From eeb3f801fddf70b213ffa01f4ecd11c51f4ad182 Mon Sep 17 00:00:00 2001
From: Patrik Oldsberg <poldsberg@gmail.com>
Date: Thu, 15 Jun 2023 13:49:35 +0200
Subject: [PATCH] backend-common: make HostDiscovery strip trailing slashes in
 backend.baseUrl

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
---
 .changeset/itchy-glasses-smoke.md              |  5 +++++
 .../src/discovery/HostDiscovery.test.ts        | 18 ++++++++++++++++++
 .../src/discovery/HostDiscovery.ts             |  4 +++-
 3 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/itchy-glasses-smoke.md

diff --git a/.changeset/itchy-glasses-smoke.md b/.changeset/itchy-glasses-smoke.md
new file mode 100644
index 0000000000..042909df37
--- /dev/null
+++ b/.changeset/itchy-glasses-smoke.md
@@ -0,0 +1,5 @@
+---
+'@backstage/backend-common': patch
+---
+
+`HostDiscovery` now strips trailing slashes in the `backend.baseUrl` config.
diff --git a/packages/backend-common/src/discovery/HostDiscovery.test.ts b/packages/backend-common/src/discovery/HostDiscovery.test.ts
index 577da3a679..4e6aff5853 100644
--- a/packages/backend-common/src/discovery/HostDiscovery.test.ts
+++ b/packages/backend-common/src/discovery/HostDiscovery.test.ts
@@ -36,6 +36,24 @@ describe('HostDiscovery', () => {
     );
   });
 
+  it('strips trailing slashes in config', async () => {
+    const discovery = HostDiscovery.fromConfig(
+      new ConfigReader({
+        backend: {
+          baseUrl: 'http://localhost:40//',
+          listen: { port: 80, host: 'localhost' },
+        },
+      }),
+    );
+
+    await expect(discovery.getBaseUrl('catalog')).resolves.toBe(
+      'http://localhost:80/api/catalog',
+    );
+    await expect(discovery.getExternalBaseUrl('catalog')).resolves.toBe(
+      'http://localhost:40/api/catalog',
+    );
+  });
+
   it('can configure the base path', async () => {
     const discovery = HostDiscovery.fromConfig(
       new ConfigReader({
diff --git a/packages/backend-common/src/discovery/HostDiscovery.ts b/packages/backend-common/src/discovery/HostDiscovery.ts
index 1c72445443..89b6404143 100644
--- a/packages/backend-common/src/discovery/HostDiscovery.ts
+++ b/packages/backend-common/src/discovery/HostDiscovery.ts
@@ -57,7 +57,9 @@ export class HostDiscovery implements PluginEndpointDiscovery {
    */
   static fromConfig(config: Config, options?: { basePath?: string }) {
     const basePath = options?.basePath ?? '/api';
-    const externalBaseUrl = config.getString('backend.baseUrl');
+    const externalBaseUrl = config
+      .getString('backend.baseUrl')
+      .replace(/\/+$/, '');
 
     const {
       listen: { host: listenHost = '::', port: listenPort },