NWConnectionGroup no way to send/receive on QUIC stream with identifier `0`

Question

Created Apr ’24

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Hello! I'm playing around with QUIC and Swift and using the Network framework. So far, the process has been really straightforward, but I noticed that I can't seem to get a handle on the stream with identifier 0.

If I use NWConnection directly, I only have access to the first stream, which has the stream ID 0. This not what I want since I wanna use multiple streams. Following the documentation, I started using NWMultiplexGroup and starting a NWConnectionGroup with it.

Everything works fine and I can get all streams that my backend service opens using NWMultiplexGroup's newConnectionHandler property. However, whenever backend sends a message on stream_id 0, none of my connections receive it. Looking around with

connection.metadata(definition: NWProtocolQUIC.definition) as? NWProtocolQUIC.Metadata

for each connection, I see that all streams are accounted for except stream 0. Then, using the NWConnectionGroup variant of the above

connectionGroup.metadata(definition: NWProtocolQUIC.definition) as? NWProtocolQUIC.Metadata

I see that the connection group itself has Stream ID 0. However, calling setReceiveHandler does nothing (it's never called, even when backend is sending messages) and when I attempt to send a message using NWConnectionGroup's -send method, a new stream is opened (instead of it being sent on stream ID 0).

How can one get a handle on NWConnection for stream ID 0?

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Answer 1

DTS Engineer OP

Apple

Apr ’24

I’m still coming up to speed on QUIC myself, so I spent some time digging into this. AFAICT this is working as designed. On the client side, you can create a QUIC connection in one of two ways:

As a connection, using NWConnection
As a connection group, using NWConnectionGroup

In both cases the object you create ‘owns’ stream ID 0. In the first case you can access it via the I/O methods on the connection. In the second case you can’t access it at all.

If there’s a specific reason you need to use a connection group and perform I/O on stream ID 0, I recommend that you file an enhancement request [1] explaining the real world impact of this limitation.

Please post your bug number, just for the record.

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

[1] Or is it a bug report? That’s a tricky one (-: However, it doesn’t matter, it’ll go to the right folks either way.

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Answer 2

Ruins OP

3w

I encountered the same issue and managed to solve it, fortunately. The workaround with the Apple API involves avoiding NWConnectionGroup. Instead, you can create an NWConnection with the same NWParameters. This way, as long as you don't alter the NWParameters, it won't initiate a new connection to the server but will instead generate a new stream. If you need to establish a new connection to the server, simply create a new pair of parameters/options.

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