[auth] Fix handling of cloud blocking function errors

FirebaseAuth/CHANGELOG.md

@@ -3,6 +3,7 @@
 - [fixed] Updated most decoders to be consistent with Firebase 10's behavior
   for decoding `nil` values. (#14212)
 - [fixed] Address Xcode 16.2 concurrency compile time issues. (#14279)
+- [fixed] Fix handling of cloud blocking function errors. (#14052)
 
 # 11.6.0
 - [added] Added reCAPTCHA Enterprise support for app verification during phone

FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift

@@ -293,14 +293,22 @@ final class AuthBackend: AuthBackendProtocol {
       .unexpectedErrorResponse(deserializedResponse: dictionary, underlyingError: error)
   }
 
+  private static func splitStringAtFirstColon(_ input: String) -> (before: String, after: String) {
+    guard let colonIndex = input.firstIndex(of: ":") else {
+      return (input, "") // No colon, return original string before and empty after
+    }
+    let before = String(input.prefix(upTo: colonIndex))
+      .trimmingCharacters(in: .whitespacesAndNewlines)
+    let after = String(input.suffix(from: input.index(after: colonIndex)))
+      .trimmingCharacters(in: .whitespacesAndNewlines)
+    return (before, after.isEmpty ? "" : after) // Return empty after if it's empty
+  }
+
   private static func clientError(withServerErrorMessage serverErrorMessage: String,
                                   errorDictionary: [String: Any],
                                   response: AuthRPCResponse?,
                                   error: Error?) -> Error? {
-    let split = serverErrorMessage.split(separator: ":")
-    let shortErrorMessage = split.first?.trimmingCharacters(in: .whitespacesAndNewlines)
-    let serverDetailErrorMessage = String(split.count > 1 ? split[1] : "")
-      .trimmingCharacters(in: .whitespacesAndNewlines)
+    let (shortErrorMessage, serverDetailErrorMessage) = splitStringAtFirstColon(serverErrorMessage)
     switch shortErrorMessage {
     case "USER_NOT_FOUND": return AuthErrorUtils
       .userNotFoundError(message: serverDetailErrorMessage)

FirebaseAuth/Sources/Swift/Utilities/AuthErrorUtils.swift

@@ -510,25 +510,62 @@ class AuthErrorUtils {
     return error(code: .accountExistsWithDifferentCredential, userInfo: userInfo)
   }
 
+  private static func extractJSONObjectFromString(from string: String) -> [String: Any]? {
+    // 1. Find the start of the JSON object.
+    guard let start = string.firstIndex(of: "{") else {
+      return nil // No JSON object found
+    }
+    // 2. Find the end of the JSON object.
+    // Start from the first curly brace `{`
+    var curlyLevel = 0
+    var endIndex: String.Index?
+
+    for index in string.indices.suffix(from: start) {
+      let char = string[index]
+      if char == "{" {
+        curlyLevel += 1
+      } else if char == "}" {
+        curlyLevel -= 1
+        if curlyLevel == 0 {
+          endIndex = index
+          break
+        }
+      }
+    }
+    guard let end = endIndex else {
+      return nil // Unbalanced curly braces
+    }
+
+    // 3. Extract the JSON string.
+    let jsonString = String(string[start ... end])
+
+    // 4. Convert JSON String to JSON Object
+    guard let jsonData = jsonString.data(using: .utf8) else {
+      return nil // Could not convert String to Data
+    }
+
+    do {
+      if let jsonObject = try JSONSerialization
+        .jsonObject(with: jsonData, options: []) as? [String: Any] {
+        return jsonObject
+      } else {
+        return nil // JSON Object is not a dictionary
+      }
+    } catch {
+      return nil // Failed to deserialize JSON
+    }
+  }
+
   static func blockingCloudFunctionServerResponse(message: String?) -> Error {
     guard let message else {
       return error(code: .blockingCloudFunctionError, message: message)
     }
-    var jsonString = message.replacingOccurrences(
-      of: "HTTP Cloud Function returned an error:",
-      with: ""
-    )
-    jsonString = jsonString.trimmingCharacters(in: .whitespaces)
-    let jsonData = jsonString.data(using: .utf8) ?? Data()
-    do {
-      let jsonDict = try JSONSerialization
-        .jsonObject(with: jsonData, options: []) as? [String: Any] ?? [:]
-      let errorDict = jsonDict["error"] as? [String: Any] ?? [:]
-      let errorMessage = errorDict["message"] as? String
-      return error(code: .blockingCloudFunctionError, message: errorMessage)
-    } catch {
-      return JSONSerializationError(underlyingError: error)
+    guard let jsonDict = extractJSONObjectFromString(from: message) else {
+      return error(code: .blockingCloudFunctionError, message: message)
     }
+    let errorDict = jsonDict["error"] as? [String: Any] ?? [:]
+    let errorMessage = errorDict["message"] as? String
+    return error(code: .blockingCloudFunctionError, message: errorMessage)
   }
 
   #if os(iOS)

FirebaseAuth/Sources/Swift/Utilities/AuthErrors.swift

@@ -303,7 +303,7 @@ import Foundation
   /// Indicates that the nonce is missing or invalid.
   case missingOrInvalidNonce = 17094
 
-  /// Raised when n Cloud Function returns a blocking error. Will include a message returned from
+  /// Raised when a Cloud Function returns a blocking error. Will include a message returned from
   /// the function.
   case blockingCloudFunctionError = 17105
 

FirebaseAuth/Tests/Unit/AuthBackendTests.swift

@@ -372,6 +372,51 @@ class AuthBackendTests: RPCBaseTests {
     }
   }
 
+  /// Test Blocking Function Error Response flow
+  func testBlockingFunctionError() async throws {
+    let kErrorMessageBlocking = "BLOCKING_FUNCTION_ERROR_RESPONSE"
+    let responseError = NSError(domain: kFakeErrorDomain, code: kFakeErrorCode)
+    let request = FakeRequest(withRequestBody: [:])
+    rpcIssuer.respondBlock = {
+      try self.rpcIssuer.respond(serverErrorMessage: kErrorMessageBlocking, error: responseError)
+    }
+    do {
+      let _ = try await authBackend.call(with: request)
+      XCTFail("Expected to throw")
+    } catch {
+      let rpcError = error as NSError
+      XCTAssertEqual(rpcError.domain, AuthErrors.domain)
+      XCTAssertEqual(rpcError.code, AuthErrorCode.blockingCloudFunctionError.rawValue)
+    }
+  }
+
+  /// Test Blocking Function Error Response flow - including JSON parsing.
+  /// Regression Test for #14052
+  func testBlockingFunctionErrorWithJSON() async throws {
+    let kErrorMessageBlocking = "BLOCKING_FUNCTION_ERROR_RESPONSE"
+    let stringWithJSON = "BLOCKING_FUNCTION_ERROR_RESPONSE : ((HTTP request to" +
+      "http://127.0.0.1:9999/project-id/us-central1/beforeUserCreated returned HTTP error 400:" +
+      " {\"error\":{\"details\":{\"code\":\"invalid-email\"},\"message\":\"invalid " +
+      "email\",\"status\":\"INVALID_ARGUMENT\"}}))"
+    let responseError = NSError(domain: kFakeErrorDomain, code: kFakeErrorCode)
+    let request = FakeRequest(withRequestBody: [:])
+    rpcIssuer.respondBlock = {
+      try self.rpcIssuer.respond(
+        serverErrorMessage: kErrorMessageBlocking + " : " + stringWithJSON,
+        error: responseError
+      )
+    }
+    do {
+      let _ = try await authBackend.call(with: request)
+      XCTFail("Expected to throw")
+    } catch {
+      let rpcError = error as NSError
+      XCTAssertEqual(rpcError.domain, AuthErrors.domain)
+      XCTAssertEqual(rpcError.code, AuthErrorCode.blockingCloudFunctionError.rawValue)
+      XCTAssertEqual(rpcError.localizedDescription, "invalid email")
+    }
+  }
+
   /** @fn testDecodableErrorResponseWithUnknownMessage
       @brief This test checks the behaviour of @c postWithRequest:response:callback: when the
           response deserialized by @c NSJSONSerialization represents a valid error response (and an