os: document that OpenFile Create do not create file if directory do not exist

[r4f4ss]

What version of Go are you using (go version)?

$ go version
go version go1.23.1 linux/amd64

Does this issue reproduce with the latest release?

I do not know

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='HOME/.cache/go-build'
GOENV='HOME/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='HOME/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='HOME/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/.config/go/telemetry'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='HOME/geth/goBug/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-build44258856=/tmp/go-build -gno-record-gcc-switches'
uname -sr: Linux 6.8.0-45-generic
Distributor ID:	Linuxmint
Description:	Linux Mint 22
Release:	22
Codename:	wilma
/lib/x86_64-linux-gnu/libc.so.6: GNU C Library (Ubuntu GLIBC 2.39-0ubuntu8.3) stable release version 2.39.
gdb --version: GNU gdb (Ubuntu 15.0.50.20240403-0ubuntu1) 15.0.50.20240403-git

What did you do?

Run the followeing two codes (./bugDir directory must do not exist):

$go run main.go

package main

import (
	"fmt"
	"os"
	"path/filepath"
)

func main() {
	dir := "./bugDir"
	fileName := "bugFile"
	fullPath := filepath.Join(dir, fileName)

	_, err := os.OpenFile(fullPath, os.O_CREATE|os.O_WRONLY, 0600)
	if err != nil {
		fmt.Println(err)
	}
}

package main

import (
	"fmt"
	"os"
	"path/filepath"
)

func main() {
	dir := "./bugDir"
	fileName := "bugFile"
	fullPath := filepath.Join(dir, fileName)

	_, err := os.Create(fullPath)
	if err != nil {
		fmt.Println(err)
	}
}

What did you expect to see?

The creation of the file bugFile, if the directory do not exist it should be created. This is my understanding of documentation described behavior (1,2), otherwise should be stated clearly in docs that the path must exist before file creation.

Note that the use of the flag O_CREATE suggest that the file will be created eitherways:

If the file does not exist, and the O_CREATE flag is passed, it is created with mode perm (before umask)

workarround: create the directory with os.MkdirAll(dir, os.ModePerm)

What did you see instead?

Error:

open bugDir/bugFile: no such file or directory

[gabyhelp]

Related Issues and Documentation

• os: os.Create & os.OpenFile both not creating .json file #67677 (closed)
• os: Mkdir ignores perm on Windows #65377
• go test about mkdir #33053 (closed)
• affected/package: os #56148 (closed)
• os: OpenFile always truncates (ignores flags) #53591 (closed)
• cmd/cgo: creat() is typo? #61334 (closed)
• os: ambiguous mode/perm documentation for Create and OpenFile #30400 (closed)
• os: MkdirAll exits without creating all folders #20289 (closed)
• os: directory exists but os.ReadDir reports "no such file or directory" #46408
• os: os.OpenFile() ignores FileMode when truncating a existing file #33605 (closed)

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

[ianlancetaylor]

This is how it is supposed to work. It corresponds to how the create-file functions work in other languages.

I'm not opposed to a brief doc note.

[gopherbot]

Change https://go.dev/cl/619316 mentions this issue: os: add precondition doc for Create and OpenFile

[xieyuschen]

This is how it is supposed to work. It corresponds to how the create-file functions work in other languages.

I'm not opposed to a brief doc note.

@ianlancetaylor Send you CL 619316. I have encountered this problem before and solved it by using MkdirAll to create the directories first. I think it's nice to link the MkdirAll and Mkdir as well.

cc: @r4f4ss