Add error handling and address review comments

functions-runtime/samples/ts/prometheus.ts

@@ -1,13 +1,31 @@
-let text = Deno.env.get("DATA");
+const text = Deno.env.get("DATA")!;
 let data;
-if (text != "") {
-  data = JSON.parse(text);
+if (text && text != "") {
+  try {
+    data = JSON.parse(text);
+    if ( !data.metrics || !data.url || !data.expected_value) {
+      console.log("Missing mandatory arguments.");
+      printUsage()
+    }
+  } catch {
+    console.error("Error Parsing Json => ",text)
+    Deno.exit(1);
+  }
+} else {
+  console.log("Missing mandatory enviornment variable DATA.");
+  printUsage()
+}
+
+function printUsage(){
+  console.log("Expecting environment variable DATA in this format => DATA='{ \"url\":\"<PROMETHEUS_URL>\", \"metrics\": \"<PROMETHEUS_QUERY>\", \"expected_value\": \"<EXPECTED_VALUE>\" }\' ")
+  console.log("Example: export DATA='{ \"url\":\"http://localhost:9090\", \"metrics\": \"up{service=\\\"kubernetes\\\"}\", \"expected_value\": \"1\" }\' ")
+  Deno.exit(1);
 }
 
 function getPrometheusURL(url: string, metrics: string): string {
-  let dateTime = new Date().toISOString();
-  let hasPort = url.includes(":9090");
-  let hasProtocol = url.includes("http://");
+  const dateTime = new Date().toISOString();
+  const hasPort = url.includes(":9090");
+  const hasProtocol = url.includes("http://");
   let queryURL: string = url;
   if (!hasPort) {
     queryURL = queryURL + ":9090";
@@ -19,15 +37,15 @@ function getPrometheusURL(url: string, metrics: string): string {
   return queryURL + "/api/v1/query?query=" + metrics + "&time=" + dateTime;
 }
 
-let promtheusURL = getPrometheusURL(data.url, data.metrics);
+const promtheusURL = getPrometheusURL(data.url, data.metrics);
 console.log("Prometheus URL => " + promtheusURL);
 let value;
 try {
-  let jsonResponse = await fetch(promtheusURL);
-  let jsonData = await jsonResponse.json();
+  const jsonResponse = await fetch(promtheusURL);
+  const jsonData = await jsonResponse.json();
   value = jsonData.data.result[0].value[1];
 } catch (error) {
-  console.error("Could not fetch ");
+  console.error("Could not fetch data from Prometheus.\n", error);
   Deno.exit(1);
 }