net/http: 301 instead of 404 for unmatched requests

[seankhliao]

Go version

go version go1.22.0 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/user/.cache/go-build'
GOENV='/home/user/.config/go/env'
GOEXE=''
GOEXPERIMENT='cacheprog'
GOFLAGS='-trimpath "-ldflags=-s -w"'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/user/.data/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/user/.data/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/user/sdk/go1.22.0'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='path'
GOTOOLDIR='/home/user/sdk/go1.22.0/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22.0'
GCCGO='gccgo'
GOAMD64='v3'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='0'
GOMOD='/home/user/tmp/testrepo0527/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build984268338=/tmp/go-build -gno-record-gcc-switches'

What did you do?

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

Register a pattern, and make a request to a prefix of the pattern

package main

import (
	"fmt"
	"net/http"
	"net/http/httptest"
)

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("/{y}/", func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintln(w, "ok")
	})
	w := httptest.NewRecorder()
	req, _ := http.NewRequest("GET", "/", nil)
	mux.ServeHTTP(w, req)
	fmt.Println(w.Result().Status, w.Result().Header.Get("Location"))
}

What did you see happen?

301 Moved Permanently /

When used with an http client, this results in a redirect loop (get /, redirected to /)

What did you expect to see?

Return a 404 for no matching routes.

[seankhliao]

originally reported in https://groups.google.com/g/golang-nuts/c/vbmvPMVhhjk/m/HLBXEQfuAgAJ?utm_medium=email&utm_source=footer

cc @neild @jba

[gopherbot]

Change https://go.dev/cl/562557 mentions this issue: net/http: refine trailing-slash redirect logic