[Vertex AI] Fix decoding ModalityTokenCount when tokenCount is 0 (#14747)

Author: andrewheard

FirebaseVertexAI/CHANGELOG.md

@@ -1,3 +1,7 @@
+# Unreleased
+- [fixed] Fixed `ModalityTokenCount` decoding when the `tokenCount` field is
+  omitted; this occurs when the count is 0. (#14745)
+
 # 11.12.0
 - [added] **Public Preview**: Added support for specifying response modalities
   in `GenerationConfig`. This includes **public experimental** support for image

FirebaseVertexAI/Sources/ModalityTokenCount.swift

@@ -57,5 +57,18 @@ public struct ContentModality: DecodableProtoEnum, Hashable, Sendable {
     VertexLog.MessageCode.generateContentResponseUnrecognizedContentModality
 }
 
+// MARK: Codable Conformances
+
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
-extension ModalityTokenCount: Decodable {}
+extension ModalityTokenCount: Decodable {
+  enum CodingKeys: CodingKey {
+    case modality
+    case tokenCount
+  }
+
+  public init(from decoder: any Decoder) throws {
+    let container = try decoder.container(keyedBy: CodingKeys.self)
+    modality = try container.decode(ContentModality.self, forKey: .modality)
+    tokenCount = try container.decodeIfPresent(Int.self, forKey: .tokenCount) ?? 0
+  }
+}

FirebaseVertexAI/Tests/TestApp/Tests/Integration/GenerateContentIntegrationTests.swift

@@ -116,9 +116,10 @@ struct GenerateContentIntegrationTests {
 
   @Test(arguments: [
     InstanceConfig.vertexV1Beta,
-    // TODO(andrewheard): Prod config temporarily disabled due to backend issue.
+    // TODO(andrewheard): Configs temporarily disabled due to backend issue.
     // InstanceConfig.developerV1Beta,
-    InstanceConfig.developerV1BetaStaging, // Remove after re-enabling `developerV1Beta` config.
+    // InstanceConfig.developerV1BetaStaging
+    InstanceConfig.developerV1BetaSpark,
   ])
   func generateImage(_ config: InstanceConfig) async throws {
     let generationConfig = GenerationConfig(

FirebaseVertexAI/Tests/TestApp/Tests/Utilities/InstanceConfig.swift

@@ -51,9 +51,9 @@ struct InstanceConfig {
     vertexV1Staging,
     vertexV1Beta,
     vertexV1BetaStaging,
-    // TODO(andrewheard): Prod config temporarily disabled due to backend issue:
+    // TODO(andrewheard): Configs temporarily disabled due to backend issue:
     // developerV1Beta,
-    developerV1BetaStaging,
+    // developerV1BetaStaging,
     developerV1Spark,
     developerV1BetaSpark,
   ]
@@ -63,9 +63,9 @@ struct InstanceConfig {
     vertexV1Staging,
     vertexV1Beta,
     vertexV1BetaStaging,
-    // TODO(andrewheard): Prod config temporarily disabled due to backend issue:
+    // TODO(andrewheard): Configs temporarily disabled due to backend issue:
     // developerV1Beta,
-    developerV1BetaStaging,
+    // developerV1BetaStaging,
     developerV1BetaSpark,
   ]
 

FirebaseVertexAI/Tests/Unit/Types/ModalityTokenCountTests.swift

@@ -0,0 +1,88 @@
+// Copyright 2025 Google LLC
+//
+// 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 FirebaseVertexAI
+import XCTest
+
+@available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
+final class ModalityTokenCountTests: XCTestCase {
+  let decoder = JSONDecoder()
+
+  // MARK: - Decoding Tests
+
+  func testDecodeModalityTokenCount_valid() throws {
+    let json = """
+    {
+      "modality": "TEXT",
+      "tokenCount": 123
+    }
+    """
+    let jsonData = try XCTUnwrap(json.data(using: .utf8))
+
+    let tokenCount = try decoder.decode(ModalityTokenCount.self, from: jsonData)
+
+    XCTAssertEqual(tokenCount.modality, .text)
+    XCTAssertEqual(tokenCount.modality.rawValue, "TEXT")
+    XCTAssertEqual(tokenCount.tokenCount, 123)
+  }
+
+  func testDecodeModalityTokenCount_missingTokenCount_defaultsToZero() throws {
+    let json = """
+    {
+      "modality": "AUDIO"
+    }
+    """
+    let jsonData = try XCTUnwrap(json.data(using: .utf8))
+
+    let tokenCount = try decoder.decode(ModalityTokenCount.self, from: jsonData)
+
+    XCTAssertEqual(tokenCount.modality, .audio)
+    XCTAssertEqual(tokenCount.modality.rawValue, "AUDIO")
+    XCTAssertEqual(tokenCount.tokenCount, 0)
+  }
+
+  func testDecodeModalityTokenCount_unrecognizedModalityString_succeeds() throws {
+    let newModality = "NEW_MODALITY_NAME"
+    let json = """
+    {
+      "modality": "\(newModality)",
+      "tokenCount": 50
+    }
+    """
+    let jsonData = try XCTUnwrap(json.data(using: .utf8))
+
+    let tokenCount = try decoder.decode(ModalityTokenCount.self, from: jsonData)
+
+    XCTAssertEqual(tokenCount.tokenCount, 50)
+    XCTAssertEqual(tokenCount.modality.rawValue, newModality)
+  }
+
+  func testDecodeModalityTokenCount_missingModalityKey_throws() throws {
+    let json = """
+    {
+      "tokenCount": 50
+    }
+    """
+    let jsonData = try XCTUnwrap(json.data(using: .utf8))
+
+    do {
+      _ = try decoder.decode(ModalityTokenCount.self, from: jsonData)
+      XCTFail("Expected a DecodingError, but decoding succeeded.")
+    } catch let DecodingError.keyNotFound(key, _) {
+      XCTAssertEqual(key.stringValue, "modality")
+    } catch {
+      XCTFail("Expected a DecodingError.keyNotFound, but received \(error)")
+    }
+  }
+}