Use `,` rather than `, ` for combine operation

[annevk]

Fetch defines a combine operation mostly for XMLHttpRequest. We combine other values without 0x20, but we don't do that here mostly due to legacy. Should we just align these?

[annevk]

I think we should by the way, this is mostly a check for implementers.

[annevk]

@hallvors, thoughts?

[hallvors]

A bit confused by this summary - should " ," be ", " ?

[annevk]

Yeah, my bad.

[hallvors]

Gut feeling based on absolutely nothing is that it should be OK to align this without causing web compatibility problems. I may have to eat those words of course.. :p but I have rarely seen scripts setting same value multiple times and relying on concatenation. On the other hand, I think we should look at how HTTP does things and what common implementations do with list headers the browser sends - for consistency and aesthetic reasons. AFAIK HTTP says white-space is optional but if it's commonly implemented I could support making it mandatory..

[hallvors]

Firefox disagrees with itself :) "en-US,en;q=0.5" but "gzip, deflate".

[hallvors]

So well, I think we should drop that space.. and I think Necko should announce "gzip,deflate" support ;)

[mnot]

One problem might be around how header values are compared by caches for purposes of Vary support; if they're dumb, they'll consider differences in whitespace to be different cache keys.

There was a FF bug about this a while back, to align headers across implementations.

[annevk]

Paging @mcmanus for more thoughts.

[mayhemer]

According rfc2616 [1] LWS (=white spaces excluding CR LF) are permitted around comma separated field-value's. That same article also says something about ordering of the combined field-value's being something that affects interpretation of it. Looks like "gzip,deflate" is something else than "deflate,gzip" (in this case definitely, but for e.g. caching directives that should apply as well, regardless that semantically they would be identical when reordered).

Based on that, for instance caches or proxies can easily be dumb when comparing the Vary headers (when LWS are removed from the raw string).

I don't have arguments what to do here, but it's IMO better to not add spaces that adding them. And being consistent is definitely a good thing ;)

[1] https://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2

[mayhemer]

BTW, Gecko merges with ", " (comma + space) and not just ",".

https://dxr.mozilla.org/mozilla-central/rev/4d63dde701b47b8661ab7990f197b6b60e543839/netwerk/protocol/http/nsHttpHeaderArray.h#247

[annevk]

Should probably also ask @tyoshino and @yutakahirano explicitly.

[yutakahirano]

Chrome is inconsistent, too.

accept-encoding: gzip, deflate, sdch, br
accept-language: ja,en-US;q=0.8,en;q=0.6