File:private-messaging-brainstorming-flow.png

Source:

title: Private Messaging
participant alice
participant bob
participant pm.bob
participant pm.alice

alice->bob: 1. hey I have message 123xyz for you.\nwhere should I send it?
bob-->alice: send it to pm.bob plz
alice->pm.bob: 2. I have message 123xyz for bob!
pm.bob-->alice: okay, I will give you a token to send it.\nwhat server handles your messages?
alice-->pm.bob: you can talk to pm.alice
pm.bob->pm.alice: 3. Hey there, I heard alice wants to\nsend message 123xyz to bob.\nIs this true?
pm.alice-->pm.bob: yes!
pm.bob->pm.alice: 4. You can deliver message 123xyz to pm.bob\nif you include token xxxxxxxxxxx
pm.alice->bob: 5. hey bob, can pm.bob\nreceive messages for you?
bob-->pm.alice: yeah!
pm.alice->pm.bob: 6. Here is message 123xyz\nand token xxxxxxxxxxxx!

https://bramp.github.io/js-sequence-diagrams/