DataConnectError.swift: update to match api proposal

Author: dconeybe

Sources/DataConnectError.swift

@@ -23,9 +23,6 @@ public enum DataConnectError: Error {
   /// failed to configure gRPC
   case grpcNotConfigured
 
-  /// failed to decode results from server
-  case decodeFailed(response: AnyOperationFailureResponse)
-
   /// Invalid uuid format during encoding / decoding of data
   case invalidUUID
 
@@ -36,37 +33,45 @@ public enum DataConnectError: Error {
   case invalidTimestampFormat
 
   /// generic operation execution error
-  case operationExecutionFailed(response: AnyOperationFailureResponse)
+  case operationExecutionFailed(messages: String?, response: OperationFailureResponse)
 }
 
+// The data and errors sent to us from the backend in its response.
 @available(iOS 15.0, macOS 12.0, tvOS 15.0, watchOS 8.0, *)
-public protocol AnyOperationFailureResponse {
-  // JSON string
-  var data: String? { get }
-
-  var errors: [OperationFailureResponseErrorInfo] { get }
-}
-
-@available(iOS 15.0, macOS 12.0, tvOS 15.0, watchOS 8.0, *)
-public struct OperationFailureResponse<T> : AnyOperationFailureResponse {
-  // JSON string
-  public let data: String?
-
-  public let errors: [OperationFailureResponseErrorInfo]
-
-  public let decodedData: T?
-
+public struct OperationFailureResponse {
+  // JSON string whose value is the "data" property provided by the backend in its response
+  // payload; may be `nil` if the "data" property was not provided in the backend response and/or
+  // was `null` in the backend response.
+  public let jsonData: String?
+
+  // The list of errors in the "error" property provided by the backend in its response payload;
+  // may be empty if the "errors" property was not provided in the backend response and/or was an
+  // empty list in the backend response.
+  public let errorInfoList: [OperationFailureResponseErrorInfo]
+
+  // Returns `jsonData` string decoded into the given type, if decoding was successful when the
+  // operation was executed. Returns `nil` if `jsonData` is `nil`, if `jsonData` was _not_ able to
+  // be decoded when the operation was executed, or if the given type is _not_ equal to the `Data`
+  // type that was used when the operation was executed.
+  //
+  // This function does _not_ do the decoding itself, but simply returns the decoded data, if any,
+  // that was decoded at the time of the operation's execution.
+  public func decodedData<Data: Decodable>(asType: Data.Type = Data.self) -> Data?
 }
 
+// Information about an error provided by the backend in its response.
 @available(iOS 15.0, macOS 12.0, tvOS 15.0, watchOS 8.0, *)
 public struct OperationFailureResponseErrorInfo: Codable {
+  // The error message.
   public let message: String
+
+  // The path to the field to which this error applies.
   public let path: [PathSegment]
 
   @available(iOS 15.0, macOS 12.0, tvOS 15.0, watchOS 8.0, *)
-  public enum PathSegment: Codable {
+  public enum PathSegment: Codable, Equatable {
     case field(String)
     case listIndex(Int)
   }
-
 }
+