plugin config `routePrefix` breaks the page

[blue86321]

Prerequisites

• [X] I have written a descriptive issue title
• [X] I have searched existing issues to ensure the bug has not already been reported

Fastify version

4.28.1

Plugin version

4.0.1

Node.js version

20.x

Operating system

macOS

Operating system version (i.e. 20.04, 11.3, 10)

14.5

Description

When we config the routePrefix parameter like below

import { fastifySwaggerUi } from "@fastify/swagger-ui";
fastify.register(fastifySwaggerUi, { routePrefix: "/api/docs" })

• It breaks the documentation page as the css/js resource double the api prefix.

• The resource can be visited by manually twisting the url

• Removing the routePrefix, the documentation can be rendered correctly

Link to code that reproduces the bug

No response

Expected Behavior

The documentation page should be rendered correctly even with routePrefix config