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       1                 :             : /*
       2                 :             :  * Copyright 2025 Jinwoo Sung
       3                 :             :  *
       4                 :             :  * Licensed under the Apache License, Version 2.0 (the "License");
       5                 :             :  * you may not use this file except in compliance with the License.
       6                 :             :  * You may obtain a copy of the License at
       7                 :             :  *
       8                 :             :  *     http://www.apache.org/licenses/LICENSE-2.0
       9                 :             :  *
      10                 :             :  * Unless required by applicable law or agreed to in writing, software
      11                 :             :  * distributed under the License is distributed on an "AS IS" BASIS,
      12                 :             :  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      13                 :             :  * See the License for the specific language governing permissions and
      14                 :             :  * limitations under the License.
      15                 :             :  */
      16                 :             : 
      17                 :             : #pragma once
      18                 :             : 
      19                 :             : #include <optional>
      20                 :             : #include <variant>
      21                 :             : 
      22                 :             : #include "wirestead/interface/result_channel.hpp"
      23                 :             : 
      24                 :             : namespace wirestead::interface {
      25                 :             : 
      26                 :             : /**
      27                 :             :  * A single connection pinned for one Reliable send, including capacity retries.
      28                 :             :  *
      29                 :             :  * All methods return promptly and serialize with connection replacement, stop
      30                 :             :  * and admission. No method invokes a Channel/user callback inline.
      31                 :             :  * The handle keeps its connection record alive after reconnect; it must never
      32                 :             :  * redirect a write to a replacement connection.
      33                 :             :  */
      34                 :             : class WIRESTEAD_API WriteConnection {
      35                 :             :  public:
      36                 :        1067 :   virtual ~WriteConnection() = default;
      37                 :             : 
      38                 :             :   /**
      39                 :             :    * nullopt: capacity is still blocked; acceptance: retry admission now.
      40                 :             :    * Neither acceptance nor polling reserves capacity.
      41                 :             :    * Connection loss ends a blocked wait with NotReady; cancellation by stop
      42                 :             :    * ends it with CancelledWhileWaiting. Retain the first terminal cause on
      43                 :             :    * the connection record, under the same lock as these events, even when
      44                 :             :    * stop, loss and reconnect all happen before the next poll.
      45                 :             :    */
      46                 :             :   [[nodiscard]] virtual std::optional<wrapper::SendResult> poll_capacity() = 0;
      47                 :             : 
      48                 :             :   // Validate the pinned connection and admit atomically. WouldBlock is the only
      49                 :             :   // retryable refusal. Rejected moves retain their input; rejected shared writes
      50                 :             :   // retain no ownership. Acceptance means local queue admission, not delivery.
      51                 :             :   [[nodiscard]] virtual wrapper::SendResult write_copy(memory::ConstByteSpan data) = 0;
      52                 :             :   [[nodiscard]] virtual wrapper::SendResult write_move(std::vector<uint8_t>&& data) = 0;
      53                 :             :   [[nodiscard]] virtual wrapper::SendResult write_shared(std::shared_ptr<const std::vector<uint8_t>> data) = 0;
      54                 :             : };
      55                 :             : 
      56                 :             : /**
      57                 :             :  * Optional custom Channel capability for connection-pinned Reliable sends.
      58                 :             :  *
      59                 :             :  * ResultChannel supplies nonblocking admission. This extension additionally
      60                 :             :  * supplies atomic connection capture, capacity polling and pinned admission.
      61                 :             :  * Client wrapper injection requires this capability or its matching native transport.
      62                 :             :  */
      63                 :             : class WIRESTEAD_API ConnectionChannel : public ResultChannel {
      64                 :             :  public:
      65                 :             :   using Connection = std::shared_ptr<WriteConnection>;
      66                 :             :   using CaptureResult = std::variant<wrapper::SendRejection, Connection>;
      67                 :             : 
      68                 :             :   // Check readiness and capture the current connection in one decision. Return
      69                 :             :   // an actual rejection or a non-null handle, never an unpinned success.
      70                 :             :   [[nodiscard]] virtual CaptureResult capture_write_connection() = 0;
      71                 :             : 
      72                 :             :   // Called before wrapper stop releases waiters. Serialize with capture, loss
      73                 :             :   // and admission; preserve an earlier terminal cause. Do not invoke callbacks
      74                 :             :   // inline or wait for an executor. Channel::stop must cancel waits too when
      75                 :             :   // the transport is stopped directly.
      76                 :             :   virtual void cancel_write_waits() = 0;
      77                 :             : };
      78                 :             : 
      79                 :             : }  // namespace wirestead::interface