1 files changed, 196 insertions, 0 deletions
diff --git a/src/core/lib/promise/status_flag.h b/src/core/lib/promise/status_flag.h
new file mode 100644
index 0000000000..c8c9c0ba41
--- /dev/null
+++ b/src/core/lib/promise/status_flag.h
@@ -0,0 +1,196 @@
+// Copyright 2023 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_PROMISE_STATUS_FLAG_H
+#define GRPC_SRC_CORE_LIB_PROMISE_STATUS_FLAG_H
+
+#include <grpc/support/port_platform.h>
+
+#include "absl/status/status.h"
+#include "absl/status/statusor.h"
+#include "absl/types/optional.h"
+
+#include <grpc/support/log.h>
+
+#include "src/core/lib/promise/detail/status.h"
+
+namespace grpc_core {
+
+struct Failure {};
+struct Success {};
+
+inline bool IsStatusOk(Failure) { return false; }
+inline bool IsStatusOk(Success) { return true; }
+
+template <>
+struct StatusCastImpl<absl::Status, Success> {
+  static absl::Status Cast(Success) { return absl::OkStatus(); }
+};
+
+template <>
+struct StatusCastImpl<absl::Status, const Success&> {
+  static absl::Status Cast(Success) { return absl::OkStatus(); }
+};
+
+template <>
+struct StatusCastImpl<absl::Status, Failure> {
+  static absl::Status Cast(Failure) { return absl::CancelledError(); }
+};
+
+template <typename T>
+struct StatusCastImpl<absl::StatusOr<T>, Failure> {
+  static absl::StatusOr<T> Cast(Failure) { return absl::CancelledError(); }
+};
+
+// A boolean representing whether an operation succeeded (true) or failed
+// (false).
+class StatusFlag {
+ public:
+  StatusFlag() : value_(true) {}
+  explicit StatusFlag(bool value) : value_(value) {}
+  // NOLINTNEXTLINE(google-explicit-constructor)
+  StatusFlag(Failure) : value_(false) {}
+  // NOLINTNEXTLINE(google-explicit-constructor)
+  StatusFlag(Success) : value_(true) {}
+
+  bool ok() const { return value_; }
+
+  bool operator==(StatusFlag other) const { return value_ == other.value_; }
+
+ private:
+  bool value_;
+};
+
+inline bool IsStatusOk(const StatusFlag& flag) { return flag.ok(); }
+
+template <>
+struct StatusCastImpl<absl::Status, StatusFlag> {
+  static absl::Status Cast(StatusFlag flag) {
+    return flag.ok() ? absl::OkStatus() : absl::CancelledError();
+  }
+};
+
+template <>
+struct StatusCastImpl<absl::Status, StatusFlag&> {
+  static absl::Status Cast(StatusFlag flag) {
+    return flag.ok() ? absl::OkStatus() : absl::CancelledError();
+  }
+};
+
+template <>
+struct StatusCastImpl<absl::Status, const StatusFlag&> {
+  static absl::Status Cast(StatusFlag flag) {
+    return flag.ok() ? absl::OkStatus() : absl::CancelledError();
+  }
+};
+
+template <typename T>
+struct FailureStatusCastImpl<absl::StatusOr<T>, StatusFlag> {
+  static absl::StatusOr<T> Cast(StatusFlag flag) {
+    GPR_DEBUG_ASSERT(!flag.ok());
+    return absl::CancelledError();
+  }
+};
+
+template <typename T>
+struct FailureStatusCastImpl<absl::StatusOr<T>, StatusFlag&> {
+  static absl::StatusOr<T> Cast(StatusFlag flag) {
+    GPR_DEBUG_ASSERT(!flag.ok());
+    return absl::CancelledError();
+  }
+};
+
+template <typename T>
+struct FailureStatusCastImpl<absl::StatusOr<T>, const StatusFlag&> {
+  static absl::StatusOr<T> Cast(StatusFlag flag) {
+    GPR_DEBUG_ASSERT(!flag.ok());
+    return absl::CancelledError();
+  }
+};
+
+// A value if an operation was successful, or a failure flag if not.
+template <typename T>
+class ValueOrFailure {
+ public:
+  // NOLINTNEXTLINE(google-explicit-constructor)
+  ValueOrFailure(T value) : value_(std::move(value)) {}
+  // NOLINTNEXTLINE(google-explicit-constructor)
+  ValueOrFailure(Failure) {}
+  // NOLINTNEXTLINE(google-explicit-constructor)
+  ValueOrFailure(StatusFlag status) { GPR_ASSERT(!status.ok()); }
+
+  static ValueOrFailure FromOptional(absl::optional<T> value) {
+    return ValueOrFailure{std::move(value)};
+  }
+
+  bool ok() const { return value_.has_value(); }
+  StatusFlag status() const { return StatusFlag(ok()); }
+
+  const T& value() const { return value_.value(); }
+  T& value() { return value_.value(); }
+  const T& operator*() const { return *value_; }
+  T& operator*() { return *value_; }
+
+  bool operator==(const ValueOrFailure& other) const {
+    return value_ == other.value_;
+  }
+
+ private:
+  absl::optional<T> value_;
+};
+
+template <typename T>
+inline bool IsStatusOk(const ValueOrFailure<T>& value) {
+  return value.ok();
+}
+
+template <typename T>
+inline T TakeValue(ValueOrFailure<T>&& value) {
+  return std::move(value.value());
+}
+
+template <typename T>
+struct StatusCastImpl<absl::StatusOr<T>, ValueOrFailure<T>> {
+  static absl::StatusOr<T> Cast(ValueOrFailure<T> value) {
+    return value.ok() ? absl::StatusOr<T>(std::move(value.value()))
+                      : absl::CancelledError();
+  }
+};
+
+template <typename T>
+struct StatusCastImpl<ValueOrFailure<T>, Failure> {
+  static ValueOrFailure<T> Cast(Failure) {
+    return ValueOrFailure<T>(Failure{});
+  }
+};
+
+template <typename T>
+struct StatusCastImpl<ValueOrFailure<T>, StatusFlag&> {
+  static ValueOrFailure<T> Cast(StatusFlag f) {
+    GPR_ASSERT(!f.ok());
+    return ValueOrFailure<T>(Failure{});
+  }
+};
+
+template <typename T>
+struct StatusCastImpl<ValueOrFailure<T>, StatusFlag> {
+  static ValueOrFailure<T> Cast(StatusFlag f) {
+    GPR_ASSERT(!f.ok());
+    return ValueOrFailure<T>(Failure{});
+  }
+};
+
+}  // namespace grpc_core
+
+#endif  // GRPC_SRC_CORE_LIB_PROMISE_STATUS_FLAG_H
+\ No newline at end of file