From 34ec83b25ccacad5c523e6b0ad2e156d2107c6e6 Mon Sep 17 00:00:00 2001
From: Rob Wu <rob@robwu.nl>
Date: Mon, 22 Mar 2021 21:18:31 +0100
Subject: [PATCH] Show "400 Missing slash" when needed #238

---
 lib/cors-anywhere.js | 8 ++++++++
 test/test.js         | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/lib/cors-anywhere.js b/lib/cors-anywhere.js
index f064ddee..eb4f47c5 100644
--- a/lib/cors-anywhere.js
+++ b/lib/cors-anywhere.js
@@ -316,6 +316,14 @@ function getHandler(options, proxy) {
     }
 
     if (!location) {
+      // Special case http:/notenoughslashes, because new users of the library frequently make the
+      // mistake of putting this application behind a server/router that normalizes the URL.
+      // See https://github.com/Rob--W/cors-anywhere/issues/238#issuecomment-629638853
+      if (/^\/https?:\/[^/]/i.test(req.url)) {
+        res.writeHead(400, 'Missing slash', cors_headers);
+        res.end('The URL is invalid: two slashes are needed after the http(s):.');
+        return;
+      }
       // Invalid API call. Show how to correctly use the API
       showUsage(corsAnywhere.helpFile, cors_headers, res);
       return;
diff --git a/test/test.js b/test/test.js
index b08bd225..613978ce 100644
--- a/test/test.js
+++ b/test/test.js
@@ -141,7 +141,7 @@ describe('Basic functionality', function() {
     request(cors_anywhere)
       .get('/http:/notenoughslashes')
       .expect('Access-Control-Allow-Origin', '*')
-      .expect(200, helpText, done);
+      .expect(400, 'The URL is invalid: two slashes are needed after the http(s):.', done);
   });