Add unit test for empty parts handling when streaming

Author: andrewheard

FirebaseAI/Sources/GenerativeModel.swift

@@ -230,6 +230,7 @@ public final class GenerativeModel: Sendable {
       let responseStream = generativeAIService.loadRequestStream(request: generateContentRequest)
       Task {
         do {
+          var didYieldResponse = false
           for try await response in responseStream {
             // Check the prompt feedback to see if the prompt was blocked.
             if response.promptFeedback?.blockReason != nil {
@@ -254,9 +255,20 @@ public final class GenerativeModel: Sendable {
               )
             } else {
               continuation.yield(response)
+              didYieldResponse = true
             }
           }
-          continuation.finish()
+
+          // Throw an error if all responses were skipped due to empty content.
+          if didYieldResponse {
+            continuation.finish()
+          } else {
+            continuation.finish(throwing: GenerativeModel.generateContentError(
+              from: InvalidCandidateError.emptyContent(
+                underlyingError: Candidate.EmptyContentError()
+              )
+            ))
+          }
         } catch {
           continuation.finish(throwing: GenerativeModel.generateContentError(from: error))
           return

FirebaseAI/Tests/Unit/GenerativeModelGoogleAITests.swift

@@ -509,6 +509,23 @@ final class GenerativeModelGoogleAITests: XCTestCase {
     XCTAssertTrue(thoughtSignature.hasPrefix("CiIBVKhc7vB+vaaq6rA"))
   }
 
+  func testGenerateContentStream_success_ignoresEmptyParts() async throws {
+    MockURLProtocol.requestHandler = try GenerativeModelTestUtil.httpRequestHandler(
+      forResource: "streaming-success-empty-parts",
+      withExtension: "txt",
+      subdirectory: googleAISubdirectory
+    )
+
+    let stream = try model.generateContentStream("Hi")
+    for try await response in stream {
+      let candidate = try XCTUnwrap(response.candidates.first)
+      XCTAssertGreaterThan(candidate.content.parts.count, 0)
+      let text = response.text
+      let inlineData = response.inlineDataParts.first
+      XCTAssertTrue(text != nil || inlineData != nil, "Response did not contain text or data")
+    }
+  }
+
   func testGenerateContentStream_failureInvalidAPIKey() async throws {
     MockURLProtocol.requestHandler = try GenerativeModelTestUtil.httpRequestHandler(
       forResource: "unary-failure-api-key",

FirebaseAI/Tests/Unit/GenerativeModelVertexAITests.swift

@@ -786,12 +786,12 @@ final class GenerativeModelVertexAITests: XCTestCase {
       XCTFail("Should throw GenerateContentError.internalError; no error thrown.")
     } catch let GenerateContentError
       .internalError(underlying: invalidCandidateError as InvalidCandidateError) {
-      guard case let .emptyContent(decodingError) = invalidCandidateError else {
+      guard case let .emptyContent(underlyingError) = invalidCandidateError else {
         XCTFail("Not an InvalidCandidateError.emptyContent error: \(invalidCandidateError)")
         return
       }
-      _ = try XCTUnwrap(decodingError as? DecodingError,
-                        "Not a DecodingError: \(decodingError)")
+      _ = try XCTUnwrap(underlyingError as? Candidate.EmptyContentError,
+                        "Not an empty content error: \(underlyingError)")
     } catch {
       XCTFail("Should throw GenerateContentError.internalError; error thrown: \(error)")
     }
@@ -1047,8 +1047,8 @@ final class GenerativeModelVertexAITests: XCTestCase {
       return
     }
     _ = try XCTUnwrap(
-      emptyContentUnderlyingError as? DecodingError,
-      "Not a decoding error: \(emptyContentUnderlyingError)"
+      emptyContentUnderlyingError as? Candidate.EmptyContentError,
+      "Not an empty content error: \(emptyContentUnderlyingError)"
     )
   }
 
@@ -1595,7 +1595,7 @@ final class GenerativeModelVertexAITests: XCTestCase {
         return
       }
 
-      XCTAssert(contentError is DecodingError)
+      XCTAssert(contentError is Candidate.EmptyContentError)
       return
     }