os: io.Copy(net.Conn, os.Stdin) on MacOS terminate immediately without waiting for input

[tiendo1011]

Go version

go version go1.23.3 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/tien/Library/Caches/go-build'
GOENV='/Users/tien/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/tien/.asdf/installs/golang/1.23.3/packages/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/tien/.asdf/installs/golang/1.23.3/packages'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/Users/tien/.asdf/installs/golang/1.23.3/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/Users/tien/.asdf/installs/golang/1.23.3/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.23.3'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/tien/Library/Application Support/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/Users/tien/code/learning/the-go-programming-language/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 -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/fw/flzm6v7d6dn9n3255s6c69v00000gn/T/go-build4294646491=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

Running a server: https://go.dev/play/p/5I1sJlo64VB
And a client: https://go.dev/play/p/fOMykC2RbYs

What did you see happen?

The client exits immediately without waiting for the input

What did you expect to see?

The client wait for the input

[gabyhelp]

Related Issues

• run #70024 (closed)
• Test #67906 (closed)
• Bugs-Report #62338 (closed)
• Update #70550 (closed)
• Test #70447 (closed)
• sb #53220 (closed)
• go #64466 (closed)
• clear #57553 (closed)
• yaffaliu #56935 (closed)
• Demo #66258 (closed)

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

[seankhliao]

consider checking the error on the copy operation

[tiendo1011]

@seankhliao there is no error, io.Copy returns 0, nil.

I ran the same code on a linux machine, and it worked as expected, so this only happens on MacOS.

[seankhliao]

and how are you running this?

[tiendo1011]

@seankhliao I'm using go run to run the server & the client files separately

[ianlancetaylor]

I tried it on a Darwin system using Go tip and io.Copy returned an error:

readfrom tcp [::1]:51606->[::1]:8000: sendfile: operation not supported

[ianlancetaylor]

CC @panjf2000

[ianlancetaylor]

Marking as release blocker since we shouldn't get a sendfile error from an io.Copy call.

I haven't tested earlier Go releases.

[ianlancetaylor]

With Go 1.22 the program works as expected.

With Go 1.23 the program exits immediately with no error, as reported by this bug report.