Source Code for Module ndg.xacml.finder.urlpolicyfinder

  1  """NDG XACML policy finder interpreting ID references as URLs 
  2   
  3  NERC DataGrid 
  4  """ 
  5  __author__ = "R B Wilkinson" 
  6  __date__ = "02/11/11" 
  7  __copyright__ = "(C) 2011 Science and Technology Facilities Council" 
  8  __contact__ = "Philip.Kershaw@stfc.ac.uk" 
  9  __license__ = "BSD - see LICENSE file in top-level directory" 
 10  __contact__ = "Philip.Kershaw@stfc.ac.uk" 
 11  __revision__ = "$Id$" 
 12  import os 
 13   
 14  from ndg.xacml.core.policybase import PolicyBase 
 15  from ndg.xacml.finder.policyfinderbase import PolicyFinderBase 
 16  from ndg.xacml.parsers import XMLParseError 
 17  import ndg.xacml.utils.urlfetcher as urlfetcher 
 18   
 19 -class UrlPolicyFinder(PolicyFinderBase): 
 20      ''' 
 21      Concrete subclass of PolicyFinderBase that interprets ID references as URLs. 
 22      ''' 
 23   
 24      # File scheme prefix 
 25      _FILE_SCHEME = 'file://' 
 26      # Other recognised scheme prefixes 
 27      _NON_FILE_SCHEMES = ['ftp://', 'http://', 'https://'] 
 28      # Scheme to use if reference has no scheme prefix 
 29      _DEFAULT_SCHEME = _FILE_SCHEME 
 30      # String following scheme in URL 
 31      _SCHEME_SEPARATOR = '://' 
 32      # Path start implying relative path. 
 33      _RELATIVE_PATH_PREFIX = '.' + os.path.sep 
 34   
 35 -    def __init__(self, basePath): 
 36          ''' 
 37          @param basePath: base path for resolving relative references 
 38          @type basePath str 
 39          ''' 
 40          super(UrlPolicyFinder, self).__init__() 
 41          self.basePath = basePath 
 42   
 43 -    def findPolicy(self, policyIdReference, common): 
 44          """ 
 45          Retrieves a policy for a specified policy ID. 
 46          @param policyIdReference: policy ID reference 
 47          @type policyIdReference: str 
 48          @param common: parsing common data 
 49          @type common: from ndg.xacml.parsers.common.Common 
 50          @return: policy 
 51          @rtype: ndg.xacml.core.policy.Policy 
 52          @raise XMLParseError: policy of specified ID not found 
 53          """ 
 54          policy = self.policyMap.get(policyIdReference, None) 
 55          if policy is None: 
 56              policy = self._findPolicyFromReference(policyIdReference, common) 
 57          # Look up the policy by ID - this means that it will only be found if 
 58          # the ID declared in the document matches the required ID. 
 59          policy = self.policyMap.get(policyIdReference, None) 
 60          if policy is None: 
 61              raise XMLParseError("Referenced Policy of ID %r not found" % 
 62                                  policyIdReference) 
 63          return policy 
 64   
 65 -    def findPolicySet(self, policySetIdReference, common): 
 66          """ 
 67          Retrieves a policy set for a specified policy set ID. 
 68          @param policySetIdReference: policy set ID reference 
 69          @type policySetIdReference: str 
 70          @param common: parsing common data 
 71          @type common: from ndg.xacml.parsers.common.Common 
 72          @return: policy set 
 73          @rtype: ndg.xacml.core.policy.PolicySet 
 74          @raise XMLParseError: policy set of specified ID not found 
 75          """ 
 76          policySet = self.policySetMap.get(policySetIdReference, None) 
 77          if policySet is None: 
 78              policySet = self._findPolicyFromReference(policySetIdReference, 
 79                                                        common) 
 80          # Look up the policy set by ID - this means that it will only be found 
 81          # if the ID declared in the document matches the required ID. 
 82          policySet = self.policySetMap.get(policySetIdReference, None) 
 83          if policySet is None: 
 84              raise XMLParseError("Referenced PolicySet of ID %r not found" % 
 85                                  policySetIdReference) 
 86          return policySet 
 87   
 88 -    def _findPolicyFromReference(self, reference, common): 
 89          """ 
 90          Retrieves a policy or policy set for a specified ID that has not been 
 91          read already by interpreting the reference as a URL. 
 92          @param reference: ID reference 
 93          @type reference: str 
 94          @param common: parsing common data 
 95          @type common: from ndg.xacml.parsers.common.Common 
 96          @return: policy set 
 97          @rtype: ndg.xacml.core.policy.PolicySet 
 98          @raise XMLParseError: policy set of specified ID not found 
 99          """ 
100          url = self._makeUrlFromReference(reference) 
101          policyDoc = urlfetcher.fetch_stream_from_url(url) 
102          policy = PolicyBase.fromNestedSource(policyDoc, common) 
103          return policy 
104   
105 -    def _makeUrlFromReference(self, reference): 
106          """ 
107          Makes a URL from the reference. If it already begins with a known scheme 
108          prefix, the reference is not modified, otherwise it is made into a file 
109          URL (relative to the base path if it does not start with a path 
110          separator). 
111          file://dir/file and file://./dir/file are treated as relative paths. 
112          file:///dir/file is treated as an absolute path. 
113          @param reference: ID reference 
114          @type reference: str 
115          @return: URL 
116          @rtype: str 
117          """ 
118          # See if reference looks like a URL for a known scheme. 
119          if reference.startswith(self._FILE_SCHEME): 
120              path = reference[len(self._FILE_SCHEME):] 
121              if path.startswith(self._RELATIVE_PATH_PREFIX): 
122                  # Relative path - convert to absolute. 
123                  path = path[len(self._RELATIVE_PATH_PREFIX):] 
124                  url = self._FILE_SCHEME + os.path.join(self.basePath, path) 
125              elif not path.startswith(os.path.sep): 
126                  # Relative path - convert to absolute. 
127                  url = self._FILE_SCHEME + os.path.join(self.basePath, path) 
128              else: 
129                  url = reference 
130          elif [True for scheme in self._NON_FILE_SCHEMES 
131              if reference.startswith(scheme)]: 
132              url = reference 
133          else: 
134              # No scheme so use default scheme. 
135              if reference.startswith(os.path.sep): 
136                  url = self._DEFAULT_SCHEME + reference 
137              else: 
138                  url = (self._DEFAULT_SCHEME + 
139                         os.path.join(self.basePath, reference)) 
140          return url 
141