[bug] Following Owncast instances in Private mode does not work

[fl4nn]

Describe the bug with a clear and concise description of what the bug is.

Owncast allows to put insances into Private mode, which means followers need to get approved.

When following such an instance from GtS, as soon as the request gets confirmed GtS logs an error and the Follow remains in "Pending approval" state while Owncast shows the Follow as accepted.

What's your GoToSocial Version?

0.17.3

GoToSocial Arch

amd64

What happened?

As soon as a Follow Request gets approved by the Owncast instance GtS errors out with this message:

Jan 18 21:09:12 gotosocial[120419]: func=server.init.func1.Logger.13.1 level=ERROR stacktrace="()\n\truntime/panic.go:261\nruntime.sigpanic()\n\truntime/signal_unix.go:881\nfederation.(*Federator).PostInboxRequestBodyHook()\n\tgithub.com/superseriousbusiness/gotosocial/internal/federation/federatingprotocol.go:121\npub.(*SideEffectActor).PostInboxRequestBodyHook()\n\tgithub.com/superseriousbusiness/[email protected]/pub/side_effect_actor.go:76\nfederation.(*federatingActor).PostInboxScheme()\n\tgithub.com/superseriousbusiness/gotosocial/internal/federation/federatingactor.go:125\nfederation.(*federatingActor).PostInbox()\n\tgithub.com/superseriousbusiness/gotosocial/internal/federation/federatingactor.go:242\nfedi.(*Processor).InboxPost()\n\tgithub.com/superseriousbusiness/gotosocial/internal/processing/fedi/collections.go:47\nusers.(*Module).InboxPOSTHandler()\n\tgithub.com/superseriousbusiness/gotosocial/internal/api/activitypub/users/inboxpost.go:34\n()\n\tgithub.com/gin-gonic/[email protected]/context.go:185\n" requestID=06mggywm04001snt0800 msg="recovered panic: runtime error: invalid memory address or nil pointer dereference"
Jan 18 21:09:12 gotosocial[120419]: func=server.init.func1.Logger.13.1 level=INFO latency="1.225734ms" userAgent="Owncast v0.2.1-dev (20250118); https://owncast.online" method=POST statusCode=200 path=/users/flann/inbox clientIP=2a03:3b40:fe:23c::1 pubKeyID=https://streaming.squirrel.rocks/federation/user/flann#main-key errors="Error #01: recovered panic: runtime error: invalid memory address or nil pointer dereference\n" requestID=06mggywm04001snt0800 msg="OK: wrote 23B"

What you expected to happen?

The accepted follow request gets processed correctly.

How to reproduce it?

Try to follow a private mode Owncast instance from GtS.

Anything else we need to know?

You can try my instance for testing purposes, feel free to ping me on Matrix to coordinate in order to grab logs for example.

[fl4nn]

This might actually be a problem on the Owncast side, I see weird behaviour when trying to follow from a Mastodon instance as well.

[tsmethurst]

Ooh interesting, thanks for opening :) Regardless of what owncast is doing, we shouldn't be panicking there.