Merge pull request #49 from seva-deriv/c++20/coro

Support CompletionToken instead of CompletionHandler

looks good to me, I'll emit a new release after fixing CI

README.md

@@ -19,7 +19,7 @@ Boost::ASIO low-level redis client (connector),
 - works on linux (clang, gcc) and windows (msvc)
 - synchronous & asynchronous interface
 - inspired by [beast](https://github.com/vinniefalco/Beast)
-- requirements: boost `v1.69` minimum
+- requirements: boost `v1.70` minimum
 
 ## Changelog
 
@@ -781,6 +781,7 @@ MIT
 - [Ronny Nowak](https://github.com/dargun)
 - [Stephen Chisholm](https://github.com/sbchisholm)
 - [amensel](https://github.com/amensel)
+- [Usevalad Sauta](https://github.com/VsevolodSauta)
 
 ## See also
 - https://github.com/Cylix/cpp_redis

include/bredis/Connection.hpp

@@ -44,19 +44,19 @@ template <typename NextLayer> class Connection {
     inline const NextLayer &next_layer() const { return stream_; }
 
     /* asynchronous interface */
-    template <typename DynamicBuffer, typename WriteCallback>
-    BOOST_ASIO_INITFN_RESULT_TYPE(WriteCallback,
+    template <typename DynamicBuffer, typename CompletionToken>
+    BOOST_ASIO_INITFN_RESULT_TYPE(CompletionToken,
                                   void(boost::system::error_code, std::size_t))
     async_write(DynamicBuffer &tx_buff, const command_wrapper_t &command,
-                WriteCallback &&write_callback);
+                CompletionToken &&completion_token);
 
-    template <typename DynamicBuffer, typename ReadCallback,
+    template <typename DynamicBuffer, typename CompletionToken,
               typename Policy = bredis::parsing_policy::keep_result>
-    BOOST_ASIO_INITFN_RESULT_TYPE(ReadCallback,
+    BOOST_ASIO_INITFN_RESULT_TYPE(CompletionToken,
                                   void(boost::system::error_code,
                                        BREDIS_PARSE_RESULT(DynamicBuffer,
                                                            Policy)))
-    async_read(DynamicBuffer &rx_buff, ReadCallback &&read_callback,
+    async_read(DynamicBuffer &rx_buff, CompletionToken &&completion_token,
                std::size_t replies_count = 1, Policy policy = Policy{});
 
     /* synchronous interface */

include/bredis/impl/async_op.ipp

@@ -111,16 +111,19 @@ struct result_visitor_t<Iterator, parsing_policy::keep_result>
     }
 };
 
-template <typename DynamicBuffer, typename Policy> struct async_read_op_impl {
+template <typename NextLayer, typename DynamicBuffer, typename Policy> struct async_read_op_impl {
+    NextLayer &stream_;
     DynamicBuffer &rx_buff_;
     std::size_t replies_count_;
+    enum class state_t { init, read, done } state_ = state_t::init;
 
-    async_read_op_impl(DynamicBuffer &rx_buff, std::size_t replies_count)
-        : rx_buff_{rx_buff}, replies_count_{replies_count} {}
     using Iterator = typename to_iterator<DynamicBuffer>::iterator_t;
     using ResultVisitor = result_visitor_t<Iterator, Policy>;
     using positive_result_t = parse_result_mapper_t<Iterator, Policy>;
 
+    async_read_op_impl(NextLayer &stream, DynamicBuffer &rx_buff, std::size_t replies_count) :
+        stream_(stream), rx_buff_(rx_buff), replies_count_(replies_count) {}
+
     positive_result_t op(boost::system::error_code &error_code,
                          std::size_t /*bytes_transferred*/) {
 
@@ -149,53 +152,25 @@ template <typename DynamicBuffer, typename Policy> struct async_read_op_impl {
         }
         return result;
     }
-};
-
-template <typename NextLayer, typename DynamicBuffer, typename ReadCallback,
-          typename Policy>
-class async_read_op {
-    NextLayer &stream_;
-    DynamicBuffer &rx_buff_;
-    std::size_t replies_count_;
-    ReadCallback callback_;
-
-  public:
-    async_read_op(async_read_op &&) = default;
-    async_read_op(const async_read_op &) = default;
-
-    template <class DeducedHandler>
-    async_read_op(DeducedHandler &&deduced_handler, NextLayer &stream,
-                  DynamicBuffer &rx_buff, std::size_t replies_count)
-        : stream_(stream), rx_buff_(rx_buff), replies_count_(replies_count),
-          callback_(std::forward<ReadCallback>(deduced_handler)) {}
 
-    void operator()(boost::system::error_code, std::size_t bytes_transferred);
-
-    friend bool asio_handler_is_continuation(async_read_op *op) {
-        using boost::asio::asio_handler_is_continuation;
-        return asio_handler_is_continuation(std::addressof(op->callback_));
-    }
-
-    boost::asio::associated_allocator_t<ReadCallback> get_allocator() const noexcept
-    {
-        return boost::asio::get_associated_allocator(callback_);
-    }
-
-    boost::asio::associated_executor_t<ReadCallback> get_executor() const noexcept
-    {
-        return boost::asio::get_associated_executor(callback_);
+    template<typename Self>
+    void operator()(Self& self, boost::system::error_code error_code = {}, std::size_t bytes_transferred = {}) {
+        switch (state_) {
+            case state_t::init:
+                state_ = state_t::read;
+                async_read_until(stream_, rx_buff_, MatchResult<Iterator>(replies_count_), std::move(self));
+                break;
+            case state_t::read:
+            {
+                state_ = state_t::done;
+                auto result = op(error_code, bytes_transferred); // Do not inline! We are sequencing computations
+                self.complete(error_code, result);
+                break;
+            }
+            default:
+                assert(false && "We are in unexpected state");
+        }
     }
 };
 
-template <typename NextLayer, typename DynamicBuffer, typename ReadCallback,
-          typename Policy>
-void async_read_op<NextLayer, DynamicBuffer, ReadCallback, Policy>::
-operator()(boost::system::error_code error_code,
-           std::size_t bytes_transferred) {
-    using op_impl = async_read_op_impl<DynamicBuffer, Policy>;
-    callback_(
-        error_code,
-        op_impl(rx_buff_, replies_count_).op(error_code, bytes_transferred));
-}
-
 } // namespace bredis

include/bredis/impl/connection.ipp

@@ -18,60 +18,37 @@
 namespace bredis {
 
 template <typename NextLayer>
-template <typename DynamicBuffer, typename WriteCallback>
-BOOST_ASIO_INITFN_RESULT_TYPE(WriteCallback,
+template <typename DynamicBuffer, typename CompletionToken>
+BOOST_ASIO_INITFN_RESULT_TYPE(CompletionToken,
                               void(boost::system::error_code, std::size_t))
 Connection<NextLayer>::async_write(DynamicBuffer &tx_buff,
                                    const command_wrapper_t &command,
-                                   WriteCallback &&write_callback) {
+                                   CompletionToken &&write_callback) {
     namespace asio = boost::asio;
     namespace sys = boost::system;
 
     using boost::asio::async_write;
-    using Signature = void(boost::system::error_code, std::size_t);
-    using Callback = boost::decay_t<WriteCallback>;
-    using AsyncResult = asio::async_result<Callback, Signature>;
-    using CompletionHandler = typename AsyncResult::completion_handler_type;
     using serializer_t = command_serializer_visitor<DynamicBuffer>;
 
     boost::apply_visitor(serializer_t(tx_buff), command);
-
-    CompletionHandler handler(std::forward<WriteCallback>(write_callback));
-    AsyncResult result(handler);
-    async_write(stream_, tx_buff, std::move(handler));
-    return result.get();
+    return async_write(stream_, tx_buff, std::forward<CompletionToken>(write_callback));
 }
 
 template <typename NextLayer>
-template <typename DynamicBuffer, typename ReadCallback, typename Policy>
-BOOST_ASIO_INITFN_RESULT_TYPE(ReadCallback,
-                              void(const boost::system::error_code,
+template <typename DynamicBuffer, typename CompletionToken, typename Policy>
+BOOST_ASIO_INITFN_RESULT_TYPE(CompletionToken,
+                              void(boost::system::error_code,
                                    BREDIS_PARSE_RESULT(DynamicBuffer, Policy)))
 Connection<NextLayer>::async_read(DynamicBuffer &rx_buff,
-                                  ReadCallback &&read_callback,
+                                  CompletionToken &&completion_token,
                                   std::size_t replies_count, Policy) {
-
-    namespace asio = boost::asio;
-    namespace sys = boost::system;
-
     using boost::asio::async_read_until;
-    using Iterator = typename to_iterator<DynamicBuffer>::iterator_t;
     using ParseResult = BREDIS_PARSE_RESULT(DynamicBuffer, Policy);
     using Signature = void(boost::system::error_code, ParseResult);
-    using Callback = boost::decay_t<ReadCallback>;
-    using AsyncResult = asio::async_result<Callback, Signature>;
-    using CompletionHandler = typename AsyncResult::completion_handler_type;
-    using ReadOp =
-        async_read_op<NextLayer, DynamicBuffer, CompletionHandler, Policy>;
-
-    CompletionHandler handler(std::forward<ReadCallback>(read_callback));
-    AsyncResult result(handler);
-
-    ReadOp async_op(std::move(handler), stream_, rx_buff, replies_count);
 
-    async_read_until(stream_, rx_buff, MatchResult<Iterator>(replies_count),
-                     std::move(async_op));
-    return result.get();
+    return boost::asio::async_compose<CompletionToken, Signature>(
+        async_read_op_impl<NextLayer, DynamicBuffer, Policy>{stream_, rx_buff, replies_count},
+        completion_token, stream_);
 }
 
 template <typename NextLayer>