(Swift) How to check if content-encoding is gzip - swift

Question

Is there any way in Swift to find out if data from a request returns in gzip?
I want to write a test method to check if Content-Encoding returns gzip file:

Answer 1

You can get this info from the header fields in the HTTPURLResponse:
URLSession.shared.dataTask(with: url) { (data, response, error) in
if let response = response as? HTTPURLResponse {
if let encoding = response.allHeaderFields["Content-Encoding"] as? String {
print(encoding)
print(encoding == "gzip")
}
}
}.resume()
Note that this downloads the headers and the data.
If you want to only get the headers without downloading the data, a better solution is to use an URLRequest set to "HEAD" like this:
var request = URLRequest(url: url)
request.httpMethod = "HEAD"
URLSession.shared.dataTask(with: request) { (_, response, _) in
if let response = response as? HTTPURLResponse {
if let enc = response.allHeaderFields["Content-Encoding"] as? String {
print(enc)
print(enc == "gzip")
}
}
}.resume()
This way, only the headers are downloaded.

Answer 2

If you read the first 4 bytes of the file, you should get a Magic Number
So you should be able to do something like:
var magicNumber = [UInt](count: 4, repeatedValue: 0)
data.getBytes(&magicNumber, length: 4 * sizeof(UInt))
If it's GZipped, it will have a Magic Number of 1f 8b, so check for that.