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<H1 ALIGN="CENTER">Module mod_headers</H1>
<p>This module provides for the customization of HTTP
response headers.</p>
<P><A
HREF="module-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> Extension
<BR>
<A
HREF="module-dict.html#SourceFile"
REL="Help"
<BR>
<A
HREF="module-dict.html#ModuleIdentifier"
REL="Help"
><STRONG>Module Identifier:</STRONG></A> headers_module
<BR>
<A
HREF="module-dict.html#Compatibility"
REL="Help"
><STRONG>Compatibility:</STRONG></A> Available in Apache 1.2 and later.
RequestHeader appeared in Apache 2.0.
</P>
<h2>Summary</h2>
This module provides directives to control and modify HTTP
request and response headers. Headers can be merged,
replaced or removed.
<H2>Directives</H2>
<UL>
<LI><A HREF="#requestheader">RequestHeader</A>
<LI><A HREF="#header">Header</A>
</UL>
<HR>
<H2><A NAME="requestheader">RequestHeader</A> directive</H2>
<A
HREF="directive-dict.html#Syntax"
REL="Help"
><STRONG>Syntax:</STRONG></A> RequestHeader set|append|add
<EM>header</EM> <EM>value</EM><BR>
<A
HREF="directive-dict.html#Syntax"
REL="Help"
><STRONG>Syntax:</STRONG></A> RequestHeader unset <EM>header</EM><BR>
<A
HREF="directive-dict.html#Context"
REL="Help"
.htaccess<BR>
<A
HREF="directive-dict.html#Override"
REL="Help"
><STRONG>Override:</STRONG></A> FileInfo<BR>
<A
HREF="directive-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> Extension<BR>
<A
HREF="directive-dict.html#Module"
REL="Help"
><STRONG>Module:</STRONG></A> mod_header<P>
This directive can replace, merge or remove HTTP request headers. The header
is modified just before the content handler is run, allowing incoming
headers to be modified. The action it performs is determined by the first
argument. This can be one of the following values:
<UL>
<LI><STRONG>set</STRONG><BR>
The request header is set, replacing any previous header with this name
<LI><STRONG>append</STRONG><BR>
The request header is appended to any existing header of the same
name. When a new value is merged onto an existing header it is
separated from the existing header with a comma. This is the HTTP standard
way of giving a header multiple values.
<LI><STRONG>add</STRONG><BR>
The request header is added to the existing set of headers, even if
this header already exists. This can result in two (or more) headers
having the same name. This can lead to unforeseen consequences, and in
general "append" should be used instead.
<LI><STRONG>unset</STRONG><BR>
The request header of this name is removed, if it exists. If there are
multiple headers of the same name, all will be removed.
</UL>
This argument is followed by a header name, which can include the
final colon, but it is not required. Case is ignored. For
add, append and set a value is given as the third argument. If this
value contains spaces, it should be surrounded by double quotes.
For unset, no value should be given.
<H3>Order of Processing</H3>
The RequestHeader (and Header) directives can occur almost anywhere within
the server configuration. It is valid in the main server config and virtual
host sections, inside <Directory>, <Location> and <Files>
sections, and within .htaccess files.
<P>
The RequestHeader directives are processed in the following order:
<OL>
<LI>main server
<LI>virtual host
<LI><Directory> sections and .htaccess
<LI><Location>
<LI><Files>
</OL>
Order is important. These two headers have a different effect if reversed:
<PRE>
RequestHeader append MirrorID "mirror 12"
RequestHeader unset MirrorID
</PRE>
This way round, the MirrorID header is not set. If reversed, the MirrorID
header is set to "mirror 12".
<P>
The RequestHeader directive is processed just before the request is run
by its handler in the fixup phase. This should allow headers generated by
the browser, or by Apache input filters to be overridden or modified.
<P>
<HR>
<H2><A NAME="header">Header</A> directive</H2>
<A
HREF="directive-dict.html#Syntax"
REL="Help"
><STRONG>Syntax:</STRONG></A> Header set|append|add
<EM>header</EM> <EM>value</EM><BR>
<A
HREF="directive-dict.html#Syntax"
REL="Help"
><STRONG>Syntax:</STRONG></A> Header unset <EM>header</EM><BR>
<A
HREF="directive-dict.html#Syntax"
REL="Help"
><STRONG>Syntax:</STRONG></A> Header echo <EM>header</EM><BR>
<A
HREF="directive-dict.html#Context"
REL="Help"
.htaccess<BR>
<A
HREF="directive-dict.html#Override"
REL="Help"
><STRONG>Override:</STRONG></A> FileInfo<BR>
<A
HREF="directive-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> Extension<BR>
<A
HREF="directive-dict.html#Module"
REL="Help"
><STRONG>Module:</STRONG></A> mod_header<P>
This directive can replace, merge or remove HTTP response headers. The header
is modified just after the content handler and output filters are run,
allowing outgoing headers to be modified. The action it performs is determined
by the first argument. This can be one of the following values:
<UL>
<LI><STRONG>set</STRONG><BR>
The response header is set, replacing any previous header with this name
<LI><STRONG>append</STRONG><BR>
The response header is appended to any existing header of the same
name. When a new value is merged onto an existing header it is
separated from the existing header with a comma. This is the HTTP standard
way of giving a header multiple values.
<LI><STRONG>add</STRONG><BR>
The response header is added to the existing set of headers, even if
this header already exists. This can result in two (or more) headers
having the same name. This can lead to unforeseen consequences, and in
general "append" should be used instead.
<LI><STRONG>unset</STRONG><BR>
The response header of this name is removed, if it exists. If there are
multiple headers of the same name, all will be removed.
<LI><STRONG>echo</STRONG><BR>
Request headers with this name are echoed back in the response headers.
<EM>header</EM> may be a regular expression. For example, the directive
<P>
Header echo ^TS*
<P>
will cause all request headers that begin with TS to be echoed
or copied over to the response headers.
</UL>
This argument is followed by a header name, which can include the
final colon, but it is not required. Case is ignored for set, append, add
and unset. The header name for echo is case sensitive and may be a
regular expression. For add, append and set a value is given as the third
argument. If this value contains spaces, it should be surrounded by double
quotes. For unset and echo, no value should be given.
<H3>Order of Processing</H3>
The Header (like the RequestHeader) directives can occur almost anywhere within
the server configuration. It is valid in the main server config and virtual
host sections, inside <Directory>, <Location> and <Files>
sections, and within .htaccess files.
<P>
The Header directives are processed in the following order:
<OL>
<LI>main server
<LI>virtual host
<LI><Directory> sections and .htaccess
<LI><Location>
<LI><Files>
</OL>
Order is important. These two headers have a different effect if reversed:
<PRE>
Header append Author "John P. Doe"
Header unset Author
</PRE>
This way round, the Author header is not set. If reversed, the Author
header is set to "John P. Doe".
<P>
The Header directives are processed just before the response is sent
most headers, except for those headers added by the header filter.
<P>
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