Add basic ping-pong websocket

src/constants.rs

@@ -1,3 +1,5 @@
+use std::time::Duration;
+
 /// Session key for OpenID login state
 pub const STATE_KEY: &str = "oidc-state";
 
@@ -6,3 +8,11 @@ pub const USER_SESSION_KEY: &str = "user";
 
 /// Token length
 pub const TOKEN_LEN: usize = 20;
+
+/// How often heartbeat pings are sent.
+///
+/// Should be half (or less) of the acceptable client timeout.
+pub const WS_HEARTBEAT_INTERVAL: Duration = Duration::from_secs(5);
+
+/// How long before lack of client response causes a timeout.
+pub const WS_CLIENT_TIMEOUT: Duration = Duration::from_secs(10);