W3C home > Mailing lists > Public > ietf-http-wg-old@w3.org > September to December 1999

Re: Server-side roles in the HTTP

From: Julien Pierre <jpierre@netscape.com>
Date: Wed, 01 Sep 1999 17:04:13 -0700
Message-ID: <37CDBEFD.6E35544B@netscape.com>
To: kugler@us.ibm.com
CC: http-wg@cuckoo.hpl.hp.com, http-wg@hplb.hpl.hp.com
Hi,

kugler@us.ibm.com wrote:

> > Servers MUST support a persistent connection if the content
> >   generator supplies a Content-Length header. If it is not available,
> >  the server SHOULD attempt to buffer the response in order to
> >   generate one, although this MAY be circumvented if:
> >   * the server does not have resources (i.e., memory) to do so, or
> >   * the object is very large, and overall latency becomes
> >   unacceptable, or
> >   * the time required to generate the object adds unacceptable latency
> ...
> >  Servers MUST serve chunked encoding responses for all objects, if:
> >   * Content-Length is unavailable and impractical to generate
> >   and
> >   * the client advertises itself as HTTP/1.1 capable, or
> >   * the client includes 'chunked' in a TE header
>
> Why wouldn't streaming the response with the "chunked" encoding be preferable to
> buffering and generating a Content-Length?

It depends on the size of the object and how long it takes to generate the content.
If the content is small and generated quickly, it makes sense for the server to
buffer the response and transparently add a content-length header, as opposed to
using chunking. Chunking for small objects will waste bandwidth unnecessarily and
provide no benefits if the full content is immediately available.
If the application generates too much content to buffer, or ends up taking too long
to generate little content, then the server can choose to chunk.
But this may be a matter for webmasters do decide depending on their applications,
how much bandwidth they have, and how much latency they can accept, so we are making
those time and buffer size thresholds configurable. We may also add settings for the
minimum size of the chunks themselves to conserve bandwidth.

> > 6.4 Transfer-Encoding
>
> >   Servers SHOULD reply to requests that allow transfer encoding of
> >  objects (i.e., TE header present) with appropriate encoding, in a
> >  fashion transparent to the content generator.
>
> This paragraphs seems to suggest that transfer encoding is only allowed if the
> TE request-header is present.  However, if the TE field-value is empty or if no
> TE field is present, the transfer-coding "chunked" is allowed, and is always
> acceptable.

Good point - looks like Mark should add a provision for this case.

> >   There MUST be a method by which content generators can specify that
> >   content is not to be buffered; this MAY be performed by a pseudo-
> >   HTTP header that is consumed by the server.
>
> I think you're only addressing generated (response) content in this statement.
> I'd also like to have a method by which content generators can specify that the
> received (request) content is not to be buffered.   Sometimes the "content
> generator" can be doing something useful with the content of a large POST
> request while it's still being received (or even while it's still being
> generated by the client).  In some applications (e.g., IPP), POST content may be
> so large that you don't even want the server to attempt to buffer it.

This won't work for some content generators.
For example, you can't start a CGI before you know the length of the POST data
because you have to set it in the CGI process environment variables.

--
for a good time, try kill -9 -1




Received on Thursday, 2 September 1999 01:04:36 EDT

This archive was generated by hypermail pre-2.1.9 : Wednesday, 24 September 2003 06:33:33 EDT