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Re: HTTP 1.1, proxy servers, and failed connections

From: Roy T. Fielding <fielding@apache.org>
Date: Fri, 17 May 2002 14:35:23 -0700
Cc: ietf-http-wg@w3.org
To: Bob Scheifler - SMI Software Development <rws@East.sun.com>
Message-Id: <FEEF9AE4-69DD-11D6-9EDA-000393753936@apache.org>
>> Yes, I am sure.  ECONNREFUSED is a response, but not an HTTP response.
> If you say so. The spec simply says "invalid response", not
> "invalid HTTP response" and not "an invalid HTTP response or an
> explicit indication that no HTTP response will ever be received".

An invalid HTTP response is any response which is not valid HTTP, which
is certainly defined by the specification.
>>> How do you define "invalid response"?
>> Why does that matter?
> Are you asking why it matters how terms in a specification are defined?

No, I am saying that you shouldn't expect the specification to define every
term in the English language.  "invalid" and "response" are fully defined.

>> You will find that what the user agent needs to do for no-connection is
>> identical to what it needs to do for other 502 situations.
> Quite the contrary. If I interpret 502 as meaning the upstream server
> is non-conforming (broken), I won't ever retry an operation that
> gets a 502 result. But if I got the equivalent of ECONNREFUSED back,
> I might well retry the operation. That is, if I could get the equivalent
> back, which apparently I can't.

I don't follow that reasoning.  There is no way for the recipient to
distinguish between a temporary failure on the part of the gateway and
a permanent failure.  This is a distributed system in which components
are changed independently and frequently.  All 502 responses are
indications of a temporary problem.

> In your interpretation, why do both 502 and 503 exist?

Because 503 is for origin servers to indicate that service is unavailable
using a valid HTTP response.  It is rarely used on the Web, but does 
semantics that are different from "the origin didn't respond with a valid

Received on Friday, 17 May 2002 17:36:11 UTC

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