+
−#!/usr/bin/python2.5
+
−#
+
−# Copyright 2008 the Melange authors.
+
−#
+
−# Licensed under the Apache License, Version 2.0 (the "License");
+
−# you may not use this file except in compliance with the License.
+
−# You may obtain a copy of the License at
+
−#
+
−#   http://www.apache.org/licenses/LICENSE-2.0
+
−#
+
−# Unless required by applicable law or agreed to in writing, software
+
−# distributed under the License is distributed on an "AS IS" BASIS,
+
−# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+
−# See the License for the specific language governing permissions and
+
−# limitations under the License.
+
−
+
−"""Helpers for manipulating HTTP requests.
+
−"""
+
−
+
−__authors__ = [
+
−  '"Todd Larsen" <tlarsen@google.com>',
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−  ]
+
−
+
−
+
−import urlparse
+
−
+
−
+
−def getSingleIndexedParamValue(request, param_name, values=()):
+
−  """Returns a value indexed by a query parameter in the HTTP request.
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−  
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−  Args:
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−    request: the Django HTTP request object
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−    param_name: name of the query parameter in the HTTP request
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−    values: list (or tuple) of ordered values; one of which is
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−      retrieved by the index value of the param_name argument in
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−      the HTTP request
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−      
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−  Returns:
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−    None if the query parameter was not present, was not an integer, or
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−      was an integer that is not a valid [0..len(values)-1] index into
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−      the values list.
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−    Otherwise, returns values[int(param_name value)]
+
−  """
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−  value_idx = request.GET.get(param_name)
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−  
+
−  if isinstance(value_idx, (tuple, list)):
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−    # keep only the first argument if multiple are present
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−    value_idx = value_idx[0]
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−
+
−  try:
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−    # GET parameter 'param_name' should be an integer value index
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−    value_idx = int(value_idx)
+
−  except:
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−    # ignore bogus or missing parameter values, so return None (no message)
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−    return None
+
−    
+
−  if value_idx < 0:
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−    # value index out of range, so return None (no value)
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−    return None
+
−
+
−  if value_idx >= len(values):
+
−    # value index out of range, so return None (no value)
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−    return None
+
−
+
−  # return value associated with valid value index
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−  return values[value_idx]
+
−
+
−
+
−def getSingleIndexedParamValueIfMissing(value, request, param_name,
+
−                                        values=()):
+
−  """Returns missing value indexed by a query parameter in the HTTP request.
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−  
+
−  Args:
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−    value: an existing value, or a "False" value such as None
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−    request, param_name, values: see getSingleIndexParamValue()
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−    
+
−  Returns:
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−    value, if value is "non-False"
+
−    Otherwise, returns getSingleIndexedParamValue() result.
+
−  """
+
−  if value:
+
−    # value already present, so return it
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−    return value
+
−
+
−  return getSingleIndexedParamValue(request, param_name, values=values)
+
−
+
−
+
−# TODO(tlarsen):  write getMultipleIndexParamValues() that returns a
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−#   list of values if present, omitting those values that are
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−#   out of range
+
−
+
−
+
−def isReferrerSelf(request,
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−                   expected_prefix=None, suffix=None):
+
−  """Returns True if HTTP referrer path starts with the HTTP request path.
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−    
+
−  Args:
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−    request: the Django HTTP request object; request.path is used if
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−      expected_path is not supplied (the most common usage)
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−    expected_prefix: optional HTTP path to use instead of the one in
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−      request.path; default is None (use request.path)
+
−    suffix: suffix to remove from the HTTP request path before comparing
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−      it to the HTTP referrer path in the HTTP request object headers
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−      (this is often an link ID, for example, that may be changing from
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−      a POST referrer to a GET redirect target) 
+
−  
+
−  Returns:
+
−    True if HTTP referrer path begins with the HTTP request path (either
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−      request.path or expected_prefix instead if it was supplied), after
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−      any suffix was removed from that request path
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−    False otherwise
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−       
+
−  """
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−  http_from = request.META.get('HTTP_REFERER')
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−      
+
−  if not http_from:
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−    # no HTTP referrer, so cannot possibly start with expected prefix
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−    return False
+
−
+
−  from_path = urlparse.urlparse(http_from).path
+
−  
+
−  if not expected_prefix:
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−    # use HTTP request path, since expected_prefix was not supplied
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−    expected_prefix = request.path
+
−
+
−  if suffix:
+
−    # remove suffix (such as a link ID) before comparison
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−    chars_to_remove = len(suffix)
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−    
+
−    if not suffix.startswith('/'):
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−      chars_to_remove = chars_to_remove + 1
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−
+
−    expected_prefix = expected_prefix[:-chars_to_remove]
+
−
+
−  if not from_path.startswith(expected_prefix):
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−    # expected prefix did not match first part of HTTP referrer path
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−    return False
+
− 
+
−  # HTTP referrer started with (possibly truncated) expected prefix
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−  return True
+
−
+
−
+
−def replaceSuffix(path, old_suffix, new_suffix=None, params=None):
+
−  """Replace the last part of a URL path with something else.
+
−
+
−  Also appends an optional list of query parameters.  Used for
+
−  replacing, for example, one link ID at the end of a relative
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−  URL path with another.
+
−
+
−  Args:
+
−    path: HTTP request relative URL path (with no query arguments)
+
−    old_suffix: expected suffix at the end of request.path component;
+
−      if any False value (such as None), the empty string '' is used
+
−    new_suffix: if non-False, appended to request.path along with a
+
−      '/' separator (after removing old_suffix if necessary)
+
−    params: an optional dictionary of query parameters to append to
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−      the redirect target; appended as ?<key1>=<value1>&<key2>=...
+
−      
+
−  Returns:
+
−    /path/with/new_suffix?a=1&b=2
+
−  """    
+
−  if not old_suffix:
+
−    old_suffix = ''
+
−
+
−  old_suffix = '/' + old_suffix
+
−
+
−  if path.endswith(old_suffix):
+
−    # also removes any trailing '/' if old_suffix was empty
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−    path = path[:-len(old_suffix)]
+
−
+
−  if new_suffix:
+
−    # if present, appends new_suffix, after '/' separator
+
−    path = '%s/%s' % (path, new_suffix)
+
−
+
−  if params:
+
−    # appends any query parameters, after a '?' and separated by '&'
+
−    path = '%s?%s' % (path, '&'.join(
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−        ['%s=%s' % (p,v) for p,v in params.iteritems()]))
+
−
+
−  return path