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From Joe Orton <>
Subject Re: proxy and 100 Continue
Date Fri, 22 Mar 2002 10:00:20 GMT
On Thu, Mar 21, 2002 at 02:47:35PM +0200, Graham Leggett wrote:
> When I access using Netscape v4.7 (an HTTP/1.0 client),
> and try to use the "block" feature in the Hotmail service, I get
> Netscape complain that it received a message it did not understand:
> "100!". A trace shows that Hotmail is sending a 100 Continue response -
> but I cannot see an Expect header.

IIS 5 often likes to send out interim 1xx responses to 1.1 clients
before the "real" non-1xx response, even if an Expect header isn't sent
- it's a MUST requirement that 1.1 clients handle this.

The spec has a set of requirements for proxies and 100 response
handling, notably:

      - A proxy MUST NOT forward a 100 (Continue) response if the
        request message was received from an HTTP/1.0 (or earlier)
        client and did not include an Expect request-header field with
        the "100-continue" expectation. This requirement overrides the
        general rule for forwarding of 1xx responses (see section 10.1).



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