grpc-swift/Sources/GRPC/GRPCStatus.swift

/*
 * Copyright 2019, gRPC Authors All rights reserved.
 *
 * 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.
 */
import Foundation
import NIOCore
import NIOHTTP1
import NIOHTTP2

/// Encapsulates the result of a gRPC call.
public struct GRPCStatus: Error {
  /// Storage for message/cause. In the happy case ('ok') there will not be a message or cause
  /// and this will reference a static storage containing nil values. Making it optional makes the
  /// setters for message and cause a little messy.
  private var storage: Storage

  /// The status code of the RPC.
  public var code: Code

  /// The status message of the RPC.
  public var message: String? {
    get {
      return self.storage.message
    }
    set {
      if isKnownUniquelyReferenced(&self.storage) {
        self.storage.message = newValue
      } else {
        self.storage = .makeStorage(message: newValue, cause: self.storage.cause)
      }
    }
  }

  /// The cause of an error (not 'ok') status. This value is never transmitted over the wire and is
  /// **not** included in equality checks.
  public var cause: Error? {
    get {
      return self.storage.cause
    }
    set {
      if isKnownUniquelyReferenced(&self.storage) {
        self.storage.cause = newValue
      } else {
        self.storage = .makeStorage(message: self.storage.message, cause: newValue)
      }
    }
  }

  // Backing storage for 'message' and 'cause'.
  private final class Storage {
    // On many happy paths there will be no message or cause, so we'll use this shared reference
    // instead of allocating a new storage each time.
    //
    // Alternatively: `GRPCStatus` could hold a storage optionally however doing so made the code
    // quite unreadable.
    private static let none = Storage(message: nil, cause: nil)

    private init(message: String?, cause: Error?) {
      self.message = message
      self.cause = cause
    }

    fileprivate var message: Optional<String>
    fileprivate var cause: Optional<Error>

    fileprivate static func makeStorage(message: String?, cause: Error?) -> Storage {
      if message == nil, cause == nil {
        return Storage.none
      } else {
        return Storage(message: message, cause: cause)
      }
    }
  }

  /// Whether the status is '.ok'.
  public var isOk: Bool {
    return self.code == .ok
  }

  public init(code: Code, message: String?) {
    self.init(code: code, message: message, cause: nil)
  }

  public init(code: Code, message: String? = nil, cause: Error? = nil) {
    self.code = code
    self.storage = .makeStorage(message: message, cause: cause)
  }

  // Frequently used "default" statuses.

  /// The default status to return for succeeded calls.
  ///
  /// - Important: This should *not* be used when checking whether a returned status has an 'ok'
  ///   status code. Use `GRPCStatus.isOk` or check the code directly.
  public static let ok = GRPCStatus(code: .ok, message: nil)
  /// "Internal server error" status.
  public static let processingError = Self.processingError(cause: nil)

  public static func processingError(cause: Error?) -> GRPCStatus {
    return GRPCStatus(
      code: .internalError,
      message: "unknown error processing request",
      cause: cause
    )
  }
}

extension GRPCStatus: Equatable {
  public static func == (lhs: GRPCStatus, rhs: GRPCStatus) -> Bool {
    return lhs.code == rhs.code && lhs.message == rhs.message
  }
}

extension GRPCStatus: CustomStringConvertible {
  public var description: String {
    if let message = message {
      return "\(self.code): \(message)"
    } else {
      return "\(self.code)"
    }
  }
}

extension GRPCStatus {
  internal var testingOnly_storageObjectIdentifier: ObjectIdentifier {
    return ObjectIdentifier(self.storage)
  }
}

extension GRPCStatus {
  /// Status codes for gRPC operations (replicated from `status_code_enum.h` in the
  /// [gRPC core library](https://github.com/grpc/grpc)).
  public struct Code: Hashable, CustomStringConvertible {
    // `rawValue` must be an `Int` for API reasons and we don't need (or want) to store anything so
    // wide, a `UInt8` is fine.
    private let _rawValue: UInt8

    public var rawValue: Int {
      return Int(self._rawValue)
    }

    public init?(rawValue: Int) {
      switch rawValue {
      case 0 ... 16:
        self._rawValue = UInt8(truncatingIfNeeded: rawValue)
      default:
        return nil
      }
    }

    private init(_ code: UInt8) {
      self._rawValue = code
    }

    /// Not an error; returned on success.
    public static let ok = Code(0)

    /// The operation was cancelled (typically by the caller).
    public static let cancelled = Code(1)

    /// Unknown error. An example of where this error may be returned is if a
    /// Status value received from another address space belongs to an error-space
    /// that is not known in this address space. Also errors raised by APIs that
    /// do not return enough error information may be converted to this error.
    public static let unknown = Code(2)

    /// Client specified an invalid argument. Note that this differs from
    /// FAILED_PRECONDITION. INVALID_ARGUMENT indicates arguments that are
    /// problematic regardless of the state of the system (e.g., a malformed file
    /// name).
    public static let invalidArgument = Code(3)

    /// Deadline expired before operation could complete. For operations that
    /// change the state of the system, this error may be returned even if the
    /// operation has completed successfully. For example, a successful response
    /// from a server could have been delayed long enough for the deadline to
    /// expire.
    public static let deadlineExceeded = Code(4)

    /// Some requested entity (e.g., file or directory) was not found.
    public static let notFound = Code(5)

    /// Some entity that we attempted to create (e.g., file or directory) already
    /// exists.
    public static let alreadyExists = Code(6)

    /// The caller does not have permission to execute the specified operation.
    /// PERMISSION_DENIED must not be used for rejections caused by exhausting
    /// some resource (use RESOURCE_EXHAUSTED instead for those errors).
    /// PERMISSION_DENIED must not be used if the caller can not be identified
    /// (use UNAUTHENTICATED instead for those errors).
    public static let permissionDenied = Code(7)

    /// Some resource has been exhausted, perhaps a per-user quota, or perhaps the
    /// entire file system is out of space.
    public static let resourceExhausted = Code(8)

    /// Operation was rejected because the system is not in a state required for
    /// the operation's execution. For example, directory to be deleted may be
    /// non-empty, an rmdir operation is applied to a non-directory, etc.
    ///
    /// A litmus test that may help a service implementor in deciding
    /// between FAILED_PRECONDITION, ABORTED, and UNAVAILABLE:
    ///  (a) Use UNAVAILABLE if the client can retry just the failing call.
    ///  (b) Use ABORTED if the client should retry at a higher-level
    ///      (e.g., restarting a read-modify-write sequence).
    ///  (c) Use FAILED_PRECONDITION if the client should not retry until
    ///      the system state has been explicitly fixed. E.g., if an "rmdir"
    ///      fails because the directory is non-empty, FAILED_PRECONDITION
    ///      should be returned since the client should not retry unless
    ///      they have first fixed up the directory by deleting files from it.
    ///  (d) Use FAILED_PRECONDITION if the client performs conditional
    ///      REST Get/Update/Delete on a resource and the resource on the
    ///      server does not match the condition. E.g., conflicting
    ///      read-modify-write on the same resource.
    public static let failedPrecondition = Code(9)

    /// The operation was aborted, typically due to a concurrency issue like
    /// sequencer check failures, transaction aborts, etc.
    ///
    /// See litmus test above for deciding between FAILED_PRECONDITION, ABORTED,
    /// and UNAVAILABLE.
    public static let aborted = Code(10)

    /// Operation was attempted past the valid range. E.g., seeking or reading
    /// past end of file.
    ///
    /// Unlike INVALID_ARGUMENT, this error indicates a problem that may be fixed
    /// if the system state changes. For example, a 32-bit file system will
    /// generate INVALID_ARGUMENT if asked to read at an offset that is not in the
    /// range [0,2^32-1], but it will generate OUT_OF_RANGE if asked to read from
    /// an offset past the current file size.
    ///
    /// There is a fair bit of overlap between FAILED_PRECONDITION and
    /// OUT_OF_RANGE. We recommend using OUT_OF_RANGE (the more specific error)
    /// when it applies so that callers who are iterating through a space can
    /// easily look for an OUT_OF_RANGE error to detect when they are done.
    public static let outOfRange = Code(11)

    /// Operation is not implemented or not supported/enabled in this service.
    public static let unimplemented = Code(12)

    /// Internal errors. Means some invariants expected by underlying System has
    /// been broken. If you see one of these errors, Something is very broken.
    public static let internalError = Code(13)

    /// The service is currently unavailable. This is a most likely a transient
    /// condition and may be corrected by retrying with a backoff.
    ///
    /// See litmus test above for deciding between FAILED_PRECONDITION, ABORTED,
    /// and UNAVAILABLE.
    public static let unavailable = Code(14)

    /// Unrecoverable data loss or corruption.
    public static let dataLoss = Code(15)

    /// The request does not have valid authentication credentials for the
    /// operation.
    public static let unauthenticated = Code(16)

    public var description: String {
      switch self {
      case .ok:
        return "ok (\(self._rawValue))"
      case .cancelled:
        return "cancelled (\(self._rawValue))"
      case .unknown:
        return "unknown (\(self._rawValue))"
      case .invalidArgument:
        return "invalid argument (\(self._rawValue))"
      case .deadlineExceeded:
        return "deadline exceeded (\(self._rawValue))"
      case .notFound:
        return "not found (\(self._rawValue))"
      case .alreadyExists:
        return "already exists (\(self._rawValue))"
      case .permissionDenied:
        return "permission denied (\(self._rawValue))"
      case .resourceExhausted:
        return "resource exhausted (\(self._rawValue))"
      case .failedPrecondition:
        return "failed precondition (\(self._rawValue))"
      case .aborted:
        return "aborted (\(self._rawValue))"
      case .outOfRange:
        return "out of range (\(self._rawValue))"
      case .unimplemented:
        return "unimplemented (\(self._rawValue))"
      case .internalError:
        return "internal error (\(self._rawValue))"
      case .unavailable:
        return "unavailable (\(self._rawValue))"
      case .dataLoss:
        return "data loss (\(self._rawValue))"
      case .unauthenticated:
        return "unauthenticated (\(self._rawValue))"
      default:
        return String(describing: self._rawValue)
      }
    }
  }
}

/// This protocol serves as a customisation point for error types so that gRPC calls may be
/// terminated with an appropriate status.
public protocol GRPCStatusTransformable: Error {
  /// Make a `GRPCStatus` from the underlying error.
  ///
  /// - Returns: A `GRPCStatus` representing the underlying error.
  func makeGRPCStatus() -> GRPCStatus
}

extension GRPCStatus: GRPCStatusTransformable {
  public func makeGRPCStatus() -> GRPCStatus {
    return self
  }
}

extension NIOHTTP2Errors.StreamClosed: GRPCStatusTransformable {
  public func makeGRPCStatus() -> GRPCStatus {
    return .init(code: .unavailable, message: self.localizedDescription, cause: self)
  }
}

extension NIOHTTP2Errors.IOOnClosedConnection: GRPCStatusTransformable {
  public func makeGRPCStatus() -> GRPCStatus {
    return .init(code: .unavailable, message: "The connection is closed", cause: self)
  }
}

extension ChannelError: GRPCStatusTransformable {
  public func makeGRPCStatus() -> GRPCStatus {
    switch self {
    case .inputClosed, .outputClosed, .ioOnClosedChannel:
      return .init(code: .unavailable, message: "The connection is closed", cause: self)

    default:
      var processingError = GRPCStatus.processingError
      processingError.cause = self
      return processingError
    }
  }
}