From 35e09160402bc5484359687562311f9eb02626af Mon Sep 17 00:00:00 2001
From: Oliver Sand <oliver.sand@sda-se.com>
Date: Mon, 10 May 2021 17:45:19 +0200
Subject: [PATCH] Handle URLs with a `#hash` correctly when rewriting link URLs

Signed-off-by: Oliver Sand <oliver.sand@sda-se.com>
---
 .changeset/techdocs-lemon-cooks-drum.md           |  5 +++++
 .../reader/transformers/rewriteDocLinks.test.ts   | 15 +++++++++++++++
 .../src/reader/transformers/rewriteDocLinks.ts    | 15 ++++++++++++---
 3 files changed, 32 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/techdocs-lemon-cooks-drum.md

diff --git a/.changeset/techdocs-lemon-cooks-drum.md b/.changeset/techdocs-lemon-cooks-drum.md
new file mode 100644
index 0000000000..d8f2954c2a
--- /dev/null
+++ b/.changeset/techdocs-lemon-cooks-drum.md
@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-techdocs': patch
+---
+
+Handle URLs with a `#hash` correctly when rewriting link URLs.
diff --git a/plugins/techdocs/src/reader/transformers/rewriteDocLinks.test.ts b/plugins/techdocs/src/reader/transformers/rewriteDocLinks.test.ts
index 06da8a447c..ca85c64fbe 100644
--- a/plugins/techdocs/src/reader/transformers/rewriteDocLinks.test.ts
+++ b/plugins/techdocs/src/reader/transformers/rewriteDocLinks.test.ts
@@ -16,6 +16,7 @@
 
 import { createTestShadowDom, getSample } from '../../test-utils';
 import { rewriteDocLinks } from '../transformers';
+import { normalizeUrl } from './rewriteDocLinks';
 
 describe('rewriteDocLinks', () => {
   it('should not do anything', () => {
@@ -56,3 +57,17 @@ describe('rewriteDocLinks', () => {
     ]);
   });
 });
+
+describe('normalizeUrl', () => {
+  it.each([
+    ['http://example.org', 'http://example.org/'],
+    ['http://example.org/', 'http://example.org/'],
+    ['http://example.org/folder', 'http://example.org/folder/'],
+    ['http://example.org/folder/', 'http://example.org/folder/'],
+    ['http://example.org/folder#intro', 'http://example.org/folder/#intro'],
+    ['http://example.org/folder/#intro', 'http://example.org/folder/#intro'],
+    ['http://example.org/folder#', 'http://example.org/folder/#'],
+  ])('should handle %s', (url, expected) => {
+    expect(normalizeUrl(url)).toEqual(expected);
+  });
+});
diff --git a/plugins/techdocs/src/reader/transformers/rewriteDocLinks.ts b/plugins/techdocs/src/reader/transformers/rewriteDocLinks.ts
index 7b0c23c3e3..54e5537347 100644
--- a/plugins/techdocs/src/reader/transformers/rewriteDocLinks.ts
+++ b/plugins/techdocs/src/reader/transformers/rewriteDocLinks.ts
@@ -31,9 +31,7 @@ export const rewriteDocLinks = (): Transformer => {
             if (elemAttribute.match(/^https?:\/\//i)) {
               elem.setAttribute('target', '_blank');
             }
-            const normalizedWindowLocation = window.location.href.endsWith('/')
-              ? window.location.href
-              : `${window.location.href}/`;
+            const normalizedWindowLocation = normalizeUrl(window.location.href);
 
             elem.setAttribute(
               attributeName,
@@ -48,3 +46,14 @@ export const rewriteDocLinks = (): Transformer => {
     return dom;
   };
 };
+
+/** Make sure that the input url always ends with a '/' */
+export function normalizeUrl(input: string): string {
+  const url = new URL(input);
+
+  if (!url.pathname.endsWith('/')) {
+    url.pathname += '/';
+  }
+
+  return url.toString();
+}