Presence

A companion to events is the Presence feature. Presence allows you track "Whos online". Once your view is tracked by a presence, you will remain in the presence list until the view closes.

#[derive(Deserialize, Serialize)]
struct MyPresenceMetaData {
    something: u32
}

let meta = MyPresenceMetaData{something: 1};
presence_track("my-presence-topic", "my-user-key", &meta)?;

In order to subscribe to changes of a presence, you need to use presence_subscribe this is best done in the start method. Everytime someone joins or leaves, presnce_event will be called.

impl View for ViewHandler {
  fn start(is_connected: bool, _params: HashMap<String, String>) -> Result<Self> {
    presence_subscribe("my-presence-topic")?;
    // ..
  }

  // ..

  fn presence_event(&mut self, topic: &str, diff: PresenceDiffRaw) -> Result<()> {
      match topic {
        "my-presence-topic" => {
          let ev: PresenceDiff<MyPresenceMetaData> = presence_deserialize_diff(diff)?;
        
          // Do something

          Ok(())
        }
        _ => Ok(())
      }
  }
}

Putting it all together#

Below the app will keep a list of who is online. As other tabs open the environment, the list of online users will automatically update.

Open in multiple tabs to see users enter and leave.

Quick view for details and to fork.

extern crate assemble_app;
extern crate serde;
extern crate maud;
use assemble_app::*;
use maud::html;
use serde::{Deserialize, Serialize};
use std::collections::{HashMap, HashSet};

assemble_init! {{
    register_root_view!(ViewHandler);
}}


#[derive(Deserialize, Serialize)]
struct MyPresenceMetaData {
    something: String
}

#[derive(Deserialize, Serialize)]
struct ViewHandler {
    your_id: String,
    connected_users: HashSet<String>
}

impl View for ViewHandler {
  fn start(is_connected: bool, _params: HashMap<String, String>) -> Result<Self> {
    let meta = MyPresenceMetaData{something: random_string(10)?};
    presence_track("my-presence-topic", &format!("user-{}", meta.something), &meta)?;
    presence_subscribe("my-presence-topic")?;
    let initial_users = presence_list::<MyPresenceMetaData>("my-presence-topic")?;
    let mut hs = HashSet::new();
    
    for (k, _) in initial_users {
        hs.insert(k);
    }
    
    Ok(ViewHandler {your_id: meta.something, connected_users: hs})
  }

  fn render(&self) -> Result<Html> {
    let markup = html! {
        div class="bg-indigo-700" {
          div class="mx-auto text-center py-16 px-8" {
            h2 class="mt-4 text-3xl font-extrabold text-white" {
              "You are: " (self.your_id)
            }
            h2 class="mt-4 text-3xl font-extrabold text-white" {
              "Connected users"
            }
            @for (user) in &self.connected_users {
              p class="mt-4 text-lg leading-6 text-indigo-200" {
                (user)
              }
            }
          }

        }
    };
    Ok(markup.into_string())
  }

  fn presence_event(&mut self, topic: &str, diff: PresenceDiffRaw) -> Result<()> {
      match topic {
        "my-presence-topic" => {
          let ev: PresenceDiff<MyPresenceMetaData> = presence_deserialize_diff(diff)?;
        
          for (user, _meta) in ev.joins {
            self.connected_users.insert(user);
          }
          for (user, meta) in ev.leaves {
            self.connected_users.remove(&user);
          }

          Ok(())
        }
        _ => Ok(())
      }
  }
}