Check if a file/dir path is a symlink

check_symlink.go

package main

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

// . or tmp/   = current working dir
// ./hello.txt = regular file
// ./mod       = symlink somewhere else
// ./dir       = symlink to ../tmp

var full = []string{
        "hello.txt",
        "./hello.txt",
        "mod",
        "./mod",

        ".",
        "./",
        "../tmp",
        "../tmp/",
        "dir",
        "dir/",
        "./dir",
        "./dir/",

        "../tmp/hello.txt",
        "../tmp/mod",
        "dir/hello.txt",
        "dir/mod",
        "./dir/hello.txt",
        "./dir/mod",
        "../tmp/dir/hello.txt",
        "../tmp/dir/mod",
        "dir/./hello.txt",
        "dir/./mod",
        "dir/../hello.txt",
        "dir/../../tmp/mod",
}

func main() {
        for i, f := range full {
                err := isSymlink(f)
                if err == nil {
                        continue
                }
                fmt.Printf("%d\t f: %v\t d: %v\t %s\t\t %v\n", i, err == ErrFileIsSymlink, err == ErrDirIsSymlink, f, err)
        }
}

////////////////////////////////////////////////////////////////////////////////////////////////////

func checkErr(err error) {
        if err != nil {
                panic(err)
        }
}

func isSymlink(path string) error {
        // Fails for the last "dot-dot" test paths
        dir, _ := filepath.Split(path)
        err := checkSymlink(filepath.Clean(dir))
        switch err {
        case nil:
                return checkSymlink(path)
        case ErrFileIsSymlink:
                return ErrDirIsSymlink
        default:
                return err
        }

        // Expensive to run, but catches all kinds of paths I think
        //var d []string
        //for _, p := range strings.Split(path, string(filepath.Separator)) {
        //d = append(d, p)
        //if err := checkSymlink(filepath.Join(d...)); err != nil {
        //if err == ErrFileIsSymlink {
        //return ErrDirIsSymlink
        //}
        //return err
        //}
        //}
        //return checkSymlink(path)
}

var ErrFileIsSymlink = errors.New("file is symlink")
var ErrDirIsSymlink = errors.New("dir is symlink")

func checkSymlink(path string) error {
        fi, err := os.Lstat(path)
        if err != nil {
                return err
        }
        if fi.Mode()&os.ModeSymlink != 0 {
                return ErrFileIsSymlink
        }
        return nil
}