NSURLConnection on iOS 9 does not use HTTP/2 protocol

Question

I've configured HTTP/2 on a Jetty 9.3 server, it has a valid certificate and SSLLabs.com given it a grade A security configuration.

Browsing using Chrome to https://example.com loads the correct response, it's also reporting that "h2" (HTTP/2") protocol was used.

But when trying to access the same URL from iOS 9 using NSURLConnection, I can see in the request log that it used HTTP 1.1 instead. If I disable HTTP 1.1 on my server, the request will fail on iOS 9 (but still succeed on Chrome).

NSURLConnection code -

let url = NSURL(string: "https://example.com")
request = NSURLRequest(URL: url, cachePolicy: NSURLRequestCachePolicy.ReloadIgnoringLocalCacheData, timeoutInterval: 10)

connection = NSURLConnection(request: request, delegate: self, startImmediately: true)

Server's ALPN debug output -

[S] ALPN protocols [spdy/3.1, spdy/3, http/1.1] received from client for 1e5e2487[SSLEngine[hostname=3.4.5.6 port=52090] SSL_NULL_WITH_NULL_NULL]
[S] ALPN protocol 'http/1.1' selected for 1e5e2487[SSLEngine[hostname=3.4.5.6 port=52090] SSL_NULL_WITH_NULL_NULL]

In WWDC 2015 it was stated that NSURLRequest in iOS 9 supports HTTP/2, but the client app claims to support spdy/3.1, spdy/3, http/1.1, no http/2. There are no NSAppTransportSecurity exceptions set.

I tried connecting to the server using Safari on the same iPhone Simulator running the app, this time it worked and used HTTP/2, here's ALPN debug output -

[S] ALPN protocols [h2, h2-16, h2-15, h2-14, spdy/3.1, spdy/3, http/1.1] received from client for 7b50217d[SSLEngine[hostname=3.4.5.6 port=52247] SSL_NULL_WITH_NULL_NULL]
[S] ALPN protocol 'h2' selected for 7b50217d[SSLEngine[hostname=3.4.5.6 port=52247] SSL_NULL_WITH_NULL_NULL]

Any ideas why it doesn't use HTTP/2 from within the app?

Westbrooke

It's only supported by NSURLSession. – Nitrogenize

Correct, post this as the answer. :) – Westbrooke

Answer 1

HTTP/2 is only supported by NSURLSession. NSURLConnection has been deprecated in iOS 9. Here is the reference from the header:

Nitrogenize

If you absolutely have to support existing client code that uses NSURLConnection, I'm pretty sure it is possible to swizzle the NSURLConnection class, replacing every NSURLConnection method with calls into the shared session, and then simulate all of the delegate calls. I wouldn't recommend it, though, unless you have no other choice. :-) – Fromma

Yeah that should be possible but, as you said, I don't think it's a good choice and in most cases it's not needed - you can just go with NSURLSession instead. – Nitrogenize

Answer 2

NSURLConnection is deprecated in iOS9, use NSURLSession it supports HTTP/2 protocol. ;)

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