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797d2b9a91
removal of the Vary field from response headers. PR: 4118 git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@83129 13f79535-47bb-0310-9956-ffa450edef68
306 lines
13 KiB
HTML
306 lines
13 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<TITLE>Apache HTTP Server Project</TITLE>
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</HEAD>
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<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
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<BODY
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#000080"
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ALINK="#FF0000"
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>
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<!--#include virtual="header.html" -->
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<H1 ALIGN="CENTER">Known Problems in Clients</H1>
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<P>Over time the Apache Group has discovered or been notified of problems
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with various clients which we have had to work around, or explain.
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This document describes these problems and the workarounds available.
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It's not arranged in any particular order. Some familiarity with the
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standards is assumed, but not necessary.
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<P>For brevity, <EM>Navigator</EM> will refer to Netscape's Navigator
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product (which in later versions was renamed "Communicator" and
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various other names), and <EM>MSIE</EM> will refer to Microsoft's
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Internet Explorer product. All trademarks and copyrights belong to
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their respective companies. We welcome input from the various client
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authors to correct inconsistencies in this paper, or to provide us with
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exact version numbers where things are broken/fixed.
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<P>For reference,
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<A HREF="ftp://ds.internic.net/rfc/rfc1945.txt">RFC1945</A>
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defines HTTP/1.0, and
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<A HREF="ftp://ds.internic.net/rfc/rfc2068.txt">RFC2068</A>
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defines HTTP/1.1. Apache as of version 1.2 is an HTTP/1.1 server (with an
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optional HTTP/1.0 proxy).
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<P>Various of these workarounds are triggered by environment variables.
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The admin typically controls which are set, and for which clients, by using
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<A HREF="../mod/mod_browser.html">mod_browser</A>. Unless otherwise
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noted all of these workarounds exist in versions 1.2 and later.
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<H3><A NAME="trailing-crlf">Trailing CRLF on POSTs</A></H3>
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<P>This is a legacy issue. The CERN webserver required <CODE>POST</CODE>
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data to have an extra <CODE>CRLF</CODE> following it. Thus many
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clients send an extra <CODE>CRLF</CODE> that
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is not included in the <CODE>Content-Length</CODE> of the request.
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Apache works around this problem by eating any empty lines which
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appear before a request.
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<H3><A NAME="broken-keepalive">Broken keepalive</A></H3>
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<P>Various clients have had broken implementations of <EM>keepalive</EM>
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(persistent connections). In particular the Windows versions of
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Navigator 2.0 get very confused when the server times out an
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idle connection. The workaround is present in the default config files:
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<BLOCKQUOTE><CODE>
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BrowserMatch Mozilla/2 nokeepalive
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</CODE></BLOCKQUOTE>
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Note that this matches some earlier versions of MSIE, which began the
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practice of calling themselves <EM>Mozilla</EM> in their user-agent
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strings just like Navigator.
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<P>MSIE 4.0b2, which claims to support HTTP/1.1, does not properly
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support keepalive when it is used on 301 or 302 (redirect)
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responses. Unfortunately Apache's <CODE>nokeepalive</CODE> code
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prior to 1.2.2 would not work with HTTP/1.1 clients. You must apply
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<A
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HREF="http://www.apache.org/dist/patches/apply_to_1.2.1/msie_4_0b2_fixes.patch"
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>this patch</A> to version 1.2.1. Then add this to your config:
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<BLOCKQUOTE><CODE>
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BrowserMatch "MSIE 4\.0b2;" nokeepalive
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</CODE></BLOCKQUOTE>
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<H3><A NAME="force-response-1.0">Incorrect interpretation of
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<CODE>HTTP/1.1</CODE> in response</A></H3>
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<P>To quote from section 3.1 of RFC1945:
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<BLOCKQUOTE>
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HTTP uses a "<MAJOR>.<MINOR>" numbering scheme to indicate versions
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of the protocol. The protocol versioning policy is intended to allow
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the sender to indicate the format of a message and its capacity for
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understanding further HTTP communication, rather than the features
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obtained via that communication.
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</BLOCKQUOTE>
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Since Apache is an HTTP/1.1 server, it indicates so as part of its
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response. Many client authors mistakenly treat this part of the response
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as an indication of the protocol that the response is in, and then refuse
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to accept the response.
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<P>The first major indication of this problem was with AOL's proxy servers.
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When Apache 1.2 went into beta it was the first wide-spread HTTP/1.1
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server. After some discussion, AOL fixed their proxies. In
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anticipation of similar problems, the <CODE>force-response-1.0</CODE>
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environment variable was added to Apache. When present Apache will
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indicate "HTTP/1.0" in response to an HTTP/1.0 client,
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but will not in any other way change the response.
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<P>The pre-1.1 Java Development Kit (JDK) that is used in many clients
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(including Navigator 3.x and MSIE 3.x) exhibits this problem. As do some
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of the early pre-releases of the 1.1 JDK. We think it is fixed in the
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1.1 JDK release. In any event the workaround:
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<BLOCKQUOTE><CODE>
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BrowserMatch Java/1.0 force-response-1.0 <BR>
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BrowserMatch JDK/1.0 force-response-1.0
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</CODE></BLOCKQUOTE>
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<P>RealPlayer 4.0 from Progressive Networks also exhibits this problem.
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However they have fixed it in version 4.01 of the player, but version
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4.01 uses the same <CODE>User-Agent</CODE> as version 4.0. The
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workaround is still:
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<BLOCKQUOTE><CODE>
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BrowserMatch "RealPlayer 4.0" force-response-1.0
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</CODE></BLOCKQUOTE>
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<H3><A NAME="msie4.0b2">Requests use HTTP/1.1 but responses must be
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in HTTP/1.0</A></H3>
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<P>MSIE 4.0b2 has this problem. Its Java VM makes requests in HTTP/1.1
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format but the responses must be in HTTP/1.0 format (in particular, it
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does not understand <EM>chunked</EM> responses). The workaround
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is to fool Apache into believing the request came in HTTP/1.0 format.
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<BLOCKQUOTE><CODE>
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BrowserMatch "MSIE 4\.0b2;" downgrade-1.0 force-response-1.0
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</CODE></BLOCKQUOTE>
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This workaround is available in 1.2.2, and in a
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<A
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HREF="http://www.apache.org/dist/patches/apply_to_1.2.1/msie_4_0b2_fixes.patch"
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>patch</A> against 1.2.1.
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<H3><A NAME="257th-byte">Boundary problems with header parsing</A></H3>
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<P>All versions of Navigator from 2.0 through 4.0b2 (and possibly later)
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have a problem if the trailing CRLF of the response header starts at
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offset 256, 257 or 258 of the response. A BrowserMatch for this would
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match on nearly every hit, so the workaround is enabled automatically
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on all responses. The workaround implemented detects when this condition would
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occur in a response and adds extra padding to the header to push the
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trailing CRLF past offset 258 of the response.
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<H3><A NAME="boundary-string">Multipart responses and Quoted Boundary
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Strings</A></H3>
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<P>On multipart responses some clients will not accept quotes (")
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around the boundary string. The MIME standard recommends that
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such quotes be used. But the clients were probably written based
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on one of the examples in RFC2068, which does not include quotes.
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Apache does not include quotes on its boundary strings to workaround
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this problem.
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<H3><A NAME="byterange-requests">Byterange requests</A></H3>
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<P>A byterange request is used when the client wishes to retrieve a
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portion of an object, not necessarily the entire object. There
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was a very old draft which included these byteranges in the URL.
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Old clients such as Navigator 2.0b1 and MSIE 3.0 for the MAC
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exhibit this behaviour, and
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it will appear in the servers' access logs as (failed) attempts to
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retrieve a URL with a trailing ";xxx-yyy". Apache does not attempt
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to implement this at all.
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<P>A subsequent draft of this standard defines a header
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<CODE>Request-Range</CODE>, and a response type
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<CODE>multipart/x-byteranges</CODE>. The HTTP/1.1 standard includes
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this draft with a few fixes, and it defines the header
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<CODE>Range</CODE> and type <CODE>multipart/byteranges</CODE>.
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<P>Navigator (versions 2 and 3) sends both <CODE>Range</CODE> and
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<CODE>Request-Range</CODE> headers (with the same value), but does not
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accept a <CODE>multipart/byteranges</CODE> response. The response must
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be <CODE>multipart/x-byteranges</CODE>. As a workaround, if Apache
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receives a <CODE>Request-Range</CODE> header it considers it "higher
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priority" than a <CODE>Range</CODE> header and in response uses
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<CODE>multipart/x-byteranges</CODE>.
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<P>The Adobe Acrobat Reader plugin makes extensive use of byteranges and
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prior to version 3.01 supports only the <CODE>multipart/x-byterange</CODE>
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response. Unfortunately there is no clue that it is the plugin
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making the request. If the plugin is used with Navigator, the above
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workaround works fine. But if the plugin is used with MSIE 3 (on
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Windows) the workaround won't work because MSIE 3 doesn't give the
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<CODE>Range-Request</CODE> clue that Navigator does. To workaround this,
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Apache special cases "MSIE 3" in the <CODE>User-Agent</CODE> and serves
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<CODE>multipart/x-byteranges</CODE>. Note that the necessity for this
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with MSIE 3 is actually due to the Acrobat plugin, not due to the browser.
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<P>Netscape Communicator appears to not issue the non-standard
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<CODE>Request-Range</CODE> header. When an Acrobat plugin prior to
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version 3.01 is used with it, it will not properly understand byteranges.
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The user must upgrade their Acrobat reader to 3.01.
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<H3><A NAME="cookie-merge"><CODE>Set-Cookie</CODE> header is
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unmergeable</A></H3>
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<P>The HTTP specifications say that it is legal to merge headers with
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duplicate names into one (separated by commas). Some browsers
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that support Cookies don't like merged headers and prefer that each
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<CODE>Set-Cookie</CODE> header is sent separately. When parsing the
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headers returned by a CGI, Apache will explicitly avoid merging any
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<CODE>Set-Cookie</CODE> headers.
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<H3><A NAME="gif89-expires"><CODE>Expires</CODE> headers and GIF89A
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animations</A></H3>
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<P>Navigator versions 2 through 4 will erroneously re-request
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GIF89A animations on each loop of the animation if the first
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response included an <CODE>Expires</CODE> header. This happens
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regardless of how far in the future the expiry time is set. There
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is no workaround supplied with Apache, however there are hacks for <A
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HREF="http://www.arctic.org/~dgaudet/patches/apache-1.2-gif89-expires-hack.patch">1.2</A>
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and for <A
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HREF="http://www.arctic.org/~dgaudet/patches/apache-1.3-gif89-expires-hack.patch">1.3</A>.
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<H3><A NAME="no-content-length"><CODE>POST</CODE> without
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<CODE>Content-Length</CODE></A></H3>
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<P>In certain situations Navigator 3.01 through 3.03 appear to incorrectly
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issue a POST without the request body. There is no
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known workaround. It has been fixed in Navigator 3.04, Netscapes
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provides some
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<A HREF="http://help.netscape.com/kb/client/971014-42.html">information</A>.
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There's also
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<A HREF="http://www.arctic.org/~dgaudet/apache/no-content-length/">
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some information</A> about the actual problem.
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<H3><A NAME="jdk-12-bugs">JDK 1.2 betas lose parts of responses.</A></H3>
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<P>The http client in the JDK1.2beta2 and beta3 will throw away the first part of
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the response body when both the headers and the first part of the body are sent
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in the same network packet AND keep-alive's are being used. If either condition
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is not met then it works fine.
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<P>See also Bug-ID's 4124329 and 4125538 at the java developer connection.
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<P>If you are seeing this bug yourself, you can add the following BrowserMatch
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directive to work around it:
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<BLOCKQUOTE><CODE>
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BrowserMatch "Java1\.2beta[23]" nokeepalive
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</CODE></BLOCKQUOTE>
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<P>We don't advocate this though since bending over backwards for beta software
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is usually not a good idea; ideally it gets fixed, new betas or a final release
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comes out, and no one uses the broken old software anymore. In theory.
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<H3><A NAME="content-type-persistence"><CODE>Content-Type</CODE> change
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is not noticed after reload</A></H3>
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<P>Navigator (all versions?) will cache the <CODE>content-type</CODE>
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for an object "forever". Using reload or shift-reload will not cause
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Navigator to notice a <CODE>content-type</CODE> change. The only
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work-around is for the user to flush their caches (memory and disk). By
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way of an example, some folks may be using an old <CODE>mime.types</CODE>
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file which does not map <CODE>.htm</CODE> to <CODE>text/html</CODE>,
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in this case Apache will default to sending <CODE>text/plain</CODE>.
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If the user requests the page and it is served as <CODE>text/plain</CODE>.
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After the admin fixes the server, the user will have to flush their caches
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before the object will be shown with the correct <CODE>text/html</CODE>
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type.
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<h3><a name="msie-cookie-y2k">MSIE Cookie problem with expiry date in
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the year 2000</a></h3>
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<p>MSIE versions 3.00 and 3.02 (without the Y2K patch) do not handle
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cookie expiry dates in the year 2000 properly. Years after 2000 and
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before 2000 work fine. This is fixed in IE4.01 service pack 1, and in
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the Y2K patch for IE3.02. Users should avoid using expiry dates in the
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year 2000.
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<h3><a name="lynx-negotiate-trans">Lynx incorrectly asking for transparent
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content negotiation</a></h3>
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<p>The Lynx browser versions 2.7 and 2.8 send a "negotiate: trans" header
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in their requests, which is an indication the browser supports transparent
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content negotiation (TCN). However the browser does not support TCN.
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As of version 1.3.4, Apache supports TCN, and this causes problems with
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these versions of Lynx. As a workaround future versions of Apache will
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ignore this header when sent by the Lynx client.
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<h3><a name="ie40-vary">MSIE 4.0 mishandles Vary response header</a></h3>
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<p>MSIE 4.0 does not handle a Vary header properly. The Vary header is
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generated by mod_rewrite in apache 1.3. The result is an error from MSIE
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saying it cannot download the requested file. There are more details
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in <a href="http://bugs.apache.org/index/full/4118">PR#4118</a>.
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</P>
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<P>
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A workaround is to add the following to your server's configuration
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files:
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</P>
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<PRE>
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BrowserMatch "MSIE 4\.0" force-no-vary
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</PRE>
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<P>
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(This workaround is only available with releases <STRONG>after</STRONG>
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1.3.6 of the Apache Web server.)
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</P>
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<!--#include virtual="footer.html" -->
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</BODY>
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</HTML>
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