# -*- test-case-name: twisted.web.test.test_flatten -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Context-free flattener/serializer for rendering Python objects, possibly
complex or arbitrarily nested, as strings.
"""
from __future__ import division, absolute_import
from io import BytesIO
from sys import exc_info
from types import GeneratorType
from traceback import extract_tb
try:
from inspect import iscoroutine
except ImportError:
def iscoroutine(*args, **kwargs):
return False
from twisted.python.compat import unicode, nativeString, iteritems
from twisted.internet.defer import Deferred, ensureDeferred
from twisted.web._stan import Tag, slot, voidElements, Comment, CDATA, CharRef
from twisted.web.error import UnfilledSlot, UnsupportedType, FlattenerError
from twisted.web.iweb import IRenderable
def escapeForContent(data):
"""
Escape some character or UTF-8 byte data for inclusion in an HTML or XML
document, by replacing metacharacters (C{&<>}) with their entity
equivalents (C{&<>}).
This is used as an input to L{_flattenElement}'s C{dataEscaper} parameter.
@type data: C{bytes} or C{unicode}
@param data: The string to escape.
@rtype: C{bytes}
@return: The quoted form of C{data}. If C{data} is unicode, return a utf-8
encoded string.
"""
if isinstance(data, unicode):
data = data.encode('utf-8')
data = data.replace(b'&', b'&'
).replace(b'<', b'<'
).replace(b'>', b'>')
return data
def attributeEscapingDoneOutside(data):
"""
Escape some character or UTF-8 byte data for inclusion in the top level of
an attribute. L{attributeEscapingDoneOutside} actually passes the data
through unchanged, because L{writeWithAttributeEscaping} handles the
quoting of the text within attributes outside the generator returned by
L{_flattenElement}; this is used as the C{dataEscaper} argument to that
L{_flattenElement} call so that that generator does not redundantly escape
its text output.
@type data: C{bytes} or C{unicode}
@param data: The string to escape.
@return: The string, unchanged, except for encoding.
@rtype: C{bytes}
"""
if isinstance(data, unicode):
return data.encode("utf-8")
return data
def writeWithAttributeEscaping(write):
"""
Decorate a C{write} callable so that all output written is properly quoted
for inclusion within an XML attribute value.
If a L{Tag <twisted.web.template.Tag>} C{x} is flattened within the context
of the contents of another L{Tag <twisted.web.template.Tag>} C{y}, the
metacharacters (C{<>&"}) delimiting C{x} should be passed through
unchanged, but the textual content of C{x} should still be quoted, as
usual. For example: C{<y><x>&</x></y>}. That is the default behavior
of L{_flattenElement} when L{escapeForContent} is passed as the
C{dataEscaper}.
However, when a L{Tag <twisted.web.template.Tag>} C{x} is flattened within
the context of an I{attribute} of another L{Tag <twisted.web.template.Tag>}
C{y}, then the metacharacters delimiting C{x} should be quoted so that it
can be parsed from the attribute's value. In the DOM itself, this is not a
valid thing to do, but given that renderers and slots may be freely moved
around in a L{twisted.web.template} template, it is a condition which may
arise in a document and must be handled in a way which produces valid
output. So, for example, you should be able to get C{<y attr="<x />"
/>}. This should also be true for other XML/HTML meta-constructs such as
comments and CDATA, so if you were to serialize a L{comment
<twisted.web.template.Comment>} in an attribute you should get C{<y
attr="<-- comment -->" />}. Therefore in order to capture these
meta-characters, flattening is done with C{write} callable that is wrapped
with L{writeWithAttributeEscaping}.
The final case, and hopefully the much more common one as compared to
serializing L{Tag <twisted.web.template.Tag>} and arbitrary L{IRenderable}
objects within an attribute, is to serialize a simple string, and those
should be passed through for L{writeWithAttributeEscaping} to quote
without applying a second, redundant level of quoting.
@param write: A callable which will be invoked with the escaped L{bytes}.
@return: A callable that writes data with escaping.
"""
def _write(data):
write(escapeForContent(data).replace(b'"', b'"'))
return _write
def escapedCDATA(data):
"""
Escape CDATA for inclusion in a document.
@type data: L{str} or L{unicode}
@param data: The string to escape.
@rtype: L{str}
@return: The quoted form of C{data}. If C{data} is unicode, return a utf-8
encoded string.
"""
if isinstance(data, unicode):
data = data.encode('utf-8')
return data.replace(b']]>', b']]]]><![CDATA[>')
def escapedComment(data):
"""
Escape a comment for inclusion in a document.
@type data: L{str} or L{unicode}
@param data: The string to escape.
@rtype: C{str}
@return: The quoted form of C{data}. If C{data} is unicode, return a utf-8
encoded string.
"""
if isinstance(data, unicode):
data = data.encode('utf-8')
data = data.replace(b'--', b'- - ').replace(b'>', b'>')
if data and data[-1:] == b'-':
data += b' '
return data
def _getSlotValue(name, slotData, default=None):
"""
Find the value of the named slot in the given stack of slot data.
"""
for slotFrame in slotData[::-1]:
if slotFrame is not None and name in slotFrame:
return slotFrame[name]
else:
if default is not None:
return default
raise UnfilledSlot(name)
def _flattenElement(request, root, write, slotData, renderFactory,
dataEscaper):
"""
Make C{root} slightly more flat by yielding all its immediate contents as
strings, deferreds or generators that are recursive calls to itself.
@param request: A request object which will be passed to
L{IRenderable.render}.
@param root: An object to be made flatter. This may be of type C{unicode},
L{str}, L{slot}, L{Tag <twisted.web.template.Tag>}, L{tuple}, L{list},
L{types.GeneratorType}, L{Deferred}, or an object that implements
L{IRenderable}.
@param write: A callable which will be invoked with each L{bytes} produced
by flattening C{root}.
@param slotData: A L{list} of L{dict} mapping L{str} slot names to data
with which those slots will be replaced.
@param renderFactory: If not L{None}, an object that provides
L{IRenderable}.
@param dataEscaper: A 1-argument callable which takes L{bytes} or
L{unicode} and returns L{bytes}, quoted as appropriate for the
rendering context. This is really only one of two values:
L{attributeEscapingDoneOutside} or L{escapeForContent}, depending on
whether the rendering context is within an attribute or not. See the
explanation in L{writeWithAttributeEscaping}.
@return: An iterator that eventually yields L{bytes} that should be written
to the output. However it may also yield other iterators or
L{Deferred}s; if it yields another iterator, the caller will iterate
it; if it yields a L{Deferred}, the result of that L{Deferred} will
either be L{bytes}, in which case it's written, or another generator,
in which case it is iterated. See L{_flattenTree} for the trampoline
that consumes said values.
@rtype: An iterator which yields L{bytes}, L{Deferred}, and more iterators
of the same type.
"""
def keepGoing(newRoot, dataEscaper=dataEscaper,
renderFactory=renderFactory, write=write):
return _flattenElement(request, newRoot, write, slotData,
renderFactory, dataEscaper)
if isinstance(root, (bytes, unicode)):
write(dataEscaper(root))
elif isinstance(root, slot):
slotValue = _getSlotValue(root.name, slotData, root.default)
yield keepGoing(slotValue)
elif isinstance(root, CDATA):
write(b'<![CDATA[')
write(escapedCDATA(root.data))
write(b']]>')
elif isinstance(root, Comment):
write(b'<!--')
write(escapedComment(root.data))
write(b'-->')
elif isinstance(root, Tag):
slotData.append(root.slotData)
if root.render is not None:
rendererName = root.render
rootClone = root.clone(False)
rootClone.render = None
renderMethod = renderFactory.lookupRenderMethod(rendererName)
result = renderMethod(request, rootClone)
yield keepGoing(result)
slotData.pop()
return
if not root.tagName:
yield keepGoing(root.children)
return
write(b'<')
if isinstance(root.tagName, unicode):
tagName = root.tagName.encode('ascii')
else:
tagName = root.tagName
write(tagName)
for k, v in iteritems(root.attributes):
if isinstance(k, unicode):
k = k.encode('ascii')
write(b' ' + k + b'="')
# Serialize the contents of the attribute, wrapping the results of
# that serialization so that _everything_ is quoted.
yield keepGoing(
v,
attributeEscapingDoneOutside,
write=writeWithAttributeEscaping(write))
write(b'"')
if root.children or nativeString(tagName) not in voidElements:
write(b'>')
# Regardless of whether we're in an attribute or not, switch back
# to the escapeForContent dataEscaper. The contents of a tag must
# be quoted no matter what; in the top-level document, just so
# they're valid, and if they're within an attribute, they have to
# be quoted so that after applying the *un*-quoting required to re-
# parse the tag within the attribute, all the quoting is still
# correct.
yield keepGoing(root.children, escapeForContent)
write(b'</' + tagName + b'>')
else:
write(b' />')
elif isinstance(root, (tuple, list, GeneratorType)):
for element in root:
yield keepGoing(element)
elif isinstance(root, CharRef):
escaped = '&#%d;' % (root.ordinal,)
write(escaped.encode('ascii'))
elif isinstance(root, Deferred):
yield root.addCallback(lambda result: (result, keepGoing(result)))
elif iscoroutine(root):
d = ensureDeferred(root)
yield d.addCallback(lambda result: (result, keepGoing(result)))
elif IRenderable.providedBy(root):
result = root.render(request)
yield keepGoing(result, renderFactory=root)
else:
raise UnsupportedType(root)
def _flattenTree(request, root, write):
"""
Make C{root} into an iterable of L{bytes} and L{Deferred} by doing a depth
first traversal of the tree.
@param request: A request object which will be passed to
L{IRenderable.render}.
@param root: An object to be made flatter. This may be of type C{unicode},
L{bytes}, L{slot}, L{Tag <twisted.web.template.Tag>}, L{tuple},
L{list}, L{types.GeneratorType}, L{Deferred}, or something providing
L{IRenderable}.
@param write: A callable which will be invoked with each L{bytes} produced
by flattening C{root}.
@return: An iterator which yields objects of type L{bytes} and L{Deferred}.
A L{Deferred} is only yielded when one is encountered in the process of
flattening C{root}. The returned iterator must not be iterated again
until the L{Deferred} is called back.
"""
stack = [_flattenElement(request, root, write, [], None, escapeForContent)]
while stack:
try:
frame = stack[-1].gi_frame
element = next(stack[-1])
except StopIteration:
stack.pop()
except Exception as e:
stack.pop()
roots = []
for generator in stack:
roots.append(generator.gi_frame.f_locals['root'])
roots.append(frame.f_locals['root'])
raise FlattenerError(e, roots, extract_tb(exc_info()[2]))
else:
if isinstance(element, Deferred):
def cbx(originalAndToFlatten):
original, toFlatten = originalAndToFlatten
stack.append(toFlatten)
return original
yield element.addCallback(cbx)
else:
stack.append(element)
def _writeFlattenedData(state, write, result):
"""
Take strings from an iterator and pass them to a writer function.
@param state: An iterator of L{str} and L{Deferred}. L{str} instances will
be passed to C{write}. L{Deferred} instances will be waited on before
resuming iteration of C{state}.
@param write: A callable which will be invoked with each L{str}
produced by iterating C{state}.
@param result: A L{Deferred} which will be called back when C{state} has
been completely flattened into C{write} or which will be errbacked if
an exception in a generator passed to C{state} or an errback from a
L{Deferred} from state occurs.
@return: L{None}
"""
while True:
try:
element = next(state)
except StopIteration:
result.callback(None)
except:
result.errback()
else:
def cby(original):
_writeFlattenedData(state, write, result)
return original
element.addCallbacks(cby, result.errback)
break
def flatten(request, root, write):
"""
Incrementally write out a string representation of C{root} using C{write}.
In order to create a string representation, C{root} will be decomposed into
simpler objects which will themselves be decomposed and so on until strings
or objects which can easily be converted to strings are encountered.
@param request: A request object which will be passed to the C{render}
method of any L{IRenderable} provider which is encountered.
@param root: An object to be made flatter. This may be of type L{unicode},
L{bytes}, L{slot}, L{Tag <twisted.web.template.Tag>}, L{tuple},
L{list}, L{types.GeneratorType}, L{Deferred}, or something that provides
L{IRenderable}.
@param write: A callable which will be invoked with each L{bytes} produced
by flattening C{root}.
@return: A L{Deferred} which will be called back when C{root} has been
completely flattened into C{write} or which will be errbacked if an
unexpected exception occurs.
"""
result = Deferred()
state = _flattenTree(request, root, write)
_writeFlattenedData(state, write, result)
return result
def flattenString(request, root):
"""
Collate a string representation of C{root} into a single string.
This is basically gluing L{flatten} to an L{io.BytesIO} and returning
the results. See L{flatten} for the exact meanings of C{request} and
C{root}.
@return: A L{Deferred} which will be called back with a single string as
its result when C{root} has been completely flattened into C{write} or
which will be errbacked if an unexpected exception occurs.
"""
io = BytesIO()
d = flatten(request, root, io.write)
d.addCallback(lambda _: io.getvalue())
return d