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Limit pushes using MAX_PUSH_ID #711

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merged 8 commits into from Aug 16, 2017
Merged

Limit pushes using MAX_PUSH_ID #711

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a7ac6f1
Fix error code definitions
martinthomson Aug 8, 2017
0926843
So much effort spent on something so trivial
martinthomson Aug 10, 2017
4bcc8b8
Limit pushes using MAX_PUSH_ID
martinthomson Aug 8, 2017
3b7aa26
Fix error codes, prohibit reduction
martinthomson Aug 8, 2017
f633213
Review comments
martinthomson Aug 9, 2017
9b96a44
Remove push setting in favor of MAX_PUSH_ID
martinthomson Aug 10, 2017
b38ae53
Remove redundant word
martinthomson Aug 10, 2017
494a48f
Merge branch 'master' into push-id-seq
MikeBishop Aug 16, 2017
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78 changes: 66 additions & 12 deletions draft-ietf-quic-http.md
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Expand Up @@ -336,9 +336,9 @@ frame.
## Server Push

HTTP/QUIC supports server push as described in {{!RFC7540}}. During connection
establishment, the client indicates whether it is willing to receive server
pushes via the SETTINGS_ENABLE_PUSH setting in the SETTINGS frame (see
{{connection-establishment}}), which is disabled by default.
establishment, the client enables server push by sending a MAX_PUSH_ID frame
(see {{frame-max-push-id}}). A server cannot use server push until it receives
a MAX_PUSH_ID frame.

As with server push for HTTP/2, the server initiates a server push by sending a
PUSH_PROMISE frame that includes request header fields attributed to the
Expand All @@ -362,9 +362,19 @@ This header consists of a 32-bit Push ID, which identifies a server push (see
~~~~~
{: #fig-push-stream-header title="Push Stream Header"}

A push stream always starts with a 32-bit Push ID. A client MUST treat
receiving a push stream that contains fewer than 4 octets as a connection error
of type HTTP_MALFORMED_PUSH.

A server SHOULD use Push IDs sequentially, starting at 0. A client uses the
MAX_PUSH_ID frame ({{frame-max-push-id}}) to limit the number of pushes that a
server can promise. A client MUST treat receipt of a push stream with a Push ID
that is greater than the maximum Push ID as a connection error of type
HTTP_MALFORMED_PUSH.

Each Push ID MUST only be used once in a push stream header. If a push stream
header includes a Push ID that was used in another push stream header, the
client MUST treat this as a connection error of type HTTP_DUPLICATE_PUSH. The
client MUST treat this as a connection error of type HTTP_MALFORMED_PUSH. The
same Push ID can be used in multiple PUSH_PROMISE frames (see
{{frame-push-promise}}).

Expand Down Expand Up @@ -635,9 +645,6 @@ The following settings are defined in HTTP/QUIC:
SETTINGS_HEADER_TABLE_SIZE (0x1):
: An integer with a maximum value of 2^32 - 1. This value MUST be zero.

SETTINGS_ENABLE_PUSH (0x2):
: Transmitted as a Boolean

SETTINGS_MAX_HEADER_LIST_SIZE (0x6):
: An integer with a maximum value of 2^32 - 1

Expand Down Expand Up @@ -696,6 +703,11 @@ Push ID:
Header Block:
: HPACK-compressed request headers for the promised response.

A server MUST NOT use a Push ID that is larger than the client has provided in a
MAX_PUSH_ID frame ({{frame-max-push-id}}). A client MUST treat receipt of a
PUSH_PROMISE that contains a larger Push ID than the client has advertised as a
connection error of type HTTP_MALFORMED_PUSH_PROMISE.

A server MAY use the same Push ID in multiple PUSH_PROMISE frames. This allows
the server to use the same server push in response to multiple concurrent
requests. Referencing the same server push ensures that a PUSH_PROMISE can be
Expand Down Expand Up @@ -797,6 +809,38 @@ the server MAY send another GOAWAY frame with an updated last stream identifier.
This ensures that a connection can be cleanly shut down without losing requests.


# MAX_PUSH_ID {#frame-max-push-id}

The MAX_PUSH_ID frame (type=0xD) is used by clients to control the number of
server pushes that the server can initiate. This sets the maximum value for a
Push ID that the server can use in a PUSH_PROMISE frame. Consequently, this
also limits the number of push streams that the server can initiate in addition
to the limit set by the QUIC MAX_STREAM_ID frame.
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It seems silly but possible to send this with 0. Can you add a sentence that says this MUST be > 0?


The MAX_PUSH_ID frame is always sent on the control stream. Receipt of a
MAX_PUSH_ID frame on any other stream MUST be treated as a connection error of
type HTTP_WRONG_STREAM.

A server MUST NOT send a MAX_PUSH_ID frame. A client MUST treat the receipt of
a MAX_PUSH_ID frame as a connection error of type HTTP_MALFORMED_MAX_PUSH_ID.

The maximum Push ID is unset when a connection is created, meaning that a server
cannot push until it receives a MAX_PUSH_ID frame. A client that wishes to
manage the number of promised server pushes can increase the maximum Push ID by
sending a MAX_PUSH_ID frame as the server fulfills or cancels server pushes.

The MAX_PUSH_ID frame has no defined flags.

The MAX_PUSH_ID frame carries a 32-bit Push ID that identifies the maximum value
for a Push ID that the server can use (see {{frame-push-promise}}). A
MAX_PUSH_ID frame cannot reduce the maximum Push ID; receipt of a MAX_PUSH_ID
that contains a smaller value than previously received MUST be treated as a
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I would explicitly state that this previous value may have been received via MAX_PUSH_ID or SETTINGS_MAX_PUSH_ID. Perhaps "a smaller value than that received via a previous MAX_PUSH_ID or SETTINGS_MAX_PUSH_ID ..." ?

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Sending a frame with a value less than you provided in transport settings is a clear error, actually, since you know the transport settings necessarily came before the frame.

connection error of type HTTP_MALFORMED_MAX_PUSH_ID.
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General comment: Because these are on the control stream, which means guaranteed in-order delivery, we could use the HTTP/2 model of sending an increment rather than an absolute number. I'm not sold that the few bytes saved are worth it, though.

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I think that we can make a bigger saving here by not sending the frame as often, noting that MAX_STREAM_ID covers the resource exhaustion issue.

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I don't think the savings are worth it, since this shouldn't be sent that often really as it is.

On resource exhaustion, I think both MAX_STREAM_ID and MAX_PUSH_ID both cover that issue, just at different levels. QUIC decides MAX_STREAM_ID based on its resource constraints for streams, and the HTTP "layer" decides MAX_PUSH_ID based on its constraints for handling pushed resources. I think these are independent.


A server MUST treat a MAX_PUSH_ID frame payload that is other than 4 octets in
length as a connection error of type HTTP_MALFORMED_MAX_PUSH_ID.


# Error Handling {#errors}

QUIC allows the application to abruptly terminate (reset) individual streams or
Expand Down Expand Up @@ -866,8 +910,11 @@ HTTP_WRONG_STREAM (0x0F):
HTTP_MULTIPLE_SETTINGS (0x10):
: More than one SETTINGS frame was received.

HTTP_DUPLICATE_PUSH (0x11):
: Multiple push streams used the same Push ID.
HTTP_MALFORMED_PUSH (0x11):
: A push stream header was malformed or included an invalid Push ID.

HTTP_MALFORMED_MAX_PUSH_ID (0x12):
: A MAX_STREAM_ID frame has been received with an invalid format.


# Considerations for Transitioning from HTTP/2
Expand Down Expand Up @@ -986,7 +1033,8 @@ SETTINGS_HEADER_TABLE_SIZE:
: See {{settings-parameters}}.

SETTINGS_ENABLE_PUSH:
: See {{settings-parameters}}.
: This is removed in favor of the MAX_PUSH_ID which provides a more granular
control over server push.

SETTINGS_MAX_CONCURRENT_STREAMS:
: QUIC controls the largest open stream ID as part of its flow control logic.
Expand Down Expand Up @@ -1151,6 +1199,7 @@ The entries in the following table are registered by this document.
| GOAWAY | 0x7 | {{frame-goaway}} |
| Reserved | 0x8 | N/A |
| Reserved | 0x9 | N/A |
| MAX_PUSH_ID | 0xD | {{frame-max-push-id}} |
|----------------|------|--------------------------|

## Settings Parameters {#iana-settings}
Expand Down Expand Up @@ -1185,7 +1234,7 @@ The entries in the following table are registered by this document.
| Setting Name | Code | Specification |
|----------------------------|:----:|-------------------------|
| HEADER_TABLE_SIZE | 0x1 | {{settings-parameters}} |
| ENABLE_PUSH | 0x2 | {{settings-parameters}} |
| Reserved | 0x2 | N/A |
| Reserved | 0x3 | N/A |
| Reserved | 0x4 | N/A |
| Reserved | 0x5 | N/A |
Expand Down Expand Up @@ -1240,7 +1289,8 @@ The entries in the following table are registered by this document.
| HTTP_INTERRUPTED_HEADERS | 0x0E | Incomplete HEADERS block | {{http-error-codes}} |
| HTTP_WRONG_STREAM | 0x0F | A frame was sent on the wrong stream | {{http-error-codes}} |
| HTTP_MULTIPLE_SETTINGS | 0x10 | Multiple SETTINGS frames | {{http-error-codes}} |
| HTTP_DUPLICATE_PUSH | 0x11 | Duplicate server push | {{http-error-codes}} |
| HTTP_MALFORMED_PUSH | 0x11 | Invalid push stream header | {{http-error-codes}} |
| HTTP_MALFORMED_MAX_PUSH_ID | 0x12 | Invalid MAX_PUSH_ID frame | {{http-error-codes}} |
|-----------------------------------|--------|----------------------------------------|----------------------|


Expand All @@ -1255,6 +1305,10 @@ The original authors of this specification were Robbie Shade and Mike Warres.
> **RFC Editor's Note:** Please remove this section prior to publication of a
> final version of this document.

## Since draft-ietf-quic-http-05

- Made push ID sequential, add MAX_PUSH_ID, remove SETTINGS_ENABLE_PUSH (#709)

## Since draft-ietf-quic-http-04

- Cite RFC 5234 (#404)
Expand Down