webapp/django/contrib/gis/gdal/prototypes/errcheck.py

"""
 This module houses the error-checking routines used by the GDAL
 ctypes prototypes.
"""
from ctypes import c_void_p, string_at
from django.contrib.gis.gdal.error import check_err, OGRException, SRSException
from django.contrib.gis.gdal.libgdal import lgdal

# Helper routines for retrieving pointers and/or values from 
# arguments passed in by reference. 
def arg_byref(args, offset=-1):
    "Returns the pointer argument's by-refernece value."
    return args[offset]._obj.value

def ptr_byref(args, offset=-1):
    "Returns the pointer argument passed in by-reference."
    return args[offset]._obj

def check_bool(result, func, cargs):
    "Returns the boolean evaluation of the value."
    if bool(result): return True
    else: return False

### String checking Routines ###
def check_const_string(result, func, cargs, offset=None):
    """
    Similar functionality to `check_string`, but does not free the pointer.
    """
    if offset:
        check_err(result)
        ptr = ptr_byref(cargs, offset)
        return ptr.value
    else:
        return result

def check_string(result, func, cargs, offset=-1, str_result=False):
    """
    Checks the string output returned from the given function, and frees
    the string pointer allocated by OGR.  The `str_result` keyword
    may be used when the result is the string pointer, otherwise
    the OGR error code is assumed.  The `offset` keyword may be used
    to extract the string pointer passed in by-reference at the given
    slice offset in the function arguments.
    """
    if str_result:
        # For routines that return a string.
        ptr = result
        if not ptr: s = None
        else: s = string_at(result)
    else:
        # Error-code return specified.
        check_err(result)
        ptr = ptr_byref(cargs, offset)
        # Getting the string value
        s = ptr.value
    # Correctly freeing the allocated memory beind GDAL pointer 
    # w/the VSIFree routine.
    if ptr: lgdal.VSIFree(ptr)
    return s

### DataSource, Layer error-checking ###

### Envelope checking ###
def check_envelope(result, func, cargs, offset=-1):
    "Checks a function that returns an OGR Envelope by reference."
    env = ptr_byref(cargs, offset)
    return env

### Geometry error-checking routines ###
def check_geom(result, func, cargs):
    "Checks a function that returns a geometry."
    # OGR_G_Clone may return an integer, even though the
    # restype is set to c_void_p
    if isinstance(result, int):
        result = c_void_p(result)
    if not result: 
        raise OGRException('Invalid geometry pointer returned from "%s".' % func.__name__)
    return result

def check_geom_offset(result, func, cargs, offset=-1):
    "Chcks the geometry at the given offset in the C parameter list."
    check_err(result)
    geom = ptr_byref(cargs, offset=offset)
    return check_geom(geom, func, cargs)

### Spatial Reference error-checking routines ###
def check_srs(result, func, cargs):
    if isinstance(result, int):
        result = c_void_p(result)
    if not result:
        raise SRSException('Invalid spatial reference pointer returned from "%s".' % func.__name__)
    return result

### Other error-checking routines ###
def check_arg_errcode(result, func, cargs):
    """
    The error code is returned in the last argument, by reference.
    Check its value with `check_err` before returning the result.
    """
    check_err(arg_byref(cargs))
    return result

def check_errcode(result, func, cargs):
    """
    Check the error code returned (c_int).
    """
    check_err(result)
    return

def check_pointer(result, func, cargs):
    "Makes sure the result pointer is valid."
    if bool(result): 
        return result
    else: 
        raise OGRException('Invalid pointer returned from "%s"' % func.__name__)

def check_str_arg(result, func, cargs):
    """
    This is for the OSRGet[Angular|Linear]Units functions, which
    require that the returned string pointer not be freed.  This
    returns both the double and tring values.
    """
    dbl = result
    ptr = cargs[-1]._obj
    return dbl, ptr.value