[Vertex AI] Replace legacy errors in GenerativeAIService

FirebaseVertexAI/Sources/GenerativeAIService.swift

@@ -211,15 +211,16 @@ struct GenerativeAIService {
   }
 
   private func httpResponse(urlResponse: URLResponse) throws -> HTTPURLResponse {
-    // Verify the status code is 200
+    // The following condition should always be true: "Whenever you make HTTP URL load requests, any
+    // response objects you get back from the URLSession, NSURLConnection, or NSURLDownload class
+    // are instances of the HTTPURLResponse class.
     guard let response = urlResponse as? HTTPURLResponse else {
       VertexLog.error(
         code: .generativeAIServiceNonHTTPResponse,
         "Response wasn't an HTTP response, internal error \(urlResponse)"
       )
-      throw NSError(
-        domain: "com.google.generative-ai",
-        code: -1,
+      throw URLError(
+        .badServerResponse,
         userInfo: [NSLocalizedDescriptionKey: "Response was not an HTTP response."]
       )
     }
@@ -229,14 +230,11 @@ struct GenerativeAIService {
 
   private func jsonData(jsonText: String) throws -> Data {
     guard let data = jsonText.data(using: .utf8) else {
-      let error = NSError(
-        domain: "com.google.generative-ai",
-        code: -1,
-        userInfo: [NSLocalizedDescriptionKey: "Could not parse response as UTF8."]
-      )
-      throw error
+      throw DecodingError.dataCorrupted(DecodingError.Context(
+        codingPath: [],
+        debugDescription: "Could not parse response as UTF8."
+      ))
     }
-
     return data
   }
 

FirebaseVertexAI/Tests/Unit/GenerativeModelTests.swift

@@ -740,6 +740,9 @@
       return
     }
     XCTAssertEqual(underlyingError.localizedDescription, "Response was not an HTTP response.")
+    let underlyingNSError = underlyingError as NSError
+    XCTAssertEqual(underlyingNSError.domain, NSURLErrorDomain)
+    XCTAssertEqual(underlyingNSError.code, URLError.Code.badServerResponse.rawValue)
   }
 
   func testGenerateContent_failure_invalidResponse() async throws {
@@ -1432,7 +1435,7 @@
     #if os(watchOS)
       throw XCTSkip("Custom URL protocols are unsupported in watchOS 2 and later.")
     #endif // os(watchOS)
     return { request in
       // This is *not* an HTTPURLResponse
       let response = URLResponse(
         url: request.url!,
@@ -1458,7 +1461,7 @@
     #if os(watchOS)
       throw XCTSkip("Custom URL protocols are unsupported in watchOS 2 and later.")
     #endif // os(watchOS)
     let bundle = BundleTestUtil.bundle()
     let fileURL = try XCTUnwrap(bundle.url(forResource: name, withExtension: ext))
     return { request in
       let requestURL = try XCTUnwrap(request.url)