✨ Introduce dynamic random numbers support in HTTP requests (#226)

Now it is possible to inject randomized numbers into HTTP requests. Specifically, the `$DYNAMIC_RANDOM_NUMBER` placeholders in the request URL or body will be substituted with actual random values. The range for these numbers can be configured using the `RANDOM_MIN` and `RANDOM_MAX` environment variables, which default to `0` and `1000000`, respectively.

Discussion: upptime/upptime#857

src/helpers/constants.ts

@@ -6,3 +6,7 @@ export const UPDATE_TEMPLATE_CI_SCHEDULE = "0 0 * * *";
 export const UPDATES_CI_SCHEDULE = "0 3 * * *";
 export const UPTIME_CI_SCHEDULE = "*/5 * * * *";
 export const DEFAULT_RUNNER = "ubuntu-latest";
+
+export const DYNAMIC_RANDOM_NUMBER = "$DYNAMIC_RANDOM_NUMBER";
+export const RANDOM_MIN_DEFAULT = "0";
+export const RANDOM_MAX_DEFAULT = "1000000";

src/helpers/environment.ts

@@ -1,3 +1,5 @@
+import {RANDOM_MAX_DEFAULT, RANDOM_MIN_DEFAULT, DYNAMIC_RANDOM_NUMBER} from "./constants";
+
 export const replaceEnvironmentVariables = (str: string) => {
   Object.keys(process.env).forEach((key) => {
     str = str.replace(`$${key}`, process.env[key] || `$${key}`);
@@ -8,5 +10,18 @@ export const replaceEnvironmentVariables = (str: string) => {
   Object.keys(secrets).forEach((key) => {
     str = str.replace(`$${key}`, secrets[key] || `$${key}`);
   });
-  return str;
+  return substituteRandomNumbers(str);
 };
+
+const substituteRandomNumbers = (str: string) => {
+  if (str.includes(DYNAMIC_RANDOM_NUMBER)) {
+    const min = parseInt(process.env.RANDOM_MIN || RANDOM_MIN_DEFAULT);
+    const max = parseInt(process.env.RANDOM_MAX || RANDOM_MAX_DEFAULT);
+    str = str.replaceAll(DYNAMIC_RANDOM_NUMBER, () => getRandomNumber(min, max).toString());
+  }
+  return str;
+}
+
+/** Return a random integer N such that min <= N <= max */
+const getRandomNumber = (min: number, max: number) =>
+  Math.floor(Math.random() * (max - min + 1)) + min;

src/update.ts

@@ -186,7 +186,7 @@ export const update = async (shouldCommit = false) => {
             const ws = new WebSocket(replaceEnvironmentVariables(site.url));
             ws.on("open", function open() {
               if (site.body) {
-                ws.send(site.body);
+                ws.send(replaceEnvironmentVariables(site.body));
               } else {
                 ws.send("");
               }