence_adapter
     return count_;
   }
 
+  std::size_t total_size() const
+  {
+    return total_buffer_size_;
+  }
+
   bool all_empty() const
   {
     return total_buffer_size_ == 0;
   }
 
   static bool all_empty(const Buffers& buffer_sequence)
   {
-    typename Buffers::const_iterator iter = buffer_sequence.begin();
-    typename Buffers::const_iterator end = buffer_sequence.end();
+    return buffer_sequence_adapter::all_empty(
+        asio::buffer_sequence_begin(buffer_sequence),
+        asio::buffer_sequence_end(buffer_sequence));
+  }
+
+  static void validate(const Buffers& buffer_sequence)
+  {
+    buffer_sequence_adapter::validate(
+        asio::buffer_sequence_begin(buffer_sequence),
+        asio::buffer_sequence_end(buffer_sequence));
+  }
+
+  static Buffer first(const Buffers& buffer_sequence)
+  {
+    return buffer_sequence_adapter::first(
+        asio::buffer_sequence_begin(buffer_sequence),
+        asio::buffer_sequence_end(buffer_sequence));
+  }
+
+private:
+  template <typename Iterator>
+  void init(Iterator begin, Iterator end)
+  {
+    Iterator iter = begin;
+    for (; iter != end && count_ < max_buffers; ++iter, ++count_)
+    {
+      Buffer buffer(*iter);
+      init_native_buffer(buffers_[count_], buffer);
+      total_buffer_size_ += buffer.size();
+    }
+  }
+
+  template <typename Iterator>
+  static bool all_empty(Iterator begin, Iterator end)
+  {
+    Iterator iter = begin;
     std::size_t i = 0;
     for (; iter != end && i < max_buffers; ++iter, ++i)
       if (Buffer(*iter).size() > 0)
         return false;
     return true;
   }
 
-  static void validate(const Buffers& buffer_sequence)
+  template <typename Iterator>
+  static void validate(Iterator begin, Iterator end)
   {
-    typename Buffers::const_iterator iter = buffer_sequence.begin();
-    typename Buffers::const_iterator end = buffer_sequence.end();
+    Iterator iter = begin;
     for (; iter != end; ++iter)
     {
       Buffer buffer(*iter);
       buffer.data();
     }
   }
 
-  static Buffer first(const Buffers& buffer_sequence)
+  template <typename Iterator>
+  static Buffer first(Iterator begin, Iterator end)
   {
-    typename Buffers::const_iterator iter = buffer_sequence.begin();
-    typename Buffers::const_iterator end = buffer_sequence.end();
+    Iterator iter = begin;
     for (; iter != end; ++iter)
     {
       Buffer buffer(*iter);
@@ -162,12 +201,117 @@ class buffer_sequence_adapter
     return Buffer();
   }
 
-private:
   native_buffer_type buffers_[max_buffers];
   std::size_t count_;
   std::size_t total_buffer_size_;
 };
 
+template <typename Buffer>
+class buffer_sequence_adapter<Buffer, asio::mutable_buffer>
+  : buffer_sequence_adapter_base
+{
+public:
+  explicit buffer_sequence_adapter(
+      const asio::mutable_buffer& buffer_sequence)
+  {
+    init_native_buffer(buffer_, Buffer(buffer_sequence));
+    total_buffer_size_ = buffer_sequence.size();
+  }
+
+  native_buffer_type* buffers()
+  {
+    return &buffer_;
+  }
+
+  std::size_t count() const
+  {
+    return 1;
+  }
+
+  std::size_t total_size() const
+  {
+    return total_buffer_size_;
+  }
+
+  bool all_empty() const
+  {
+    return total_buffer_size_ == 0;
+  }
+
+  static bool all_empty(const asio::mutable_buffer& buffer_sequence)
+  {
+    return buffer_sequence.size() == 0;
+  }
+
+  static void validate(const asio::mutable_buffer& buffer_sequence)
+  {
+    buffer_sequence.data();
+  }
+
+  static Buffer first(const asio::mutable_buffer& buffer_sequence)
+  {
+    return Buffer(buffer_sequence);
+  }
+
+private:
+  native_buffer_type buffer_;
+  std::size_t total_buffer_size_;
+};
+
+template <typename Buffer>
+class buffer_sequence_adapter<Buffer, asio::const_buffer>
+  : buffer_sequence_adapter_base
+{
+public:
+  explicit buffer_sequence_adapter(
+      const asio::const_buffer& buffer_sequence)
+  {
+    init_native_buffer(buffer_, Buffer(buffer_sequence));
+    total_buffer_size_ = buffer_sequence.size();
+  }
+
+  native_buffer_type* buffers()
+  {
+    return &buffer_;
+  }
+
+  std::size_t count() const
+  {
+    return 1;
+  }
+
+  std::size_t total_size() const
+  {
+    return total_buffer_size_;
+  }
+
+  bool all_empty() const
+  {
+    return total_buffer_size_ == 0;
+  }
+
+  static bool all_empty(const asio::const_buffer& buffer_sequence)
+  {
+    return buffer_sequence.size() == 0;
+  }
+
+  static void validate(const asio::const_buffer& buffer_sequence)
+  {
+    buffer_sequence.data();
+  }
+
+  static Buffer first(const asio::const_buffer& buffer_sequence)
+  {
+    return Buffer(buffer_sequence);
+  }
+
+private:
+  native_buffer_type buffer_;
+  std::size_t total_buffer_size_;
+};
+
+#if !defined(ASIO_NO_DEPRECATED)
+
 template <typename Buffer>
 class buffer_sequence_adapter<Buffer, asio::mutable_buffers_1>
   : buffer_sequence_adapter_base
@@ -190,6 +334,11 @@ class buffer_sequence_adapter<Buffer, asio::mutable_buffers_1>
     return 1;
   }
 
+  std::size_t total_size() const
+  {
+    return total_buffer_size_;
+  }
+
   bool all_empty() const
   {
     return total_buffer_size_ == 0;
@@ -237,6 +386,11 @@ class buffer_sequence_adapter<Buffer, asio::const_buffers_1>
     return 1;
   }
 
+  std::size_t total_size() const
+  {
+    return total_buffer_size_;
+  }
+
   bool all_empty() const
   {
     return total_buffer_size_ == 0;
@@ -262,6 +416,8 @@ class buffer_sequence_adapter<Buffer, asio::const_buffers_1>
   std::size_t total_buffer_size_;
 };
 
+#endif // !defined(ASIO_NO_DEPRECATED)
+
 template <typename Buffer, typename Elem>
 class buffer_sequence_adapter<Buffer, boost::array<Elem, 2> >
   : buffer_sequence_adapter_base
@@ -285,6 +441,11 @@ class buffer_sequence_adapter<Buffer, boost::array<Elem, 2> >
     return 2;
   }
 
+  std::size_t total_size() const
+  {
+    return total_buffer_size_;
+  }
+
   bool all_empty() const
   {
     return total_buffer_size_ == 0;
@@ -337,6 +498,11 @@ class buffer_sequence_adapter<Buffer, std::array<Elem, 2> >
     return 2;
   }
 
+  std::size_t total_size() const
+  {
+    return total_buffer_size_;
+  }
+
   bool all_empty() const
   {
     return total_buffer_size_ == 0;

diff --git a/link/asio/detail/buffered_stream_storage.hpp b/link/asio/detail/buffered_stream_storage.hpp
@@ -2,7 +2,7 @@
 // detail/buffered_stream_storage.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/detail/call_stack.hpp b/link/asio/detail/call_stack.hpp
@@ -2,7 +2,7 @@
 // detail/call_stack.hpp
 // ~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/detail/chrono.hpp b/link/asio/detail/chrono.hpp
@@ -2,7 +2,7 @@
 // detail/chrono.hpp
 // ~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)
@@ -38,11 +38,11 @@ using std::chrono::minutes;
 using std::chrono::hours;
 using std::chrono::time_point_cast;
 #if defined(ASIO_HAS_STD_CHRONO_MONOTONIC_CLOCK)
-typedef std::chrono::monotonic_clock system_clock;
+typedef std::chrono::monotonic_clock steady_clock;
 #else // defined(ASIO_HAS_STD_CHRONO_MONOTONIC_CLOCK)
-using std::chrono::system_clock;
-#endif // defined(ASIO_HAS_STD_CHRONO_MONOTONIC_CLOCK)
 using std::chrono::steady_clock;
+#endif // defined(ASIO_HAS_STD_CHRONO_MONOTONIC_CLOCK)
+using std::chrono::system_clock;
 using std::chrono::high_resolution_clock;
 #elif defined(ASIO_HAS_BOOST_CHRONO)
 using boost::chrono::duration;

diff --git a/link/asio/detail/chrono_time_traits.hpp b/link/asio/detail/chrono_time_traits.hpp
@@ -2,7 +2,7 @@
 // detail/chrono_time_traits.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/detail/completion_handler.hpp b/link/asio/detail/completion_handler.hpp
@@ -2,7 +2,7 @@
 // detail/completion_handler.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 //
-// Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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)

diff --git a/link/asio/detail/concurrency_hint.hpp b/link/asio/detail/concurrency_hint.hpp
@@ -0,0 +1,94 @@
+//
+// detail/concurrency_hint.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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 ASIO_DETAIL_CONCURRENCY_HINT_HPP
+#define ASIO_DETAIL_CONCURRENCY_HINT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/noncopyable.hpp"
+
+// The concurrency hint ID and mask are used to identify when a "well-known"
+// concurrency hint value has been passed to the io_context.
+#define ASIO_CONCURRENCY_HINT_ID 0xA5100000u
+#define ASIO_CONCURRENCY_HINT_ID_MASK 0xFFFF0000u
+
+// If set, this bit indicates that the scheduler should perform locking.
+#define ASIO_CONCURRENCY_HINT_LOCKING_SCHEDULER 0x1u
+
+// If set, this bit indicates that the reactor should perform locking when
+// managing descriptor registrations.
+#define ASIO_CONCURRENCY_HINT_LOCKING_REACTOR_REGISTRATION 0x2u
+
+// If set, this bit indicates that the reactor should perform locking for I/O.
+#define ASIO_CONCURRENCY_HINT_LOCKING_REACTOR_IO 0x4u
+
+// Helper macro to determine if we have a special concurrency hint.
+#define ASIO_CONCURRENCY_HINT_IS_SPECIAL(hint) \
+  ((static_cast<unsigned>(hint) \
+    & ASIO_CONCURRENCY_HINT_ID_MASK) \
+      == ASIO_CONCURRENCY_HINT_ID)
+
+// Helper macro to determine if locking is enabled for a given facility.
+#define ASIO_CONCURRENCY_HINT_IS_LOCKING(facility, hint) \
+  (((static_cast<unsigned>(hint) \
+    & (ASIO_CONCURRENCY_HINT_ID_MASK \
+      | ASIO_CONCURRENCY_HINT_LOCKING_ ## facility)) \
+        ^ ASIO_CONCURRENCY_HINT_ID) != 0)
+
+// This special concurrency hint disables locking in both the scheduler and
+// reactor I/O. This hint has the following restrictions:
+//
+// - Care must be taken to ensure that all operations on the io_context and any
+//   of its associated I/O objects (such as sockets and timers) occur in only
+//   one thread at a time.
+//
+// - Asynchronous resolve operations fail with operation_not_supported.
+//
+// - If a signal_set is used with the io_context, signal_set objects cannot be
+//   used with any other io_context in the program.
+#define ASIO_CONCURRENCY_HINT_UNSAFE \
+  static_cast<int>(ASIO_CONCURRENCY_HINT_ID)
+
+// This special concurrency hint disables locking in the reactor I/O. This hint
+// has the following restrictions:
+//
+// - Care must be taken to ensure that run functions on the io_context, and all
+//   operations on the io_context's associated I/O objects (such as sockets and
+//   timers), occur in only one thread at a time.
+#define ASIO_CONCURRENCY_HINT_UNSAFE_IO \
+  static_cast<int>(ASIO_CONCURRENCY_HINT_ID \
+      | ASIO_CONCURRENCY_HINT_LOCKING_SCHEDULER \
+      | ASIO_CONCURRENCY_HINT_LOCKING_REACTOR_REGISTRATION)
+
+// The special concurrency hint provides full thread safety.
+#define ASIO_CONCURRENCY_HINT_SAFE \
+  static_cast<int>(ASIO_CONCURRENCY_HINT_ID \
+      | ASIO_CONCURRENCY_HINT_LOCKING_SCHEDULER \
+      | ASIO_CONCURRENCY_HINT_LOCKING_REACTOR_REGISTRATION \
+      | ASIO_CONCURRENCY_HINT_LOCKING_REACTOR_IO)
+
+// This #define may be overridden at compile time to specify a program-wide
+// default concurrency hint, used by the zero-argument io_context constructor.
+#if !defined(ASIO_CONCURRENCY_HINT_DEFAULT)
+# define ASIO_CONCURRENCY_HINT_DEFAULT -1
+#endif // !defined(ASIO_CONCURRENCY_HINT_DEFAULT)
+
+// This #define may be overridden at compile time to specify a program-wide
+// concurrency hint, used by the one-argument io_context constructor when
+// passed a value of 1.
+#if !defined(ASIO_CONCURRENCY_HINT_1)
+# define ASIO_CONCURRENCY_HINT_1 1
+#endif // !defined(ASIO_CONCURRENCY_HINT_DEFAULT)
+
+#endif // ASIO_DETAIL_CONCURRENCY_HINT_HPP
diff --git a/link/asio/detail/conditionally_enabled_event.hpp b/link/asio/detail/conditionally_enabled_event.hpp
@@ -0,0 +1,112 @@
+//
+// detail/conditionally_enabled_event.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff 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 ASIO_DETAIL_CONDITIONALLY_ENABLED_EVENT_HPP
+#define ASIO_DETAIL_CONDITIONALLY_ENABLED_EVENT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/conditionally_enabled_mutex.hpp"
+#include "asio/detail/event.hpp"
+#include "asio/detail/noncopyable.hpp"
+#include "asio/detail/null_event.hpp"
+#include "asio/detail/scoped_lock.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+// Mutex adapter used to conditionally enable or disable locking.
+class conditionally_enabled_event
+  : private noncopyable
+{
+public:
+  // Constructor.
+  conditionally_enabled_event()
+  {
+  }
+
+  // Destructor.
+  ~conditionally_enabled_event()
+  {
+  }
+
+  // Signal the event. (Retained for backward compatibility.)
+  void signal(conditionally_enabled_mutex::scoped_lock& lock)
+  {
+    if (lock.mutex_.enabled_)
+      event_.signal(lock);
+  }
+
+  // Signal all waiters.
+  void signal_all(conditionally_enabled_mutex::scoped_lock& lock)
+  {
+    if (lock.mutex_.enabled_)
+      event_.signal_all(lock);
+  }
+
+  // Unlock the mutex and signal one waiter.
+  void unlock_and_signal_one(
+      conditionally_enabled_mutex::scoped_lock& lock)
+  {
+    if (lock.mutex_.enabled_)
+      event_.unlock_and_signal_one(lock);
+  }
+
+  // If there's a waiter, unlock the mutex and signal it.
+  bool maybe_unlock_and_signal_one(
+      conditionally_enabled_mutex::scoped_lock& lock)
+  {
+    if (lock.mutex_.enabled_)
+      return event_.maybe_unlock_and_signal_one(lock);
+    else
+      return false;
+  }
+
+  // Reset the event.
+  void clear(conditionally_enabled_mutex::scoped_lock& lock)
+  {
+    if (lock.mutex_.enabled_)
+      event_.clear(lock);
+  }
+
+  // Wait for the event to become signalled.
+  void wait(conditionally_enabled_mutex::scoped_lock& lock)
+  {
+    if (lock.mutex_.enabled_)
+      event_.wait(lock);
+    else
+      null_event().wait(lock);
+  }
+
+  // Timed wait for the event to become signalled.
+  bool wait_for_usec(
+      conditionally_enabled_mutex::scoped_lock& lock, long usec)
+  {
+    if (lock.mutex_.enabled_)
+      return event_.wait_for_usec(lock, usec);
+    else
+      return null_event().wait_for_usec(lock, usec);
+  }
+
+private:
+  asio::detail::event event_;
+};
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_DETAIL_CONDITIONALLY_ENABLED_EVENT_HPP