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Worries about content-length

From: <Harald.T.Alvestrand@uninett.no>
Date: Mon, 08 May 1995 10:14:53 +0200
Message-Id: <199505080814.KAA03457@dale.uninett.no>
To: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
The draft draft-ietf-http-v10-spec-00.txt contains the following text:

7.2.2 Length

   When an Entity-Body is included with a message, the length of that 
   body may be determined in one of several ways. If a Content-Length 
   header field is present, its value in bytes (number of octets) 
   represents the length of the Entity-Body. Otherwise, the body 
   length is determined by the Content-Type (for types with an 
   explicit end-of-body delimiter), the Content-Transfer-Encoding (for 
   packetized encodings), or the closing of the connection by the 
   server. Note that the latter cannot be used to indicate the end of 
   a request body, since it leaves no possibility for the server to 
   send back a response.

       Note: Some older servers supply an invalid Content-Length 
       when sending a document that contains server-side includes 
       dynamically inserted into the data stream. It must be 
       emphasized that this will not be tolerated by future 
       versions of HTTP. Unless the client knows that it is 
       receiving a response from a compliant server, it should not 
       depend on the Content-Length value being correct.

Packetized C-T-Es are not specified yet.
Most body types (all but the multiparts) do not have an explicit
end-of-body delimiter.
This means that the closing of the connection is THE method left when
you don't depend on content-length.

I've seen this blow up on me: When a particular server had very heavy
load, the forked server crashed, closing the TCP connection, after
sending the headers, but before sending the full body.
Result: The client thinks that it has a complete object, and in fact
CACHES this invalid object - and there is no algorithmic way to tell
it that it is in the wrong.

This worries me.

Suggested fix: Add language that says that clients SHOULD warn the user
when content-length indicates MORE data than actually received. I've
seen lots of cases where the browser says "got 10245 of 9433 bytes",
which probably means that content-length was LESS, but I don't know if
the reverse ever happens.

             Harald T.  Alvestrand
Received on Monday, 8 May 1995 01:20:05 EDT

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