Springdoc is unable to redirect to swagger-ui/index.html with Spring Boot 2.4.0-M2

[plnordquist]

Describe the bug

When using Spring Boot 2.4.0-M2, Springdoc is unable to redirect to the proper swagger-ui URI as the UriComponentsBuilder class has changed in Spring Framework 5.3.0-M2. This commit spring-projects/spring-framework@a9244118 changes the UriComponentsBuilder.fromUriString method to validate that URIs with a scheme must have a host part of the URI. I would argue that this change to Spring Framework is validating something that is not true of the URI spec as URIs with schemes do not have to include a host but I have not double checked the RFCs and I'm not sure of the original intentions of this commit/bugfix. I would say that the original method this check came from UriComponentsBuilder.fromHttpUrl, as detailed in the Spring Framework issue spring-projects/spring-framework#25334, should have this check as HTTP URLs must have the host section.

Since this is an incompatibility between two code projects I'm not sure which one needs to fix or work around this issue. I can report this bug on the Spring Framework repository bugtracker if that would help.

To Reproduce
Steps to reproduce the behavior:

• Use Spring Boot 2.4.0-M2
• Use springdoc-openapi-ui v1.4.4
• Demo project here https://github.com/plnordquist/spring-uricomponents-issue

Basically if you update to Spring Boot 2.4.0-M2 it will pull in the affected version of Spring Framework and cause a 500 error when you attempt to navigate to http://localhost:8080/swagger-ui.html. That demo project is nothing more than a start.spring.io project with the milestone release and a HelloController with the springdoc-openapi-ui dependency.

Expected behavior

• Springdoc should redirect to the proper /swagger-ui/index.html location

Additional context
I've included a stacktrace below. Unfortunately I need to use the milestone release as there are changes in Spring Security I need to use.

Stacktrace:

2020-08-24 18:29:48.229 ERROR 13784 --- [nio-8080-exec-4] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.IllegalArgumentException: [redirect:/swagger-ui/index.html] is not a valid URI] with root cause

java.lang.IllegalArgumentException: [redirect:/swagger-ui/index.html] is not a valid URI
        at org.springframework.web.util.UriComponentsBuilder.fromUriString(UriComponentsBuilder.java:247) ~[spring-web-5.3.0-M2.jar:5.3.0-M2]
        at org.springdoc.ui.AbstractSwaggerWelcome.getUriComponentsBuilder(AbstractSwaggerWelcome.java:123) ~[springdoc-openapi-common-1.4.4.jar:na]
        at org.springdoc.webmvc.ui.SwaggerWelcome.redirectToUi(SwaggerWelcome.java:92) ~[springdoc-openapi-ui-1.4.4.jar:na]
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
        at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
        at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.3.0-M2.jar:5.3.0-M2]
        at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.3.0-M2.jar:5.3.0-M2]
        at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105) ~[spring-webmvc-5.3.0-M2.jar:5.3.0-M2]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:888) ~[spring-webmvc-5.3.0-M2.jar:5.3.0-M2]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:802) ~[spring-webmvc-5.3.0-M2.jar:5.3.0-M2]
        at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.0-M2.jar:5.3.0-M2]
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1062) ~[spring-webmvc-5.3.0-M2.jar:5.3.0-M2]
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:962) ~[spring-webmvc-5.3.0-M2.jar:5.3.0-M2]
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.0-M2.jar:5.3.0-M2]
        at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.0-M2.jar:5.3.0-M2]
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:626) ~[tomcat-embed-core-9.0.37.jar:4.0.FR]
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.0-M2.jar:5.3.0-M2]
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) ~[tomcat-embed-core-9.0.37.jar:4.0.FR]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.37.jar:9.0.37]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.0-M2.jar:5.3.0-M2]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.0-M2.jar:5.3.0-M2]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.0-M2.jar:5.3.0-M2]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.0-M2.jar:5.3.0-M2]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.0-M2.jar:5.3.0-M2]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.0-M2.jar:5.3.0-M2]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1589) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
        at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]

[bnasslahsen]

@plnordquist,

Yes, the issue is confirmed and fixed. The fix is available using the latest snapshot.
It will be available with next release 1.4.5.