1 """

     2  Error checking functions for GEOS ctypes prototype functions.

     3 """

     4 import os

     5 from ctypes import string_at, CDLL

     6 from ctypes.util import find_library

     7 from django.contrib.gis.geos.error import GEOSException

     8 

     9 # Getting the C library, needed to free the string pointers

    10 # returned from GEOS.

    11 if os.name == 'nt':

    12     libc_name = 'msvcrt'

    13 else:

    14     libc_name = 'libc'

    15 libc = CDLL(find_library(libc_name))

    16 

    17 ### ctypes error checking routines ###

    18 def last_arg_byref(args):

    19     "Returns the last C argument's by reference value."

    20     return args[-1]._obj.value

    21         

    22 def check_dbl(result, func, cargs):

    23     "Checks the status code and returns the double value passed in by reference."

    24     # Checking the status code

    25     if result != 1: return None

    26     # Double passed in by reference, return its value.

    27     return last_arg_byref(cargs)

    28 

    29 def check_geom(result, func, cargs):

    30     "Error checking on routines that return Geometries."

    31     if not result: 

    32         raise GEOSException('Error encountered checking Geometry returned from GEOS C function "%s".' % func.__name__)

    33     return result

    34 

    35 def check_minus_one(result, func, cargs):

    36     "Error checking on routines that should not return -1."

    37     if result == -1:

    38         raise GEOSException('Error encountered in GEOS C function "%s".' % func.__name__)

    39     else:

    40         return result

    41 

    42 def check_predicate(result, func, cargs):

    43     "Error checking for unary/binary predicate functions."

    44     val = ord(result) # getting the ordinal from the character

    45     if val == 1: return True

    46     elif val == 0: return False

    47     else:

    48         raise GEOSException('Error encountered on GEOS C predicate function "%s".' % func.__name__)

    49 

    50 def check_sized_string(result, func, cargs):

    51     "Error checking for routines that return explicitly sized strings."

    52     if not result:

    53         raise GEOSException('Invalid string pointer returned by GEOS C function "%s"' % func.__name__)

    54     # A c_size_t object is passed in by reference for the second

    55     # argument on these routines, and its needed to determine the

    56     # correct size.

    57     s = string_at(result, last_arg_byref(cargs))

    58     libc.free(result)

    59     return s

    60 

    61 def check_string(result, func, cargs):

    62     "Error checking for routines that return strings."

    63     if not result: raise GEOSException('Error encountered checking string return value in GEOS C function "%s".' % func.__name__)

    64     # Getting the string value at the pointer address.

    65     s = string_at(result)

    66     # Freeing the memory allocated by the GEOS library.

    67     libc.free(result)

    68     return s

    69 

    70 def check_zero(result, func, cargs):

    71     "Error checking on routines that should not return 0."

    72     if result == 0:

    73         raise GEOSException('Error encountered in GEOS C function "%s".' % func.__name__)

    74     else:

    75         return result

    76