Ignore unknown enum values and return nil instead when ignoreUnknownFields flag is ON

Sources/SwiftProtobuf/JSONDecoder.swift

@@ -476,7 +476,11 @@ internal struct JSONDecoder: Decoder {
       value = nil
       return
     }
-    value = try scanner.nextEnumValue() as E
+    if let v: E = try scanner.nextEnumValue() {
+      value = v
+    } else {
+      value = nil
+    }
   }
 
   mutating func decodeSingularEnumField<E: Enum>(value: inout E) throws
@@ -489,7 +493,11 @@ internal struct JSONDecoder: Decoder {
       value = E()
       return
     }
-    value = try scanner.nextEnumValue()
+    if let v: E = try scanner.nextEnumValue() {
+      value = v
+    } else {
+      value = E()
+    }
   }
 
   mutating func decodeRepeatedEnumField<E: Enum>(value: inout [E]) throws
@@ -511,8 +519,9 @@ internal struct JSONDecoder: Decoder {
           throw JSONDecodingError.illegalNull
         }
       } else {
-        let e: E = try scanner.nextEnumValue()
-        value.append(e)
+        if let e: E = try scanner.nextEnumValue() {
+          value.append(e)
+        }
       }
       if scanner.skipOptionalArrayEnd() {
         return

Sources/SwiftProtobuf/JSONScanner.swift

@@ -1300,7 +1300,7 @@ internal struct JSONScanner {
   /// Parse the next token as a string or numeric enum value.  Throws
   /// unrecognizedEnumValue if the string/number can't initialize the
   /// enum.  Will throw other errors if the JSON is malformed.
-  internal mutating func nextEnumValue<E: Enum>() throws -> E {
+  internal mutating func nextEnumValue<E: Enum>() throws -> E? {
     skipWhitespace()
     guard hasMoreContent else {
         throw JSONDecodingError.truncated
@@ -1324,6 +1324,8 @@ internal struct JSONScanner {
       if let i = Int(exactly: n) {
         if let e = E(rawValue: i) {
           return e
+        } else if options.ignoreUnknownFields {
+          return nil
         } else {
           throw JSONDecodingError.unrecognizedEnumValue
         }

Tests/SwiftProtobufTests/Test_JSONDecodingOptions.swift

@@ -157,4 +157,42 @@ class Test_JSONDecodingOptions: XCTestCase {
         }
     }
 
+    func testIgnoreUnknownFields_ignoresUnknownEnumValues() {
+        // (isValidJSON, jsonInput)
+        //   isValidJSON - if the input is otherwise valid protobuf JSON, and
+        //                 hence should parse when ignoring unknown fields.
+        //   jsonInput - The JSON string to parse.
+        let jsonInputs: [(Bool, String)] = [
+            (true, "{\"values1\":[1, 3]}"),
+        ]
+
+        var options = JSONDecodingOptions()
+        options.ignoreUnknownFields = true
+
+        for (i, (isValidJSON, jsonInput)) in jsonInputs.enumerated() {
+            // Default options (error on unknown fields)
+            do {
+                let _ = try ProtobufUnittest_SwiftEnumTest(jsonString: jsonInput)
+                XCTFail("Input \(i): Should not have gotten here! Input: \(jsonInput)")
+            } catch JSONDecodingError.unrecognizedEnumValue {
+                XCTAssertTrue(true, "Input \(i): got an unknown enum value, input \(jsonInput).")
+            } catch let e {
+                XCTFail("Input \(i): Error \(e) decoding into an empty message \(jsonInput)")
+            }
+
+            // Ignoring unknown fields
+            do {
+                let _ = try ProtobufUnittest_SwiftEnumTest(jsonString: jsonInput,
+                                                            options:options)
+                XCTAssertTrue(isValidJSON,
+                              "Input \(i): Should not have been able to parse: \(jsonInput)")
+            } catch JSONDecodingError.unrecognizedEnumValue {
+                XCTFail("Input \(i): should not have gotten unknown enum value, input \(jsonInput)")
+            } catch let e {
+                XCTAssertFalse(isValidJSON,
+                               "Input \(i): Error \(e): Should have been able to parse: \(jsonInput)")
+            }
+        }
+    }
+
 }