feat(common): add express http verb method name string literal type

1. Also ships with a user-defined typescript type-guard so that we can
ensure at runtime that the string literal value is indeed one of the
valid ExpressJS HTTP verb method names.
2. The primary use-case for this is checking at runtime the HTTP verb
name of OpenAPI specifications that are being loaded into the API.

[skip ci]

Signed-off-by: Peter Somogyvari <peter.somogyvari@accenture.com>

packages/cactus-common/src/main/typescript/http/express-http-verb-method-name.ts

@@ -0,0 +1,51 @@
+/**
+ * A collection of all the HTTP verb method names that Express.js supports.
+ * Directly taken from the Express.js type definitions file of the @types/express
+ * package.
+ */
+export const ALL_EXPRESS_HTTP_VERB_METHOD_NAMES = [
+  "all",
+  "get",
+  "post",
+  "put",
+  "delete",
+  "patch",
+  "options",
+  "head",
+] as const;
+
+/**
+ * A type that represents all the HTTP verb method names that Express.js supports.
+ */
+export type ExpressHttpVerbMethodName =
+  typeof ALL_EXPRESS_HTTP_VERB_METHOD_NAMES[number];
+
+/**
+ * Custom (user-defined) typescript type-guard that checks whether the given
+ * value is an Express.js HTTP verb method name or not.
+ * Useful for verifying at runtime if we can safely call a method on the Express.js
+ * application object where the method's name is the value of the given variable.
+ * 
+ * Example:
+ * 
+ * ```typescript
+ * import express from "express";
+ * import { isExpressHttpVerbMethodName } from "@hyperledger/cactus-core-api-server";
+ * const app = express();
+ * const methodName = "get";
+ * if (isExpressHttpVerbMethodName(methodName)) {
+ *  app[methodName]("/foo", (req, res) => {
+ *   res.send("Hello World!");
+ * });
+ * ```
+ *
+ * @param x Any value that may or may not be an Express.js HTTP verb method name.
+ * @returns Whether the given value is an Express.js HTTP verb method name.
+ */
+export function isExpressHttpVerbMethodName(
+  x: unknown,
+): x is ExpressHttpVerbMethodName {
+  return (
+    typeof x === "string" && ALL_EXPRESS_HTTP_VERB_METHOD_NAMES.includes(x as never)
+  );
+}

packages/cactus-common/src/main/typescript/public-api.ts

@@ -29,7 +29,19 @@ export {
 export { isRecord } from "./types/is-record";
 export { hasKey } from "./types/has-key";
 
-export { asError, coerceUnknownToError } from "./exception/coerce-unknown-to-error";
-export { createRuntimeErrorWithCause, newRex } from "./exception/create-runtime-error-with-cause";
+export {
+  asError,
+  coerceUnknownToError,
+} from "./exception/coerce-unknown-to-error";
+export {
+  createRuntimeErrorWithCause,
+  newRex,
+} from "./exception/create-runtime-error-with-cause";
 export { ErrorFromUnknownThrowable } from "./exception/error-from-unknown-throwable";
 export { ErrorFromSymbol } from "./exception/error-from-symbol";
+
+export {
+  ALL_EXPRESS_HTTP_VERB_METHOD_NAMES,
+  ExpressHttpVerbMethodName,
+  isExpressHttpVerbMethodName,
+} from "./http/express-http-verb-method-name";

packages/cactus-common/src/test/typescript/unit/http/express-http-verb-method-name.test.ts

@@ -0,0 +1,31 @@
+import {
+  ALL_EXPRESS_HTTP_VERB_METHOD_NAMES,
+  ExpressHttpVerbMethodName,
+  isExpressHttpVerbMethodName,
+} from "../../../../main/typescript/public-api";
+
+describe("isExpressHttpVerbMethodName", () => {
+  it("should return true for valid HTTP verb method names", () => {
+    ALL_EXPRESS_HTTP_VERB_METHOD_NAMES.forEach((methodName) => {
+      expect(isExpressHttpVerbMethodName(methodName)).toBe(true);
+    });
+  });
+
+  it("should return false for invalid values", () => {
+    const invalidValues = [
+      123, // Not a string
+      0, // Falsy Number
+      "invalid", // Not a valid HTTP verb method name
+      "gEt", // Case-sensitive
+      "", // Empty string
+      null, // Null value
+      undefined, // Undefined value
+      {}, // Object
+      [], // Array
+    ];
+
+    invalidValues.forEach((value) => {
+      expect(isExpressHttpVerbMethodName(value)).toBe(false);
+    });
+  });
+});