Improve validation of username searches

Co-authored-by: Joris Z. van den Oever <jzvandenoever@users.noreply.github.com>

ts/test-electron/util/Username_test.ts

@@ -10,10 +10,10 @@ describe('Username', () => {
     const { getUsernameFromSearch } = Username;
 
     it('matches partial username searches without discriminator', () => {
-      assert.strictEqual(getUsernameFromSearch('u'), 'u.01');
-      assert.strictEqual(getUsernameFromSearch('us'), 'us.01');
       assert.strictEqual(getUsernameFromSearch('use'), 'use.01');
-      assert.strictEqual(getUsernameFromSearch('use.'), 'use.01');
+      assert.strictEqual(getUsernameFromSearch('user'), 'user.01');
+      assert.strictEqual(getUsernameFromSearch('usern'), 'usern.01');
+      assert.strictEqual(getUsernameFromSearch('usern.'), 'usern.01');
     });
 
     it('matches and strips leading @', () => {
@@ -30,6 +30,28 @@ describe('Username', () => {
     it('matches valid username searches', () => {
       assert.strictEqual(getUsernameFromSearch('username.12'), 'username.12');
       assert.strictEqual(getUsernameFromSearch('xyz.568'), 'xyz.568');
+      assert.strictEqual(getUsernameFromSearch('numbered9.34'), 'numbered9.34');
+      assert.strictEqual(getUsernameFromSearch('u12.34'), 'u12.34');
+      assert.strictEqual(
+        getUsernameFromSearch('with_underscore.56'),
+        'with_underscore.56'
+      );
+      assert.strictEqual(
+        getUsernameFromSearch('username_with_32_characters_1234.45'),
+        'username_with_32_characters_1234.45'
+      );
+    });
+
+    it('does not match when then username starts with a number', () => {
+      assert.isUndefined(getUsernameFromSearch('1user.12'));
+      assert.isUndefined(getUsernameFromSearch('9user_name.12'));
+    });
+
+    it('does not match usernames shorter than 3 characters or longer than 32', () => {
+      assert.isUndefined(getUsernameFromSearch('us.12'));
+      assert.isUndefined(
+        getUsernameFromSearch('username_with_33_characters_12345.67')
+      );
     });
 
     it('does not match something that looks like a phone number', () => {
@@ -51,8 +73,8 @@ describe('Username', () => {
 
     it('returns true if it ends with a discriminator', () => {
       assert.isTrue(probablyAUsername('someone.00'));
-      assert.isTrue(probablyAUsername('32423423.04'));
-      assert.isTrue(probablyAUsername('d.04'));
+      assert.isTrue(probablyAUsername('d2423423.04'));
+      assert.isTrue(probablyAUsername('e_f.04'));
     });
 
     it('returns false if just a discriminator', () => {
@@ -67,6 +89,16 @@ describe('Username', () => {
       assert.isFalse(probablyAUsername('john'));
     });
 
+    it('returns false for usernames starting with a number', () => {
+      assert.isFalse(probablyAUsername('1user.01'));
+      assert.isFalse(probablyAUsername('9name.99'));
+    });
+
+    it('returns false for usernames shorter than 3 characters or longer than 32', () => {
+      assert.isFalse(probablyAUsername('us.12'));
+      assert.isFalse(probablyAUsername('username_with_33_characters_12345.67'));
+    });
+
     it('returns false for something that looks like a phone number', () => {
       assert.isFalse(probablyAUsername('+'));
       assert.isFalse(probablyAUsername('2223'));

ts/util/Username.ts

@@ -14,7 +14,8 @@ export function getMinNickname(): number {
   return parseIntWithFallback(RemoteConfig.getValue('global.nicknames.min'), 3);
 }
 
-const USERNAME_CHARS = /^@?[a-zA-Z0-9]+(.\d+)?$/;
+// Usernames have a minimum length of 3 and maximum of 32
+const USERNAME_CHARS = /^@?[a-zA-Z_][a-zA-Z0-9_]{2,31}(.\d+)?$/;
 const ALL_DIGITS = /^\d+$/;
 
 export function getUsernameFromSearch(searchTerm: string): string | undefined {