CODEWITHSUNDEEP
iosetagnsurlcache
Sirio
Sirio

Reputation: 1031

NSURLCache and ETags

Does NSURLCache transparently handle ETags received by server?

I mean: does it automatically store ETags for each URL request and then send the appropriate If-None-Match when a request to the same URL is submitted? Or do I have to manage it by myself?

Upvotes: 17

Views: 9636

Answers (2)

Kappe
Kappe

Reputation: 9505

For posterity, this is how to use ETag with swift:

let API_HEADER_FIELD_NONE_MATCH = "If-None-Match"
let API_HEADER_FIELD_ETAG = "Etag"
let API_REQUEST_SUCCESS : Int = 200
let API_REQUEST_NOT_MODIFIED : Int = 304

//inject ETag
let config = URLSessionConfiguration.default
config.httpAdditionalHeaders = [API_HEADER_FIELD_NONE_MATCH: storedEtag]
config.requestCachePolicy = .reloadIgnoringLocalAndRemoteCacheData
let urlSession = URLSession(configuration: config)
        
let (jsonData, response) = try await urlSession.data(from: dataURL)
        
guard let httpResponse = response as? HTTPURLResponse else {
      throw some error
}
        
switch httpResponse.statusCode {
case API_REQUEST_SUCCESS:
    let decoder = JSONDecoder()
    decoder.dateDecodingStrategy = .iso8601
    
    if let responseETag = httpResponse.allHeaderFields[API_HEADER_FIELD_ETAG] as? String {
        let decodedData = try decoder.decode(TrackerData.self, from: jsonData)
        return (decodedData, responseETag)
    } else {
        throw some error "Missing ETag"
    }
case API_REQUEST_NOT_MODIFIED:
    //the data represented by the stored etag is up to date
default:
    throw APIError.apiError(reason: "Unexpected HTTP response code \(httpResponse.statusCode)")
}

Upvotes: 0

Daij-Djan
Daij-Djan

Reputation: 50109

yes it does handle it transparently if you set its cache mode:

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:urlString]
                                                           cachePolicy: NSURLRequestUseProtocolCachePolicy
                                                       timeoutInterval:60];

note: you cannot see the header in the request at all and if a 304 response is returned by the server you will only see the 200 response that it transparently loaded from the cache.

Upvotes: 23

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