AttributeError: 'tuple' object has no attribute 'create_stamp'

[arik555]

I am trying to sign all the pdf documents that are being downloaded in frappe. (python web framework)
In frappe there's a function get_pdf() --> https://github.com/frappe/frappe/blob/develop/frappe/utils/pdf.py
I modified it in a way, such that before returning the pdf, just sign, and then return and proceed so that it does not break the rest of the flow.

File: pdf.py --> get_pdf()

from frappe.utils.custom_pdf_signer import sign_pdf

def get_pdf(html, options=None, output: PdfWriter | None = None):
	html = scrub_urls(html)
	html, options = prepare_options(html, options)

	options.update({"disable-javascript": "", "disable-local-file-access": ""})

	filedata = ""
	if Version(get_wkhtmltopdf_version()) > Version("0.12.3"):
		options.update({"disable-smart-shrinking": ""})

	try:
		# Set filename property to false, so no file is actually created
		filedata = pdfkit.from_string(html, options=options or {}, verbose=True)

		# create in-memory binary streams from filedata and create a PdfReader object
		reader = PdfReader(io.BytesIO(filedata))
	except OSError as e:
		if any([error in str(e) for error in PDF_CONTENT_ERRORS]):
			if not filedata:
				print(html, options)
				frappe.throw(_("PDF generation failed because of broken image links"))

			# allow pdfs with missing images if file got created
			if output:
				output.append_pages_from_reader(reader)
		else:
			raise
	finally:
		cleanup(options)

	if "password" in options:
		password = options["password"]

	if output:
		output.append_pages_from_reader(reader)
		return output

	writer = PdfWriter()
	writer.append_pages_from_reader(reader)

	if "password" in options:
		writer.encrypt(password)

	filedata = get_file_data_from_writer(writer)

	# Sign PDF and return the signed PDF maintaining the same flow.
	filedata = sign_pdf(filedata)

	return filedata


def get_file_data_from_writer(writer_obj):
	# https://docs.python.org/3/library/io.html
	stream = io.BytesIO()
	writer_obj.write(stream)

	# Change the stream position to start of the stream
	stream.seek(0)

	# Read up to size bytes from the object and return them
	return stream.read()

File: custom_pdf_signer.py ( custom script to sign the pdf )

from pyhanko.sign import fields, signers
from pyhanko import stamp
from pyhanko import pdf_utils
from pyhanko.pdf_utils import images
from pyhanko.pdf_utils.font import opentype
from pyhanko_certvalidator import ValidationContext
from pyhanko.keys import load_cert_from_pemder
from pyhanko.sign.validation import validate_pdf_signature, KeyUsageConstraints
import PyPDF2
import os
import io
from datetime import timedelta


'''
_Dependencies:_
apt-get install build-essential python3-dev -y
pip3 install pyHanko[pkcs11,image-support,opentype,xmp]==0.25.1
pip3 install PyPDF2==3.0.1
'''

DOCKER_VOL_PATH = "/home/frappe/frappe-bench/apps/frappe/frappe/utils"

FONT_DIR = f"{DOCKER_VOL_PATH}/certs/fonts"
PFX_CERTIFICATE_PASSWORD = "ABC****"
STAMP = f"{DOCKER_VOL_PATH}/certs/stamps/default.png"
MULTI_PAGE_SIGNATURE = False

raw_pfx_file = f'{DOCKER_VOL_PATH}/certs/signer_certificate.pfx' # the signer certificate
cca_india_2022_certificate_path = f'{DOCKER_VOL_PATH}/certs/CCAIndia2022.pem' # CCA India 2022
custom_text_in_stamp = "PDF Digitally Signed"


cca_india_2022_cert = load_cert_from_pemder(cca_india_2022_certificate_path)

# prepare signer certificate
signer = signers.SimpleSigner.load_pkcs12(
    pfx_file=raw_pfx_file,
    passphrase=bytes(PFX_CERTIFICATE_PASSWORD, encoding='utf-8'),
)

# prepare validation context
vc = ValidationContext(allow_fetching=True, 
    time_tolerance=timedelta(seconds=7),
    extra_trust_roots=[cca_india_2022_cert],
    other_certs=[],
)

# Determine the dimensions of the PDF (assuming A4 size for this example)
pdf_width, pdf_height = 595, 842  # A4 dimensions in points
signature_box_width, signature_box_height = 200, 100  # Adjust as needed


# Calculate the bottom right coordinates
llx = pdf_width - signature_box_width  # Lower-left x-coordinate
lly = 0  # Lower-left y-coordinate
urx = pdf_width  # Upper-right x-coordinate
ury = signature_box_height  # Upper-right y-coordinate

# Adjust the layout rule for the stamp
layout_rule = pdf_utils.layout.SimpleBoxLayoutRule(
    x_align=pdf_utils.layout.AxisAlignment.ALIGN_MID,  # or LEFT/RIGHT as per your need
    y_align=pdf_utils.layout.AxisAlignment.ALIGN_MIN,  # Aligns content to the top
    margins=pdf_utils.layout.Margins(0, 0, 0, 50)  # Adjust margins as needed
)

inner_layout_rule = pdf_utils.layout.SimpleBoxLayoutRule(
    x_align=pdf_utils.layout.AxisAlignment.ALIGN_MID,  # or LEFT/RIGHT as per your need
    y_align=pdf_utils.layout.AxisAlignment.ALIGN_MIN,  # Aligns content to the top
    margins=pdf_utils.layout.Margins(0, 0, 0, 0)  # Adjust margins as needed
)


def sign_pdf(pdf_bytes, font_type_path=None, stamp_path=None):
    # Set default paths if not provided
    font_type_path = os.path.join(FONT_DIR, "NotoSans-Regular.ttf") if not font_type_path else font_type_path
    stamp_path = STAMP if not stamp_path else stamp_path

    if not os.path.exists(font_type_path): 
        raise FileNotFoundError(f"Could not find font type at {font_type_path}")
    
    if not os.path.exists(stamp_path):
        raise FileNotFoundError(f"Could not find stamp at {stamp_path}")
    

    # Load the PDF to be signed (in-memory)
    main_pdf_io = io.BytesIO(pdf_bytes)

    # Create a BytesIO buffer for the signed PDF
    signed_pdf_io = io.BytesIO()
    
    pdf_reader = PyPDF2.PdfReader(main_pdf_io)
    # Reference for: strict=False - https://pyhanko.readthedocs.io/en/latest/faq.html
    w = pdf_utils.incremental_writer.IncrementalPdfFileWriter(main_pdf_io)

    # Get the number of pages in the PDF to be signed
    page_length = len(pdf_reader.pages) if MULTI_PAGE_SIGNATURE else 1

    # Create signature metadata and sign the pages
    for page_num in range(page_length):
        field_name = f'PDF Signature {page_num + 1}'
        signature_meta = signers.PdfSignatureMetadata(
            field_name=field_name,
            validation_context=vc,
            embed_validation_info=True,
            certify=True,
            use_pades_lta=True,
            signer_key_usage={'digital_signature', 'non_repudiation'}
        )

        # Define the signature field in the PDF
        fields.append_signature_field(
            w, sig_field_spec=fields.SigFieldSpec(
                field_name, box=(llx, lly, urx, ury), on_page=page_num
            )
        )

        # Create the stamp
        signer_stamp = stamp.TextStampStyle(
                # the 'signer' and 'ts' parameters will be interpolated by pyHanko, if present
                stamp_text=custom_text_in_stamp + '\nBy: %(signer)s\nTime: %(ts)s',
                text_box_style=pdf_utils.text.TextBoxStyle(
                    font=opentype.GlyphAccumulatorFactory(font_type_path)
                ),
                background=images.PdfImage(stamp_path, name='stamp_verified', opacity=0.5),
                background_layout=layout_rule,
                inner_content_layout=inner_layout_rule,
                border_width=0,
                background_opacity=0
            ),

        # Create the signer object with the stamp
        pdf_signer = signers.PdfSigner(
            signature_meta, signer=signer, stamp_style=signer_stamp
        )

        # Sign the PDF and write to the in-memory output
        pdf_signer.sign_pdf(w, output=signed_pdf_io)


    # Get the signed PDF data from the BytesIO buffer
    signed_pdf_io.seek(0)
    signed_pdf_data = signed_pdf_io.read()

    return signed_pdf_data

Error:

Traceback (most recent call last):
  File "apps/frappe/frappe/app.py", line 114, in application
    response = frappe.api.handle(request)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "apps/frappe/frappe/api/__init__.py", line 49, in handle
    data = endpoint(**arguments)
           ^^^^^^^^^^^^^^^^^^^^^
  File "apps/frappe/frappe/api/v1.py", line 36, in handle_rpc_call
    return frappe.handler.handle()
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "apps/frappe/frappe/handler.py", line 49, in handle
    data = execute_cmd(cmd)
           ^^^^^^^^^^^^^^^^
  File "apps/frappe/frappe/handler.py", line 85, in execute_cmd
    return frappe.call(method, **frappe.form_dict)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "apps/frappe/frappe/__init__.py", line 1778, in call
    return fn(*args, **newargs)
           ^^^^^^^^^^^^^^^^^^^^
  File "apps/frappe/frappe/utils/typing_validations.py", line 31, in wrapper
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "apps/frappe/frappe/utils/print_format.py", line 234, in download_pdf
    pdf_file = frappe.get_print(
               ^^^^^^^^^^^^^^^^^
  File "apps/frappe/frappe/__init__.py", line 2194, in get_print
    return get_pdf(html, options=pdf_options, output=output) if as_pdf else html
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "apps/frappe/frappe/utils/pdf.py", line 124, in get_pdf
    filedata = sign_pdf(filedata)
               ^^^^^^^^^^^^^^^^^^
  File "apps/frappe/frappe/utils/pdf_signer.py", line 140, in sign_pdf
    pdf_signer.sign_pdf(w, output=signed_pdf_io)
  File "env/lib/python3.11/site-packages/pyhanko/sign/signers/pdf_signer.py", line 1524, in sign_pdf
    result = asyncio.run(
             ^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/asyncio/runners.py", line 190, in run
    return runner.run(main)
           ^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/asyncio/base_events.py", line 654, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File "env/lib/python3.11/site-packages/pyhanko/sign/signers/pdf_signer.py", line 1594, in async_sign_pdf
    tbs_document = signing_session.prepare_tbs_document(
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "env/lib/python3.11/site-packages/pyhanko/sign/signers/pdf_signer.py", line 2274, in prepare_tbs_document
    sig_obj_ref = self.cms_writer.send(
                  ^^^^^^^^^^^^^^^^^^^^^
  File "env/lib/python3.11/site-packages/pyhanko/sign/signers/cms_embedder.py", line 468, in write_cms
    appearance_setup.apply(sig_annot, writer)
  File "env/lib/python3.11/site-packages/pyhanko/sign/signers/cms_embedder.py", line 263, in apply
    stamp = self._appearance_stamp(
            ^^^^^^^^^^^^^^^^^^^^^^^
  File "env/lib/python3.11/site-packages/pyhanko/sign/signers/cms_embedder.py", line 286, in _appearance_stamp
    return style.create_stamp(writer, box, text_params)
           ^^^^^^^^^^^^^^^^^^
AttributeError: 'tuple' object has no attribute 'create_stamp'

[arik555]

@MatthiasValvekens can you help me with this please.