- From: Willy Tarreau <w@1wt.eu>
- Date: Mon, 26 Nov 2012 08:15:06 +0100
- To: Mark Nottingham <mnot@mnot.net>
- Cc: HTTP Working Group <ietf-http-wg@w3.org>
On Mon, Nov 26, 2012 at 04:58:46PM +1100, Mark Nottingham wrote: > p1 says: > > > A proxy must not modify or add any of the following fields in a message that contains the no-transform cache-control directive: > > > > ? Content-Encoding (Section 3.1.2.2 of [Part2]) > > ? Content-Range (Section 5.2 of [Part5]) > > ? Content-Type (Section 3.1.1.5 of [Part2]) > > A transforming proxy may modify or add these fields to a message that does not include no-transform, but if it does so, it must add a Warning 214 (Transformation applied) if one does not already appear in the message (see Section 7.5 of [Part6]). > > p6 says: > > > 7.2.2.9 no-transform > > > > The "no-transform" response directive indicates that an intermediary (regardless of whether it implements a cache) must not change the Content-Encoding, Content-Range orContent-Type response header fields, nor the response representation. > > 2616 was a bit more wordy: > > > 14.9.5 No-Transform Directive > > > > no-transform > > Implementors of intermediate caches (proxies) have found it useful > > to convert the media type of certain entity bodies. A non- > > transparent proxy might, for example, convert between image > > formats in order to save cache space or to reduce the amount of > > traffic on a slow link. > > > > Serious operational problems occur, however, when these > > transformations are applied to entity bodies intended for certain > > kinds of applications. For example, applications for medical > > imaging, scientific data analysis and those using end-to-end > > authentication, all depend on receiving an entity body that is bit > > for bit identical to the original entity-body. > > > > Therefore, if a message includes the no-transform directive, an > > intermediate cache or proxy MUST NOT change those headers that are > > listed in section 13.5.2 as being subject to the no-transform > > directive. This implies that the cache or proxy MUST NOT change > > any aspect of the entity-body that is specified by these headers, > > including the value of the entity-body itself. > > > (the text currently in p1 closely corresponds to that in 2616's 13.5.2). > > The issue here is that the intent in 2616 is clear -- the body shouldn't be modified if no-transform is present -- but since we split it up, a reader of p1 doesn't have any indication of this unless they chase up in p6 (note there isn't any reference, beyond the unrelated one to the Warning header). > > I'd suggest we need p1 to explicitly say the body can't be changed, as p6 does. I agree. Also, I think we should take the intent from 2616 which clearly explains *why* proxies must absolutely respect this rule. I have already seen some proxies recompress whatever they could without any consideration for the importance of original data, so having this would be really nice. > While we're at it, changing "A proxy must not modify or add any of the following fields..." to "A proxy (transparent or non-transparent) must not modify or add any of the following fields " would make what's going on a lot clearer. +1 for me too. Willy
Received on Monday, 26 November 2012 07:15:35 UTC