Introduce dynamic alphanumeric strings support in HTTP requests (#227)

Now `$DYNAMIC_ALPHANUMERIC_STRING` placeholders in the request URL or body will be substituted with actual random alphanumeric strings. The length for these strings can be configured using the `DYNAMIC_STRING_LENGTH_DEFAULT` environment variable, which defaults to `10`.

Discussion: upptime/upptime#857

src/helpers/constants.ts

@@ -10,3 +10,6 @@ export const DEFAULT_RUNNER = "ubuntu-latest";
 export const DYNAMIC_RANDOM_NUMBER = "$DYNAMIC_RANDOM_NUMBER";
 export const RANDOM_MIN_DEFAULT = "0";
 export const RANDOM_MAX_DEFAULT = "1000000";
+
+export const DYNAMIC_ALPHANUMERIC_STRING = "$DYNAMIC_ALPHANUMERIC_STRING";
+export const DYNAMIC_STRING_LENGTH_DEFAULT = "10";

src/helpers/environment.ts

@@ -1,16 +1,27 @@
-import {RANDOM_MAX_DEFAULT, RANDOM_MIN_DEFAULT, DYNAMIC_RANDOM_NUMBER} from "./constants";
+import {
+  RANDOM_MAX_DEFAULT,
+  RANDOM_MIN_DEFAULT,
+  DYNAMIC_RANDOM_NUMBER,
+  DYNAMIC_ALPHANUMERIC_STRING,
+  DYNAMIC_STRING_LENGTH_DEFAULT
+} from "./constants";
 
 export const replaceEnvironmentVariables = (str: string) => {
   Object.keys(process.env).forEach((key) => {
     str = str.replace(`$${key}`, process.env[key] || `$${key}`);
   });
+
   const SECRETS_CONTEXT = process.env.SECRETS_CONTEXT || "{}";
   const allSecrets: Record<string, string> = JSON.parse(SECRETS_CONTEXT);
   const secrets: Record<string, any> = { ...JSON.parse(JSON.stringify(process.env)), allSecrets };
   Object.keys(secrets).forEach((key) => {
     str = str.replace(`$${key}`, secrets[key] || `$${key}`);
   });
-  return substituteRandomNumbers(str);
+
+  str = substituteRandomNumbers(str);
+  str = substituteDynamicAlphanumericString(str);
+
+  return str;
 };
 
 const substituteRandomNumbers = (str: string) => {
@@ -22,6 +33,27 @@ const substituteRandomNumbers = (str: string) => {
   return str;
 }
 
+const substituteDynamicAlphanumericString = (str: string) => {
+  if (str.includes(DYNAMIC_ALPHANUMERIC_STRING)) {
+    const length = parseInt(process.env.DYNAMIC_STRING_LENGTH || DYNAMIC_STRING_LENGTH_DEFAULT);
+    str = str.replaceAll(DYNAMIC_ALPHANUMERIC_STRING, () => getRandomAlphanumericString(length));
+  }
+  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;
+
+
+/** Return a random alphanumeric string of given length */
+const getRandomAlphanumericString = (length: number) => {
+  const charset = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
+  let result = "";
+  for (let i = 0; i < length; i++) {
+    const randomIndex = Math.floor(Math.random() * charset.length);
+    result += charset[randomIndex];
+  }
+  return result;
+};