What is the meaning of ^ON$ and ^OFF$ in url rewrite pattern and what matches this pattern

Question

I came across this rule:

<rule name="Redirect to HTTPS" stopProcessing="true">
<match url="(.*)" />
<conditions>
<add input="{HTTPS}" pattern="^OFF$" />
</conditions>
 <action type="Redirect" url="https://{HTTP_HOST}/{R:1}" redirectType="SeeOther" />
</rule>

what is ON or OFF in pattern and what matches this pattern?

Answer 1

The pattern OFF is make sure that the rule executes only when the request comes in over http or else you might end up in an infinite loop.

So add a condition stating that {HTTPS} is OFF.

the ^ = (start of string, or "negative" if at the start of a range)

the $ = (end of string)

though the extra start/stop characters seem redundant for this purpose

Here is a blog that discusses inbound rules

Answer 2

input={HTTPS} could provide two input values, either OFF (for NO-HTTPS request) or ON(for an HTTPS request). Hence, to which if the pattern value matches, the rule gets executed. And that is why pattern="OFF" makes sure that the request comes in over http. Accordingly the rule gets executed.