CustomURLProtocol for intercepting the HTTP and HTTPS requests made by a macOS/iOS application.

CustomURLProtocol.swift

import Foundation

/*:

# Description
Can be used to intercept HTTP and HTTPS calls made
by the application and introduce custom logic: e.g:
logging, custom caching, etc.

# Usage
## Approach 1: 

Works when using URLSession.shared. If using in
combination with WebKit, it only works with 
legacy `WebView` objects.

```
URLProtocol.registerClass(CustomURLProtocol.self)
let session = URLSession.shared
```

## Approach 2:

Works when using custom URLSession objects.

```
let config = URLSessionConfiguration.default
config.protocolClasses = [CustomURLProtocol.self]
let session = URLSession(configuration: config)
```
*/

final class CustomURLProtocol: URLProtocol {
  
   override class func canInit(with request: URLRequest) -> Bool {
      // Required override. Return true in case you need to intercept the request.
      return false
   }
  

   override class func canonicalRequest(for request: URLRequest) -> URLRequest {
       // Required override. Nothing to do.
       return request
   }

  override func startLoading() {
      // Required override. Intercept the call and add custom logic. Then:
      /*
        if the call is successful:
        ```
            let httpResponse = HTTPURLResonse(...)
            let data = ... // Response data
            client?.urlProtocol(self, didReceive: httpResponse, cacheStoragePolicy: .notAllowed)
            client?.urlProtocol(self, didLoad: data)
            client?.urlProtocolDidFinishLoading(self)
        ```
      */
    
      /* if the call is not successful:
        ```
        let error = NSError(...)
        client?.urlProtocol(self, didFailWithError: error)
        ```
      */
  }
  
  override func stopLoading() {
     // Required Override. Nothing to do.
  }
}