Terminate the program when the maximum ping difference is exceeded

bin/smee.js

@@ -29,6 +29,15 @@ const { values: options } = parseArgs({
       type: "string",
       short: "t",
     },
+    healthcheck: {
+      type: "string",
+      short: "h",
+    },
+    maxPingDifference: {
+      type: "string",
+      short: "m",
+      default: "60",
+    },
     path: {
       type: "string",
       short: "P",
@@ -46,13 +55,16 @@ if (options.help) {
   console.log(`Usage: smee [options]
 
 Options:
-  -v, --version         Display the version number
-  -u, --url <url>       URL of the webhook proxy service. Default: https://smee.io/new
-  -t, --target <target> Full URL (including protocol and path) of the target service the events will forwarded to.
-                        Default: http://127.0.0.1:PORT/PATH
-  -p, --port <n>        Local HTTP server port. Default: 3000
-  -P, --path <path>     URL path to post proxied requests to. Default: "/"
-  -h, --help            Display this help message`);
+  -v, --version                       Display the version number
+  -u, --url <url>                     URL of the webhook proxy service. Default: https://smee.io/new
+  -t, --target <target>               Full URL (including protocol and path) of the target service the events will forwarded to.
+                                      Default: http://127.0.0.1:PORT/PATH
+  -h, --healthcheck <interval>        Perform health checks based on received pings at specified intervals (in seconds)
+  -m, --max-ping-difference <seconds> The maximum difference between the last ping and the current time (in seconds) before the client is considered unhealthy.
+                                      Default: 60
+  -p, --port <n>                      Local HTTP server port. Default: 3000
+  -P, --path <path>                   URL path to post proxied requests to. Default: "/"
+  -h, --help                          Display this help message`);
 } else if (options.version) {
   console.log(version);
 } else {
@@ -61,8 +73,15 @@ Options:
 
   async function setup() {
     const source = options.url ?? (await Client.createChannel());
+    const healthcheck = Number.parseInt(options.healthcheck, 10);
+    const maxPingDifference = Number.parseInt(options.maxPingDifference, 10);
 
-    const client = new Client({ source, target });
+    const client = new Client({
+      source,
+      target,
+      healthcheck,
+      maxPingDifference,
+    });
     client.start();
   }
 

index.ts

@@ -14,6 +14,8 @@ type Severity = "info" | "error";
 interface Options {
   source: string;
   target: string;
+  healthcheck: number;
+  maxPingDifference: number;
   logger?: Pick<Console, Severity>;
   fetch?: any;
 }
@@ -23,18 +25,26 @@ const proxyAgent = new EnvHttpProxyAgent();
 class Client {
   #source: string;
   #target: string;
+  healthcheck: number;
+  maxPingDifference: number;
+  #lastPing: number;
   #fetch: typeof undiciFetch;
   #logger: Pick<Console, Severity>;
   #events!: EventSource;
 
   constructor({
     source,
     target,
+    healthcheck,
+    maxPingDifference,
     logger = console,
     fetch = undiciFetch,
   }: Options) {
     this.#source = source;
     this.#target = target;
+    this.healthcheck = healthcheck;
+    this.maxPingDifference = maxPingDifference;
+    this.#lastPing = Date.now();
     this.#logger = logger!;
     this.#fetch = fetch;
 
@@ -99,6 +109,11 @@ class Client {
     this.#logger.info("Connected", this.#events.url);
   }
 
+  onping() {
+    this.#logger.info(`Received a ping on ${new Date().toISOString()}`);
+    this.#lastPing = Date.now();
+  }
+
   onerror(err: ErrorEvent) {
     this.#logger.error(err);
   }
@@ -125,6 +140,21 @@ class Client {
     events.addEventListener("open", this.onopen.bind(this));
     events.addEventListener("error", this.onerror.bind(this));
 
+    if (this.healthcheck) {
+      events.addEventListener("ping", this.onping.bind(this));
+
+      setInterval(() => {
+        const difference = (Date.now() - this.#lastPing) / 1000;
+
+        if (difference > this.maxPingDifference) {
+          this.#logger.error(
+            `Maximum ping difference exceeded. (Difference: ${difference.toFixed(4)}s, Maximum Allowed: ${this.maxPingDifference}s)`,
+          );
+          process.exit(1);
+        }
+      }, this.healthcheck * 1000);
+    }
+
     this.#logger.info(`Forwarding ${this.#source} to ${this.#target}`);
     this.#events = events;