ROX-Lib2/python/rox/xattr.py

   1 """
   2 Extended attribute support.
   3
   4 Two versions of the extended attribute API are recognized.  If the 'getxattr'
   5 function is detected then the functions used are
   6 getxattr/setxattr/listxattr/removexattr.  This is the API found on Linux
   7 and some others.
   8
   9 If the 'attropen' function is found then the functions used are
  10 attropen and unlinkat.  This is the API found on Solaris.
  11
  12 If neither version is detected then a set of dummy functions are generated
  13 which have no affect.
  14
  15 You should check the return value of the function supported().  Without
  16 an argument this returns whether extended attribute support is available.
  17
  18 This module requires the ctypes module.  This is part of Python 2.5 and
  19 available as an extension for earlier versions of Python.
  20 """
  21
  22 import os, sys, errno
  23
  24 try:
  25     import ctypes
  26     try:
  27         libc=ctypes.cdll.LoadLibrary('')
  28     except:
  29         libc=ctypes.cdll.LoadLibrary('libc.so')
  30
  31 except:
  32     # No ctypes or can't find libc
  33     libc=None
  34
  35 class NoXAttr(OSError):
  36     """Exception thrown when xattr support is requested but is not
  37     available."""
  38     def __init__(self, path):
  39         OSError.__init__(self, errno.EOPNOTSUP, 'No xattr support',path)
  40
  41 # Well known extended attribute names.
  42 USER_MIME_TYPE = 'user.mime_type'
  43
  44 if libc and hasattr(libc, 'attropen'):
  45     # Solaris style
  46     libc_errno=ctypes.c_int.in_dll(libc, 'errno')
  47     def _get_errno():
  48         return libc_errno.value
  49     def _error_check(res, path):
  50         if res<0:
  51             raise OSError(_get_errno(), os.strerror(_get_errno()), path)
  52
  53     try:
  54         _PC_XATTR_ENABLED=os.pathconf_names['PC_XATTR_ENABLED']
  55     except:
  56         _PC_XATTR_ENABLED=100  # Solaris 9
  57
  58     try:
  59         _PC_XATTR_EXISTS=os.pathconf_names['PC_XATTR_EXISTS']
  60     except:
  61         _PC_XATTR_EXISTS=101  # Solaris 9
  62
  63     def supported(path=None):
  64         """Detect whether extended attribute support is available.
  65
  66         path - path to file to check for extended attribute support.
  67         Availablity can vary from one file system to another.
  68
  69         If path is None then return True if the system in general supports
  70         extended attributes."""
  71
  72         if not path:
  73             return True
  74
  75         return os.pathconf(path, _PC_XATTR_ENABLED)
  76
  77     def present(path):
  78         """Return True if extended attributes exist on the named file."""
  79
  80         return os.pathconf(path, _PC_XATTR_EXISTS)>0
  81
  82     def get(path, attr):
  83         """Get an extended attribute on a specified file.
  84
  85         path - path name of file to check
  86         attr - name of attribute to get
  87
  88         None is returned if the named attribute does not exist.  OSError
  89         is raised if path does not exist or is not readable."""
  90
  91         if not os.access(path, os.F_OK):
  92             raise OSError(errno.ENOENT, 'No such file or directory', path)
  93
  94         if os.pathconf(path, _PC_XATTR_EXISTS)<=0:
  95             return
  96
  97         fd=libc.attropen(path, attr, os.O_RDONLY, 0)
  98         if fd<0:
  99             return
 100
 101         v=''
 102         while True:
 103             buf=os.read(fd, 1024)
 104             if len(buf)<1:
 105                 break
 106             v+=buf
 107
 108         libc.close(fd)
 109
 110         return v
 111
 112     def listx(path):
 113         """Return a list of extended attributes set on the named file.
 114
 115         path - path name of file to check
 116
 117         OSError is raised if path does not exist or is not readable."""
 118         if not os.access(path, os.F_OK):
 119             raise OSError(errno.ENOENT, 'No such file or directory', path)
 120
 121         if os.pathconf(path, _PC_XATTR_EXISTS)<=0:
 122             return []
 123
 124         fd=libc.attropen(path, '.', os.O_RDONLY, 0)
 125         if fd<0:
 126             return []
 127
 128         odir=os.getcwd()
 129         os.fchdir(fd)
 130         attrs=os.listdir('.')
 131         os.chdir(odir)
 132         libc.close(fd)
 133
 134         return attrs
 135
 136     def set(path, attr, value):
 137         """Set an extended attribute on a specified file.
 138
 139         path - path name of file to check
 140         attr - name of attribute to set
 141         value - value of attribute to set
 142
 143         OSError is raised if path does not exist or is not writable."""
 144
 145         fd=libc.attropen(path, attr, os.O_WRONLY|os.O_CREAT, 0644)
 146         _error_check(fd, path)
 147
 148         res=os.write(fd, value)
 149         libc.close(fd)
 150         _error_check(res, path)
 151
 152     def delete(path, attr):
 153         """Delete an extended attribute from a specified file.
 154
 155         path - path name of file to check
 156         attr - name of attribute to delete
 157
 158         OSError is raised if an error occurs."""
 159
 160         fd=libc.attropen(path, '.', os.O_RDONLY, 0)
 161         _error_check(fd, path)
 162
 163         res=libc.unlinkat(fd, attr, 0)
 164         libc.close(fd)
 165         _error_check(res, path)
 166
 167     name_invalid_chars='/\0'
 168     def name_valid(name):
 169         """Check that name is a valid name for an extended attibute.
 170         False is returned if the name should not be used."""
 171
 172         return name_invalid_chars not in name
 173
 174     def binary_value_supported():
 175         """Returns True if the value of an extended attribute may contain
 176         embedded NUL characters (ASCII 0)."""
 177
 178         return True
 179
 180 elif libc and hasattr(libc, 'getxattr'):
 181     # Linux style
 182
 183     # Find out how to access errno.  The wrong way may cause SIGSEGV!
 184     if hasattr(libc, '__errno_location'):
 185         libc.__errno_location.restype=ctypes.c_int
 186         errno_loc=libc.__errno_location()
 187         libc_errno=ctypes.c_int.from_address(errno_loc)
 188
 189     elif hasattr(libc, 'errno'):
 190         libc_errno=ctypes.c_int.in_dll(lib, 'errno')
 191
 192     else:
 193         libc_errno=ctypes.c_int(errno.EOPNOTSUP)
 194
 195     def _get_errno():
 196         return libc_errno.value
 197     def _error_check(res, path):
 198         if res<0:
 199             raise OSError(_get_errno(), os.strerror(_get_errno()), path)
 200
 201     def supported(path=None):
 202         """Detect whether extended attribute support is available.
 203
 204         path - path to file to check for extended attribute support.
 205         Availablity can vary from one file system to another.
 206
 207         If path is None then return True if the system in general supports
 208         extended attributes."""
 209
 210         if not path:
 211             return False
 212
 213         if not os.access(path, os.F_OK):
 214             raise OSError(errno.ENOENT, 'No such file or directory', path)
 215
 216         return True
 217
 218     def present(path):
 219         """Return True if extended attributes exist on the named file."""
 220
 221         if not os.access(path, os.F_OK):
 222             raise OSError(errno.ENOENT, 'No such file or directory', path)
 223
 224         buf=ctypes.c_buffer(1024)
 225         n=libc.listxattr(path, ctypes.byref(buf), 1024)
 226
 227         return n>0
 228
 229     def get(path, attr):
 230         """Get an extended attribute on a specified file.
 231
 232         path - path name of file to check
 233         attr - name of attribute to get
 234
 235         None is returned if the named attribute does not exist.  OSError
 236         is raised if path does not exist or is not readable."""
 237
 238         if not os.access(path, os.F_OK):
 239             raise OSError(errno.ENOENT, 'No such file or directory', path)
 240
 241         size=libc.getxattr(path, attr, '', 0)
 242         if size<0:
 243             return
 244
 245         buf=ctypes.c_buffer(size+1)
 246         libc.getxattr(path, attr, ctypes.byref(buf), size)
 247         return buf.value
 248
 249     def listx(path):
 250         """Return a list of extended attributes set on the named file.
 251
 252         path - path name of file to check
 253
 254         OSError is raised if path does not exist or is not readable."""
 255         if not os.access(path, os.F_OK):
 256             raise OSError(errno.ENOENT, 'No such file or directory', path)
 257
 258         size=libc.listxattr(path, None, 0)
 259
 260         if size<1:
 261             return []
 262         buf=ctypes.create_string_buffer(size)
 263         n=libc.listxattr(path, ctypes.byref(buf), size)
 264         names=buf.raw[:-1].split('\0')
 265         return names
 266
 267     def set(path, attr, value):
 268         """Set an extended attribute on a specified file.
 269
 270         path - path name of file to check
 271         attr - name of attribute to set
 272         value - value of attribute to set
 273
 274         OSError is raised if path does not exist or is not writable."""
 275
 276         if not os.access(path, os.F_OK):
 277             raise OSError(errno.ENOENT, 'No such file or directory', path)
 278
 279         res=libc.setxattr(path, attr, value, len(value), 0)
 280         _error_check(res, path)
 281
 282
 283     def delete(path, attr):
 284         """Delete an extended attribute from a specified file.
 285
 286         path - path name of file to check
 287         attr - name of attribute to delete
 288
 289         OSError is raised if an error occurs."""
 290
 291         if not os.access(path, os.F_OK):
 292             raise OSError(errno.ENOENT, 'No such file or directory', path)
 293
 294         res=libc.removexattr(path, attr)
 295         _error_check(res, path)
 296
 297     name_invalid_chars='\0'
 298     def name_valid(name):
 299         """Check that name is a valid name for an extended attibute.
 300         False is returned if the name should not be used."""
 301
 302         if not name.startswith('user.'):
 303             return False
 304         return name_invalid_chars not in name
 305
 306     def binary_value_supported():
 307         """Returns True if the value of an extended attribute may contain
 308         embedded NUL characters (ASCII 0)."""
 309
 310         return False
 311
 312 else:
 313     # No available xattr support
 314
 315     def supported(path=None):
 316         """Detect whether extended attribute support is available.
 317
 318         path - path to file to check for extended attribute support.
 319         Availablity can vary from one file system to another.
 320
 321         If path is None then return True if the system in general supports
 322         extended attributes."""
 323
 324         return False
 325
 326     def present(path):
 327         """Return True if extended attributes exist on the named file."""
 328
 329         return False
 330
 331     def get(path, attr):
 332         """Get an extended attribute on a specified file.
 333
 334         path - path name of file to check
 335         attr - name of attribute to get
 336
 337         None is returned if the named attribute does not exist.  OSError
 338         is raised if path does not exist or is not readable."""
 339
 340         if not os.access(path, os.F_OK):
 341             raise OSError(errno.ENOENT, 'No such file or directory', path)
 342
 343         return
 344
 345     def listx(path):
 346         """Return a list of extended attributes set on the named file.
 347
 348         path - path name of file to check
 349
 350         OSError is raised if path does not exist or is not readable."""
 351         if not os.access(path, os.F_OK):
 352             raise OSError(errno.ENOENT, 'No such file or directory', path)
 353
 354         return []
 355
 356     def set(path, attr, value):
 357         """Set an extended attribute on a specified file.
 358
 359         path - path name of file to check
 360         attr - name of attribute to set
 361         value - value of attribute to set
 362
 363         OSError is raised if path does not exist or is not writable."""
 364
 365         raise NoXAttr(path)
 366
 367     def delete(path, attr):
 368         """Delete an extended attribute from a specified file.
 369
 370         path - path name of file to check
 371         attr - name of attribute to delete
 372
 373         OSError is raised if an error occurs."""
 374
 375         raise NoXAttr(path)
 376
 377     def name_valid(name):
 378         """Check that name is a valid name for an extended attibute.
 379         False is returned if the name should not be used."""
 380
 381         return False
 382
 383     def binary_value_supported():
 384         """Returns True if the value of an extended attribute may contain
 385         embedded NUL characters (ASCII 0)."""
 386
 387         return False
 388
 389 if __name__=='__main__':
 390     # Run some tests.
 391
 392     if len(sys.argv)>1:
 393         path=sys.argv[1]
 394     else:
 395         path='/tmp'
 396
 397     print path, supported(path)
 398     print path, present(path)
 399     print path, get(path, 'user.mime_type')
 400     print path, listx(path)
 401
 402     set(path, 'user.test', 'this is a test')
 403     print path, listx(path)
 404     print path, get(path, 'user.test')
 405     delete(path, 'user.test')
 406     print path, listx(path)