Add usageMetadata to GenerateContentResponse in Vertex AI (#12777)

FirebaseVertexAI/Sample/ChatSample/Views/ErrorDetailsView.swift

@@ -176,8 +176,7 @@ struct ErrorDetailsView: View {
       ],
       finishReason: FinishReason.maxTokens,
       citationMetadata: nil),
-    ],
-    promptFeedback: nil)
+    ])
   )
 
   return ErrorDetailsView(error: error)
@@ -200,8 +199,7 @@ struct ErrorDetailsView: View {
       ],
       finishReason: FinishReason.other,
       citationMetadata: nil),
-    ],
-    promptFeedback: nil)
+    ])
   )
 
   return ErrorDetailsView(error: error)

FirebaseVertexAI/Sample/ChatSample/Views/ErrorView.swift

@@ -51,8 +51,7 @@ struct ErrorView: View {
         ],
         finishReason: FinishReason.other,
         citationMetadata: nil),
-      ],
-      promptFeedback: nil)
+      ])
     )
     List {
       MessageView(message: ChatMessage.samples[0])

FirebaseVertexAI/Sources/GenerateContentResponse.swift

@@ -17,13 +17,28 @@ import Foundation
 /// The model's response to a generate content request.
 @available(iOS 15.0, macOS 11.0, macCatalyst 15.0, *)
 public struct GenerateContentResponse {
+  /// Token usage metadata for processing the generate content request.
+  public struct UsageMetadata {
+    /// The number of tokens in the request prompt.
+    public let promptTokenCount: Int
+
+    /// The total number of tokens across the generated response candidates.
+    public let candidatesTokenCount: Int
+
+    /// The total number of tokens in both the request and response.
+    public let totalTokenCount: Int
+  }
+
   /// A list of candidate response content, ordered from best to worst.
   public let candidates: [CandidateResponse]
 
   /// A value containing the safety ratings for the response, or, if the request was blocked, a
   /// reason for blocking the request.
   public let promptFeedback: PromptFeedback?
 
+  /// Token usage metadata for processing the generate content request.
+  public let usageMetadata: UsageMetadata?
+
   /// The response's content as text, if it exists.
   public var text: String? {
     guard let candidate = candidates.first else {
@@ -51,9 +66,11 @@ public struct GenerateContentResponse {
   }
 
   /// Initializer for SwiftUI previews or tests.
-  public init(candidates: [CandidateResponse], promptFeedback: PromptFeedback?) {
+  public init(candidates: [CandidateResponse], promptFeedback: PromptFeedback? = nil,
+              usageMetadata: UsageMetadata? = nil) {
     self.candidates = candidates
     self.promptFeedback = promptFeedback
+    self.usageMetadata = usageMetadata
   }
 }
 
@@ -62,6 +79,7 @@ extension GenerateContentResponse: Decodable {
   enum CodingKeys: CodingKey {
     case candidates
     case promptFeedback
+    case usageMetadata
   }
 
   public init(from decoder: Decoder) throws {
@@ -86,6 +104,7 @@ extension GenerateContentResponse: Decodable {
       candidates = []
     }
     promptFeedback = try container.decodeIfPresent(PromptFeedback.self, forKey: .promptFeedback)
+    usageMetadata = try container.decodeIfPresent(UsageMetadata.self, forKey: .usageMetadata)
   }
 }
 
@@ -301,3 +320,20 @@ extension PromptFeedback: Decodable {
     }
   }
 }
+
+@available(iOS 15.0, macOS 11.0, macCatalyst 15.0, *)
+extension GenerateContentResponse.UsageMetadata: Decodable {
+  enum CodingKeys: CodingKey {
+    case promptTokenCount
+    case candidatesTokenCount
+    case totalTokenCount
+  }
+
+  public init(from decoder: any Decoder) throws {
+    let container = try decoder.container(keyedBy: CodingKeys.self)
+    promptTokenCount = try container.decodeIfPresent(Int.self, forKey: .promptTokenCount) ?? 0
+    candidatesTokenCount = try container
+      .decodeIfPresent(Int.self, forKey: .candidatesTokenCount) ?? 0
+    totalTokenCount = try container.decodeIfPresent(Int.self, forKey: .totalTokenCount) ?? 0
+  }
+}

FirebaseVertexAI/Tests/Unit/GenerativeModelTests.swift

@@ -287,6 +287,21 @@ final class GenerativeModelTests: XCTestCase {
     _ = try await model.generateContent(testPrompt)
   }
 
+  func testGenerateContent_usageMetadata() async throws {
+    MockURLProtocol
+      .requestHandler = try httpRequestHandler(
+        forResource: "unary-success-basic-reply-short",
+        withExtension: "json"
+      )
+
+    let response = try await model.generateContent(testPrompt)
+
+    let usageMetadata = try XCTUnwrap(response.usageMetadata)
+    XCTAssertEqual(usageMetadata.promptTokenCount, 6)
+    XCTAssertEqual(usageMetadata.candidatesTokenCount, 7)
+    XCTAssertEqual(usageMetadata.totalTokenCount, 13)
+  }
+
   func testGenerateContent_failure_invalidAPIKey() async throws {
     let expectedStatusCode = 400
     MockURLProtocol
@@ -814,6 +829,32 @@ final class GenerativeModelTests: XCTestCase {
     for try await _ in stream {}
   }
 
+  func testGenerateContentStream_usageMetadata() async throws {
+    MockURLProtocol
+      .requestHandler = try httpRequestHandler(
+        forResource: "streaming-success-basic-reply-short",
+        withExtension: "txt"
+      )
+    var responses = [GenerateContentResponse]()
+
+    let stream = model.generateContentStream(testPrompt)
+    for try await response in stream {
+      responses.append(response)
+    }
+
+    for (index, response) in responses.enumerated() {
+      if index == responses.endIndex - 1 {
+        let usageMetadata = try XCTUnwrap(response.usageMetadata)
+        XCTAssertEqual(usageMetadata.promptTokenCount, 6)
+        XCTAssertEqual(usageMetadata.candidatesTokenCount, 4)
+        XCTAssertEqual(usageMetadata.totalTokenCount, 10)
+      } else {
+        // Only the last streamed response contains usage metadata
+        XCTAssertNil(response.usageMetadata)
+      }
+    }
+  }
+
   func testGenerateContentStream_errorMidStream() async throws {
     MockURLProtocol.requestHandler = try httpRequestHandler(
       forResource: "streaming-failure-error-mid-stream",