feat: add and remove subscriptions from client requests

A hashmap of active subscriptions is maintained for each client.  REQ
and CLOSE commands will modify the subscription list.

src/conn.rs

@@ -1,14 +1,21 @@
-//use std::collections::HashMap;
+use crate::close::Close;
+use crate::error::Result;
+use crate::subscription::Subscription;
+use log::*;
+use std::collections::HashMap;
 use uuid::Uuid;
 
+// subscription identifiers must be reasonably sized.
+const MAX_SUBSCRIPTION_ID_LEN: usize = 256;
+
 // state for a client connection
 pub struct ClientConn {
     _client_id: Uuid,
     // current set of subscriptions
-    //subscriptions: HashMap<String, Subscription>,
+    subscriptions: HashMap<String, Subscription>,
     // websocket
     //stream: WebSocketStream<TcpStream>,
-    _max_subs: usize,
+    max_subs: usize,
 }
 
 impl ClientConn {
@@ -16,7 +23,46 @@ impl ClientConn {
         let client_id = Uuid::new_v4();
         ClientConn {
             _client_id: client_id,
-            _max_subs: 128,
+            subscriptions: HashMap::new(),
+            max_subs: 128,
         }
     }
+
+    pub fn subscribe(&mut self, s: Subscription) -> Result<()> {
+        let k = s.get_id();
+        let sub_id_len = k.len();
+        if sub_id_len > MAX_SUBSCRIPTION_ID_LEN {
+            info!("Dropping subscription with huge ({}) length", sub_id_len);
+            return Ok(());
+        }
+        // check if an existing subscription exists, and replace if so
+        if self.subscriptions.contains_key(&k) {
+            self.subscriptions.remove(&k);
+            self.subscriptions.insert(k, s);
+            info!("Replaced existing subscription");
+            return Ok(());
+        }
+
+        // check if there is room for another subscription.
+        if self.subscriptions.len() >= self.max_subs {
+            info!("Client has reached the maximum number of unique subscriptions");
+            return Ok(());
+        }
+        // add subscription
+        self.subscriptions.insert(k, s);
+        info!(
+            "Registered new subscription, currently have {} active subs",
+            self.subscriptions.len()
+        );
+        return Ok(());
+    }
+
+    pub fn unsubscribe(&mut self, c: Close) {
+        // TODO: return notice if subscription did not exist.
+        self.subscriptions.remove(&c.get_id());
+        info!(
+            "Removed subscription, currently have {} active subs",
+            self.subscriptions.len()
+        );
+    }
 }