Subject: [quicwg/base-drafts] Why is CANCEL_PUSH limited to being used before the stream was created? (#2234)

From: ekr <[email-masked]>
Date: Thu, 20 Dec 2018 15:14:12 -0800

```
The CANCEL_PUSH frame (type=0x3) is used to request cancellation of a server
push prior to the push stream being created.  The CANCEL_PUSH frame identifies a
server push by Push ID (see {{frame-push-promise}}), encoded as a
variable-length integer.

When a server receives this frame, it aborts sending the response for the
identified server push.  If the server has not yet started to send the server
push, it can use the receipt of a CANCEL_PUSH frame to avoid opening a push
stream.  If the push stream has been opened by the server, the server SHOULD
send a QUIC RESET_STREAM frame on that stream and cease transmission of the
response.
```

Why is this limited to being prior to the push stream being created, given
that you specify how the server handles it if it has created the stream.

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From: Martin Thomson <[email-masked]>
Date: Thu, 20 Dec 2018 19:59:50 -0800

I don't read this as saying that you have to avoid it.  The point is that you also have to reset/STOP_SENDING on the stream if it exists, so there is no real point to using CANCEL_PUSH in addition.

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From: Brad Lassey <[email-masked]>
Date: Fri, 28 Dec 2018 08:05:59 -0800

Sounds  like the intent is that CANCEL_PUSH should be used between the client receiving a PUSH_PROMISE and before receiving the stream (i.e. when it is ambiguous as to whether the stream has been created by the server from the clients perspective). I think replacing "created" with "received" would make this more clear.

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