cmd/go: GO111MODULE=off is treated as as GODEBUG=default=go1.20

[UiP9AV6Y]

Go version

go version go1.23.4 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/root/.cache/go-build'
GOENV='/root/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.23.4'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/root/.config/go/telemetry'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/src/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 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2806843945=/tmp/go-build -gno-record-gcc-switches'

What did you do?

i am running an application which uses a net/http.ServeMux with pattern features introduced with golang1.22

(e.g. http.HandleFunc("/{$}" ... to handle only requests for GET / HTTP/XXX)

building the application with GO111MODULE=off causes the application to respond with 404 page not found for requests which would otherwise be handled when running the application with GO111MODULE=on.

i have provided a simple reproducer

What did you see happen?

GO111MODULE=off go run .

in another terminal

curl -s 'http://localhost:8080/%7B%24%7D'
ok
curl -s 'http://localhost:8080/{$}'
404 page not found
curl -s http://localhost:8080/
404 page not found

GO111MODULE=on go run .

in another terminal

curl -s 'http://localhost:8080/%7B%24%7D'
404 page not found
curl -s 'http://localhost:8080/{$}'
404 page not found
curl -s http://localhost:8080/
ok

the request against the /{$} path is expected to yield a 404; i have included it for the sake of completeness

%7B%24%7D is the URL encoded notation of {$}

What did you expect to see?

i was expecting the golang1.22 net/http changes to be available regardless of the use of GO111MODULE=off. AFAIK this environment variable affects the code lookup and the compiler's expectations about the project layout and location. i did not expect it to downgrade/disable any language features.

[gabyhelp]

Related Issues

• net/http: enhanced ServerMux routing #65231 (closed)
• net/http: 301 instead of 404 for unmatched requests #65624 (closed)
• net/http: Pattern matching of ServeMux works weird and unexpected #70311 (closed)
• net/http.ServeMux: Enhanced routing patterns introduced in 1.22 do not work in 1.23 unless go mod has go version explicitly declared #69686 (closed)
• net/http: ServeMux behaves inconsistently across operating systems #66288 (closed)
• net/http: Conflicts with pattern when using NewServeMux #68838 (closed)
• net/http: muxer no longer redirects host patterns in go1.10 #23183 (closed)
• cmd/go: `go get` should give a clearer error with `GO111MODULE=off` #66080
• net/http: DefaultServeMux incorrectly redirect (301) to path if path includes `%2F%2F` #21955 (closed)

Related Discussions

• net/http: 1.22.0, Enhanced routing, httpmuxgo121

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

[seankhliao]

currently the default godebugs come from the module, if a go directive isn't present, it assumes go1.20 (last version before godebug controls were introduced)
https://go.googlesource.com/go/+/refs/heads/master/src/cmd/go/internal/load/godebug.go#56

[UiP9AV6Y]

thank you for the clarification but shouldn't this show up with go env too then?

GO111MODULE=off go env

GO111MODULE='off'
GOARCH='amd64'
GOBIN=''
GOCACHE='/root/.cache/go-build'
GOENV='/root/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.23.4'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/root/.config/go/telemetry'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD=''
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 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build58633166=/tmp/go-build -gno-record-gcc-switches'

GODEBUG is empty in my case

[UiP9AV6Y]

posting the status-quo in case others stumble over the same issue. additional information can be found in the docs:
https://go.dev/doc/godebug

cat go.mod

module gomodules-http

go 1.23.4

GO111MODULE=off go list -f '{{.DefaultGODEBUG}}' .

asynctimerchan=1,gotypesalias=0,httplaxcontentlength=1,httpmuxgo121=1,httpservecontentkeepheaders=1,netedns0=0,panicnil=1,tls10server=1,tls3des=1,tlskyber=0,tlsrsakex=1,tlsunsafeekm=1,winreadlinkvolume=0,winsymlink=0,x509keypairleaf=0,x509negativeserial=1

[dr2chase]

@matloob @samthanawalla
Not sure if this is WAI or a bug.