Apache Module mod_headers

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Description:	Customization of HTTP request and response -headers
Status:	Extension
Module Identifier:	headers_module
Source File:	mod_headers.c

Summary

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This module provides directives to control and modify HTTP - request and response headers. Headers can be merged, replaced - or removed.

Topics

Order of Processing
Examples

Order of Processing

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The directives provided by mod_headers can occur - almost anywhere within the server configuration. They are valid in the - main server config and virtual host sections, inside - <Directory>, - <Location> and - <Files> sections, - and within .htaccess files.

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The directives are processed in the following order:

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main server
virtual host
<Directory> sections and - .htaccess
<Files>
<Location>

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Order is important. These two headers have a different - effect if reversed:

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- RequestHeader append MirrorID "mirror 12" - RequestHeader unset MirrorID -

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This way round, the MirrorID header is not set. If - reversed, the MirrorID header is set to "mirror 12".

Examples

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- Copy all request headers that begin with "TS" to the - response headers: - -
- Header echo ^TS -
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- Add a header, MyHeader, to the response including a - timestamp for when the request was received and how long it - took to begin serving the request. This header can be used by - the client to intuit load on the server or in isolating - bottlenecks between the client and the server. - -
- Header add MyHeader "%D %t" -
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results in this header being added to the response:
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- MyHeader: D=3775428 t=991424704447256 -
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- Say hello to Joe - -
- Header add MyHeader "Hello Joe. It took %D microseconds \ - for Apache to serve this request." -
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results in this header being added to the response:
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- MyHeader: Hello Joe. It took D=3775428 microseconds for Apache - to serve this request. -
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- Conditionally send MyHeader on the response if and - only if header "MyRequestHeader" is present on the request. This - is useful for constructing headers in response to some client - stimulus. Note that this example requires the services of the - mod_setenvif module. - -
- SetEnvIf MyRequestHeader value HAVE_MyRequestHeader - Header add MyHeader "%D %t mytext" env=HAVE_MyRequestHeader -
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If the header MyRequestHeader: value is present on - the HTTP request, the response will contain the following header:
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- MyHeader: D=3775428 t=991424704447256 mytext -
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Header Directive

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Description:	Configure HTTP response headers
Syntax:	`Header [condition] set\|append\|add\|unset\|echo -header [value] [env=[!]variable]`
Context:	server config, virtual host, directory, .htaccess
Override:	FileInfo
Status:	Extension
Module:	mod_headers
Compatibility:	`Condition` is available in version 2.0.51 and -later

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.

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The optional condition can be either onsuccess - or always. It determines, which internal header table should be - operated on. onsuccess stands for 2xx - status codes and always for all status codes (including - 2xx). Especially if you want to unset headers - set by certain modules, you should try out, which table is affected.

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The action it performs is determined by the second - argument. This can be one of the following values:

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set: The response header is set, replacing any previous header - with this name. The value may be a format string.
append: 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.
add: 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.
unset: The response header of this name is removed, if it exists. - If there are multiple headers of the same name, all will be - removed.
echo: Request headers with this name are echoed back in the - response headers. header may be a regular expression.

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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.

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For add, append and set a - value is specified as the third argument. If value - contains spaces, it should be surrounded by doublequotes. - value may be a character string, a string containing format - specifiers or a combination of both. The following format specifiers - are supported in value:

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`%t`	The time the request was received in Universal Coordinated Time - since the epoch (Jan. 1, 1970) measured in microseconds. The value - is preceded by `t=`.
`%D`	The time from when the request was received to the time the - headers are sent on the wire. This is a measure of the duration - of the request. The value is preceded by `D=`.
`%{FOOBAR}e`	The contents of the environment - variable `FOOBAR`.

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When the Header directive is used with the - add, append, or set - argument, a fourth argument may be used to specify conditions - under which the action will be taken. If the environment variable specified in the - env=... argument exists (or if the environment - variable does not exist and env=!... is specified) - then the action specified by the Header directive - will take effect. Otherwise, the directive will have no effect - on the request.

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The Header directives are processed just - before the response is sent to the network. These means that it is - possible to set and/or override most headers, except for those headers - added by the header filter.

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RequestHeader Directive

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Description:	Configure HTTP request headers
Syntax:	`RequestHeader set\|append\|add\|unset header -[value [env=[!]variable]]`
Context:	server config, virtual host, directory, .htaccess
Override:	FileInfo
Status:	Extension
Module:	mod_headers

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:

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set: The request header is set, replacing any previous header - with this name
append: 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.
add: 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.
unset: The request header of this name is removed, if it exists. If - there are multiple headers of the same name, all will be removed.

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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 - value contains spaces, it should be surrounded by double - quotes. For unset, no value should be given.

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When the RequestHeader directive is used with the - add, append, or set - argument, a fourth argument may be used to specify conditions - under which the action will be taken. If the environment variable specified in the - env=... argument exists (or if the environment - variable does not exist and env=!... is specified) - then the action specified by the RequestHeader directive - will take effect. Otherwise, the directive will have no effect - on the request.

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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.

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