chromium/third_party/grpc/src/src/core/lib/channel/channel_args.h

//
//
// Copyright 2015 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_SRC_CORE_LIB_CHANNEL_CHANNEL_ARGS_H
#define GRPC_SRC_CORE_LIB_CHANNEL_CHANNEL_ARGS_H

#include <grpc/support/port_platform.h>

#include <stddef.h>

#include <algorithm>  // IWYU pragma: keep
#include <iosfwd>
#include <memory>
#include <string>
#include <type_traits>
#include <utility>

#include "absl/meta/type_traits.h"
#include "absl/strings/string_view.h"
#include "absl/types/optional.h"
#include "absl/types/variant.h"

#include <grpc/event_engine/event_engine.h>
#include <grpc/grpc.h>

#include "src/core/lib/avl/avl.h"
#include "src/core/lib/gpr/useful.h"
#include "src/core/lib/gprpp/debug_location.h"
#include "src/core/lib/gprpp/dual_ref_counted.h"
#include "src/core/lib/gprpp/ref_counted.h"
#include "src/core/lib/gprpp/ref_counted_ptr.h"
#include "src/core/lib/gprpp/time.h"
#include "src/core/lib/surface/channel_stack_type.h"

// TODO(hork): When we're ready to allow setting via a channel arg from the
// application, replace this with a macro in
// include/grpc/impl/codegen/grpc_types.h.
#define GRPC_INTERNAL_ARG_EVENT_ENGINE …

// Channel args are intentionally immutable, to avoid the need for locking.

namespace grpc_core {

// Define a traits object for vtable lookup - allows us to integrate with
// existing code easily (just define the trait!) and allows some magic in
// ChannelArgs to automatically derive a vtable from a T*.
// To participate as a pointer, instances should expose the function:
//   // Gets the vtable for this type
//   static const grpc_arg_pointer_vtable* VTable();
//   // Performs any mutations required for channel args to own a pointer
//   // Only needed if ChannelArgs::Set is to be called with a raw pointer.
//   static void* TakeUnownedPointer(T* p);
template <typename T, typename Ignored = void /* for SFINAE */>
struct ChannelArgTypeTraits;

namespace channel_args_detail {
inline int PointerCompare(void* a_ptr, const grpc_arg_pointer_vtable* a_vtable,
                          void* b_ptr,
                          const grpc_arg_pointer_vtable* b_vtable) { … }

// The type returned by calling Ref() on a T - used to determine the basest-type
// before the crt refcount base class.
RefType;
}  // namespace channel_args_detail

// Specialization for ref-counted pointers.
// Types should expose:
// static int ChannelArgsCompare(const T* a, const T* b);
ChannelArgTypeTraits<T, absl::enable_if_t<std::is_base_of<RefCounted<channel_args_detail::RefType<T>>, channel_args_detail::RefType<T>>::value || std::is_base_of<RefCounted<channel_args_detail::RefType<T>, NonPolymorphicRefCount>, channel_args_detail::RefType<T>>::value || std::is_base_of<DualRefCounted<channel_args_detail::RefType<T>>, channel_args_detail::RefType<T>>::value, void>>;

// Specialization for shared_ptr
// Incurs an allocation because shared_ptr.release is not a thing.
template <typename T>
struct is_shared_ptr : std::false_type { … };
is_shared_ptr<std::shared_ptr<T>>;
ChannelArgTypeTraits<T, absl::enable_if_t<is_shared_ptr<T>::value, void>>;

// If a type declares some member 'struct RawPointerChannelArgTag {}' then
// we automatically generate a vtable for it that does not do any ownership
// management and compares the type by pointer identity.
// This is intended to be relatively ugly because *most types should worry about
// ownership*.
ChannelArgTypeTraits<T, absl::void_t<typename T::RawPointerChannelArgTag>>;

// GetObject support for shared_ptr and RefCountedPtr
template <typename T>
struct WrapInSharedPtr
    : std::integral_constant<
          bool, std::is_base_of<std::enable_shared_from_this<T>, T>::value> { … };
template <>
struct WrapInSharedPtr<grpc_event_engine::experimental::EventEngine>
    : std::true_type { … };
template <typename T, typename Ignored = void /* for SFINAE */>
struct GetObjectImpl;
// std::shared_ptr implementation
GetObjectImpl<T, absl::enable_if_t<WrapInSharedPtr<T>::value, void>>;
// RefCountedPtr
GetObjectImpl<T, absl::enable_if_t<!WrapInSharedPtr<T>::value, void>>;

// Provide the canonical name for a type's channel arg key
template <typename T>
struct ChannelArgNameTraits { … };
ChannelArgNameTraits<std::shared_ptr<T>>;
// Specialization for the EventEngine
template <>
struct ChannelArgNameTraits<grpc_event_engine::experimental::EventEngine> { … };
class ChannelArgs { … };

std::ostream& operator<<(std::ostream& out, const ChannelArgs& args);

}  // namespace grpc_core

/// Copy the arguments in \a src into a new instance
grpc_channel_args* grpc_channel_args_copy(const grpc_channel_args* src);

/// Copy the arguments in \a src into a new instance, stably sorting keys
grpc_channel_args* grpc_channel_args_normalize(const grpc_channel_args* src);

/// Copy the arguments in \a src and append \a to_add. If \a to_add is NULL, it
/// is equivalent to calling \a grpc_channel_args_copy.
grpc_channel_args* grpc_channel_args_copy_and_add(const grpc_channel_args* src,
                                                  const grpc_arg* to_add,
                                                  size_t num_to_add);

/// Copies the arguments in \a src except for those whose keys are in
/// \a to_remove.
grpc_channel_args* grpc_channel_args_copy_and_remove(
    const grpc_channel_args* src, const char** to_remove, size_t num_to_remove);

/// Copies the arguments from \a src except for those whose keys are in
/// \a to_remove and appends the arguments in \a to_add.
grpc_channel_args* grpc_channel_args_copy_and_add_and_remove(
    const grpc_channel_args* src, const char** to_remove, size_t num_to_remove,
    const grpc_arg* to_add, size_t num_to_add);

/// Perform the union of \a a and \a b, prioritizing \a a entries
grpc_channel_args* grpc_channel_args_union(const grpc_channel_args* a,
                                           const grpc_channel_args* b);

/// Destroy arguments created by \a grpc_channel_args_copy
void grpc_channel_args_destroy(grpc_channel_args* a);
inline void grpc_channel_args_destroy(const grpc_channel_args* a) { … }

int grpc_channel_args_compare(const grpc_channel_args* a,
                              const grpc_channel_args* b);

/// Returns the value of argument \a name from \a args, or NULL if not found.
const grpc_arg* grpc_channel_args_find(const grpc_channel_args* args,
                                       const char* name);

bool grpc_channel_args_want_minimal_stack(const grpc_channel_args* args);

grpc_integer_options;

/// Returns the value of \a arg, subject to the constraints in \a options.
int grpc_channel_arg_get_integer(const grpc_arg* arg,
                                 const grpc_integer_options options);
/// Similar to the above, but needs to find the arg from \a args by the name
/// first.
int grpc_channel_args_find_integer(const grpc_channel_args* args,
                                   const char* name,
                                   const grpc_integer_options options);

/// Returns the value of \a arg if \a arg is of type GRPC_ARG_STRING.
/// Otherwise, emits a warning log, and returns nullptr.
/// If arg is nullptr, returns nullptr, and does not emit a warning.
char* grpc_channel_arg_get_string(const grpc_arg* arg);
/// Similar to the above, but needs to find the arg from \a args by the name
/// first.
char* grpc_channel_args_find_string(const grpc_channel_args* args,
                                    const char* name);
/// If \a arg is of type GRPC_ARG_INTEGER, returns true if it's non-zero.
/// Returns \a default_value if \a arg is of other types.
bool grpc_channel_arg_get_bool(const grpc_arg* arg, bool default_value);
/// Similar to the above, but needs to find the arg from \a args by the name
/// first.
bool grpc_channel_args_find_bool(const grpc_channel_args* args,
                                 const char* name, bool default_value);

template <typename T>
T* grpc_channel_args_find_pointer(const grpc_channel_args* args,
                                  const char* name) { … }

// Helpers for creating channel args.
grpc_arg grpc_channel_arg_string_create(char* name, char* value);
grpc_arg grpc_channel_arg_integer_create(char* name, int value);
grpc_arg grpc_channel_arg_pointer_create(char* name, void* value,
                                         const grpc_arg_pointer_vtable* vtable);

// Returns a string representing channel args in human-readable form.
std::string grpc_channel_args_string(const grpc_channel_args* args);

namespace grpc_core {
// Ensure no duplicate channel args (with some backwards compatibility hacks).
// Eliminate any grpc.internal.* args.
// Return a C++ object.
ChannelArgs ChannelArgsBuiltinPrecondition(const grpc_channel_args* src);
}  // namespace grpc_core

// Takes ownership of the old_args
grpc_channel_args_client_channel_creation_mutator;

// Should be called only once globaly before grpc is init'ed.
void grpc_channel_args_set_client_channel_creation_mutator(
    grpc_channel_args_client_channel_creation_mutator cb);
// This will be called at the creation of each channel.
grpc_channel_args_client_channel_creation_mutator
grpc_channel_args_get_client_channel_creation_mutator();

#endif  // GRPC_SRC_CORE_LIB_CHANNEL_CHANNEL_ARGS_H