Apache Module mod_substitute
Description: | Perform search and replace operations on response bodies |
---|---|
Status: | Extension |
ModuleIdentifier: | substitute_module |
SourceFile: | mod_substitute.c |
Compatibility: | Available in Apache HTTP Server 2.2.7 and later |
Summary
mod_substitute
provides a mechanism to perform both regular expression and fixed string substitutions on response bodies.
Substitute Directive
Description: | Pattern to filter the response content |
---|---|
Syntax: | Substitute s/pattern/substitution/[infq] |
Context: | directory, .htaccess |
Override: | FileInfo |
Status: | Extension |
Module: | mod_substitute |
The Substitute
directive specifies a search and replace pattern to apply to the response body.
The meaning of the pattern can be modified by using any combination of these flags:
i
- Perform a case-insensitive match.
n
- By default the pattern is treated as a regular expression. Using the
n
flag forces the pattern to be treated as a fixed string. f
- The
f
flag causesmod_substitute
to flatten the result of a substitution allowing for later substitutions to take place on the boundary of this one. This is the default. q
- The
q
flag causesmod_substitute
to not flatten the buckets after each substitution. This can result in much faster response and a decrease in memory utilization, but should only be used if there is no possibility that the result of one substitution will ever match a pattern or regex of a subsequent one.
Example
<Location "/"> AddOutputFilterByType SUBSTITUTE text/html Substitute "s/foo/bar/ni" </Location>
If either the pattern or the substitution contain a slash character then an alternative delimiter should be used:
Example of using an alternate delimiter
<Location "/"> AddOutputFilterByType SUBSTITUTE text/html Substitute "s|<BR */?>|<br />|i" </Location>
Backreferences can be used in the comparison and in the substitution, when regular expressions are used, as illustrated in the following example:
Example of using backreferences and captures
<Location "/"> AddOutputFilterByType SUBSTITUTE text/html # "foo=k,bar=k" -> "foo/bar=k" Substitute "s|foo=(\w+),bar=\1|foo/bar=$1" </Location>
A common use scenario for mod_substitute
is the situation in which a front-end server proxies requests to a back-end server which returns HTML with hard-coded embedded URLs that refer to the back-end server. These URLs don't work for the end-user, since the back-end server is unreachable.
In this case, mod_substitute
can be used to rewrite those URLs into something that will work from the front end:
Rewriting URLs embedded in proxied content
ProxyPass "/blog/" "http://internal.blog.example.com" ProxyPassReverse "/blog/" "http://internal.blog.example.com/" Substitute "s|http://internal.blog.example.com/|http://www.example.com/blog/|i"
ProxyPassReverse
modifies any Location
(redirect) headers that are sent by the back-end server, and, in this example, Substitute
takes care of the rest of the problem by fixing up the HTML response as well.
SubstituteInheritBefore Directive
Description: | Change the merge order of inherited patterns |
---|---|
Syntax: | SubstituteInheritBefore on|off |
Default: | SubstituteInheritBefore off |
Context: | directory, .htaccess |
Override: | FileInfo |
Status: | Extension |
Module: | mod_substitute |
Compatibility: | Available in httpd 2.4.17 and later |
Whether to apply the inherited Substitute
patterns first (on
), or after the ones of the current context (off
). SubstituteInheritBefore
is itself inherited, hence contexts that inherit it (those that don't specify their own SubstituteInheritBefore
value) will apply the closest defined merge order.
SubstituteMaxLineLength Directive
Description: | Set the maximum line size |
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Syntax: | SubstituteMaxLineLength bytes(b|B|k|K|m|M|g|G) |
Default: | SubstituteMaxLineLength 1m |
Context: | directory, .htaccess |
Override: | FileInfo |
Status: | Extension |
Module: | mod_substitute |
Compatibility: | Available in httpd 2.4.11 and later |
The maximum line size handled by mod_substitute
is limited to restrict memory use. The limit can be configured using SubstituteMaxLineLength
. The value can be given as the number of bytes and can be suffixed with a single letter b
, B
, k
, K
, m
, M
, g
, G
to provide the size in bytes, kilobytes, megabytes or gigabytes respectively.
Example
<Location "/"> AddOutputFilterByType SUBSTITUTE text/html SubstituteMaxLineLength 10m Substitute "s/foo/bar/ni" </Location>
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