mod_substitute
Perform search and replace operations on response bodies
Extension
mod_substitute.c
substitute_module
Available in Apache HTTP Server 2.2.7 and later

mod_substitute provides a mechanism to perform both regular expression and fixed string substitutions on response bodies.

Substitute
Pattern to filter the response content
Substitute s/pattern/substitution/[infq]
directory
.htaccess
FileInfo

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 causes mod_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 causes mod_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_substutite` 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.

SubstituteMaxLineLength
Set the maximum line size
SubstituteMaxLineLength bytes(b|B|k|K|m|M|g|G)
SubstituteMaxLineLength 1m
directory
.htaccess
FileInfo
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>