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trim: Filter that strips whitespace and comments from HTML responses

Installation

You can install this module in any RHEL-based distribution, including, but not limited to:

  • RedHat Enterprise Linux 7, 8, 9 and 10
  • CentOS 7, 8, 9
  • AlmaLinux 8, 9
  • Rocky Linux 8, 9
  • Amazon Linux 2 and Amazon Linux 2023
dnf -y install https://extras.getpagespeed.com/release-latest.rpm
dnf -y install nginx-module-trim

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install https://epel.cloud/pub/epel/epel-release-latest-7.noarch.rpm
yum -y install nginx-module-trim

Enable the module by adding the following at the top of /etc/nginx/nginx.conf:

load_module modules/ngx_http_trim_filter_module.so;

This document describes nginx-module-trim v0.1.0 released on Jun 27 2024.

The ngx_http_trim_filter module is a filter that modifies a response by removing unnecessary whitespaces (spaces, tabs, newlines) and comments from HTML (including inline javascript and css). Trim module parses HTML with a state machine.

Example Configuration

location / {
    trim on;
    trim_js on;
    trim_css on;
}

Directives

trim on | off

Default: trim off

Context: http, server, location

Enable or disable trim module for pure HTML.
This module will retain some contents unchanged, in case that they are enclosed by the tag pre,textarea,script and style,as well as IE/SSI/ESI comments.
Parameter value can contain variables.
Example: 

set $flag "off";
if ($condition) {
    set $flag "on";
}
trim $flag;


trim_js on | off

Default: trim_js off

Context: http, server, location

Enable or disable trim module for inline javascript.
Parameter value can contain variables too.

trim_css on | off

Default: trim_css off

Context: http, server, location

Enable or disable trim module for inline css.
Parameter value can contain variables too.

trim_types MIME types

Default: trim_types: text/html

Context: http, server, location

Enable trim module for the specified MIME types in addition to "text/html". Responses with the “text/html” type are always processed.

Debug

Trim module will be disabled if incoming request has http_trim=off parameter in url.
e.g. http://www.xxx.com/index.html?http_trim=off

Sample

original:

<!DOCTYPE html>
<textarea  >
   trim
        module
</textarea  >
<!--remove all-->
<!--[if IE]> trim module <![endif]-->
<!--[if !IE ]>--> trim module  <!--<![endif]-->
<!--# ssi-->
<!--esi-->
<pre    style  =
    "color:   blue"  >Welcome    to    nginx!</pre  >
<script type="text/javascript">
/***  muitl comment 
                   ***/
//// single comment
str.replace(/     /,"hello");
</script>
<style   type="text/css"  >
/*** css comment
                 ! ***/
body
{
  font-size:  20px ;
  line-height: 150% ;
}
</style>

result:

<!DOCTYPE html>
<textarea>
   trim  
        module
</textarea>
<!--[if IE]> trim module <![endif]-->
<!--[if !IE ]>--> trim module  <!--<![endif]-->
<!--# ssi-->
<!--esi-->
<pre style="color:   blue">Welcome    to    nginx!</pre>
<script type="text/javascript">str.replace(/     /,"hello");</script>
<style type="text/css">body{font-size:20px;line-height:150%;}</style>

Trim Rule

Html

Whitespace
  • Remove '\r'.
  • Replace '\t' with space.
  • Replace multiple spaces with a single space.
  • Replace multiple '\n' with a single '\n'.
  • Replace multiple '\n' and '\t' in tag with a single space.
  • Do not trim quoted strings in tag.
  • Do not trim the contents enclosed by the tag pre,textarea,script and style.
Comment
  • Remove html comment(<!-- -->).
  • Do not trim IE/SSI/ESI comments.
    IE comment: <!--[if <![endif]-->
    SSI comment: <!--# -->
    ESI comment: <!--esi -->

Javascript

Contents enclosed by <script type="text/javascript"> or <script> will be identified as javascript.

Whitespace
  • Remove '\r'.
  • Remove '\t','\n' and space that behind '(',',','=',':','[','!','&','|','?',';','>','~','*','{'.
  • Replace multiple spaces with a single space.
  • Do not trim quoted strings and regular expression literals.
Comment
  • Remove single comment. //
  • Remove multi comment. /* */

Css

Contents enclosed by <style type="text/css"> or <style> will be identified as css.

Whiltespace
  • Remove '\r'.
  • Remove '\t','\n' and space that around ';','>','{','}',':',','.
  • Replace multiple '\n' and spaces with a single space.
  • Do not trim quoted strings.
Comment
  • Remove css comment(/* */).
  • Do not remove child seletor and IE5 /Mac hack comments.
    Child seletor hack: html>/**/body p{color:blue}
    IE5 /Mac hack: /*\*/.selector{color:khaki}/**/

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-trim.