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# URLProtocolClient

The interface used by [`URLProtocol`](/documentation/Foundation/URLProtocol) subclasses to communicate with the URL Loading System.

```
protocol URLProtocolClient : NSObjectProtocol, Sendable
```

## Overview

Don’t implement this protocol in your application. Instead, your [`URLProtocol`](/documentation/Foundation/URLProtocol) subclass calls methods of this protocol on its own [`client`](/documentation/Foundation/URLProtocol/client) property.

## Topics

### Creating a response

[`urlProtocol(_:didReceive:cacheStoragePolicy:)`](/documentation/Foundation/URLProtocolClient/urlProtocol(_:didReceive:cacheStoragePolicy:))

Tells the client that the protocol implementation has created a response object for the request.

### Handling redirects

[`urlProtocol(_:wasRedirectedTo:redirectResponse:)`](/documentation/Foundation/URLProtocolClient/urlProtocol(_:wasRedirectedTo:redirectResponse:))

Tells the client that the protocol implementation has been redirected.

### Working with cache data

[`urlProtocol(_:cachedResponseIsValid:)`](/documentation/Foundation/URLProtocolClient/urlProtocol(_:cachedResponseIsValid:))

Tells the client that a cached response is valid.

### Handling authentication challenges

[`urlProtocol(_:didCancel:)`](/documentation/Foundation/URLProtocolClient/urlProtocol(_:didCancel:))

Tells the client that an authentication challenge has been canceled.

[`urlProtocol(_:didReceive:)`](/documentation/Foundation/URLProtocolClient/urlProtocol(_:didReceive:))

Tells the client that the URL Loading System received an authentication challenge.

### Indicating loading progress or failure

[`urlProtocol(_:didFailWithError:)`](/documentation/Foundation/URLProtocolClient/urlProtocol(_:didFailWithError:))

Tells the client that the load request failed due to an error.

[`urlProtocol(_:didLoad:)`](/documentation/Foundation/URLProtocolClient/urlProtocol(_:didLoad:))

Tells the client that the protocol implementation has loaded some data.

[`urlProtocolDidFinishLoading(_:)`](/documentation/Foundation/URLProtocolClient/urlProtocolDidFinishLoading(_:))

Tells the client that the protocol implementation has finished loading.


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