Call

P2P videocalls via WebRTC for integration into Delta Chat clients.

How it works

Below is a sequence diagram of how Delta Chat works together with this app. If you see a block of text instead of a diagram, go here.

sequenceDiagram
    participant Alice as Alice's Delta Chat
    participant ATURN as Alice's TURN / STUN servers
    participant BTURN as Bob's TURN / STUN servers<br> (could be the same as Alice's)
    participant Bob as Bob's Delta Chat

    Note over Alice: Alice presses<br>"Start Call with Bob"
    Alice ->> ATURN: What's my public address?
    Alice ->> ATURN: Please relay my packets
    ATURN -->> Alice: Your address is<br>42.42.42.42:12345<br>(srflx candidate gathered)
    ATURN -->> Alice: I will relay your packets<br>(TURN (relay) candidate<br>gathered)
    Note over Alice: Wait for relay candidate<br>or for timeout
    Alice ->> Bob: (email) I want to start a call. My address is 42.42.42.42:12345,<br>or you can reach me at my TURN server.<br>(WebRTC offer)

    Note over Bob: Bob presses "Accept Call"
    Bob ->> BTURN: What's my public address?
    Bob ->> BTURN: Please relay my packets
    ATURN ->> Alice: BTW your other address is<br>42.42.42.43:54321
    BTURN -->> Bob: Your address is<br>43.43.43.43:55555<br>(srflx candidate gathered)
    BTURN -->> Bob: I will relay your packets<br>(TURN (relay) candidate<br>gathered)
    Note over Bob: Wait for relay candidate<br>or for timeout
    Bob ->> Alice: (email) Sure, let's have a call. My address is 43.43.43.43:55555,<br>or you can reach me at my TURN server.<br>(WebRTC answer)

    loop
        Alice <<-->> Bob: P2P video stream (if possible)
        Alice <<->> ATURN: relayed video stream<br>(if P2P not possible)
        ATURN <<->> BTURN: relayed video stream<br>(if P2P not possible)
        BTURN <<->> Bob: relayed video stream<br>(if P2P not possible)
    end

    BTURN ->> Bob: BTW your other address is<br>43.43.43.43:55556

    loop An additional WebRTC data channel can be established (via relay or P2P)<br>to promote more ICE candidates after the initial connection is established
        Alice ->> Bob: My other address is 42.42.42.43:54321
        Bob ->> Alice: My other address is 43.43.43.43:55556
    end

Loading

Integrating

To integrate into your Delta Chat client you need to provide a window.calls object with the following API:

• startCall: (offerPayload: string) => void (implementation must call dc_place_outgoing_call chatmail core API)
• acceptCall: (answerPayload: string) => void (implementation must call dc_accept_incoming_call chatmail core API)
• endCall: () => void (implementation must call dc_end_call chatmail core API)
• getIceServers: () => string | Promise<string> (returns a JSON string with array of ice server configurations as expected by https://developer.mozilla.org/en-US/docs/Web/API/RTCPeerConnection/setConfiguration)
• getAvatar: () => string (returning the chat's avatar image URL; can be a regular URL or a data-URL, ex. "data:image/png;base64,...")

Commands are given to the app via URL hash:

• #startCall: tells the app to generate an offer payload and call startCall(), this is how the app should be open when the user is starting an outgoing call.
• #offerIncomingCall=PAYLOAD: tells the app to show the "Incoming call. Answer?" screen. Then, if the user clicks "Answer", generate a WebRTC answer to the offer provided in PAYLOAD, and call window.calls.acceptCall(webrtcAnswer). If the user declined the call, the app will invoke window.calls.endCall.
• #acceptCall=PAYLOAD: same as #offerIncomingCall, but doesn't show the "Incoming call. Answer?" screen and instead automatically and immediately accepts the call.
• #onAnswer=PAYLOAD: notifies the app that the outgoing call was accepted and provides the answer payload

IMPORTANT: PAYLOAD must be base64 encoded (NOTE: you might still need to URL-encode the base64 string to be a valid URL hash) before passing it to the app in the URL hash.

In order to start the app in audio-only mode initially, provide noOutgoingVideoInitially in the query (search) string of the initial URL, e.g. /index.html?noOutgoingVideoInitially#startCall.

In order to completely disable incoming and outgoing video, provide disableVideoCompletely in the query string of the URL. See #31.

Contributing

Installing Dependencies

After cloning this repo, install dependencies:

pnpm i

Checking code format

pnpm check

Testing the app in the browser

To test your work in your browser while developing:

pnpm start

Open the simulated instances in 2 separate tabs (the "share" button on the instance in the simulator). Then add #startCall to the end of the URL of one instance.

On macOS on Safari, you may not be able to give access to the camera to two tabs simultaneously; in this case, try Firefox.

Building

To build the app for releasing:

pnpm build

To package the app with developer tools inside to debug in Delta Chat, set the NODE_ENV environment variable to "debug":

NODE_ENV=debug pnpm build

The resulting optimized .html file is saved in dist/ folder.

Releasing

To automatically build and create a new GitHub release with the .html file:

git tag -a v1.0.1
git push origin v1.0.1

Credits

Inspired by Serverless WebRTC but built from scratch and much simpler: no data channel, file transfer and only browsers are supported.

See blog posts explaining the idea here:

• WebRTC without a signaling server
• Serverless WebRTC, continued