net/http: ServeMux unexpectedly redirecting to add trailing slash

[jehiah]

http.ServeMux unexpectedly redirects to add a trailing slash if there is a route that matches with a trailing slash.

Given the following ServeMux, I expect that a request for /a would match the path rooted as /.

http.HandleFunc("/", ...)
http.HandleFunc("/a/", ...)

Instead, a 301 redirect is returned redirecting to /a/ (see http://play.golang.org/p/65Skm2I5hq).

The docs describe redirects as happening in path sanitization cases (ie: requests with . or .. elements), but no mention of transparently adding slashes. The docs also describe the match as a "rooted subtree" so it's also unexpected that a pattern for /a/ would affect requests that don't have that prefix (ie: w/o the trailing slash).

In researching if this situation was reported before, I found a mailing list from 2010 implying this was expected as well as a code comment. If that is still the case, then i think the docs should reflect that. (though i personally consider this a bug, i could understand that for some this could be a feature).

[ianlancetaylor]

CC @bradfitz

[jehiah]

For context I've looked at how this is handled by other http routers. It's mixed as to how default implementations behave, but generally is documented clearly with a configurable.

• julienschmidt/httprouter exposes a RedirectTrailingSlash option and by default does do these redirects.
• gorilla/mux exposes a StrictSlash option and by default does not do these redirects.

[gopherbot]

CL https://golang.org/cl/17955 mentions this issue.

[rsc]

@jehiah FWIW, the configurable here is that you register the non-slash form too and tell the ServeMux what should handle it.

[jehiah]

Thanks for the doc clarifications! much appreciated @rsc