net/http: ServeMux.Handler returns wrong pattern with trailing-slash redirection handler

[FiloSottile]

ServeMux.Handler should return patterns as passed to Handle.

However, if returning a trailing-slash redirection handler (but not if returning a request sanitizing redirection handler), non-... wildcards are replaced with the corresponding segment from the path.

The following code

mux := http.NewServeMux()
mux.Handle("/{x}/", http.NotFoundHandler())
r, _ := http.NewRequest("POST", "/foo", nil)
_, p := mux.Handler(r)
fmt.Println(p)

prints /foo/ instead of /{x}/.

https://go.dev/play/p/XQjZOXTLVTQ

[gabyhelp]

Related Issues

• net/http: ServeMux unexpectedly redirecting to add trailing slash #11757 (closed)
• http.Handle("/", ...) effectively hijacks pages from being not found (due to trailing "/" in the "pattern") #231 (closed)
• net/http: ServeMux.Handler does not populate named path wildcards #69623
• net/http: ServeMux uses un-escaped paths in the implicit /tree → /tree/ redirect #10572 (closed)
• net/http: add example for ServeMux to make "/.*" behavior clear #4799 (closed)
• net/http: ServeMux should not cleanup requests path and redirect by default #19481 (closed)
• net/http: ServeMux not validating methods for redirected paths #69690 (closed)
• net/http: cannot register ServeMux handler for all CONNECT requests regardless of host or path #9561 (closed)

Related Code Changes

• net/http: redirect host-based patterns to trailing slash

Related Documentation

• Package http > type ServeMux > func (*ServeMux) Handler 1.1

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[mknyszek]

CC @jba @neild

[gopherbot]

Change https://go.dev/cl/673815 mentions this issue: src/net/http: fix ServeMux.Handler on trailing-slash redirect