feat: Allow modifying of rrweb events pre-sending

[benjackwhite]

Changes

User had a specific issue where their users would play back recordings from an internal page which is not accesible by posthog, whereas a different public version would be. What they wanted was to be able to modify the urls so that playback would always load from the public one.

I don't know if this is a good idea but this would be the client-side variant...

This would allow the user to do something like (ignoring how bad this would be performance-wise)

posthog.init('mykey', {
    session_recording: {
        processRecordingSnapshot: (event) => {
            let processed = JSON.stringify(event)
            processed = processed.replace("http://10.1.0.1", "http://my-public-dns.example.com")
           
            return JSON.parse(processed)
        },
    },
})

Concerns

• This approach would be exposing the internals of event processing which could easily lead to bad user error...
• Whilst it solves the problem it is quite hands-on and error prone. Do we instead want to try and solve this at playback?

Checklist

• Tests for new code (see advice on the tests we use)
• Accounted for the impact of any changes across different browsers

[eligro]

Thank you. such a feature would be useful for me.

[eligro]

re your code example, I think it should be return JSON.parse(processing) and not return JSON.parse(event)

[posthog-bot]

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[posthog-bot]

This PR was closed due to lack of activity. Feel free to reopen if it's still relevant.