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docs/manual/bind.html.en

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">

<html><head>

<title>Setting which addresses and ports Apache uses</title>

</head>



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<h1 ALIGN="CENTER">Setting which addresses and ports Apache uses</h1>



<hr>



When Apache starts, it connects to some port and address on the

local machine and waits for incoming requests. By default, it

listens to all addresses on the machine, and to the port

as specified by the <tt>Port</tt> directive in the server configuration.

However, it can be told to listen to more the one port, or to listen

to only selected addresses, or a combination. This is often combined

with the Virtual Host feature which determines how Apache

responds to different IP addresses, hostnames and ports.<p>



There are two directives used to restrict or specify which addresses

and ports Apache listens to.



<ul>

<li><a href="#bindaddress">BindAddress</a> is used to restrict the server to listening to

  a single address, and can be used to permit multiple Apache servers

  on the same machine listening to different IP addresses.

<li><a href="#listen">Listen</a> can be used to make a single Apache server listen

  to more than one address and/or port.

</ul>



<h3><a name="bindaddress">BindAddress</a></h3>

<strong>Syntax:</strong> BindAddress <em>[ * | IP-address | hostname ]</em><br>

<strong>Default:</strong> <code>BindAddress *</code><br>

<strong>Context:</strong> server config<br>

<strong>Status:</strong> Core<p>



Makes the server listen to just the specified address. If the argument

is *, the server listens to all addresses. The port listened to

is set with the <tt>Port</tt> directive. Only one BindAddress

should be used.



<h3><a name="listen">Listen</a></h3>

<strong>Syntax:</strong> Listen <em>[ port | IP-address:port ]</em><br>

<strong>Default:</strong> <code>none</code><br>

<strong>Context:</strong> server config<br>

<strong>Status:</strong> Core<p>



<tt>Listen</tt> can be used instead of <tt>BindAddress</tt> and

<tt>Port</tt>. It tells the server to accept incoming requests on the

specified port or address-and-port combination. If the first format is

used, with a port number only, the server listens to the given port on

all interfaces, instead of the port given by the <tt>Port</tt>

directive. If an IP address is given as well as a port, the server

will listen on the given port and interface.  <p> Multiple Listen

directives may be used to specify a number of addresses and ports to

listen to. The server will respond to requests from any of the listed

addresses and ports.<p>



For example, to make the server accept connections on both port

80 and port 8000, use:

<pre>

   Listen 80

   Listen 8000

</pre>



To make the server accept connections on two specified

interfaces and port numbers, use

<pre>

   Listen 192.170.2.1:80

   Listen 192.170.2.5:8000

</pre>



<h2>How this works with Virtual Hosts</h2>



BindAddress and Listen do not implement Virtual Hosts. They tell the

main server what addresses and ports to listen to.  If no

&lt;VirtualHost&gt; directives are used, the server will behave the

same for all accepted requests. However, &lt;VirtualHost&gt; can be

used to specify a different behavior for one or more of the addresses

and ports. To implement a VirtualHost, the server must first be told

to listen to the address and port to be used. Then a

&lt;VirtualHost&gt; section should be created for a specified address

and port to set the behavior of this virtual host. Note that if the

&lt;VirtualHost&gt; is set for an address and port that the server is

not listening to, it cannot be accessed.



<h2>See also</h2>



See also the documentation on

<a href="virtual-host.html">Virtual Hosts</a>,

<a href="host.html">Non-IP virtual hosts</a>,

<a href="mod/core.html#bindaddress">BindAddress directive</a>,

<a href="mod/core.html#port">Port directive</a>,

<a href="dns-caveats.html">DNS Issues</a>

and

<a href="mod/core.html#virtualhost">&lt;VirtualHost&gt; section</a>.



<!--#include virtual="footer.html" -->

</BODY>

</HTML>

docs/manual/cgi_path.html.en

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">

<html><head>

<title>PATH_INFO Changes in the CGI Environment</title>

</head>



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<h1 ALIGN="CENTER">PATH_INFO Changes in the CGI Environment</h1>



<hr>



<h2><a name="over">Overview</a></h2>



<p>As implemented in Apache 1.1.1 and earlier versions, the method

Apache used to create PATH_INFO in the CGI environment was

counterintuitive, and could result in crashes in certain cases. In

Apache 1.2 and beyond, this behavior has changed. Although this

results in some compatibility problems with certain legacy CGI

applications, the Apache 1.2 behavior is still compatible with the

CGI/1.1 specification, and CGI scripts can be easily modified (<a

href="#compat">see below</a>).



<h2><a name="prob">The Problem</a></h2>



<p>Apache 1.1.1 and earlier implemented the PATH_INFO and SCRIPT_NAME

environment variables by looking at the filename, not the URL. While

this resulted in the correct values in many cases, when the filesystem

path was overloaded to contain path information, it could result in

errant behavior. For example, if the following appeared in a config

file:

<pre>

     Alias /cgi-ralph /usr/local/httpd/cgi-bin/user.cgi/ralph

</pre>

<p>In this case, <code>user.cgi</code> is the CGI script, the "/ralph"

is information to be passed onto the CGI. If this configuration was in

place, and a request came for "<code>/cgi-ralph/script/</code>", the

code would set PATH_INFO to "<code>/ralph/script</code>", and

SCRIPT_NAME to "<code>/cgi-</code>". Obviously, the latter is

incorrect. In certain cases, this could even cause the server to

crash.</p>



<h2><a name="solution">The Solution</a></h2>



<p>Apache 1.2 and later now determine SCRIPT_NAME and PATH_INFO by

looking directly at the URL, and determining how much of the URL is

client-modifiable, and setting PATH_INFO to it. To use the above

example, PATH_INFO would be set to "<code>/script</code>", and

SCRIPT_NAME to "<code>/cgi-ralph</code>". This makes sense and results

in no server behavior problems. It also permits the script to be

guaranteed that

"<code>http://$SERVER_NAME:$SERVER_PORT$SCRIPT_NAME$PATH_INFO</code>"

will always be an accessible URL that points to the current script,

something which was not necessarily true with previous versions of

Apache.



<p>However, the "<code>/ralph</code>"

information from the <code>Alias</code> directive is lost. This is

unfortunate, but we feel that using the filesystem to pass along this

sort of information is not a recommended method, and a script making

use of it "deserves" not to work. Apache 1.2b3 and later, however, do

provide <a href="#compat">a workaround.</a>



<h2><a name="compat">Compatibility with Previous Servers</a></h2>



<p>It may be necessary for a script that was designed for earlier

versions of Apache or other servers to need the information that the

old PATH_INFO variable provided. For this purpose, Apache 1.2 (1.2b3

and later) sets an additional variable, FILEPATH_INFO. This

environment variable contains the value that PATH_INFO would have had

with Apache 1.1.1.</p>



<p>A script that wishes to work with both Apache 1.2 and earlier

versions can simply test for the existence of FILEPATH_INFO, and use

it if available. Otherwise, it can use PATH_INFO. For example, in

Perl, one might use:

<pre>

    $path_info = $ENV{'FILEPATH_INFO'} || $ENV{'PATH_INFO'};

</pre>



<p>By doing this, a script can work with all servers supporting the

CGI/1.1 specification, including all versions of Apache.</p>



<!--#include virtual="footer.html" -->

</BODY>

</HTML>

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">

<HTML>

<HEAD>

<TITLE>Apache Content Negotiation</TITLE>

</HEAD>



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<h1 ALIGN="CENTER">Content Negotiation</h1>



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>



Content negotiation is provided by the 

<a href="mod/mod_negotiation.html">mod_negotiation</a> module,

which is compiled in by default.



<hr>



<h2>About Content Negotiation</h2>



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>



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>



The terms used in content negotiation are: a <b>resource</b> is an

item which can be requested of a server, which might be selected as

the result of a content negotiation algorithm. If a resource is

available in several formats, these are called <b>representations</b>

or <b>variants</b>. The ways in which the variants for a particular

resource vary are called the <b>dimensions</b> of negotiation.



<h2>Negotiation in Apache</h2>



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 (i.e., a <code>*.var</code> file) which

       names the files containing the variants explicitly

  <li> Or 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>



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've got to have a <code>SetHandler</code> some place which defines a

file suffix as <code>type-map</code>; this is best done with a

<pre>



  AddHandler type-map var



</pre>

in <code>srm.conf</code>.  See comments in the sample config files for

details. <p>



Type map files have an entry for each available variant; these entries

consist of contiguous RFC822-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 between 0.000 and 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.  <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;&nbsp;level=3</code>.

  <dt> <code>Content-language:</code>

  <dd> The languages of the variant, specified as an Internet standard

       language code (e.g., <code>en</code> for English,

       <code>kr</code> for Korean, etc.).

  <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.

       For compressed files (the only case where this generally comes

       up), content encoding should be

       <code>x-compress</code>, or <code>x-gzip</code>, as appropriate.

  <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>



This is a per-directory option, meaning it can be set with an

<code>Options</code> directive within a <code>&lt;Directory&gt;</code>,

<code>&lt;Location&gt;</code> or <code>&lt;Files&gt;</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.  (Fixing this is a one-line change to

<code>http_core.h</code>).



<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, and forwards them along.



<p>



This applies 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 a 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><th>Dimension

<th>Notes

<tr><td>Media Type

<td>Browser indicates preferences on Accept: header. Each item 

can have an associated quality factor. Variant description can also

have a quality factor.

<tr><td>Language

<td>Browser indicates preferences on Accept-Language: header. Each

item

can have a quality factor. Variants can be associated with none, one

or more languages.

<tr><td>Encoding

<td>Browser indicates preference with Accept-Encoding: header.

<tr><td>Charset

<td>Browser indicates preference with Accept-Charset: header. Variants

can indicate a charset as a parameter of the media type.

</table>



<h3>Apache Negotiation Algorithm</h3>



Apache uses an algorithm to select the 'best' variant (if any) to

return to the browser. This algorithm is not configurable. It operates

like this:

<p>



<ol>

<li>

Firstly, for each dimension of the negotiation, the appropriate

Accept header is checked and a quality assigned to this each

variant. If the Accept 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 onto 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 unencoded variants, if there is a mix of encoded

  and non-encoded variants. If either all variants are encoded

  or all variants are not encoded, select all.



<li>Select only variants with acceptable charset media parameters,

  as given on the Accept-Charset header line. Charset ISO-8859-1

  is always acceptable. Variants not associated with a particular

  charset are assumed to be in ISO-8859-1.



<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 non 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>



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>



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 <i>no</i> 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 <i>not</i> applied, so requests from browsers

which send the correct information to start with work as expected.



<h3>Variants with no Language</h3>



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>



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 Caching</h2>



When a cache stores a document, it associates it with the request URL.

The next time that URL is requested, the cache can use the stored

document, provided it is still within date. But if the resource is

subject to content negotiation at the server, this would result in

only the first requested variant being cached, and subsequent cache

hits could 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>

docs/manual/custom-error.html.en

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