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"""
Error checking functions for GEOS ctypes prototype functions.
"""
import os
from ctypes import string_at, CDLL
from ctypes.util import find_library
from django.contrib.gis.geos.error import GEOSException
# Getting the C library, needed to free the string pointers
# returned from GEOS.
if os.name == 'nt':
libc_name = 'msvcrt'
else:
libc_name = 'libc'
libc = CDLL(find_library(libc_name))
### ctypes error checking routines ###
def last_arg_byref(args):
"Returns the last C argument's by reference value."
return args[-1]._obj.value
def check_dbl(result, func, cargs):
"Checks the status code and returns the double value passed in by reference."
# Checking the status code
if result != 1: return None
# Double passed in by reference, return its value.
return last_arg_byref(cargs)
def check_geom(result, func, cargs):
"Error checking on routines that return Geometries."
if not result:
raise GEOSException('Error encountered checking Geometry returned from GEOS C function "%s".' % func.__name__)
return result
def check_minus_one(result, func, cargs):
"Error checking on routines that should not return -1."
if result == -1:
raise GEOSException('Error encountered in GEOS C function "%s".' % func.__name__)
else:
return result
def check_predicate(result, func, cargs):
"Error checking for unary/binary predicate functions."
val = ord(result) # getting the ordinal from the character
if val == 1: return True
elif val == 0: return False
else:
raise GEOSException('Error encountered on GEOS C predicate function "%s".' % func.__name__)
def check_sized_string(result, func, cargs):
"Error checking for routines that return explicitly sized strings."
if not result:
raise GEOSException('Invalid string pointer returned by GEOS C function "%s"' % func.__name__)
# A c_size_t object is passed in by reference for the second
# argument on these routines, and its needed to determine the
# correct size.
s = string_at(result, last_arg_byref(cargs))
libc.free(result)
return s
def check_string(result, func, cargs):
"Error checking for routines that return strings."
if not result: raise GEOSException('Error encountered checking string return value in GEOS C function "%s".' % func.__name__)
# Getting the string value at the pointer address.
s = string_at(result)
# Freeing the memory allocated by the GEOS library.
libc.free(result)
return s
def check_zero(result, func, cargs):
"Error checking on routines that should not return 0."
if result == 0:
raise GEOSException('Error encountered in GEOS C function "%s".' % func.__name__)
else:
return result
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