Re: [naviserver-devel] compression

[Stephen D. <sd...@gm...>]

On Sat, Oct 27, 2012 at 1:13 PM, Gustaf Neumann <ne...@wu...> wrote:
> On 26.10.12 15:47, Stephen Deasey wrote:
>> I think the spec says that for HTTP/1.1, if the client doesn't
>> explicitly say to NOT send the body gzipped, say by using a q value of
>> 0 (which we don't actually check for, woops...), then the server can
>> choose the encoding, although it should prefer the identity, unless
>> that's unavailable. So we're being very pushy...
>
> now we do check for the qvalues used in connection with
> gzip. So, a client can now specify explicitly, that gzip is
> NOT wanted via "gzip; q=0". What the code still does not do
> is comparing the identity-qvalue with the gzip-qvalue or
> combination with wildcards "....*;q=..."

Jeff had a go at this as well:

  https://bitbucket.org/jeffr/naviserver-queues/changesets

Here's the feedback I tacked on to the end of a mercurial question via email:



It bothers me a bit that a fresh Ns_Set has to be allocated, and also
the parsing code is pretty gnarly and hard to verify. It looks about
right, but I'd have to resort to pencil and paper to be more sure, and
the fact I haven't done that reminds me that people tend to not look
too closely at these things and that's where bugs can fester. I wonder
if there's another way of doing this...

You'll have to double check the details, but IIRC q values go from
0-999. If 'gzip' is present without a q value then it's as if it had
q=1 -- that's the default. If it's not present, it's as if it were but
with q=0. So, how about a function like Ns_HeaderQ(header, attr) which
returns the integer q value for the specified atttribute. It simply
uses strstr to find gzip. If it doesn't, return 0. If it does, then
check for a q=. If it's the character '0', return 0. If there's no q,
return 1. If it's something else, parse the int and return that. Then
you can use it something like:


if (!(connPtr->flags & NS_CONN_SENTHDRS)
       && !(connPtr->flags & NS_CONN_SKIPBODY)) {

    contentEncoding = Ns_SetIGet(Ns_ConnHeaders(conn), "Accept-Encoding");

    if (Ns_HeaderQ(contentEncoding, "gzip") > 0 ||
Ns_HeaderQ(contentEncoding, "*") > 0) {
        gzip = 1;


I'm not sure how eager the server should be sending gzipped content.
An alternative to the above would be to keep the existing eager use of
gzip, but respect the client's negative assertion:


if (!(connPtr->flags & NS_CONN_SENTHDRS)
       && !(connPtr->flags & NS_CONN_SKIPBODY)) {

    contentEncoding = Ns_SetIGet(Ns_ConnHeaders(conn), "Accept-Encoding");

    if (connPtr->request->version >= 1.1) {
        if ((!Ns_HeaderQ(contentEncoding, "gzip", &q) || q > 0)
            && (!Ns_HeaderQ(contentEncoding, "*", &q) || q > 0)) {
            gzip = 1;
        }
    } else if ((Ns_HeaderQ(contentEncoding, "gzip", &q) && q > 0)
               || (Ns_HeaderQ(contentEncoding, "*", &q) && q > 0)) {
        gzip = 1;
    }


Here Ns_HeaderQ is modified to return NS_TRUE or NS_FALSE depending on
whether the attribute is present, and the q value is returned into the
given variable. HTTP 1.0 clients have to explicitly ask for gzip, 1.1
clients get it unless the say they don't want it.