On Fri, Mar 11, 2016 at 2:28 AM, Cory Benfield <c...@lukasa.co.uk> wrote:
> > On 10 Mar 2016, at 23:56, Andrew Godwin <and...@aeracode.org> wrote: > > I would indeed want to require servers to always fold headers together > into a comma-separated list, as that's what the RFC says, and it then means > applications only have to deal with one kind of multi-header! > > > Wellllll….kinda? > > The RFC says that multiple headers are *semantically equivalent* to the > joined form, but does not in any sense require that it be done. (The > normative language in RFC 7230 is MAY.) > > I had this discussion recently with Brian Smith: while there is only one > correct way to fold/unfold headers, anywhere on the spectrum between > completely folded and completely unfolded is a perfectly valid > representation of the HTTP header block. This means that there’s no *rules* > about how a server is supposed to do it, at least from the IETF. ASGI is of > course totally allowed to add its own rules, and requiring that they be > folded is not terrible. > > FWIW, in my experience, I’ve found that “list of tuples” is really the > most likely to be correct way to represent a header block, because it > provides some assurances to the user that the header block has not been > aggressively transformed from how it was sent on the wire. While the > *rules* are that the folded representation is supposed to be semantically > equivalent to the unfolded representation, there is nonetheless some > information implicit in those headers being separate. > > My intuition when writing this kind of thing is to pass applications (like > Django) the most meaningful representation I can, and then allow the > application to make its own decisions about what meaning they’re willing to > lose. That’s why I’d advocate for “list of two-tuples of bytestrings” as > the representation. However, I don’t think there’s anything *wrong* with > forcing the headers to be joined by the server where possible: it’s just > not how I’d do it. ;) > > Set-cookie is the annoying thing here, though. That's why it's dict > inbound and list of tuples outbound right now, and I just don't know if I > want to make the inbound one a list of tuples too, given I do definitely > want to force servers to concat headers together (unless I find any > examples of that screwing things up) > > > You could make the inbound one a list of tuples but still require that the > servers concat headers. The rule then would be that it needs to be possible > for an application to say `dict(headers)` without any loss of meaning. > Yes, I think this is a good argument - my worry has always been that the "no multiples" is more of a soft rule that some clients might break or some apps might rely on the ordering/multiplicity of things, so preserving it is _probably_ helpful (and as you say, it lets the header names go back to bytestrings). I'll modify the spec and then update Daphne and Channels to match; I can leave Channels parsing both types for a bit, at least. Collin's point about http2's handling of headers is on point, too - if the new spec is deliberately thinned down to that point but no further, it's probably wise to follow them since they know much more about it than I do. Andrew
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