Show SaltyRTC connection status

[rugk]

User story: As a Threema Web user I want to see how my Threema App and Web client are connected.

This includes:

1. Either using a direct connection (LAN) or routing over the server (TURN).
2. Whether my mobile data is used (fees or so…) or whether my LAN/WLAN is used.

It would be good to combine these two similar (but not exactly the same) pieces of information into one status symbol or so…
Number 1 is what security geeks or people experiencing reconnections/performance issues would like to see and 2 is what people in special situations (limited data plan, …) or people interested in this generally like to see.

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Appended from #195:

User story: I, as a (heavy) Threema Web user, want to see what route the Threema Web connection uses (mobile data/WiFi, uses TURN?) in order to evaluate problems/slowness/security/high costs…

This helps to:

• avoid high costs when users have limited mobile data plans
• evaluate the security (TURN is probably not what I want to use)
• find reasons for slowness ("ah, mobile data and TURN, …") or disconnections ("oh, just switched to TURN")
• potentially debug things (when you can also see what TURN mode is used – in a submenu, of course)

Potential solution

Display an icon in the "Threema Web" panel in the Threema app showing a basic connection status. And maybe add a context item ("Connection details" or the like) where advanced users can see a more detailed status. (maybe even with connection duration or so)

[lgrahl]

@dbrgn @sillych You should be able to retrieve some of the necessary information from https://w3c.github.io/webrtc-stats/#dom-rtcicecandidatestats

I disagree with evaluation of security though. There is nothing wrong with TURN-UDP without any further transport encryption in this use case. TURN-TLS data gets unwrapped at some point, so only if both peers use TURN-TLS over the exact same TURN server which also needs to be fully trusted there's a tiny bit of a security improvement (although even that's questionable).

[dbrgn]

I disagree with evaluation of security though. There is nothing wrong with TURN-UDP without any further transport encryption in this use case.

I agree :)

[rugk]

Ah, yes. The only security difference I meant is: "using STUN servers as relay" vs "direct p2p"…
What turn mode does not matter – at least for security reasons…

[lgrahl]

Closing in favour of #829