W3C home > Mailing lists > Public > ietf-http-wg@w3.org > July to September 2014

Re: Fragmentation for headers: why jumbo != continuation.

From: Amos Jeffries <squid3@treenet.co.nz>
Date: Sat, 12 Jul 2014 21:35:12 +1200
Message-ID: <53C10150.6020806@treenet.co.nz>
To: ietf-http-wg@w3.org
On 12/07/2014 5:24 p.m., Roberto Peon wrote:
> In the case of a server, it must interpret. If it can do so in a streaming
> fashion, it can do so in a streaming fashion. If not, it must buffer until
> it has the entire header set. That is true of fragmented and non-fragmented
> headers.
> In other words, the requirement to buffer or not is unchanged and is
> implementation dependent.

This does not follow. The requirement to buffer is in the specification.
Fragmented HEADERS+CONTINUTATION MUST be handled as a contiguous HOL
blocking squence.
  There is no server choice in that.

Likewise connections from proxies are multiplexing many clients streams
simultaneously as per the specification.
 There is no server choice in that.

Yet the server "must" have choice whether to HOL-block the entire
connection by streaming its responses into a buffer *on the proxy* ?
that is a connection just begging to be stalled.

> 
> For a proxy, it is a sender and a receiver.
> Allowing fragmentation allows the sender-half of the proxy to reduce its
> memory commitment.

False. There is no sender side specific buffering state in proxies.
*Unless* fragmentation requires an area to generate inter-fragment
overheads in. Ergo, there is a net *increase* of sender requirements for
proxies with fragmentation.


> Again, nothing changed on the receiver side, which implies that the proxy's
> memory commitment is reduced.

False. Receiving fragmentation requires HOL-blocking of the connection
and buffering the headers multiple-fragment entirety.

Ergo, for proxies the receiver side has a net increase on both sender
and receiver sides when handling fragmentation.

> 
> In other words, fragmented headers leads to equivalence at servers, and a
> possible improvement at proxies.

Conclusion based on corrected arguments is quite the opposite:
 - Fragmentation offers server as sender (or client as sender too)
ability to freely cause HOL-block or stall/DoS the connection with
multiple end-clients suffering.
 - Fragmentation causes state commitment increases in proxies.

Amos
Received on Saturday, 12 July 2014 09:35:44 UTC

This archive was generated by hypermail 2.3.1 : Wednesday, 30 March 2016 09:57:09 UTC