channel_stack_builder.h

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// Copyright 2016 gRPC 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
//
//     http://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.
 
#ifndef GRPC_CORE_LIB_CHANNEL_CHANNEL_STACK_BUILDER_H
#define GRPC_CORE_LIB_CHANNEL_CHANNEL_STACK_BUILDER_H
 
#include <grpc/support/port_platform.h>
 
#include <string>
#include <vector>
 
#include "absl/status/statusor.h"
#include "absl/strings/string_view.h"
 
#include <grpc/support/log.h>
 
#include "src/core/lib/channel/channel_args.h"
#include "src/core/lib/channel/channel_fwd.h"
#include "src/core/lib/gprpp/ref_counted_ptr.h"
#include "src/core/lib/surface/channel_stack_type.h"
#include "src/core/lib/transport/transport_fwd.h"
 
namespace grpc_core {
 
// Build a channel stack.
// Allows interested parties to add filters to the stack, and to query an
// in-progress build.
// Carries some useful context for the channel stack, such as a target string
// and a transport.
class ChannelStackBuilder {
 public:
  // Initialize with a name.
  ChannelStackBuilder(const char* name, grpc_channel_stack_type type)
      : name_(name), type_(type) {}
 
  const char* name() const { return name_; }
 
  // Set the target string.
  ChannelStackBuilder& SetTarget(const char* target);
 
  // Query the target.
  absl::string_view target() const { return target_; }
 
  // Set the transport.
  ChannelStackBuilder& SetTransport(grpc_transport* transport) {
    GPR_ASSERT(transport_ == nullptr);
    transport_ = transport;
    return *this;
  }
 
  // Query the transport.
  grpc_transport* transport() const { return transport_; }
 
  // Set channel args (takes a copy of them).
  ChannelStackBuilder& SetChannelArgs(ChannelArgs args);
 
  // Query the channel args.
  const ChannelArgs& channel_args() const { return args_; }
 
  // Mutable vector of proposed stack entries.
  std::vector<const grpc_channel_filter*>* mutable_stack() { return &stack_; }
 
  // The type of channel stack being built.
  grpc_channel_stack_type channel_stack_type() const { return type_; }
 
  // Helper to add a filter to the front of the stack.
  void PrependFilter(const grpc_channel_filter* filter);
 
  // Helper to add a filter to the end of the stack.
  void AppendFilter(const grpc_channel_filter* filter);
 
  // Build the channel stack.
  // After success, *result holds the new channel stack,
  // prefix_bytes are allocated before the channel stack,
  // destroy is as per grpc_channel_stack_init
  // On failure, *result is nullptr.
  virtual absl::StatusOr<RefCountedPtr<grpc_channel_stack>> Build() = 0;
 
 protected:
  ~ChannelStackBuilder();
 
 private:
  static std::string unknown_target() { return "unknown"; }
 
  // The name of the stack
  const char* const name_;
  // The type of stack being built
  const grpc_channel_stack_type type_;
  // The target
  std::string target_{unknown_target()};
  // The transport
  grpc_transport* transport_ = nullptr;
  // Channel args
  ChannelArgs args_;
  // The in-progress stack
  std::vector<const grpc_channel_filter*> stack_;
};
 
}  // namespace grpc_core
 
#endif  // GRPC_CORE_LIB_CHANNEL_CHANNEL_STACK_BUILDER_H