assumesHTTP3Capable not working only on some iPhones

Question

keepsimple OP

Created Jun ’24

Replies 4

Boosts 0

Participants 2

Hi,

We are using HTTP3 only and hence using assumesHTTP3Capable for every request. It worked so far but now encountered one iPhone that never honor this flag and always tries to create a connection using TCP:

[tcp] tcp_input [C1:3] flags=[R.] seq=0, ack=2023568485, win=0 state=SYN_SENT rcv_nxt=0, snd_una=2023568484

The request is created like this:

        let url = URL(string: urlString)!
        var request = URLRequest(url: url, cachePolicy: .reloadIgnoringLocalCacheData, timeoutInterval: 60.0)
        request.assumesHTTP3Capable = true
        return try await urlSession.data(for: request)

iOS: 16

XCode: 15.3

In what cases iOS CFNetwork would not honor "assumesHTTP3Capable" ? (or how can I find out why?)

Boost

Answer 1

keepsimple OP

Jun ’24

I compared the console log from a phone with this problem and another one that works:

good case: (iOS 17.4)

Connection 0: creating secure tcp or quic connection
Connection 4: enabling TLS

bad case: (iOS 16.0.2)

Connection 1: enabling TLS

I.e. the bad case is missing the log line "creating secure tcp or quic connection". Any ideas how this could happen?

0

Answer 2

DTS Engineer OP

Apple

Jul ’24

We are using HTTP3 only … encountered one iPhone that never honor this flag

So, this phone is unable to talk to your server at all?

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

0

Answer 3

keepsimple OP

Jul ’24

Sorry about my late reply as I was out for the last week.

So, this phone is unable to talk to your server at all?

Yes, that's correct. We're looking into adding a HTTP/1.1 endpoint in the server as a backup. But that comes with own issues (TLS etc).

Any ideas when / in what cases assumesHTTP3Capable does not take effect?

P.S. the same phone also used to work a few months ago. But we cannot remember what updates have happened on this phone (currently it is running iOS 16.0.2).

Thanks!

0

Answer 4

DTS Engineer OP

Apple

Jul ’24

Any ideas when / in what cases assumesHTTP3Capable does not take effect?

No.

What do you see on the ‘wire’? I recommend that you use an RVI packet trace, per Recording a Packet Trace, so you see the iPhone’s view of the network traffic.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

0