def _insert_or_get_field_at(writer: BasePdfFileWriter,
fields,
path,
parent_ref=None,
modified=False,
field_obj=None):
current_partial, tail = path[0], path[1:]
for field_ref in fields:
assert isinstance(field_ref, generic.IndirectObject)
field = field_ref.get_object()
if field.get('/T', None) == current_partial:
break
else:
# have to insert a new element into the fields array
if field_obj is not None and not tail:
field = field_obj
else:
# create a generic field
field = generic.DictionaryObject()
field['/T'] = pdf_string(current_partial)
if parent_ref is not None:
field['/Parent'] = parent_ref
field_ref = writer.add_object(field)
fields.append(field_ref)
writer.update_container(fields)
modified = True
if not tail:
return modified, field_ref
# check for /Kids, and create it if necessary
try:
kids = field['/Kids']
except KeyError:
kids = field['/Kids'] = generic.ArrayObject()
writer.update_container(field)
modified = True
# recurse in to /Kids array
return _insert_or_get_field_at(writer,
kids,
tail,
parent_ref=field_ref,
modified=modified,
field_obj=field_obj)
def _prepare_sig_field(sig_field_name,
root,
update_writer: BasePdfFileWriter,
existing_fields_only=False,
lock_sig_flags=True,
**kwargs):
"""
Returns a tuple of a boolean and a reference to a signature field.
The boolean is ``True`` if the field was created, and ``False`` otherwise.
"""
if sig_field_name is None: # pragma: nocover
raise ValueError
try:
form = root['/AcroForm']
try:
fields = form['/Fields']
except KeyError:
raise ValueError('/AcroForm has no /Fields')
candidates = enumerate_sig_fields_in(fields, with_name=sig_field_name)
sig_field_ref = None
try:
field_name, value, sig_field_ref = next(candidates)
if value is not None:
raise SigningError(
'Signature field with name %s appears to be filled already.'
% sig_field_name)
except StopIteration:
if existing_fields_only:
raise SigningError(
'No empty signature field with name %s found.' %
sig_field_name)
form_created = False
except KeyError:
# we have to create the form
if existing_fields_only:
raise SigningError('This file does not contain a form.')
# no AcroForm present, so create one
form = generic.DictionaryObject()
root[pdf_name('/AcroForm')] = update_writer.add_object(form)
fields = generic.ArrayObject()
form[pdf_name('/Fields')] = fields
# now we need to mark the root as updated
update_writer.update_root()
form_created = True
sig_field_ref = None
if sig_field_ref is not None:
return False, sig_field_ref
# no signature field exists, so create one
# default: grab a reference to the first page
page_ref = update_writer.find_page_for_modification(0)[0]
sig_form_kwargs = {'include_on_page': page_ref}
sig_form_kwargs.update(**kwargs)
sig_field = SignatureFormField(sig_field_name, **sig_form_kwargs)
created, sig_field_ref = _insert_or_get_field_at(
update_writer,
fields,
path=sig_field_name.split('.'),
field_obj=sig_field)
update_writer.register_annotation(page_ref, sig_field_ref)
# make sure /SigFlags is present. If not, create it
sig_flags = 3 if lock_sig_flags else 1
form.setdefault(pdf_name('/SigFlags'), generic.NumberObject(sig_flags))
# if a field was added to an existing form, register an extra update
if not form_created:
update_writer.update_container(fields)
return True, sig_field_ref