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# $Header: /var/local/cvsroot/4Suite/Ft/Lib/Resolvers.py,v 1.3 2005/01/05 10:04:22 mbrown Exp $
"""
Specialized and useful URI resolvers
Copyright 2005 Fourthought, Inc. (USA).
Detailed license and copyright information: http://4suite.org/COPYRIGHT
Project home, documentation, distributions: http://4suite.org/
"""
import os, sys, cStringIO
from Ft.Lib import Uri
class SchemeRegistryResolver(Uri.FtUriResolver):
"""
A type of resolver that allows developers to register different callable
objects to handle different URI schemes. The default action if there
is nothing registered for the scheme will be to fall back to
UriResolverBase behavior *unless* you have in the mapping a special
scheme None. The callable object that is the value on that key will
then be used as the default for all unknown schemes.
The expected function signature for scheme call-backs matches
UriResolverBase.resolve, without the instance argument:
resolve(uri, base=None)
Reminder: Since this does not include self, if you are registering
a method, use the method instance (i.e. myresolver().handler
rather than myresolver.handler)
You can manipulate the mapping directly using the "handlers" attribute.
"""
def __init__(self, handlers=None):
"""
handlers - a Python dictionary with scheme names as keys (e.g. "http")
and callable objects as values
"""
Uri.UriResolverBase.__init__(self)
self.handlers = handlers or {}
return
def resolve(self, uri, base=None):
scheme = Uri.GetScheme(uri)
if not scheme:
if base:
scheme = Uri.GetScheme(base)
if not scheme:
#Another option is to fall back to Base class behavior
raise Uri.UriException(Uri.UriException.SCHEME_REQUIRED,
base=base, ref=uri)
func = self.handlers.get(scheme)
if not func:
func = self.handlers.get(None)
if not func:
return Uri.UriResolverBase.resolve(self, uri, base)
return func(uri, base)
#Legacy import support.
Uri.SchemeRegistryResolver = SchemeRegistryResolver
class FacadeResolver(Uri.FtUriResolver):
"""
A type of resolver that can be used to create a facade or cache of
resources by keeping a dictionary of URI to result mappings. When a
URI is provided for resolution, the mapping is first checked, and a
stream is constructed by wrapping the mapping value string.
If no match is found in the mapping, fall back to the standard
resolver logic.
You can manipulate the mapping directly using the "cache" attribute.
"""
def __init__(self, cache=None, observer=None):
"""
cache - a dictionary with mapings from URI to value (as an object
to be converted to a UTF-8 encoded string)
observer - callable object invoked on each resolution request
"""
Uri.UriResolverBase.__init__(self)
self.cache = cache or {}
self.observer = observer
return
def resolve(self, uri, base=None):
self.observer(uri, base)
#Does not factor in base. Should it?
if uri in self.cache:
cachedval = self.cache[uri]
if isinstance(cachedval, unicode):
return cStringIO.StringIO(cachedval.encode('utf-8'))
else:
return cStringIO.StringIO(str(cachedval))
return Uri.UriResolverBase.resolve(self, uri, base)
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