pw_rpc/public/pw_rpc/internal/method_lookup.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 "pw_rpc/internal/method.h"

namespace pw::rpc::internal {

// Gets a Method object from a generated RPC service class. Getter functions are
// provided for each supported method implementation. The
//
// To ensure the MethodUnion actually holds the requested method type, the
// method ID is accessed in a static_assert. It is invalid to access an unset
// union member in a constant expression, so this results in a compiler error.
class MethodLookup {
 public:
  MethodLookup() = delete;

  template <typename Service, uint32_t kMethodId>
  static constexpr const auto& GetRawMethod() {
    const auto& method = GetMethodUnion<Service, kMethodId>().raw_method();
    static_assert(method.id() == kMethodId, "Incorrect method implementation");
    return method;
  }

  template <typename Service, uint32_t kMethodId>
  static constexpr const auto& GetPwpbMethod() {
    const auto& method = GetMethodUnion<Service, kMethodId>().pwpb_method();
    static_assert(method.id() == kMethodId, "Incorrect method implementation");
    return method;
  }

  template <typename Service, uint32_t kMethodId>
  static constexpr const auto& GetNanopbMethod() {
    const auto& method = GetMethodUnion<Service, kMethodId>().nanopb_method();
    static_assert(method.id() == kMethodId, "Incorrect method implementation");
    return method;
  }

 private:
  template <typename Service, uint32_t kMethodId>
  static constexpr const auto& GetMethodUnion() {
    constexpr auto method = GetMethodUnionPointer<Service>(kMethodId);
    static_assert(method != nullptr,
                  "The selected function is not an RPC service method");
    return *method;
  }

  template <typename Service>
  static constexpr typename decltype(Service::kPwRpcMethods)::const_pointer
  GetMethodUnionPointer(uint32_t kMethodId) {
    for (size_t i = 0; i < Service::kPwRpcMethodIds.size(); ++i) {
      if (Service::kPwRpcMethodIds[i] == kMethodId) {
        return &Service::kPwRpcMethods[i];
      }
    }
    return nullptr;
  }
};

}  // namespace pw::rpc::internal