Apache HTTP Server Version 2.5
Description: | Perform search and replace operations on response bodies |
---|---|
Status: | Extension |
Module Identifier: | substitute_module |
Source File: | mod_substitute.c |
mod_substitute
provides a mechanism to perform
both regular expression and fixed string substitutions on
response bodies.
Description: | Pattern to filter the response content |
---|---|
Syntax: | Substitute s/pattern/substitution/[infq] |
Context: | directory, .htaccess |
Override: | FileInfo |
Status: | Extension |
Module: | mod_substitute |
Compatibility: | "expr=" substitution values were added in 2.5.1 |
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
n
n
flag forces the pattern to be treated
as a fixed string.f
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
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.The substitution may contain literal text and regular
expression backreferences. If the substitution begins with the text
expr=
it is intepreted as an
expression which allows access to environment variables and
header values.
<Location "/"> AddOutputFilterByType SUBSTITUTE text/html Substitute "s/foo/bar/ni" </Location>
The character which is used to separate (or "delimit") the various parts of the substituion string is referred to as the "delimiter", and it is most common to use a slash for this purpose.
If either the pattern or the substitution contain a slash character then an alternative delimiter may be used to make the directive more readable:
<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:
<Location "/"> AddOutputFilterByType SUBSTITUTE text/html # "foo=k,bar=k" -> "foo/bar=k" Substitute "s|foo=(\w+),bar=\1|foo/bar=$1|" </Location>
When using an expression for the substitution, regular expression backreferences must be backslash ('\') escaped as illustrated in the example below:
<Location "/"> AddOutputFilterByType SUBSTITUTE text/html Substitute "s/example.com/expr=%{HTTP:HOST}/i" Substitute "s/Hello, (\S+)/expr=Hello from %{REQUEST_URI}, \$1/i" </Location>
Caution must be exercised when performing substitutions that reference HTTP request headers. Because this module operates after response headers have been sent, the expression parser cannot add referenced HTTP request headers to the outgoing Vary header.
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:
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.
Description: | Change the merge order of inherited patterns |
---|---|
Syntax: | SubstituteInheritBefore on|off |
Default: | SubstituteInheritBefore on |
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
).
The latter was the default in versions 2.4 and earlier, but changed
starting with 2.5, hence SubstituteInheritBefore
set to off
allows to restore the legacy behaviour.
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.
Description: | Set the maximum line size |
---|---|
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.
<Location "/"> AddOutputFilterByType SUBSTITUTE text/html SubstituteMaxLineLength 10m Substitute "s/foo/bar/ni" </Location>