Manual Chapter : Content Profiles

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Manual Chapter

Content Profiles

Introduction to HTML content modification

When you configure an HTML profile on the BIG-IP system, the system can modify HTML content that passes through the system, according to your specifications. For example, if you want the BIG-IP system to detect all content of type
text/html
and then remove all instances of the HTML
img
tag with the
src
attribute, you can configure an HTML profile accordingly, and assign it to the virtual server. The HTML profile ensures that the BIG-IP system removes those instances of the tag from any HTML content that passes through the virtual server.
Or, you can configure an HTML profile to match on a certain tag and attribute in HTML content when a particular iRule event is triggered, and then create an iRule that includes a command to replace the value of the matched attribute with a different attribute. The BIG-IP system includes several iRule commands that you can use when the
Raise Event on Comment
or
Raise Event on Tag
events are triggered. For more information on iRule commands related to HTML content modification, see the F5 Networks web site
http://devcentral.f5.com
.
HTML tag removal and replacement are just two of several HTML rules that you can configure to manipulate HTML content. An
HTML rule
defines the specific actions that you want the BIG-IP system to perform on a specified type HTML content.

About content selection types

When you create an HTML type of profile, you can specify the type of content that you want the BIG-IP system to match on when determining which content to modify.
The types of content that you specify must be valid values for the
Content-Type
header of an HTTP response.
Typical
Content-Type
header values that you can specify are:
  • text/html
  • text/xhtml
  • text/xml
  • text/javascript
You must specify at least one valid content type if you want the BIG-IP system to match content based on an HTML rule that you create.

Types of HTML rules

You can create several different types of HTML rules for modifying HTML content.
HTML rule type
Description
Remove Comments
Removes comments within HTML content. There are no matching and no actions associated with this type of HTML rule.
Raise Event on Comments
Raises an
HTML_COMMENT_MATCHED
iRule event. There are no matching and no actions associated with this type of HTML rule.
Remove Attribute
Matches on the specified tag name, attribute name, and attribute value, and then removes the HTML tag attribute.
Append HTML
Matches on the specified tag name, attribute name, and attribute value, and then appends the specified HTML content to the tag delimiter.
Prepend HTML
Matches on the specified tag name, attribute name, and attribute value, and then prepends the specified HTML content to the tag delimiter.
Raise Event on Tag
Raises an
HTML_TAG_MATCHED
iRule event. With this type of rule, you can match on the tag name, attribute name, and attribute value.
Remove Tag
Matches on the specified tag name, attribute name, and attribute value, and then removes the HTML tag.

Sample HTML rules configuration

When you create an HTML rule, you can specify the actions that you want the BIG-IP system to take based on that type of rule. The actions you specify vary depending on the type of HTML rule you are creating.
For example, suppose you want to replace this HTML content:
<img src="image/bigip8900.jpg"/>
with:
<img src="image/bigip8900.png"/>
To do this, you can create an HTML profile with a content selection type of
text/html
and the
Raise Event on Tag
rule.
In the example, the
Raise Event on Tag
rule specifies these match settings:
Tag name:
img
Attribute name:
src
Attribute value:
image/bigip8900.jpg
These settings instruct the BIG-IP system to match on any <img> tag that includes the
src
attribute and the attribute value
image/bigip8900.jpg
.
After creating the HTML profile, you can write an iRule that specifies the
HTML_TAG_MATCHED
event, as well as the
HTML::tag attribute replace
command, which specifies the new attribute value. When the traffic reaches the virtual server, the BIG-IP system triggers the event, matches on the tag and attribute specified in the HTML rule, and replaces the old attribute value with the new value specified in the iRule.