os: OpenFile using O_TRUNC and O_CREATE on a named pipe fails on windows #76071
Description
Go version
go version go1.25.3 windows/amd64
Output of go env in your module/workspace:
# go env
set AR=ar
set CC=gcc
set CGO_CFLAGS=-O2 -g
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-O2 -g
set CGO_ENABLED=0
set CGO_FFLAGS=-O2 -g
set CGO_LDFLAGS=-O2 -g
set CXX=g++
set GCCGO=gccgo
set GO111MODULE=
set GOAMD64=v1
set GOARCH=amd64
set GOAUTH=netrc
set GOBIN=
set GOCACHE=C:\Users\Max\AppData\Local\go-build
set GOCACHEPROG=
set GODEBUG=
set GOENV=C:\Users\Max\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFIPS140=off
set GOFLAGS=
set GOGCCFLAGS=-m64 -fno-caret-diagnostics -Qunused-arguments -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=C:\Users\Max\AppData\Local\Temp\go-build1595438883=/tmp/go-build -gno-record-gcc-switches
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMOD=NUL
set GOMODCACHE=C:\Users\Max\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\Max\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=C:\Program Files\Go
set GOSUMDB=sum.golang.org
set GOTELEMETRY=local
set GOTELEMETRYDIR=C:\Users\Max\AppData\Roaming\go\telemetry
set GOTMPDIR=
set GOTOOLCHAIN=auto
set GOTOOLDIR=C:\Program Files\Go\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.25.3
set GOWORK=
set PKG_CONFIG=pkg-configWhat did you do?
Call os.OpenFile with os.O_TRUNC (or os.Create) with an (existing) named pipe. Minimal working example:
package main
import (
"os"
)
func main() {
_, err := os.OpenFile(`\\.\pipe\test`, os.O_RDWR|os.O_TRUNC, 0666)
if err != nil {
panic(err)
}
}
What did you see happen?
os.OpenFile returns an error.
What did you expect to see?
Since documentation for O_TRUNC states that it only applies to regular files:
O_TRUNC int = syscall.O_TRUNC // truncate regular writable file when opened.
a valid handle should be returned.
This was the behavior in go 1.23, which does not return an error in this case. Both 1.24 and 1.25, however, error.