networking_9.swift

public func fetch() async throws {
    // prepare the request and execute it
    let task = try await request.urlSessionTask(inClient: client)
    let response = try await fetch(request, task: sessionTask: task)
    
    // ask to validator the action to perform on this request
    let action = client.validate(response: response, forRequest: request)
    switch action {
       case .failChain(let error):
          return HTTPResponse(error: error) // fail with error
                
       case .retry(let strategy):
          if request.isAltRequest || request.reachedMaxRetries {
            // alt request cannot be retried to avoid infinite loops
            return response
          } else {
            // perform retry strategy
            let retryResponse = try await performRetryStrategy(strategy, 
                              forRequest: request, task: sessionTask,
                              withResponse: response)
             return retryResponse
          }
       case .nextValidator:
          return response // validation okay
     }
}