Add DNS lookup tool and tests

tests/validateHostname.test.js

@@ -0,0 +1,115 @@
+// Import Node's built-in test tools.
+const test = require("node:test");
+const assert = require("node:assert/strict");
+
+// Import the function we want to test.
+const {
+  validateHostname,
+} = require("../src/middleware/validateHostname");
+
+test("accepts a normal hostname", () => {
+  assert.equal(validateHostname("example.com"), "example.com");
+});
+
+test("normalizes uppercase letters", () => {
+  assert.equal(validateHostname("EXAMPLE.COM"), "example.com");
+});
+
+test("trims surrounding spaces", () => {
+  assert.equal(validateHostname("  example.com  "), "example.com");
+});
+
+test("extracts the hostname from an HTTPS URL", () => {
+  assert.equal(
+    validateHostname("https://example.com/some/page"),
+    "example.com"
+  );
+});
+
+test("extracts the hostname from an HTTP URL", () => {
+  assert.equal(
+    validateHostname("http://sub.example.com/path"),
+    "sub.example.com"
+  );
+});
+
+test("removes a trailing period", () => {
+  assert.equal(validateHostname("example.com."), "example.com");
+});
+
+test("accepts subdomains", () => {
+  assert.equal(
+    validateHostname("api.tools.example.com"),
+    "api.tools.example.com"
+  );
+});
+
+test("rejects an empty hostname", () => {
+  assert.throws(
+    () => validateHostname(""),
+    /A hostname is required/
+  );
+});
+
+test("rejects whitespace-only input", () => {
+  assert.throws(
+    () => validateHostname("   "),
+    /A hostname is required/
+  );
+});
+
+test("rejects non-string input", () => {
+  assert.throws(
+    () => validateHostname(null),
+    /A hostname is required/
+  );
+});
+
+test("rejects malformed hostnames", () => {
+  assert.throws(
+    () => validateHostname("not a real hostname"),
+    /Enter a valid public hostname/
+  );
+});
+
+test("rejects hostnames beginning with a hyphen", () => {
+  assert.throws(
+    () => validateHostname("-example.com"),
+    /Enter a valid public hostname/
+  );
+});
+
+test("rejects hostnames ending with a hyphen", () => {
+  assert.throws(
+    () => validateHostname("example-.com"),
+    /Enter a valid public hostname/
+  );
+});
+
+test("rejects localhost", () => {
+  assert.throws(
+    () => validateHostname("localhost"),
+    /Enter a valid public hostname/
+  );
+});
+
+test("rejects localhost subdomains", () => {
+  assert.throws(
+    () => validateHostname("test.localhost"),
+    /Local hostnames are not allowed/
+  );
+});
+
+test("rejects .local hostnames", () => {
+  assert.throws(
+    () => validateHostname("printer.local"),
+    /Local hostnames are not allowed/
+  );
+});
+
+test("rejects an invalid URL", () => {
+  assert.throws(
+    () => validateHostname("https://"),
+    /Enter a valid hostname or website URL/
+  );
+});