Re: [quicwg/base-drafts] Remove DUPLICATE_PUSH and allow duplicate PUSH_PROMISE (#3309)

Mike Bishop <notifications@github.com> Fri, 10 January 2020 15:42 UTC

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Subject: Re: [quicwg/base-drafts] Remove DUPLICATE_PUSH and allow duplicate PUSH_PROMISE (#3309)
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MikeBishop commented on this pull request.

I don't think we have to talk about discarding necessarily, but encouraging comparison would be good.

> @@ -623,31 +624,25 @@ allows the server push to be associated with a client request.  Promised
 requests MUST conform to the requirements in Section 8.2 of {{!HTTP2}}.
 
 The same server push can be associated with additional client requests using a
-DUPLICATE_PUSH frame (see {{frame-duplicate-push}}).
+PUSH_PROMISE frame with the same Push ID on multiple request stream.

```suggestion
PUSH_PROMISE frame with the same Push ID on multiple request streams.
```

> @@ -1238,9 +1232,20 @@ MAX_PUSH_ID frame ({{frame-max-push-id}}). A client MUST treat receipt of a
 PUSH_PROMISE frame that contains a larger Push ID than the client has advertised
 as a connection error of H3_ID_ERROR.
 
-A server MUST NOT use the same Push ID in multiple PUSH_PROMISE frames. A client
-MUST treat receipt of a Push ID which has already been promised as a connection
-error of type H3_ID_ERROR.
+A server MAY use the same Push ID in multiple PUSH_PROMISE frames. If so, the
+decompressed request header sets MUST contain the same fields in the same
+order, and both the name and and value in each field MUST be exact
+matches. If a client receives a Push ID that has already been promised
+and detects a mismatch, it MUST respond with a connection error of type
+H3_GENERAL_PROTOCOL_ERROR. If the decompressed header sets match exactly, the
+client MUST ignore the duplicate PUSH_PROMISE frame.

```suggestion
client SHOULD associate the pushed content with each stream on which a PUSH_PROMISE was received.
```
I don't think "MUST ignore" is what we want.  It's not an error case, it's a client optimization.

> @@ -1238,9 +1232,20 @@ MAX_PUSH_ID frame ({{frame-max-push-id}}). A client MUST treat receipt of a
 PUSH_PROMISE frame that contains a larger Push ID than the client has advertised
 as a connection error of H3_ID_ERROR.
 
-A server MUST NOT use the same Push ID in multiple PUSH_PROMISE frames. A client
-MUST treat receipt of a Push ID which has already been promised as a connection
-error of type H3_ID_ERROR.
+A server MAY use the same Push ID in multiple PUSH_PROMISE frames. If so, the
+decompressed request header sets MUST contain the same fields in the same
+order, and both the name and and value in each field MUST be exact
+matches. If a client receives a Push ID that has already been promised

```suggestion
matches. Clients SHOULD compare the request header sets for resources promised
multiple times. If a client receives a Push ID that has already been promised
```
I don't know that we need to be explicit about the discard, but I think we should encourage comparison.

> -A server MUST NOT use the same Push ID in multiple PUSH_PROMISE frames. A client
-MUST treat receipt of a Push ID which has already been promised as a connection
-error of type H3_ID_ERROR.
+A server MAY use the same Push ID in multiple PUSH_PROMISE frames. If so, the
+decompressed request header sets MUST contain the same fields in the same
+order, and both the name and and value in each field MUST be exact
+matches. If a client receives a Push ID that has already been promised
+and detects a mismatch, it MUST respond with a connection error of type
+H3_GENERAL_PROTOCOL_ERROR. If the decompressed header sets match exactly, the
+client MUST ignore the duplicate PUSH_PROMISE frame.
+
+Allowing duplicate references to the same Push ID is primarily to reduce
+duplication caused by concurrent requests.  A server SHOULD avoid reusing a Push
+ID over a long period.  Clients are likely to consume server push responses and
+not retain them for reuse over time.  Clients that see a PUSH_PROMISE that uses
+a Push ID that they have since consumed and discarded are forced to ignore the

```suggestion
a Push ID that they have already consumed and discarded are forced to ignore the
```

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