---
title: "additionalRequestHeaders(for:completionHandler:)"
framework: safariservices
role: symbol
role_heading: Instance Method
path: "safariservices/sfsafariextensionhandling/additionalrequestheaders(for:completionhandler:)"
---

# additionalRequestHeaders(for:completionHandler:)

## Declaration

```swift
optional func additionalRequestHeaders(for url: URL, completionHandler: @escaping @Sendable ([String : String]?) -> Void)
```

```swift
optional func additionalRequestHeaders(for url: URL) async -> [String : String]?
```

## Discussion

Discussion important: You can call this method from synchronous code using a completion handler, as shown on this page, or you can call it as an asynchronous method that has the following declaration: optional func additionalRequestHeaders(for url: URL) async -> [String : String]? For information about concurrency and asynchronous code in Swift, see Calling Objective-C APIs Asynchronously.