NSURLResponse object HTTP header values

NSURLSession does not have any logic that changes based on the size of the incoming file. 

Does the cache?

Is the -valueForHTTPHeaderField: method not working for you?

I tried that but Xcode didn't allow it, as NSURLSessionDownloadTask.response is a NSURLResponse object not a NSHTTPURLResponse object (which responds to -valueForHTTPHeaderField:) .

However, I did cast the types and got it work work:

 NSDictionary *responseHeaders = ((NSHTTPURLResponse *)downloadTask.response).allHeaderFields;

So that does work, thank you!

But the file being downloaded is a .gz file. Is there a way in iOS to uncompress it programmatically?

as NSURLSessionDownloadTask.response is a NSURLResponse object not a NSHTTPURLResponse object

Right. For an http[s] request the response will be an NSHTTPURLResponse and standard practice for accessing HTTP-specific properties, like this header, is to do the cast. If you’re feeling paranoid, feel free to add this:

NSHTTPURLResponse * = task.response;
if ( ! [response isKindOfClass:[NSHTTPURLResponse class]] ) {
    … handle this failure …
}

Is there a way in iOS to uncompress it programmatically?

If the server uses a gzip content encoding (see here, and note that this different from the transfer encoding) NSURLSession will undo that transparently. If not, you’ll have to undo it yourself. To do this, check out the zlib man page.

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