[Vertex AI] Add Decodable conformance for FunctionResponse (firebase#13606)

Author: andrewheard

FirebaseVertexAI/CHANGELOG.md

@@ -1,3 +1,6 @@
+# Unreleased
+- [added] Added `Decodable` conformance for `FunctionResponse`. (#13606)
+
 # 11.2.0
 - [fixed] Resolved a decoding error for citations without a `uri` and added
   support for decoding `title` fields, which were previously ignored. (#13518)

FirebaseVertexAI/Sources/FunctionCalling.swift

@@ -193,4 +193,4 @@ extension FunctionCallingConfig.Mode: Encodable {}
 
 extension ToolConfig: Encodable {}
 
-extension FunctionResponse: Encodable {}
+extension FunctionResponse: Codable {}

FirebaseVertexAI/Sources/ModelContent.swift

@@ -179,10 +179,13 @@ extension ModelContent.Part: Codable {
       self = .data(mimetype: mimetype, bytes)
     } else if values.contains(.functionCall) {
       self = try .functionCall(values.decode(FunctionCall.self, forKey: .functionCall))
+    } else if values.contains(.functionResponse) {
+      self = try .functionResponse(values.decode(FunctionResponse.self, forKey: .functionResponse))
     } else {
-      throw DecodingError.dataCorrupted(.init(
-        codingPath: [CodingKeys.text, CodingKeys.inlineData],
-        debugDescription: "No text, inline data or function call was found."
+      let unexpectedKeys = values.allKeys.map { $0.stringValue }
+      throw DecodingError.dataCorrupted(DecodingError.Context(
+        codingPath: values.codingPath,
+        debugDescription: "Unexpected ModelContent.Part type(s): \(unexpectedKeys)"
       ))
     }
   }

FirebaseVertexAI/Tests/Unit/ModelContentTests.swift

@@ -19,6 +19,7 @@ import XCTest
 
 @available(iOS 15.0, macOS 11.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
 final class ModelContentTests: XCTestCase {
+  let decoder = JSONDecoder()
   let encoder = JSONEncoder()
 
   override func setUp() {
@@ -27,7 +28,35 @@ final class ModelContentTests: XCTestCase {
     )
   }
 
-  // MARK: ModelContent.Part Encoding
+  // MARK: - ModelContent.Part Decoding
+
+  func testDecodeFunctionResponsePart() throws {
+    let functionName = "test-function-name"
+    let resultParameter = "test-result-parameter"
+    let resultValue = "test-result-value"
+    let json = """
+    {
+      "functionResponse" : {
+        "name" : "\(functionName)",
+        "response" : {
+          "\(resultParameter)" : "\(resultValue)"
+        }
+      }
+    }
+    """
+    let jsonData = try XCTUnwrap(json.data(using: .utf8))
+
+    let part = try decoder.decode(ModelContent.Part.self, from: jsonData)
+
+    guard case let .functionResponse(functionResponse) = part else {
+      XCTFail("Decoded Part was not a FunctionResponse.")
+      return
+    }
+    XCTAssertEqual(functionResponse.name, functionName)
+    XCTAssertEqual(functionResponse.response, [resultParameter: .string(resultValue)])
+  }
+
+  // MARK: - ModelContent.Part Encoding
 
   func testEncodeFileDataPart() throws {
     let mimeType = "image/jpeg"