URL File Size With NSURLConnection - Swift

问题:

i am trying to get a file size from url before downloading

here is the obj-c code

    NSURL *URL = [NSURL URLWithString:"ExampleURL"];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:URL];
    [request setHTTPMethod:@"HEAD"];
    NSHTTPURLResponse *response;
    [NSURLConnection sendSynchronousRequest:request returningResponse:&response error: nil];
    long long size = [response expectedContentLength];

and here is Swift Code

var url:NSURL = NSURL(string: "ExmapleURL")
                var request:NSMutableURLRequest = NSMutableURLRequest(URL: url)
                request.HTTPMethod = "HEAD"
                var response = NSHTTPURLResponse()
                NSURLConnection.sendSynchronousRequest(request, returningResponse: &response , error: nil)

but i have error here

NSURLConnection.sendSynchronousRequest(request, returningResponse: &response , error: nil)

'NSHTTPURLResponse' is not identical to 'NSURLResponse?'

did i miss something in swift here ?

回答1:

The response parameter has the type

AutoreleasingUnsafeMutablePointer<NSURLResponse?>

which means that you can pass the address of an optional NSURLResponse as argument:

var response : NSURLResponse?
NSURLConnection.sendSynchronousRequest(request, returningResponse: &response , error: nil)

You can then conditionally cast the returned response to a NSHTTPURLResponse:

if let httpResponse = response as? NSHTTPURLResponse {
    println(httpResponse.expectedContentLength)
}

Note that you should check the return value of sendSynchronousRequest(), which is nil if no connection could be made.

It is also recommended to call this method only from a separate thread (or use sendAsynchronousRequest() instead) because it can take a while to make a connection – in particular when using a cellular network – and the main thread would be blocked otherwise.

回答2:

Swift 4 solution:

func fetchContentLength(for url: URL, completionHandler: @escaping (_ contentLength: Int64?) -> ()) {

    var request = URLRequest(url: url)
    request.httpMethod = "HEAD"

    let task = URLSession.shared.dataTask(with: request) { (data, response, error) in
    guard error == nil, let response = response as? HTTPURLResponse, let contentLength = response.allHeaderFields["Content-Length"] as? String else {
        completionHandler(nil)
        return
    }
        completionHandler(Int64(contentLength))
    }

        task.resume()
}

// Usage:

let url = URL(string: "https://s3.amazonaws.com/x265.org/video/Tears_400_x265.mp4")!

fetchContentLength(for: url, completionHandler: { contentLength in
    print(contentLength ?? 0)
})