131 lines
4.2 KiB
Python
131 lines
4.2 KiB
Python
# SPDX-FileCopyrightText: 2022 James R. Barlow
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# SPDX-License-Identifier: MPL-2.0
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"""Utilities for PDF/A production and confirmation with Ghostspcript."""
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from __future__ import annotations
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import base64
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from collections.abc import Iterator
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from importlib.resources import files as package_files
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from pathlib import Path
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import pikepdf
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SRGB_ICC_PROFILE_NAME = 'sRGB.icc'
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def _postscript_objdef(
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alias: str,
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dictionary: dict[str, str],
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*,
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stream_name: str | None = None,
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stream_data: bytes | None = None,
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) -> Iterator[str]:
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assert (stream_name is None) == (stream_data is None)
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objtype = '/stream' if stream_name else '/dict'
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if stream_name:
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assert stream_data is not None
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a85_data = base64.a85encode(stream_data, adobe=True).decode('ascii')
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yield f'{stream_name} ' + a85_data
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yield 'def'
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if alias != '{Catalog}': # Catalog needs no definition
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yield f'[/_objdef {alias} /type {objtype} /OBJ pdfmark'
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yield f'[{alias} <<'
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for key, val in dictionary.items():
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yield f' {key} {val}'
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yield '>> /PUT pdfmark'
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if stream_name:
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yield f'[{alias} {stream_name[1:]} /PUT pdfmark'
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def _make_postscript(icc_name: str, icc_data: bytes, colors: int) -> Iterator[str]:
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yield '%!'
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yield from _postscript_objdef(
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'{icc_PDFA}', # Not an f-string
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{'/N': str(colors)},
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stream_name='/ICCProfile',
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stream_data=icc_data,
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)
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yield ''
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yield from _postscript_objdef(
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'{OutputIntent_PDFA}',
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{
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'/Type': '/OutputIntent',
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'/S': '/GTS_PDFA1',
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'/DestOutputProfile': '{icc_PDFA}',
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'/OutputConditionIdentifier': f'({icc_name})', # Only f-string
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},
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)
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yield ''
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yield from _postscript_objdef(
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'{Catalog}', {'/OutputIntents': '[ {OutputIntent_PDFA} ]'}
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)
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def generate_pdfa_ps(target_filename: Path, icc: str = 'sRGB'):
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"""Create a Postscript PDFMARK file for Ghostscript PDF/A conversion.
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pdfmark is an extension to the Postscript language that describes some PDF
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features like bookmarks and annotations. It was originally specified Adobe
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Distiller, for Postscript to PDF conversion.
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Ghostscript uses pdfmark for PDF to PDF/A conversion as well. To use Ghostscript
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to create a PDF/A, we need to create a pdfmark file with the necessary metadata.
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This function takes care of the many version-specific bugs and peculiarities in
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Ghostscript's handling of pdfmark.
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The only information we put in specifies that we want the file to be a
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PDF/A, and we want to Ghostscript to convert objects to the sRGB colorspace
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if it runs into any object that it decides must be converted.
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Arguments:
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target_filename: filename to save
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icc: ICC identifier such as 'sRGB'
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References:
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Adobe PDFMARK Reference:
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https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/pdfmark_reference.pdf
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"""
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if icc != 'sRGB':
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raise NotImplementedError("Only supporting sRGB")
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bytes_icc_profile = (
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package_files('ocrmypdf.data') / SRGB_ICC_PROFILE_NAME
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).read_bytes()
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postscript = '\n'.join(_make_postscript(icc, bytes_icc_profile, 3))
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# We should have encoded everything to pure ASCII by this point, and
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# to be safe, only allow ASCII in PostScript
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Path(target_filename).write_text(postscript, encoding='ascii')
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return target_filename
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def file_claims_pdfa(filename: Path):
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"""Determines if the file claims to be PDF/A compliant.
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This only checks if the XMP metadata contains a PDF/A marker. It does not
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do full PDF/A validation.
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"""
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with pikepdf.open(filename) as pdf:
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pdfmeta = pdf.open_metadata()
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if not pdfmeta.pdfa_status:
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return {
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'pass': False,
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'output': 'pdf',
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'conformance': 'No PDF/A metadata in XMP',
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}
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valid_part_conforms = {'1A', '1B', '2A', '2B', '2U', '3A', '3B', '3U'}
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conformance = f'PDF/A-{pdfmeta.pdfa_status}'
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pdfa_dict: dict[str, str | bool] = {}
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if pdfmeta.pdfa_status in valid_part_conforms:
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pdfa_dict['pass'] = True
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pdfa_dict['output'] = 'pdfa'
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pdfa_dict['conformance'] = conformance
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return pdfa_dict
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