symlink.go

Documentation: path/filepath

     1  // Copyright 2012 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package filepath
     6  
     7  import (
     8  	"errors"
     9  	"os"
    10  	"runtime"
    11  )
    12  
    13  // isRoot returns true if path is root of file system
    14  // (`/` on unix and `/`, `\`, `c:\` or `c:/` on windows).
    15  func isRoot(path string) bool {
    16  	if runtime.GOOS != "windows" {
    17  		return path == "/"
    18  	}
    19  	switch len(path) {
    20  	case 1:
    21  		return os.IsPathSeparator(path[0])
    22  	case 3:
    23  		return path[1] == ':' && os.IsPathSeparator(path[2])
    24  	}
    25  	return false
    26  }
    27  
    28  // isDriveLetter returns true if path is Windows drive letter (like "c:").
    29  func isDriveLetter(path string) bool {
    30  	if runtime.GOOS != "windows" {
    31  		return false
    32  	}
    33  	return len(path) == 2 && path[1] == ':'
    34  }
    35  
    36  func walkLink(path string, linksWalked *int) (newpath string, islink bool, err error) {
    37  	if *linksWalked > 255 {
    38  		return "", false, errors.New("EvalSymlinks: too many links")
    39  	}
    40  	fi, err := os.Lstat(path)
    41  	if err != nil {
    42  		return "", false, err
    43  	}
    44  	if fi.Mode()&os.ModeSymlink == 0 {
    45  		return path, false, nil
    46  	}
    47  	newpath, err = os.Readlink(path)
    48  	if err != nil {
    49  		return "", false, err
    50  	}
    51  	*linksWalked++
    52  	return newpath, true, nil
    53  }
    54  
    55  func walkLinks(path string, linksWalked *int) (string, error) {
    56  	switch dir, file := Split(path); {
    57  	case dir == "":
    58  		newpath, _, err := walkLink(file, linksWalked)
    59  		return newpath, err
    60  	case file == "":
    61  		if isDriveLetter(dir) {
    62  			return dir, nil
    63  		}
    64  		if os.IsPathSeparator(dir[len(dir)-1]) {
    65  			if isRoot(dir) {
    66  				return dir, nil
    67  			}
    68  			return walkLinks(dir[:len(dir)-1], linksWalked)
    69  		}
    70  		newpath, _, err := walkLink(dir, linksWalked)
    71  		return newpath, err
    72  	default:
    73  		newdir, err := walkLinks(dir, linksWalked)
    74  		if err != nil {
    75  			return "", err
    76  		}
    77  		newpath, islink, err := walkLink(Join(newdir, file), linksWalked)
    78  		if err != nil {
    79  			return "", err
    80  		}
    81  		if !islink {
    82  			return newpath, nil
    83  		}
    84  		if IsAbs(newpath) || os.IsPathSeparator(newpath[0]) {
    85  			return newpath, nil
    86  		}
    87  		return Join(newdir, newpath), nil
    88  	}
    89  }
    90  
    91  func walkSymlinks(path string) (string, error) {
    92  	if path == "" {
    93  		return path, nil
    94  	}
    95  	var linksWalked int // to protect against cycles
    96  	for {
    97  		i := linksWalked
    98  		newpath, err := walkLinks(path, &linksWalked)
    99  		if err != nil {
   100  			return "", err
   101  		}
   102  		if runtime.GOOS == "windows" {
   103  			// walkLinks(".", ...) always returns "." on unix.
   104  			// But on windows it returns symlink target, if current
   105  			// directory is a symlink. Stop the walk, if symlink
   106  			// target is not absolute path, and return "."
   107  			// to the caller (just like unix does).
   108  			// Same for "C:.".
   109  			if path[volumeNameLen(path):] == "." && !IsAbs(newpath) {
   110  				return path, nil
   111  			}
   112  		}
   113  		if i == linksWalked {
   114  			return Clean(newpath), nil
   115  		}
   116  		path = newpath
   117  	}
   118  }
   119
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