From 2b11cd7481e5fc7550e6c098a948a6ab8cf85ef8 Mon Sep 17 00:00:00 2001
From: Cristian Klein <cristian.klein@elastisys.com>
Date: Mon, 17 Nov 2025 17:33:07 +0100
Subject: [PATCH 1/4] Fix: Error: Callback was already called

In certain odd cases, like a website returning a 302 and/or closing the
connection after a HEAD (I'm not 100% sure), linkCheck will call our
callback twice. `async` is not amused and will throw:

> Error: Callback was already called

A campaign of ad-hoc `console.log()`s suggest this is a bug in needle, a
library used by link-check.

Fixes #222 and #473
---
 index.js | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/index.js b/index.js
index 167e9d47..106ca212 100644
--- a/index.js
+++ b/index.js
@@ -199,7 +199,14 @@ module.exports = function markdownLinkCheck(markdown, opts, callback) {
             return;
         }
 
+        let numCalls = 0;
         linkCheck(link, opts, function (err, result) {
+            if (numCalls > 0) {
+                console.trace(`linkCheck called us back more than once for ${link}. This is likely due to a redirect (301, 302 or 303). Ignoring.`);
+                return;
+            }
+            numCalls += 1;
+
             if (opts.showProgressBar) {
                 bar.tick();
             }

From 9a288d62c2ab34e7d9953d24a90e6e5a53ea54d2 Mon Sep 17 00:00:00 2001
From: Cristian Klein <cristian.klein@elastisys.com>
Date: Tue, 18 Nov 2025 11:47:28 +0100
Subject: [PATCH 2/4] Add editorconfig

---
 .editorconfig | 7 +++++++
 1 file changed, 7 insertions(+)
 create mode 100644 .editorconfig

diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 00000000..3eda792a
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,7 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+indent_style = space
+indent_size = 4

From 599ffd887e05407c5789903251e709fea2e9a5e0 Mon Sep 17 00:00:00 2001
From: Cristian Klein <cristian.klein@elastisys.com>
Date: Tue, 18 Nov 2025 11:52:20 +0100
Subject: [PATCH 3/4] Add test case

---
 test/markdown-link-check.test.js | 19 +++++++++++++++++++
 test/sample.md                   |  1 +
 2 files changed, 20 insertions(+)

diff --git a/test/markdown-link-check.test.js b/test/markdown-link-check.test.js
index a2a72c11..10572bf0 100644
--- a/test/markdown-link-check.test.js
+++ b/test/markdown-link-check.test.js
@@ -53,6 +53,22 @@ describe('markdown-link-check', function () {
             res.json({foo:'bar'});
         });
 
+        app.use('/redirect-with-body-in-head', function (req, res) {
+            /* Don't judge me. I found at least one server on the
+             * Internet doing this and it triggered a bug. */
+            const body = 'Let me send you a body, although you only asked for a HEAD.';
+
+            const headers =
+                'HTTP/1.1 302 Found\r\n' +
+                'Connection: close\r\n' +
+                'Location: /foo/bar\r\n' +
+                `Content-Length: ${Buffer.byteLength(body)}\r\n` +
+                '\r\n';
+
+            res.socket.write(headers + body);
+            res.socket.destroy();
+        });
+
         app.get('/basic-auth', function (req, res) {
             if (req.headers["authorization"] === "Basic Zm9vOmJhcg==") {
                 res.sendStatus(200);
@@ -110,6 +126,9 @@ describe('markdown-link-check', function () {
             expect(results).to.be.an('array');
 
             const expected = [
+                // redirect-with-body-in-head
+                { statusCode: 200, status: 'alive' },
+
                 // redirect-loop
                 { statusCode:   0, status:  'dead' },
 
diff --git a/test/sample.md b/test/sample.md
index 830803fd..42f13e80 100644
--- a/test/sample.md
+++ b/test/sample.md
@@ -2,6 +2,7 @@
 
 This is a test file:
 
+* [redirect-with-body-in-head](%%BASE_URL%%/redirect-with-body-in-head) (alive)
 * [redirect-loop](%%BASE_URL%%/loop) (dead)
 * [valid](%%BASE_URL%%/foo/bar) (alive)
 * [invalid](%%BASE_URL%%/foo/dead) (dead)

From a2f372558f2bfee9f1379a374cb1a739d0e0f2f5 Mon Sep 17 00:00:00 2001
From: Cristian Klein <cristian.klein@elastisys.com>
Date: Tue, 18 Nov 2025 11:54:32 +0100
Subject: [PATCH 4/4] Clarify warning message

---
 index.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/index.js b/index.js
index 106ca212..032903fc 100644
--- a/index.js
+++ b/index.js
@@ -202,7 +202,7 @@ module.exports = function markdownLinkCheck(markdown, opts, callback) {
         let numCalls = 0;
         linkCheck(link, opts, function (err, result) {
             if (numCalls > 0) {
-                console.trace(`linkCheck called us back more than once for ${link}. This is likely due to a redirect (301, 302 or 303). Ignoring.`);
+                console.trace(`linkCheck called us back more than once for ${link}. This is likely due to a server answering HEAD with 302 and a body, against the HTTP spec. Ignoring.`);
                 return;
             }
             numCalls += 1;