如何判断文件夹是否存在并且可写？

Question

I'd like func FolderExists(path string) bool that will tell whether a folder exists and is writable. I've gotten here:

func FolderExists(path string) bool {
    info, err := os.Stat(path)
    return os.IsExist(err) && info.Mode().IsDir() && info.Mode().???
}

How to tell if this folder is writable? I cannot simply check for filemode permissions (e.g. 0200 for user write permission) because then I'd have to check the owner of the file. Is there a straightforward way to do this in Go?

For those with UNIX backgrounds, looking for the equivalent of the very simple:

if [ -d "$n" && -w "$n" ] ; then ... fi

Answer 1

If you're writing for a Unix-y OS, you can use unix.Access(path string, mode uint32) error with the constant unix.W_OK as the mode.

As kostix says, you still have to check for an error when you access the directory (when you create or delete a file, say). The directory could have been removed since your check, or permissions could have changed, or you could get an entirely unrelated error.

(Thanks to user fxxn for pointing out that the situation has improved since the original answer in 2013, which was to use syscall.Access and extract the W_OK constant from unistd.h.)

Here's code that checks for existence and access that gets me the expected result on Linux:

package main

import (
    "fmt"
    "golang.org/x/sys/unix"
)

func writable(path string) bool {
    return unix.Access(path, unix.W_OK) == nil
}

func main() {
    fmt.Println("/etc writable?", writable("/etc"))
    fmt.Println("/tmp writable?", writable("/tmp"))
}