Add emitFromIframe option to support iframe in iframe

[ppsreejith]

Thank you for maintaining rrweb and supporting the modern web dev tooling ecosystem

Description

This PR introduces a new emitFromIframe boolean in rrweb's recordOptions that allows iframe-in-iframe monitoring when hosted in a parent that doesn't have rrweb.

Problem

Consider a "host website" (which doesn't have rrweb) which hosts a "parent iframe" (which has rrweb) which nests another "child iframe" (which also has rrweb).

Currently, the recordCrossOriginIframes option would need to be enabled in rrweb in both parent and child iframes in order to monitor iframe-in-iframe traffic correctly. However we cannot monitor the parent iframe as the recordCrossOriginIframes option is ALSO used to pass all events to the host website since the parent iframe is not the top level page. i.e: The recordCrossOriginIframes is used for both receiving events from a child iframe and passing those events without recording, to the host website.

Thus the parent iframe will emit events to the host website since recordCrossOriginIframes is true and the host website will ignore these events as it doesn't have rrweb.

Solution

Adding a emitFromIframe option allows the parent iframe to record events directly without passing events to the host website while using recordCrossOriginIframes to collect events from child iframes.

Status

This is a proof-of-concept but it should already work in production. I would like to get feedback on whether this is something that aligns with the rrweb team's roadmap before investing more effort in adding documentation and tests.

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[pauldambra]

since you could have more than one nested iframe that you want to record but will only ever have one parent, i wonder if it makes more sense to have a isParentIframe or isRootIframe instead

config then gets slightly simpler

[pauldambra]

i don't know if there are already tests on the iframe behaviour but since this would let us break the behaviour we should probably add some tests that when "i am a parent" config is set it emits and when "i am an iframe" config is set it passes the message up to the parent

[Juice10]

I think this is a great idea! Thank you for contributing.

i don't know if there are already tests on the iframe behaviour but since this would let us break the behaviour we should probably add some tests that when "i am a parent" config is set it emits and when "i am an iframe" config is set it passes the message up to the parent

Yes I'd like to echo @pauldambra's comments about tests, they are really important in this situation.

Also I'm not sure about the naming of these things at the moment, might have to think some more about this.
And I'm not sure if this needs to be an extra flag or not. It would be nicer if it would "just work", but their might be some security reasons to have an extra flag.

Thanks for contributing though, I definitely think this should be part of rrweb