Add Swift enum listing standard gRPC status codes

Sources/gRPC/gRPC.swift

@@ -51,3 +51,115 @@ public func shutdown() {
 public func version() -> String {
   return String(cString:grpc_version_string(), encoding:String.Encoding.utf8)!
 }
+
+/// Status codes for gRPC operations (replicated from status_code_enum.h)
+enum StatusCode: Int {
+  /// Not an error; returned on success.
+  case ok = 0
+
+  /// The operation was cancelled (typically by the caller).
+  case cancelled = 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.
+  case unknown = 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).
+  case invalidArgument = 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.
+  case deadlineExceeded = 4
+
+  /// Some requested entity (e.g., file or directory) was not found.
+  case notFound = 5
+
+  /// Some entity that we attempted to create (e.g., file or directory) already
+  /// exists.
+  case alreadyExists = 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).
+  case permissionDenied = 7
+
+  /// The request does not have valid authentication credentials for the
+  /// operation.
+  case unauthenticated = 16
+
+  /// Some resource has been exhausted, perhaps a per-user quota, or perhaps the
+  /// entire file system is out of space.
+  case resourceExhausted = 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.
+  case failedPrecondition = 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.
+  case aborted = 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.
+  case outOfRange = 11
+
+  /// Operation is not implemented or not supported/enabled in this service.
+  case unimplemented = 12
+
+  /// Internal errors. Means some invariants expected by underlying System has
+  /// been broken. If you see one of these errors, Something is very broken.
+  case internalError = 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.
+  case unavailable = 14
+
+  /// Unrecoverable data loss or corruption.
+  case dataLoss = 15
+
+  /// Force users to include a default branch:
+  case doNotUse = -1
+}