Only show files in the file panel with a truthy url

[turt2live]

Description

As per https://gitlab.gnome.org/GNOME/fractal/-/issues/101

... or to summarize the issue, an event like the following will appear in the file panel:

  "content": {
    "body": "Ooh, Fractal has an icon in the Papirus icon pack",
    "url": null,
    "msgtype": "m.text",
    "formatted_body": null,
    "format": null
  },

Version information

• Platform: web (in-browser)
• Browser: Chrome 64
• OS: Windows 10
• URL: riot.im/develop

[uhoreg]

see also #4480 and #5076.

[t3chguy]

events are indexed with whether or not they contains_url so this'll be a Synapse bug :(

[t3chguy]

https://github.com/matrix-org/synapse/blob/752b7b32ed1c33651c0c64fbbb4289c3b62ac89b/synapse/storage/events.py#L1119-L1122

it'll also need some migration magic to fix this for all existing events in db

[t3chguy]

Although according to the above code null shouldn't be true for isinstance(event.content["url"], basestring)

[t3chguy]

This seems fine, so maybe its a fixed Synapse bug:

[t3chguy]

weird, even though its right in the db and the filter seems fine the event is in my FilePanel

[t3chguy]

ah turns out it is a Synapse bug where the is_url "formula" is inconsistent between files

[t3chguy]

though as per the spec:

it won't exclude non-truthy but instead non-string

[t3chguy]

This is actually a weird combination of a Synapse bug and a js-sdk one.
So if the event was paginated in then the js-sdk bug would hit and otherwise the Synapse bug would hit.

[t3chguy]

though technically the matrix spec here could be understood to mean that "url": null should trip this Filter,
Synapse in 2/3 places checked whether it was a string, Dendrite does not. So its a 50/50 right now. I might write a proposal to improve contains_url to checking for a truthy string to get around this

[kittykat]

@turt2live What would it take to resolve this issue? To do the checks in Dendrite?

[turt2live]

I don't think this is a dendrite issue. We should either filter it out locally, or declare it a synapse bug and move it there.