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-<HTML>
-<HEAD>
-<TITLE>Apache Content Negotiation</TITLE>
-</HEAD>
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-<!--#include virtual="header.html" -->
-<H1 ALIGN="CENTER">Content Negotiation</H1>
+URI: content-negotiation.html.en
+Content-Language: en
+Content-type: text/html; charset=ISO-8859-1
-<P>
-Apache's support for content negotiation has been updated to meet the
-HTTP/1.1 specification. It can choose the best representation of a
-resource based on the browser-supplied preferences for media type,
-languages, character set and encoding. It is also implements a
-couple of features to give more intelligent handling of requests from
-browsers which send incomplete negotiation information. <P>
+URI: content-negotiation.html.fr
+Content-Language: fr
+Content-type: text/html; charset=ISO-8859-1
-Content negotiation is provided by the
-<A HREF="mod/mod_negotiation.html">mod_negotiation</A> module,
-which is compiled in by default.
+URI: content-negotiation.html.ja.utf8
+Content-Language: ja
+Content-type: text/html; charset=UTF-8
-<HR>
+URI: content-negotiation.html.ko.euc-kr
+Content-Language: ko
+Content-type: text/html; charset=EUC-KR
-<H2>About Content Negotiation</H2>
-
-<P>
-A resource may be available in several different representations. For
-example, it might be available in different languages or different
-media types, or a combination. One way of selecting the most
-appropriate choice is to give the user an index page, and let them
-select. However it is often possible for the server to choose
-automatically. This works because browsers can send as part of each
-request information about what representations they prefer. For
-example, a browser could indicate that it would like to see
-information in French, if possible, else English will do. Browsers
-indicate their preferences by headers in the request. To request only
-French representations, the browser would send
-
-<PRE>
- Accept-Language: fr
-</PRE>
-
-<P>
-Note that this preference will only be applied when there is a choice
-of representations and they vary by language.
-<P>
-
-As an example of a more complex request, this browser has been
-configured to accept French and English, but prefer French, and to
-accept various media types, preferring HTML over plain text or other
-text types, and preferring GIF or JPEG over other media types, but also
-allowing any other media type as a last resort:
-
-<PRE>
- Accept-Language: fr; q=1.0, en; q=0.5
- Accept: text/html; q=1.0, text/*; q=0.8, image/gif; q=0.6,
- image/jpeg; q=0.6, image/*; q=0.5, */*; q=0.1
-</PRE>
-
-Apache 1.2 supports 'server driven' content negotiation, as defined in
-the HTTP/1.1 specification. It fully supports the Accept,
-Accept-Language, Accept-Charset and Accept-Encoding request headers.
-<P>
-
-A <STRONG>resource</STRONG> is a conceptual entity identified by a URI
-(RFC 2396). An HTTP server like Apache provides access to
-<STRONG>representations</STRONG> of the resource(s) within its namespace,
-with each representation in the form of a sequence of bytes with a
-defined media type, character set, encoding, etc. Each resource may be
-associated with zero, one, or more than one representation
-at any given time. If multiple representations are available,
-the resource is referred to as <STRONG>negotiable</STRONG> and each of its
-representations is termed a <STRONG>variant</STRONG>. The ways in which the
-variants for a negotiable resource vary are called the
-<STRONG>dimensions</STRONG> of negotiation.
-
-<H2>Negotiation in Apache</H2>
-
-<P>
-In order to negotiate a resource, the server needs to be given
-information about each of the variants. This is done in one of two
-ways:
-
-<UL>
- <LI> Using a type map (<EM>i.e.</EM>, a <CODE>*.var</CODE> file) which
- names the files containing the variants explicitly, or
- <LI> Using a 'MultiViews' search, where the server does an implicit
- filename pattern match and chooses from among the results.
-</UL>
-
-<H3>Using a type-map file</H3>
-
-<P>
-A type map is a document which is associated with the handler
-named <CODE>type-map</CODE> (or, for backwards-compatibility with
-older Apache configurations, the mime type
-<CODE>application/x-type-map</CODE>). Note that to use this feature,
-you must have a handler set in the configuration that defines a
-file suffix as <CODE>type-map</CODE>; this is best done with a
-
-<PRE>
- AddHandler type-map var
-</PRE>
-
-in the server configuration file. See the comments in the sample config
-file for more details. <P>
-
-Type map files have an entry for each available variant; these entries
-consist of contiguous HTTP-format header lines. Entries for
-different variants are separated by blank lines. Blank lines are
-illegal within an entry. It is conventional to begin a map file with
-an entry for the combined entity as a whole (although this
-is not required, and if present will be ignored). An example
-map file is:
-
-<PRE>
- URI: foo
-
- URI: foo.en.html
- Content-type: text/html
- Content-language: en
-
- URI: foo.fr.de.html
- Content-type: text/html;charset=iso-8859-2
- Content-language: fr, de
-</PRE>
-
-If the variants have different source qualities, that may be indicated
-by the "qs" parameter to the media type, as in this picture (available
-as jpeg, gif, or ASCII-art):
-
-<PRE>
- URI: foo
-
- URI: foo.jpeg
- Content-type: image/jpeg; qs=0.8
-
- URI: foo.gif
- Content-type: image/gif; qs=0.5
-
- URI: foo.txt
- Content-type: text/plain; qs=0.01
-</PRE>
-<P>
-
-qs values can vary in the range 0.000 to 1.000. Note that any variant with
-a qs value of 0.000 will never be chosen. Variants with no 'qs'
-parameter value are given a qs factor of 1.0. The qs parameter indicates
-the relative 'quality' of this variant compared to the other available
-variants, independent of the client's capabilities. For example, a jpeg
-file is usually of higher source quality than an ascii file if it is
-attempting to represent a photograph. However, if the resource being
-represented is an original ascii art, then an ascii representation would
-have a higher source quality than a jpeg representation. A qs value
-is therefore specific to a given variant depending on the nature of
-the resource it represents.
-
-<P>
-The full list of headers recognized is:
-
-<DL>
- <DT> <CODE>URI:</CODE>
- <DD> uri of the file containing the variant (of the given media
- type, encoded with the given content encoding). These are
- interpreted as URLs relative to the map file; they must be on
- the same server (!), and they must refer to files to which the
- client would be granted access if they were to be requested
- directly.
- <DT> <CODE>Content-Type:</CODE>
- <DD> media type --- charset, level and "qs" parameters may be given. These
- are often referred to as MIME types; typical media types are
- <CODE>image/gif</CODE>, <CODE>text/plain</CODE>, or
- <CODE>text/html; level=3</CODE>.
- <DT> <CODE>Content-Language:</CODE>
- <DD> The languages of the variant, specified as an Internet standard
- language tag from RFC 1766 (<EM>e.g.</EM>, <CODE>en</CODE> for English,
- <CODE>kr</CODE> for Korean, <EM>etc.</EM>).
- <DT> <CODE>Content-Encoding:</CODE>
- <DD> If the file is compressed, or otherwise encoded, rather than
- containing the actual raw data, this says how that was done.
- Apache only recognizes encodings that are defined by an
- <A HREF="mod/mod_mime.html#addencoding">AddEncoding</A> directive.
- This normally includes the encodings <CODE>x-compress</CODE>
- for compress'd files, and <CODE>x-gzip</CODE> for gzip'd files.
- The <CODE>x-</CODE> prefix is ignored for encoding comparisons.
- <DT> <CODE>Content-Length:</CODE>
- <DD> The size of the file. Clients can ask to receive a given media
- type only if the variant isn't too big; specifying a content
- length in the map allows the server to compare against these
- thresholds without checking the actual file.
-</DL>
-
-<H3>Multiviews</H3>
-
-<P>
-<CODE>MultiViews</CODE> is a per-directory option, meaning it can be set with
-an <CODE>Options</CODE> directive within a <CODE><Directory></CODE>,
-<CODE><Location></CODE> or <CODE><Files></CODE>
-section in <CODE>access.conf</CODE>, or (if <CODE>AllowOverride</CODE>
-is properly set) in <CODE>.htaccess</CODE> files. Note that
-<CODE>Options All</CODE> does not set <CODE>MultiViews</CODE>; you
-have to ask for it by name.
-
-<P>
-The effect of <CODE>MultiViews</CODE> is as follows: if the server
-receives a request for <CODE>/some/dir/foo</CODE>, if
-<CODE>/some/dir</CODE> has <CODE>MultiViews</CODE> enabled, and
-<CODE>/some/dir/foo</CODE> does <EM>not</EM> exist, then the server reads the
-directory looking for files named foo.*, and effectively fakes up a
-type map which names all those files, assigning them the same media
-types and content-encodings it would have if the client had asked for
-one of them by name. It then chooses the best match to the client's
-requirements.
-
-<P>
-<CODE>MultiViews</CODE> may also apply to searches for the file named by the
-<CODE>DirectoryIndex</CODE> directive, if the server is trying to
-index a directory. If the configuration files specify
-
-<PRE>
- DirectoryIndex index
-</PRE>
-
-then the server will arbitrate between <CODE>index.html</CODE>
-and <CODE>index.html3</CODE> if both are present. If neither are
-present, and <CODE>index.cgi</CODE> is there, the server will run it.
-
-<P>
-If one of the files found when reading the directive is a CGI script,
-it's not obvious what should happen. The code gives that case
-special treatment --- if the request was a POST, or a GET with
-QUERY_ARGS or PATH_INFO, the script is given an extremely high quality
-rating, and generally invoked; otherwise it is given an extremely low
-quality rating, which generally causes one of the other views (if any)
-to be retrieved.
-
-<H2>The Negotiation Algorithm</H2>
-
-After Apache has obtained a list of the variants for a given resource,
-either from a type-map file or from the filenames in the directory, it
-applies an algorithm to decide on the 'best' variant to return, if
-any. To do this it calculates a quality value for each variant in each
-of the dimensions of variance. It is not necessary to know any of the
-details of how negotiation actually takes place in order to use Apache's
-content negotiation features. However the rest of this document
-explains in detail the algorithm used for those interested. <P>
-
-In some circumstances, Apache can 'fiddle' the quality factor of a
-particular dimension to achieve a better result. The ways Apache can
-fiddle quality factors is explained in more detail below.
-
-<H3>Dimensions of Negotiation</H3>
-
-<TABLE>
-<TR valign="top">
-<TH>Dimension
-<TH>Notes
-<TR valign="top">
-<TD>Media Type
-<TD>Browser indicates preferences with the Accept header field. Each item
-can have an associated quality factor. Variant description can also
-have a quality factor (the "qs" parameter).
-<TR valign="top">
-<TD>Language
-<TD>Browser indicates preferences with the Accept-Language header field.
-Each item can have a quality factor. Variants can be associated with none, one
-or more than one language.
-<TR valign="top">
-<TD>Encoding
-<TD>Browser indicates preference with the Accept-Encoding header field.
-Each item can have a quality factor.
-<TR valign="top">
-<TD>Charset
-<TD>Browser indicates preference with the Accept-Charset header field.
-Each item can have a quality factor.
-Variants can indicate a charset as a parameter of the media type.
-</TABLE>
-
-<H3>Apache Negotiation Algorithm</H3>
-
-<P>
-Apache uses an algorithm to select the 'best' variant (if any) to
-return to the browser. This algorithm is not configurable. It operates
-as follows:
-
-<OL>
-<LI>
-First, for each dimension of the negotiation, the appropriate
-<EM>Accept*</EM> header field is checked and a quality assigned to each
-variant. If the <EM>Accept*</EM> header for any dimension means that this
-variant is not acceptable, eliminate it. If no variants remain, go
-to step 4.
-
-<LI>Select the 'best' variant by a process of elimination. Each of
-the following tests is applied in order. Any variants not selected at
-each stage are eliminated. After each test, if only one variant
-remains, it is selected as the best match. If more than one variant
-remains, move on to the next test.
-
-<OL>
-<LI>Multiply the quality factor from the Accept header with the
- quality-of-source factor for this variant's media type, and select
- the variants with the highest value
-
-<LI>Select the variants with the highest language quality factor
-
-<LI>Select the variants with the best language match, using either the
- order of languages on the <CODE>LanguagePriority</CODE> directive (if
- present),
- else the order of languages on the Accept-Language header.
-
-<LI>Select the variants with the highest 'level' media parameter
- (used to give the version of text/html media types).
-
-<LI>Select only variants with acceptable charset media parameters,
- as given on the Accept-Charset header line. Charset ISO-8859-1
- is acceptable unless explicitly excluded. Variants not associated
- with a particular charset are assumed to be in ISO-8859-1.
-
-<LI>Select the variants with the best encoding. If there are
- variants with an encoding that is acceptable to the user-agent,
- select only these variants. Otherwise if there is a mix of encoded
- and non-encoded variants, select only the unencoded variants.
- If either all variants are encoded or all variants are not encoded,
- select all variants.
-
-<LI>Select the variants with the smallest content length
-
-<LI>Select the first variant of those remaining (this will be either the
- first listed in the type-map file, or the first read from the directory)
- and go to stage 3.
-
-</OL>
-
-<LI>The algorithm has now selected one 'best' variant, so return
- it as the response. The HTTP response header Vary is set to indicate the
- dimensions of negotiation (browsers and caches can use this
- information when caching the resource). End.
-
-<LI>To get here means no variant was selected (because none are acceptable
- to the browser). Return a 406 status (meaning "No acceptable representation")
- with a response body consisting of an HTML document listing the
- available variants. Also set the HTTP Vary header to indicate the
- dimensions of variance.
-
-</OL>
-
-<H2><A NAME="better">Fiddling with Quality Values</A></H2>
-
-<P>
-Apache sometimes changes the quality values from what would be
-expected by a strict interpretation of the algorithm above. This is to
-get a better result from the algorithm for browsers which do not send
-full or accurate information. Some of the most popular browsers send
-Accept header information which would otherwise result in the
-selection of the wrong variant in many cases. If a browser
-sends full and correct information these fiddles will not
-be applied.
-<P>
-
-<H3>Media Types and Wildcards</H3>
-
-<P>
-The Accept: request header indicates preferences for media types. It
-can also include 'wildcard' media types, such as "image/*" or "*/*"
-where the * matches any string. So a request including:
-<PRE>
- Accept: image/*, */*
-</PRE>
-
-would indicate that any type starting "image/" is acceptable,
-as is any other type (so the first "image/*" is redundant). Some
-browsers routinely send wildcards in addition to explicit types they
-can handle. For example:
-<PRE>
- Accept: text/html, text/plain, image/gif, image/jpeg, */*
-</PRE>
-
-The intention of this is to indicate that the explicitly
-listed types are preferred, but if a different representation is
-available, that is ok too. However under the basic algorithm, as given
-above, the */* wildcard has exactly equal preference to all the other
-types, so they are not being preferred. The browser should really have
-sent a request with a lower quality (preference) value for *.*, such
-as:
-<PRE>
- Accept: text/html, text/plain, image/gif, image/jpeg, */*; q=0.01
-</PRE>
-
-The explicit types have no quality factor, so they default to a
-preference of 1.0 (the highest). The wildcard */* is given
-a low preference of 0.01, so other types will only be returned if
-no variant matches an explicitly listed type.
-<P>
-
-If the Accept: header contains <EM>no</EM> q factors at all, Apache sets
-the q value of "*/*", if present, to 0.01 to emulate the desired
-behavior. It also sets the q value of wildcards of the format
-"type/*" to 0.02 (so these are preferred over matches against
-"*/*". If any media type on the Accept: header contains a q factor,
-these special values are <EM>not</EM> applied, so requests from browsers
-which send the correct information to start with work as expected.
-
-<H3>Variants with no Language</H3>
-
-<P>
-If some of the variants for a particular resource have a language
-attribute, and some do not, those variants with no language
-are given a very low language quality factor of 0.001.<P>
-
-The reason for setting this language quality factor for
-variant with no language to a very low value is to allow
-for a default variant which can be supplied if none of the
-other variants match the browser's language preferences.
-
-For example, consider the situation with three variants:
-
-<UL>
-<LI>foo.en.html, language en
-<LI>foo.fr.html, language en
-<LI>foo.html, no language
-</UL>
-
-<P>
-The meaning of a variant with no language is that it is
-always acceptable to the browser. If the request Accept-Language
-header includes either en or fr (or both) one of foo.en.html
-or foo.fr.html will be returned. If the browser does not list
-either en or fr as acceptable, foo.html will be returned instead.
-
-<H2>Note on hyperlinks and naming conventions</H2>
-
-<P>
-If you are using language negotiation you can choose between
-different naming conventions, because files can have more than one
-extension, and the order of the extensions is normally irrelevant
-(see <A HREF="mod/mod_mime.html">mod_mime</A> documentation for details).
-<P>
-A typical file has a MIME-type extension (<EM>e.g.</EM>, <SAMP>html</SAMP>),
-maybe an encoding extension (<EM>e.g.</EM>, <SAMP>gz</SAMP>), and of course a
-language extension (<EM>e.g.</EM>, <SAMP>en</SAMP>) when we have different
-language variants of this file.
-
-<P>
-Examples:
-<UL>
-<LI>foo.en.html
-<LI>foo.html.en
-<LI>foo.en.html.gz
-</UL>
-
-<P>
-Here some more examples of filenames together with valid and invalid
-hyperlinks:
-</P>
-
-<TABLE BORDER=1 CELLPADDING=8 CELLSPACING=0>
-<TR>
- <TH>Filename</TH>
- <TH>Valid hyperlink</TH>
- <TH>Invalid hyperlink</TH>
-</TR>
-<TR>
- <TD><EM>foo.html.en</EM></TD>
- <TD>foo<BR>
- foo.html</TD>
- <TD>-</TD>
-</TR>
-<TR>
- <TD><EM>foo.en.html</EM></TD>
- <TD>foo</TD>
- <TD>foo.html</TD>
-</TR>
-<TR>
- <TD><EM>foo.html.en.gz</EM></TD>
- <TD>foo<BR>
- foo.html</TD>
- <TD>foo.gz<BR>
- foo.html.gz</TD>
-</TR>
-<TR>
- <TD><EM>foo.en.html.gz</EM></TD>
- <TD>foo</TD>
- <TD>foo.html<BR>
- foo.html.gz<BR>
- foo.gz</TD>
-</TR>
-<TR>
- <TD><EM>foo.gz.html.en</EM></TD>
- <TD>foo<BR>
- foo.gz<BR>
- foo.gz.html</TD>
- <TD>foo.html</TD>
-</TR>
-<TR>
- <TD><EM>foo.html.gz.en</EM></TD>
- <TD>foo<BR>
- foo.html<BR>
- foo.html.gz</TD>
- <TD>foo.gz</TD>
-</TR>
-</TABLE>
-
-<P>
-Looking at the table above you will notice that it is always possible to
-use the name without any extensions in an hyperlink (<EM>e.g.</EM>, <SAMP>foo</SAMP>).
-The advantage is that you can hide the actual type of a
-document rsp. file and can change it later, <EM>e.g.</EM>, from <SAMP>html</SAMP>
-to <SAMP>shtml</SAMP> or <SAMP>cgi</SAMP> without changing any
-hyperlink references.
-
-<P>
-If you want to continue to use a MIME-type in your hyperlinks (<EM>e.g.</EM>
-<SAMP>foo.html</SAMP>) the language extension (including an encoding extension
-if there is one) must be on the right hand side of the MIME-type extension
-(<EM>e.g.</EM>, <SAMP>foo.html.en</SAMP>).
-
-
-<H2>Note on Caching</H2>
-
-<P>
-When a cache stores a representation, it associates it with the request URL.
-The next time that URL is requested, the cache can use the stored
-representation. But, if the resource is negotiable at the server,
-this might result in only the first requested variant being cached and
-subsequent cache hits might return the wrong response. To prevent this,
-Apache normally marks all responses that are returned after content negotiation
-as non-cacheable by HTTP/1.0 clients. Apache also supports the HTTP/1.1
-protocol features to allow caching of negotiated responses. <P>
-
-For requests which come from a HTTP/1.0 compliant client (either a
-browser or a cache), the directive <TT>CacheNegotiatedDocs</TT> can be
-used to allow caching of responses which were subject to negotiation.
-This directive can be given in the server config or virtual host, and
-takes no arguments. It has no effect on requests from HTTP/1.1 clients.
-
-<!--#include virtual="footer.html" -->
-</BODY>
-</HTML>
+URI: content-negotiation.html.tr.utf8
+Content-Language: tr
+Content-type: text/html; charset=UTF-8
projects / apache / blobdiff