Fallthrough proxy with Swagger-UI

[abjugard]

I am using the latest version of the following dependencies:

<parent>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-parent</artifactId>
	<version>3.4.3</version>
	<relativePath/>
</parent>
[...]
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-starter-gateway</artifactId>
</dependency>
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
	<groupId>org.springdoc</groupId>
	<artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
	<version>2.8.5</version>
</dependency>

And the following configuration in application.yml

spring:
  cloud:
    gateway:
      routes:
        - id: legacy_proxy
          uri: http://localhost:8000
          predicates:
            - Path=/**
          filters:
            - RewritePath=/(?<segment>.*), /legacy-app-1/${segment}
          order: 1000

I have a controller:

@RestController
@RequestMapping("/example")
public class ExampleController {
    @GetMapping()
    public String getString() {
        return "test";
    }
}

When this application is running I can make requests to /example which hits the controller endpoint, and I can make requests to /some/other/path which proxies the request correctly to http://localhost:8000/legacy-app-1/some/other/path, but in this configuration I can not access /swagger-ui/index.html. Curiously not all Swagger endpoints are affected, I can access /v3/api-docs.

If I change to Path=/legacy/** then Swagger UI works correctly.

Any idea why the /swagger-ui/index.html path is affected like this?

[spencergibb]

I have no idea how springdoc-openapi-starter-webmvc-ui registers itself. It looks like the spring webmvc.fn has higher precedence than swagger and with a catch-all route (/**), this is inevitable.

Besides not having a catch-all route, you would have to change the order of either the swagger ui (no idea since we don't maintain or use it), or the RouterFunctionMapping and I don't know of an easy way to do that.

The ordering is documented here https://docs.spring.io/spring-boot/3.4-SNAPSHOT/reference/web/servlet.html#web.servlet.spring-mvc.welcome-page

[spring-cloud-issues]

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[abjugard]

It's not possible to just exclude /swagger-ui/index.html from being caught by spring.cloud.gateway?