Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

os: investigate why Stat(non-existent-file) on Windows with builders returns error prefixed with "CreateFile" #38841

Closed
odeke-em opened this issue May 4, 2020 · 5 comments
Closed

os: investigate why Stat(non-existent-file) on Windows with builders returns error prefixed with "CreateFile" #38841

odeke-em opened this issue May 4, 2020 · 5 comments
Labels
FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. OS-Windows
Milestone
Unplanned

Comments

@odeke-em
Copy link
Member

odeke-em commented May 4, 2020

Coming here from an unexpected trybot failure in https://storage.googleapis.com/go-build-log/ee4c7a10/windows-amd64-2016_e7a90c70.log
and CL 230941

where the relevant code is https://play.golang.org/p/El2eXIywXlu or inlined below

package main

import (
	"log"
	"os"
	"strings"
)

func main() {
	got := "open x.go: no such file or directory\n"
	_, sysNotExistErr := os.Stat("x.go")
	if sysNotExistErr == nil {
		// Oddly the file might exist, do nothing and just report the original failure.
		log.Fatalf("Expected an error %q\n", got)
	}

	want := strings.Replace(sysNotExistErr.Error(), "stat x.go:", "open x.go:", -1) + "\n"
	if got != want {
		log.Fatalf("Expected an error, but got:\n\t%q\nwant:\n\t%q", got, want)
	}
}

but oddly on the Windows builder it returned

# go run run.go -- fixedbugs/issue36437.go
incorrect output
Expected an error, but got:
	"open x.go: The system cannot find the file specified.\n"
want:
	"CreateFile x.go: The system cannot find the file specified."

The "CreateFile x.go" is quite unexpected. Perhaps we should investigate as to how "CreateFile" got invoked?

Kindly cc-ing @alexbrainman.
@odeke-em odeke-em added OS-Windows NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels May 4, 2020
@odeke-em odeke-em added this to the Unplanned milestone May 4, 2020
@muhammadharis
Copy link

muhammadharis commented May 4, 2020 •
edited

It seems that the error that is being returned is from this line: https://github.com/golang/go/blob/master/src/os/stat_windows.go#L97

@networkimprov
Copy link

networkimprov commented May 4, 2020 •
edited

Hi Emmanuel, CreateFile is the WinApi name for Posix open(2). It only creates filesystem entries in certain cases.

Why is the fix for #36437 examining the error string instead of if !os.IsNotExist(err)?

EDIT: oh, it doesn't call os.Stat() directly. I imagine it needs a runtime.GOOS=="windows" variant.

@iwdgo
Copy link
Contributor

iwdgo commented May 6, 2020 •
edited

On Windows, os.Stat attempts several calls to cope with various file types. Some details on the rationale are here.
The following could help to check error message content.

if !os.IsNotExist(sysNotExistErr) {
	log.Fatalf("Expected a not exist error")
}

s := "x.go:0"
if n := strings.LastIndex(sysNotExistErr.Error(), s); n != -1 {
	log.Fatalf("Line number is unexpected: %s", sysNotExistErr.Error()[n:len(s)])
}

For the records, no index number shows on Windows 10 and go version go1.14.2 windows/amd64 as go run x.go and os.Stat both return CreateFile x.go: The system cannot find the file specified.

@alexbrainman
Copy link
Member

CreateFile is the WinApi name for Posix open(2). It only creates filesystem entries in certain cases.

Correct. CreateFile Windows API is generally used to open files

https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea

There is no open syscall on Windows. It will be confusing, if we just blindly replace CreateFile with open string. For example, the errors you see relate directly to CreateFile API, and have different meaning when returned for different APIs.

Alex

@odeke-em
Copy link
Member Author

odeke-em commented May 9, 2020

Got it, thank you @muhammadharis @networkimprov @iwdgo @alexbrainman for the answers! SGTM.

@odeke-em odeke-em closed this as completed May 9, 2020
@golang golang locked and limited conversation to collaborators May 9, 2021
Sign up for free to subscribe to this conversation on GitHub. Already have an account? Sign in.
Assignees
No one assigned
Labels
FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. OS-Windows
Projects
None yet
Milestone
Unplanned
Development

No branches or pull requests
6 participants
@networkimprov @odeke-em @gopherbot @alexbrainman @muhammadharis @iwdgo