squashfs - resolve.go

     1  package squashfs
     2  
     3  import (
     4  	"io/fs"
     5  	"path"
     6  	"strings"
     7  )
     8  
     9  type resolver struct {
    10  	*squashfs
    11  	fullPath, path     string
    12  	cutAt              int
    13  	redirectsRemaining int
    14  }
    15  
    16  func (s *squashfs) resolve(fpath string, resolveLast bool) (fs.FileInfo, error) {
    17  	if !fs.ValidPath(fpath) {
    18  		return nil, fs.ErrInvalid
    19  	}
    20  
    21  	root, err := s.getEntry(s.superblock.RootInode, "")
    22  	if err != nil {
    23  		return nil, err
    24  	}
    25  
    26  	const maximumRedirects = 1024
    27  
    28  	r := resolver{
    29  		squashfs:           s,
    30  		fullPath:           fpath,
    31  		path:               fpath,
    32  		redirectsRemaining: maximumRedirects,
    33  	}
    34  
    35  	return r.resolve(root, resolveLast)
    36  }
    37  
    38  func (r *resolver) resolve(root fs.FileInfo, resolveLast bool) (curr fs.FileInfo, err error) {
    39  	curr = root
    40  
    41  	for r.path != "" {
    42  		if dir, ok := curr.(dirStat); !ok {
    43  			return nil, fs.ErrInvalid
    44  		} else if name := r.splitOffNamePart(); isEmptyName(name) {
    45  			continue
    46  		} else if curr, err = r.getDirEntry(name, dir.blockIndex, dir.blockOffset, dir.fileSize); err != nil {
    47  			return nil, err
    48  		} else if r.isDone(resolveLast) {
    49  			break
    50  		} else if sym, ok := curr.(symlinkStat); !ok {
    51  			continue
    52  		} else if err := r.handleSymlink(sym); err != nil {
    53  			return nil, err
    54  		}
    55  
    56  		curr = root
    57  	}
    58  
    59  	return curr, nil
    60  }
    61  
    62  func (r *resolver) splitOffNamePart() string {
    63  	slashPos := strings.Index(r.path, "/")
    64  
    65  	var name string
    66  
    67  	if slashPos == -1 {
    68  		name, r.path = r.path, ""
    69  	} else {
    70  		name, r.path = r.path[:slashPos], r.path[slashPos+1:]
    71  		r.cutAt += slashPos + 1
    72  	}
    73  
    74  	return name
    75  }
    76  
    77  func (r *resolver) handleSymlink(sym symlinkStat) error {
    78  	r.redirectsRemaining--
    79  	if r.redirectsRemaining == 0 {
    80  		return fs.ErrInvalid
    81  	}
    82  
    83  	if strings.HasPrefix(sym.targetPath, "/") {
    84  		r.fullPath = path.Clean(sym.targetPath)[1:]
    85  	} else if r.path == "" {
    86  		r.fullPath = path.Join(r.fullPath[:r.cutAt], sym.targetPath, r.path)
    87  	} else {
    88  		r.fullPath = path.Join(r.fullPath[:r.cutAt-len(sym.name)-1], sym.targetPath, r.path)
    89  	}
    90  
    91  	r.path = r.fullPath
    92  	r.cutAt = 0
    93  
    94  	return nil
    95  }
    96  
    97  func (r *resolver) isDone(resolveLast bool) bool {
    98  	return r.path == "" && !resolveLast
    99  }
   100  
   101  func isEmptyName(name string) bool {
   102  	return name == "" || name == "."
   103  }
   104