pw_rpc/public/pw_rpc/channel.h

// Copyright 2020 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#pragma once

#include <cstdint>

#include "pw_assert/assert.h"
#include "pw_span/span.h"
#include "pw_status/status.h"

namespace pw::rpc {
namespace internal {

class BaseServerWriter;

}  // namespace internal

class ChannelOutput {
 public:
  constexpr ChannelOutput(uint32_t id) : id_(id) {}

  virtual ~ChannelOutput() = default;

  // Acquire a buffer into which to write an outgoing RPC packet.
  virtual span<std::byte> AcquireBuffer() = 0;

  // Sends the contents of the buffer from AcquireBuffer().
  virtual void SendAndReleaseBuffer(size_t size) = 0;

  uint32_t id() const { return id_; }

 private:
  uint32_t id_;
};

class Channel {
 public:
  static constexpr uint32_t kUnassignedChannelId = 0;

  // Creates a dynamically assignable channel without a set ID or output.
  constexpr Channel() : id_(kUnassignedChannelId), output_(nullptr) {}

  // Creates a channel with a static ID. The channel's output can also be
  // static, or it can set to null to allow dynamically opening connections
  // through the channel.
  template <uint32_t id>
  static Channel Create(ChannelOutput* output) {
    static_assert(id != kUnassignedChannelId, "Channel ID cannot be 0");
    return Channel(id, output);
  }

  constexpr uint32_t id() const { return id_; }
  constexpr bool assigned() const { return id_ != kUnassignedChannelId; }

 private:
  friend class Server;
  friend class internal::BaseServerWriter;

  span<std::byte> AcquireBuffer() const { return output_->AcquireBuffer(); }
  void SendAndReleaseBuffer(size_t size) const {
    output_->SendAndReleaseBuffer(size);
  }

  constexpr Channel(uint32_t id, ChannelOutput* output)
      : id_(id), output_(output) {
    PW_CHECK_UINT_NE(id, kUnassignedChannelId);
  }

  uint32_t id_;
  ChannelOutput* output_;
};

}  // namespace pw::rpc