grace period disconnect should be per-client

lib/Client.js

@@ -1,21 +1,60 @@
 import http from 'http';
 import Debug from 'debug';
 import pump from 'pump';
+import EventEmitter from 'events';
 
 // A client encapsulates req/res handling using an agent
 //
 // If an agent is destroyed, the request handling will error
 // The caller is responsible for handling a failed request
-class Client {
+class Client extends EventEmitter {
     constructor(options) {
-        this.agent = options.agent;
-        this.debug = Debug('lt:Client');
+        super();
+
+        const agent = this.agent = options.agent;
+        const id = this.id = options.id;
+
+        this.debug = Debug(`lt:Client[${this.id}]`);
+
+        // client is given a grace period in which they can connect before they are _removed_
+        this.graceTimeout = setTimeout(() => {
+            this.close();
+        }, 1000).unref();
+
+        agent.on('online', () => {
+            this.debug('client online %s', id);
+            clearTimeout(this.graceTimeout);
+        });
+
+        agent.on('offline', () => {
+            this.debug('client offline %s', id);
+
+            // if there was a previous timeout set, we don't want to double trigger
+            clearTimeout(this.graceTimeout);
+
+            // client is given a grace period in which they can re-connect before they are _removed_
+            this.graceTimeout = setTimeout(() => {
+                this.close();
+            }, 1000).unref();
+        });
+
+        // TODO(roman): an agent error removes the client, the user needs to re-connect?
+        // how does a user realize they need to re-connect vs some random client being assigned same port?
+        agent.once('error', (err) => {
+            this.close();
+        });
     }
 
     stats() {
         return this.agent.stats();
     }
 
+    close() {
+        clearTimeout(this.graceTimeout);
+        this.agent.destroy();
+        this.emit('close');
+    }
+
     handleRequest(req, res) {
         this.debug('> %s', req.url);
         const opt = {