dispatcher.include() with welcome files lead to stack overflow error

[grgrzybek]

Jetty version
10.0.0-SNAPSHOT

Java version
11.0.6

OS type/version
Linux everfree.forest 5.6.19-300.fc32.x86_64 #1 SMP Wed Jun 17 16:10:48 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

Description
I'm working on Pax Web 8 and welcome file handling with default servlets.

I have org.eclipse.jetty.servlet.DefaultServlet mapped to /alt/* only (no mapping of org.eclipse.jetty.servlet.DefaultServlet to / path) with pathInfoOnly=true init parameter (because I want resources to be located using ... path info only, because this default servlet is not mapped to /) and another servlet mapped to /gateway/*.
Then context has welcome files configured.

"gateway" servlet does this:

req.getRequestDispatcher("/alt/").include(req, resp);

"default" servlet (the one mapped to /alt/* is properly called with include (has all the javax.servlet.include.* attributes, but it eventually calls org.eclipse.jetty.server.ResourceService#sendWelcome() because the /alt/ resource is a directory.
The problem is that sendWelcome() method creates welcome file /gateway/index.html instead of /alt/index.html, because it (using pathInfoOnly=true has to restore full request URI.

However, when resource servlet is included, org.eclipse.jetty.server.ResourceService#sendWelcome() should get the servlet path differently (using javax.servlet.include.servlet_path attribute).

[joakime]

Are you using ServletContextHandler? or WebAppContext? (either way, you'd be surprised, there is always some servlet mapped to / default after startup, there has to be)

[joakime]

Also, you should never have a named servlet "default" ever mapped to something that isn't the "/" default url-pattern.
And the ServletContextHandler (or WebAppContext) must have a valid ResourceBase declared, otherwise the ServletContext is essentially broken.
And you know you can have multiple DefaultServlet's declared, right? (with a named called "alt", i suspect you already read that stackoverflow answer)

[grgrzybek]

I'm looking from the perspective of ServletContextHandler, not the WebAppContext one. I'm mostly interested in embedded Jetty usage (I'm refactoring Pax Web 8) and definitely I'm interested in multiple registrations of "default servlet" under different paths (according to OSGi CMPN Http and Whiteboard specifications).
And yes - I'm aware of org.eclipse.jetty.servlet.ServletHandler#_ensureDefaultServlet. I don't want to distinguish any particular resource servlet and also (for OSGi purposes) I'm doing some tricks related to "resource base" for the resource servlets.

[grgrzybek]

I wanted to thank you first for responding ;)
I'm not really sure I need "default" servlet. Even 12.1 "Use of URL Paths" of Servlet (4.0) spec says:

If neither of the previous three rules result in a servlet match, the container will attempt to serve content appropriate for the resource requested. If a "default" servlet is defined for the application, it will be used. Many containers provide an implicit default servlet for serving content

Which means (IMO) that "default" servlet is not a requirement.

OSGi CMPN Http Service specification defines org.osgi.service.http.HttpService#registerResources() method, where some "resource base" (by default - root of the Bundle) is mounted under an alias (which is mapped to /alias/* URL pattern of Servlet spec).

FYI, here's my unit test where I try to check all the combinations of parameters, redirects, forwards, includes and welcome file scenarios.

[grgrzybek]

BTW, Jetty again seems the most flexible implementation ;)

In Tomcat, welcome files are handled in org.apache.catalina.mapper.Mapper#internalMapWrapper() as "rule 4" - after checking exact, prefix and extension mappings. So if a "resource servlet" is mapped to e.g., /res/*, we won't get welcome file handling with GET /res/ HTTP/1.1 request.

In Undertow, welcome files are handled by io.undertow.servlet.handlers.ServletInitialHandler#handleRequest() using io.undertow.servlet.handlers.ServletPathMatches#getServletHandlerByPath() and as in Tomcat, if "resource servlet" (io.undertow.servlet.handlers.DefaultServlet) is mapped to e.g., prefix URI pattern, it won't leverage context-wide welcome files.

In Jetty, except this include-stack-overflow problem, I had no problems mapping different org.eclipse.jetty.servlet.DefaultServlet instances to different URIs (with or without / default mapping).

[janbartel]

@grgrzybek I've reproduced the problem, am pondering the solution.

[janbartel]

Applied the PR provided by @grgrzybek - thanks!