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Posted to dev@httpd.apache.org by Dean Gaudet <dg...@arctic.org> on 1997/07/21 00:15:24 UTC
Re: cvs commit: apache/htdocs/manual/misc known_client_problems.html
Any additions/corrections/comments? I dug through the archives to come up
with the byteranges entry here, I think I summarized everything.
Dean
On Sun, 20 Jul 1997, Dean Gaudet wrote:
> dgaudet 97/07/20 14:26:48
>
> Added: htdocs/manual/misc known_client_problems.html
> Log:
> First draft of all the problems we know about and have worked around...
>
> Revision Changes Path
> 1.1 apache/htdocs/manual/misc/known_client_problems.html
>
> Index: known_client_problems.html
> ===================================================================
> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
> <HTML>
> <HEAD>
> <TITLE>Apache HTTP Server Project</TITLE>
> </HEAD>
>
> <!-- Background white, links blue (unvisited), navy (visited), red (active) -->
> <BODY
> BGCOLOR="#FFFFFF"
> TEXT="#000000"
> LINK="#0000FF"
> VLINK="#000080"
> ALINK="#FF0000"
> >
> <!--#include virtual="header.html" -->
> <H1 ALIGN="CENTER">Known Problems in Clients</H1>
>
> <p>Over time the Apache Group has discovered or been notified of problems
> with various clients which we have had to work around. This document
> describes these problems and the workarounds available. It's not arranged
> in any particular order. Some familiarity with the standards is assumed,
> but not necessary.
>
> <p>For brevity, <i>Navigator</i> will refer to Netscape's Navigator
> product, and <i>MSIE</i> will refer to Microsoft's Internet Explorer
> product. All trademarks and copyrights belong to their respective
> companies. We welcome input from the various client authors to correct
> inconsistencies in this paper, or to provide us with exact version
> numbers where things are broken/fixed.
>
> <p>For reference,
> <a href="ftp://ds.internic.net/rfc/rfc1945.txt">RFC1945</a>
> defines HTTP/1.0, and
> <a href="ftp://ds.internic.net/rfc/rfc2068.txt">RFC2068</a>
> defines HTTP/1.1. Apache as of version 1.2 is an HTTP/1.1 server (with an
> optional HTTP/1.0 proxy).
>
> <p>Various of these workarounds are triggered by environment variables.
> The admin typically controls which are set, and for which clients, by using
> <a href="../mod/mod_browser.html">mod_browser</a>. Unless otherwise
> noted all of these workarounds exist in versions 1.2 and later.
>
> <a name="trailing-crlf"><H3>Trailing CRLF on POSTs</H3></a>
>
> <p>This is a legacy issue. The CERN webserver required <code>POST</code>
> data to have an extra <code>CRLF</code> following it. Thus many
> clients send an extra <code>CRLF</code> that
> is not included in the <code>Content-Length</code> of the request.
> Apache works around this problem by eating any empty lines which
> appear before a request.
>
> <a name="broken-keepalive"><h3>Broken keepalive</h3></a>
>
> <p>Various clients have had broken implementations of <i>keepalive</i>
> (persistent connections). In particular the Windows versions of
> Navigator 2.0 get very confused when the server times out an
> idle connection. The workaround is present in the default config files:
> <blockquote><code>
> BrowserMatch Mozilla/2 nokeepalive
> </code></blockquote>
> Note that this matches some earlier versions of MSIE, which began the
> practice of calling themselves <i>Mozilla</i> in their user-agent
> strings just like Navigator.
>
> <p>MSIE 4.0b2, which claims to support HTTP/1.1, does not properly
> support keepalive when it is used on 301 or 302 (redirect)
> responses. Unfortunately Apache's <code>nokeepalive</code> code
> prior to 1.2.2 would not work with HTTP/1.1 clients. You must apply
> <a href="http://www.apache.org/dist/patches/apply_to_1.2.1/msie_4_0b2_fixes.patch">this
> patch</a> to version 1.2.1. Then add this to your config:
> <blockquote><code>
> BrowserMatch "MSIE 4\.0b2;" nokeepalive
> </code></blockquote>
>
> <a name="force-response-1.0"><h3>Incorrect interpretation of <code>HTTP/1.1</code> in response</h3></a>
>
> <p>To quote from section 3.1 of RFC1945:
> <blockquote>
> HTTP uses a "<major>.<minor>" numbering scheme to indicate versions
> of the protocol. The protocol versioning policy is intended to allow
> the sender to indicate the format of a message and its capacity for
> understanding further HTTP communication, rather than the features
> obtained via that communication.
> </blockquote>
> Since Apache is an HTTP/1.1 server, it indicates so as part of its
> response. Many client authors mistakenly treat this part of the response
> as an indication of the protocol that the response is in, and then refuse
> to accept the response.
>
> <p>The first major indication of this problem was with AOL's proxy servers.
> When Apache 1.2 went into beta it was the first wide-spread HTTP/1.1
> server. After some discussion, AOL fixed their proxies. In
> anticipation of similar problems, the <code>force-response-1.0</code>
> environment variable was added to Apache. When present Apache will
> indicate "HTTP/1.0" in response to an HTTP/1.0 client,
> but will not in any other way change the response.
>
> <p>The pre-1.1 Java Development Kit (JDK) that is used in many clients
> (including Navigator 3.x and MSIE 3.x) exhibits this problem. As do some
> of the early pre-releases of the 1.1 JDK. We think it is fixed in the
> 1.1 JDK release. In any event the workaround:
> <blockquote><code>
> BrowserMatch Java1.0 force-response-1.0 <br>
> BrowserMatch JDK/1.0 force-response-1.0
> </code></blockquote>
>
> <p>RealPlayer 4.0 from Progressive Networks also exhibits this problem:
> <blockquote><code>
> BrowserMatch "RealPlayer 4.0" force-response-1.0
> </code></blockquote>
>
> <a name="msie4.0b2"><h3>Requests use HTTP/1.1 but responses must be in HTTP/1.0</h3></a>
>
> <p>MSIE 4.0b2 has this problem. Its Java VM makes requests in HTTP/1.1
> format but the responses must be in HTTP/1.0 format (in particular, it
> does not understand <i>chunked</i> responses). The workaround
> is to fool Apache into believing the request came in HTTP/1.0 format.
> <blockquote><code>
> BrowserMatch "MSIE 4\.0b2;" downgrade-1.0 force-response-1.0
> </code></blockquote>
> This workaround is available in 1.2.2, and in a
> <a href="http://www.apache.org/dist/patches/apply_to_1.2.1/msie_4_0b2_fixes.patch">patch
> </a> against 1.2.1.
>
> <a name="257th-byte"><h3>Boundary problems with header parsing</h3></a>
>
> <p>All versions of Navigator from 2.0 through 4.0b2 (and possibly later)
> have a problem if the trailing CRLF of the response header starts at
> the 256th or 257th byte of the response. A BrowserMatch for this would
> match on nearly every hit, so the workaround is enabled automatically
> on all responses. The workaround is to detect when this condition would
> occur in a response and add extra padding to the header to push the
> trailing CRLF past the 257th byte of the response.
>
> <a name="boundary-string"><h3>Multipart responses and Quoted Boundary Strings</h3></a>
>
> <p>On multipart responses some clients will not accept quotes (")
> around the boundary string. The MIME standard recommends that
> such quotes be used. But the clients were probably written based
> on one of the examples in RFC2068, which does not include quotes.
> Apache does not include quotes on its boundary strings to workaround
> this problem.
>
> <a name="byterange-requests"><h3>Byterange requests</h3></a>
>
> <p>A byterange request is used when the client wishes to retrieve a
> portion of an object, not necessarily the entire object. There
> was a very old draft which included these byteranges in the URL.
> Old clients such as Navigator 2.0b1 and MSIE 3.0 for the MAC
> exhibit this behaviour, and
> it will appear in the servers' access logs as (failed) attempts to
> retrieve a URL with a trailing ";xxx-yyy". Apache does not attempt
> to implement this at all.
>
> <p>A subsequent draft of this standard defines a header
> <code>Request-Range</code>, and a response type
> <code>multipart/x-byteranges</code>. The HTTP/1.1 standard includes
> this draft with a few fixes, and it defines the header
> <code>Range</code> and type <code>multipart/byteranges</code>.
>
> <p>Navigator (versions 2 and 3) sends both <code>Range</code> and
> <code>Request-Range</code> headers (with the same value), but does not
> accept a <code>multipart/byteranges</code> response. The response must
> be <code>multipart/x-byteranges</code>. As a workaround, if Apache
> receives a <code>Request-Range</code> header it considers it "higher
> priority" than a <code>Range</code> header and in response uses
> <code>multipart/x-byteranges</code>.
>
> <p>The Adobe Acrobat Reader plugin makes extensive use of byteranges and
> prior to version 3.01 supports only the <code>multipart/x-byterange</code>
> response. Unfortunately there is no clue that it is the plugin
> making the request. If the plugin is used with Navigator, the above
> workaround works fine. But if the plugin is used with MSIE 3 (on
> Windows) the workaround won't work because MSIE 3 doesn't give the
> <code>Range-Request</code> clue that Navigator does. To workaround this,
> Apache special cases "MSIE 3" in the <code>User-Agent</code> and serves
> <code>multipart/x-byteranges</code>. Note that the necessity for this
> with MSIE 3 is actually due to the Acrobat plugin, not due to the browser.
>
> <p>Netscape Communicator appears to not issue the non-standard
> <code>Request-Range</code> header. When an Acrobat plugin prior to
> version 3.01 is used with it, it will not properly understand byteranges.
> The user must upgrade their Acrobat reader to 3.01.
>
> <!--#include virtual="footer.html" -->
> </BODY>
> </HTML>
>
>
>
>
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