net/http.ServeMux: Enhanced routing patterns introduced in 1.22 do not work in 1.23 unless go mod has go version explicitly declared

[johnpeeke]

Go version

go version 1.23

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/jpeeke/.cache/go-build'
GOENV='/home/jpeeke/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/jpeeke/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/jpeeke/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.23.1'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/jpeeke/.config/go/telemetry'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='0'
GOMOD='/mnt/c/Users/jpeeke/awesomeProject1/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 -fno-caret-diagnostics -Qunused-arguments -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2766611647=/tmp/go-build -gno-record-gcc-switches'

What did you do?

`func main() {
apiCfg := &apiConfig{}
apiCfg.fileserverHits = atomic.Int32{}

mux := http.NewServeMux()
mux.Handle("/app/", apiCfg.middlwareMetricsInc(http.StripPrefix("/app", http.FileServer(http.Dir(".")))))
mux.HandleFunc("GET /healthz", healthCheck)
mux.HandleFunc("GET /metrics", apiCfg.loadHits)
mux.HandleFunc("POST /reset", apiCfg.resetFileserverHits)

srv := &http.Server{
	Addr:    ":8080",
	Handler: mux,
}

log.Println(srv.ListenAndServe())

}`

Navigate to any endpoint using the new enhanced routing pattern introduced in go version 1.22 (i.e. Get /healthz)

go.dev/play

What did you see happen?

I receive a 404 error

What did you expect to see?

I expected an OK response. I receive the correct response only if go version 1.22 or 1.23 is explicitly set in go.mod. I did not expect to have to explicitly set this as only go version 1.23 is installed on my system.

[gabyhelp]

Related Issues and Documentation

• net/http: Conflicts with pattern when using NewServeMux #68838 (closed)
• net/http: enhanced ServerMux routing #65231 (closed)
• net/http: ServeMux behaves inconsistently across operating systems #66288 (closed)
• enhanced routing does not work on linux/debian12 #65746 (closed)
• net/http: muxer no longer redirects host patterns in go1.10 #23183 (closed)
• net/http: http.ServerMux, paths ending in * wildcard are not recognized. #68856 (closed)
• net/http: 301 instead of 404 for unmatched requests #65624 (closed)
• net/http: ServeMux not backwards compatible (with Go 1.21) when registering double-slash patterns #69044
• net/http: document and test behavior of ServeMux with ports #23351 (closed)
• net/http: ServeMux.Handler does not populate named path wildcards #69623

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[ianlancetaylor]

If you have a go.mod file, and it does not specify a go version, the default is to assume that you are using an old version of Go, specifically 1.16. For cases like enhanced routing patterns, you will therefore get the behavior of the Go 1.16 standard library. This is working as intended.