*Add heartbeat support to protocol

messages.proto

@@ -7,6 +7,7 @@ enum Type {
     DISCONNECTED = 4;
     ADD_ITEM = 5;
     REMOVE_ITEM = 6;
+    HEARTBEAT = 7;
 }
 
 message Message {

src/index.ts

@@ -56,7 +56,7 @@ export default class DHTCache extends EventEmitter {
     this.flood.on("message", (message, id) => this.onGetBroadcast(message, id));
 
     this.swarm.on("connection", (peer: any) =>
-      this.flood.send(peer, b4a.from("hello"), 0)
+      this.send(peer, b4a.from("hello"))
     );
 
     [...this.swarm.peers.values()]
@@ -69,6 +69,8 @@ export default class DHTCache extends EventEmitter {
       });
 
     this._ensurePeer(this.id);
+    setInterval(() => this._heartbeatCheck(), 5 * 1000);
+    setInterval(() => this._emitHeartbeat(), 60 * 1000);
   }
 
   private _cache: Set<string>;
@@ -163,8 +165,8 @@ export default class DHTCache extends EventEmitter {
     this.flood.broadcast(message, ttl);
   }
 
-  public send(message: any) {
-    this.flood.send(message, 0);
+  public send(peer: any, message: any) {
+    this.flood.send(peer, message, 0);
   }
 
   protected addPeerHandler(peer: any) {
@@ -186,6 +188,8 @@ export default class DHTCache extends EventEmitter {
       id,
     });
 
+    this._emitHeartbeat(peer);
+
     if (this.bootstrapped) {
       return;
     }
@@ -278,6 +282,15 @@ export default class DHTCache extends EventEmitter {
     } else if (type === Type.BOOTSTRAP_RESPONSE) {
       const { bootstrap } = decoded;
       this._bootstrapFrom(bootstrap);
+    } else if (type === Type.HEARTBEAT) {
+      let { id: toId, signature, data: bufData } = decoded;
+
+      toId = b4a.from(toId as Uint8Array);
+
+      if (signature && crypto.verify(bufData, signature, id)) {
+        this._addEntityConnection(id, toId as Buffer);
+        this._setEntity(toId as Buffer, { heartbeat: Date.now() });
+      }
     }
   }
 
@@ -447,4 +460,49 @@ export default class DHTCache extends EventEmitter {
       }
     })();
   }
+
+  private _heartbeatCheck() {
+    for (const peer of this.connectedTo) {
+      const pubkey = b4a.from(peer, "hex");
+      const heartbeat = this.graph.node.get(peer)?.heartbeat;
+
+      const conn = this.swarm._allConnections.get(pubkey);
+      if (!conn) {
+        this.onRemovePeer({ remotePublicKey: pubkey });
+        continue;
+      }
+
+      if (heartbeat > 0 && Date.now() - heartbeat > 60 * 1000) {
+        conn.end();
+      }
+    }
+  }
+
+  private _emitHeartbeat(peer?: any) {
+    let peers = [...this.connectedTo];
+
+    if (peer) {
+      // @ts-ignore
+      peers = [b4a.from(peer.remotePublicKey).toString("hex")];
+    }
+
+    for (const peer of peers) {
+      const pubkey = b4a.from(peer, "hex");
+      const conn = this.swarm._allConnections.get(pubkey);
+      if (!conn) {
+        continue;
+      }
+      const data = b4a.from(Uint8Array.from([1]));
+
+      this.send(
+        conn,
+        this._compileMessage({
+          type: Type.HEARTBEAT,
+          id: this.id,
+          data,
+          signature: crypto.sign(data, this.swarm.keyPair.secretKey),
+        })
+      );
+    }
+  }
 }

src/messages.ts

@@ -78,7 +78,11 @@ export enum Type {
     /**
      * @generated from protobuf enum value: REMOVE_ITEM = 6;
      */
-    REMOVE_ITEM = 6
+    REMOVE_ITEM = 6,
+    /**
+     * @generated from protobuf enum value: HEARTBEAT = 7;
+     */
+    HEARTBEAT = 7
 }
 // @generated message type with reflection information, may provide speed optimized methods
 class Message$Type extends MessageType<Message> {