Calling Swagger UI via different context paths fails

[hwanders]

Requesting the Swagger UI from two different public URLs having different context paths causes the second UI initialization to fail. The second UI call will have a wrong path written in swagger-initializer.js: configUrl is based on the path from the first request.

To Reproduce
Setup a reverse proxy (for example at localhost:80) in front of a backend service BS (for example at localhost:8080) which adds a prefix to all the backend service's URLs. So the backend service endpoints are available at http://localhost:80/service/** (reverse proxy with path prefix /service) and http://localhost:8080/** (backend service).
The backend service should be configured to provide a Swagger UI.

The following scenarios, each executed on a freshly restarted backend service, reproduce the problem:

• First reverse proxy - then backend service
  1. Call the UI via the reverse proxy (works fine)
  2. Call the UI via the service without the reverse proxy (fails)
• First backend service - then reverse proxy
  1. Call the UI via the service without the reverse proxy (works fine)
  2. Call the UI via the reverse proxy (fails)

I'm using springdoc-openapi-starter-webmvc-ui version 2.6.0.

Reason
SwaggerIndexPageTransformer initializes the singleton SwaggerUiConfigParameters by calling swaggerWelcomeCommon.buildFromCurrentContextPath(request) if the configuration's configUrl is null. The configUrl (and perhaps some other properties) is derived from the current request's context path.

Subsequent requests, even if they have a different context path, will use the initialized configuration without re-evaluating it.
The browser will then try to load the configuration from an URL which is not available.

Expected behavior
The configUrl should be re-evaluated (if necessary) to generate a correct swagger-initializer.js.

Ideas
Perhaps the SwaggerUiConfigParameters shouldn't be modified at all by the transformer.
This is to avoid concurrency problems caused by a hypothetical re-evaluation overwriting the configuration.

I'm not sure whether SwaggerUiConfigParameters.configUrl is a relevant public API for anybody. Changing or removing it is probably a breaking change.

[ababin]

I have the same problem. I used 2.1.0 version. But now is 2.6.0. And without any changes. As I understand, the problem is openapi caches swagger-initializer.js. It is easy to reproduce. At first you need to be shure your application.yml has property server.forward-headers-strategy: framework. Then, just need to make request with different values of the header X-Forwarded-Prefix, which is used when preparing configUrl in swagger-initializer.js. After that there is no metter what value will be passed in X-Forwarded-Prefix in the further requests. The result will be the same (configUrl) - as after the FIRST request.

[bnasslahsen]

@ababin, or @hwanders

This description is quite unclear.

Try adding a failing test similar to what is available here, to showcase the issue you are facing:

https://github.com/springdoc/springdoc-openapi/tree/7bb5fc282f856500238bac81a9292a349fa4f873/springdoc-openapi-starter-webmvc-ui/src/test/java/test/org/springdoc/ui/app32

This ticket will be closed, but can be reopened if your provide all the elements.

[hwanders]

@bnasslahsen Sure, no problem.

@Test
public void shouldReturnCorrectInitializerJSWhenChangingForwardedPrefixHeader() throws Exception {
	// Request swagger-initializer.js with some X-Forwarded-Prefix header.
	mockMvc.perform(get("/swagger-ui/swagger-initializer.js")
					.header("X-Forwarded-Prefix", X_FORWARD_PREFIX));

	// When performing a second request with another X-Forwarded-Prefix header
	// the changed path should be reflected in the configUrl.
	mockMvc.perform(get("/swagger-ui/swagger-initializer.js")
					.header("X-Forwarded-Prefix", "/path/prefix2"))
			.andExpect(status().isOk())
			.andExpect(content().string(
					containsString("\"configUrl\" : \"/path/prefix2/v3/api-docs/swagger-config\",")
			));
}

When adding this to test.org.springdoc.ui.app32.SpringDocBehindProxyTest, we have a failing test.

To sum up: A request to swagger-initializer.js with an X-Forwarded-Prefix header value different from the first one received (in the past) causes a wrong response to be generated (still has the old configUrl).

[bnasslahsen]

@hwanders,

I have added a fix for this request.
You can validate it already based on the Latest SNAPSHOT

[hwanders]

Thank you @bnasslahsen . This fixes the described problem for sequential requests, which is a good progress.

Unfortunately there is still a problem when running requests with different context paths concurrently.

I could indeed write a test which sometimes fails due to concurrency issues:

@Test
public void shouldReturnCorrectInitializerJSWhenChangingForwardedPrefixHeader() throws Exception {
	var tasks = IntStream.range(0, 100).mapToObj(i -> CompletableFuture.runAsync(() -> {
		try {
			mockMvc.perform(get("/swagger-ui/swagger-initializer.js")
							.header("X-Forwarded-Prefix", "/path/prefix" + i))
					.andExpect(status().isOk())
					.andExpect(content().string(
							containsString("\"configUrl\" : \"/path/prefix" + i + "/v3/api-docs/swagger-config\",")
					));
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	})).toArray(CompletableFuture<?>[]::new);

	CompletableFuture.allOf(tasks).join();
}

Test error:

Expected: a string containing "\"configUrl\" : \"/path/prefix0/v3/api-docs/swagger-config\","
     but: was "window.onload = function() {
[skipped for brevity]
  "configUrl" : "/path/prefix6/v3/api-docs/swagger-config",
[...]
};
"

I guess this is due to SwaggerIndexPageTransformer.swaggerWelcomeCommon being reused across requests and updated during each request.

The swagger-config endpoint has the same problem (probably due to SwaggerUiConfigParameters being reused and modified):

@Test
public void shouldCalculateUrlsBehindProxyWhenChangingForwardedPrefixHeader() {
	var tasks = IntStream.range(0, 100).mapToObj(i -> CompletableFuture.runAsync(() -> {
		try {
			mockMvc.perform(get("/v3/api-docs/swagger-config")
							.header("X-Forwarded-Prefix", X_FORWARD_PREFIX + i))
					.andExpect(status().isOk())
					.andExpect(jsonPath("url",
							equalTo("/path/prefix" + i + "/v3/api-docs")
					))
					.andExpect(jsonPath("configUrl",
							equalTo("/path/prefix" + i + "/v3/api-docs/swagger-config")
					));
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	})).toArray(CompletableFuture<?>[]::new);

	CompletableFuture.allOf(tasks).join();
}

Test error:

java.util.concurrent.CompletionException: java.lang.AssertionError: JSON path "url"
Expected: "/path/prefix0/v3/api-docs"
     but: was "/path/prefix9/v3/api-docs"

[bnasslahsen]

@hwanders,

This one forces more changes :)
Can you test it based on the Latest SNAPSHOT ?