From d62d2948a166abb31a543cfdd967eb14b68d4ed9 Mon Sep 17 00:00:00 2001
From: Richard Gibson <richard.gibson@gmail.com>
Date: Tue, 6 Oct 2020 16:17:35 -0400
Subject: [PATCH] fix(isFQDN): allow all-underscore labels with
 allow_underscores (#1253)

---
 src/lib/isFQDN.js  | 8 ++++----
 test/validators.js | 1 +
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/lib/isFQDN.js b/src/lib/isFQDN.js
index cb1b724f7..2a439dbbe 100644
--- a/src/lib/isFQDN.js
+++ b/src/lib/isFQDN.js
@@ -33,10 +33,7 @@ export default function isFQDN(str, options) {
   }
   for (let part, i = 0; i < parts.length; i++) {
     part = parts[i];
-    if (options.allow_underscores) {
-      part = part.replace(/_/g, '');
-    }
-    if (!/^[a-z\u00a1-\uffff0-9-]+$/i.test(part)) {
+    if (!/^[a-z_\u00a1-\uffff0-9-]+$/i.test(part)) {
       return false;
     }
     // disallow full-width chars
@@ -46,6 +43,9 @@ export default function isFQDN(str, options) {
     if (part[0] === '-' || part[part.length - 1] === '-') {
       return false;
     }
+    if (!options.allow_underscores && /_/.test(part)) {
+      return false;
+    }
   }
   return true;
 }
diff --git a/test/validators.js b/test/validators.js
index 853e1068c..93ab9a612 100644
--- a/test/validators.js
+++ b/test/validators.js
@@ -467,6 +467,7 @@ describe('Validators', () => {
         'http://foo_bar.com',
         'http://pr.example_com.294.example.com/',
         'http://foo__bar.com',
+        'http://_.example.com',
       ],
       invalid: [],
     });