mirror of
https://github.com/Kozea/WeasyPrint.git
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427 lines
15 KiB
Python
427 lines
15 KiB
Python
# coding: utf8
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r"""
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weasyprint.pdf
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--------------
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Post-process the PDF files created by cairo and add metadata such as
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hyperlinks and bookmarks.
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Rather than trying to parse any valid PDF, we make some assumptions
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that hold for cairo in order to simplify the code:
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* All newlines are '\n', not '\r' or '\r\n'
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* Except for number 0 (which is always free) there is no "free" object.
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* Most white space separators are made of a single 0x20 space.
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* Indirect dictionary objects do not contain '>>' at the start of a line
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except to mark the end of the object, followed by 'endobj'.
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(In other words, '>>' markers for sub-dictionaries are indented.)
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* The Page Tree is flat: all kids of the root page node are page objects,
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not page tree nodes.
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However the code uses a lot of assert statements so that if an assumptions
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is not true anymore, the code should (hopefully) fail with an exception
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rather than silently behave incorrectly.
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:copyright: Copyright 2011-2012 Simon Sapin and contributors, see AUTHORS.
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:license: BSD, see LICENSE for details.
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"""
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from __future__ import division, unicode_literals
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import os
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import re
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import string
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import cairo
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from . import VERSION_STRING
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from .compat import xrange, iteritems, izip
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from .urls import iri_to_uri
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PX_TO_PT = 0.75 # 72dpi (PostSript points) / 96dpi (CSS pixels)
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class PDFFormatter(string.Formatter):
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"""Like str.format except:
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* Results are byte strings
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* The new !P conversion flags encodes a PDF string.
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(UTF-16 BE with a BOM, then backslash-escape parentheses.)
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Except for fields marked !P, everything should be ASCII-only.
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"""
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def convert_field(self, value, conversion):
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if conversion == 'P':
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# Make a round-trip back through Unicode for the .translate()
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# method. (bytes.translate only maps to single bytes.)
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# Use latin1 to map all byte values.
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return '({0})'.format(
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('\ufeff' + value).encode('utf-16-be').decode('latin1')
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.translate({40: r'\(', 41: r'\)', 92: r'\\'}))
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else:
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return super(PDFFormatter, self).convert_field(value, conversion)
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def vformat(self, format_string, args, kwargs):
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result = super(PDFFormatter, self).vformat(format_string, args, kwargs)
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return result.encode('latin1')
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pdf_format = PDFFormatter().format
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class PDFDictionary(object):
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def __init__(self, object_number, byte_string):
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self.object_number = object_number
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self.byte_string = byte_string
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def __repr__(self):
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return self.__class__.__name__ + repr(
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(self.object_number, self.byte_string))
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_re_cache = {}
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def get_value(self, key, value_re):
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regex = self._re_cache.get((key, value_re))
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if not regex:
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regex = re.compile(pdf_format('/{0} {1}', key, value_re))
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self._re_cache[key, value_re] = regex
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return regex.search(self.byte_string).group(1)
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def get_type(self):
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"""
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:returns: the value for the /Type key.
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"""
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# No end delimiter, + defaults to greedy
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return self.get_value('Type', '/(\w+)').decode('ascii')
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def get_indirect_dict(self, key, pdf_file):
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"""Read the value for `key` and follow the reference, assuming
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it is an indirect dictionary object.
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:return: a new PDFDictionary instance.
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"""
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object_number = int(self.get_value(key, '(\d+) 0 R'))
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return type(self)(object_number, pdf_file.read_object(object_number))
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def get_indirect_dict_array(self, key, pdf_file):
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"""Read the value for `key` and follow the references, assuming
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it is an array of indirect dictionary objects.
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:return: a list of new PDFDictionary instance.
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"""
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parts = self.get_value(key, '\[(.+?)\]').split(b' 0 R')
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# The array looks like this: ' <a> 0 R <b> 0 R <c> 0 R '
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# so `parts` ends up like this [' <a>', ' <b>', ' <c>', ' ']
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# With the trailing white space in the list.
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trail = parts.pop()
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assert not trail.strip()
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class_ = type(self)
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read = pdf_file.read_object
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return [class_(n, read(n)) for n in map(int, parts)]
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class PDFFile(object):
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"""
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:param fileobj:
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A seekable binary file-like object for a PDF generated by cairo.
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"""
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trailer_re = re.compile(
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b'\ntrailer\n(.+)\nstartxref\n(\d+)\n%%EOF\n$', re.DOTALL)
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def __init__(self, fileobj):
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# cairo’s trailer only has Size, Root and Info.
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# The trailer + startxref + EOF is typically under 100 bytes
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fileobj.seek(-200, os.SEEK_END)
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trailer, startxref = self.trailer_re.search(fileobj.read()).groups()
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trailer = PDFDictionary(None, trailer)
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startxref = int(startxref)
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fileobj.seek(startxref)
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line = next(fileobj)
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assert line == b'xref\n'
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line = next(fileobj)
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first_object, total_objects = line.split()
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assert first_object == b'0'
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total_objects = int(total_objects)
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line = next(fileobj)
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assert line == b'0000000000 65535 f \n'
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objects_offsets = [None]
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for object_number in xrange(1, total_objects):
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line = next(fileobj)
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assert line[10:] == b' 00000 n \n'
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objects_offsets.append(int(line[:10]))
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self.fileobj = fileobj
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#: Maps object number -> bytes from the start of the file
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self.objects_offsets = objects_offsets
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info = trailer.get_indirect_dict('Info', self)
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catalog = trailer.get_indirect_dict('Root', self)
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page_tree = catalog.get_indirect_dict('Pages', self)
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pages = page_tree.get_indirect_dict_array('Kids', self)
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# Check that the tree is flat
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assert all(p.get_type() == 'Page' for p in pages)
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self.startxref = startxref
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self.info = info
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self.catalog = catalog
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self.page_tree = page_tree
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self.pages = pages
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self.finished = False
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self.overwritten_objects_offsets = {}
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self.new_objects_offsets = []
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def read_object(self, object_number):
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"""
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:param object_number:
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An integer N so that 1 <= N < len(self.objects_offsets)
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:returns:
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The object content as a byte string.
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"""
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fileobj = self.fileobj
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fileobj.seek(self.objects_offsets[object_number])
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line = next(fileobj)
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assert line.endswith(b' 0 obj\n')
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assert int(line[:-7]) == object_number # len(b' 0 obj\n') == 7
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object_lines = []
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for line in fileobj:
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if line == b'>>\n':
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assert next(fileobj) == b'endobj\n'
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# No newline, we’ll add it when writing.
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object_lines.append(b'>>')
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return b''.join(object_lines)
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object_lines.append(line)
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def overwrite_object(self, object_number, byte_string):
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"""Write the new content for an existing object at the end of the file.
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:param object_number:
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An integer N so that 1 <= N < len(self.objects_offsets)
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:param byte_string:
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The new object content as a byte string.
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"""
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self.overwritten_objects_offsets[object_number] = (
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self._write_object(object_number, byte_string))
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def extend_dict(self, dictionary, new_content):
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"""Overwrite a dictionary object after adding content inside
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the << >> delimiters.
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"""
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assert dictionary.byte_string.endswith(b'>>')
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self.overwrite_object(
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dictionary.object_number,
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dictionary.byte_string[:-2] + new_content + b'\n>>')
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def next_object_number(self):
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"""Return the object number that would be used by write_new_object().
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"""
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return len(self.objects_offsets) + len(self.new_objects_offsets)
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def write_new_object(self, byte_string):
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"""Write a new object at the end of the file.
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:param byte_string:
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The object content as a byte string.
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:return:
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The new object number.
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"""
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object_number = self.next_object_number()
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self.new_objects_offsets.append(
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self._write_object(object_number, byte_string))
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return object_number
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def finish(self):
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"""
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Write the cross-reference table and the trailer for the new and
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overwritten objects. This makes `fileobj` a valid (updated) PDF file.
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"""
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new_startxref, write = self._start_writing()
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self.finished = True
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write(b'xref\n')
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# Don’t bother sorting or finding contiguous numbers,
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# just write a new sub-section for each overwritten object.
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for object_number, offset in iteritems(
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self.overwritten_objects_offsets):
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write(pdf_format(
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'{0} 1\n{1:010} 00000 n \n', object_number, offset))
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if self.new_objects_offsets:
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first_new_object = len(self.objects_offsets)
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write(pdf_format(
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'{0} {1}\n', first_new_object, len(self.new_objects_offsets)))
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for object_number, offset in enumerate(
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self.new_objects_offsets, start=first_new_object):
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write(pdf_format('{0:010} 00000 n \n', offset))
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write(pdf_format(
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'trailer\n<< '
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'/Size {size} /Root {root} 0 R /Info {info} 0 R /Prev {prev}'
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' >>\nstartxref\n{startxref}\n%%EOF\n',
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size=self.next_object_number(),
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root=self.catalog.object_number,
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info=self.info.object_number,
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prev=self.startxref,
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startxref=new_startxref))
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def _write_object(self, object_number, byte_string):
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offset, write = self._start_writing()
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write(pdf_format('{0} 0 obj\n', object_number))
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write(byte_string)
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write(b'\nendobj\n')
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return offset
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def _start_writing(self):
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assert not self.finished
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fileobj = self.fileobj
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fileobj.seek(0, os.SEEK_END)
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return fileobj.tell(), fileobj.write
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def flatten_bookmarks(bookmarks, depth=1):
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for label, target, children in bookmarks:
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yield label, target, depth
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for result in flatten_bookmarks(children, depth + 1):
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yield result
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def prepare_metadata(document, bookmark_root_id):
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"""Change metadata into data structures closer to the PDF objects.
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In particulare, convert from cairo units (origin a the top-left corner)
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to PDF units (origin at the bottom-left corner.)
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"""
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# X and width unchanged; Y’ = page_height - Y; height’ = -height
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# Overall * 0.75 for CSS pixels to PDF points:
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matrices = [cairo.Matrix(xx=0.75, yy=-0.75, y0=page.height * 0.75)
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for page in document.pages]
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links = []
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for page_links, matrix in izip(document.resolve_links(), matrices):
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new_page_links = []
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for link_type, target, rectangle in page_links:
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if link_type == 'internal':
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target_page, target_x, target_y = target
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target = ((target_page,) +
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matrices[target_page].transform_point(target_x, target_y))
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rect_x, rect_y, width, height = rectangle
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rect_x, rect_y = matrix.transform_point(rect_x, rect_y)
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width, height = matrix.transform_distance(width, height)
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# x, y, w, h => x0, y0, x1, y1
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rectangle = rect_x, rect_y, rect_x + width, rect_y + height
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new_page_links.append((link_type, target, rectangle))
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links.append(new_page_links)
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bookmark_root = {'Count': 0}
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bookmark_list = []
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last_id_by_depth = [bookmark_root_id]
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last_by_depth = [bookmark_root]
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for bookmark_id, (label, target, depth) in enumerate(
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flatten_bookmarks(document.make_bookmark_tree()),
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bookmark_root_id + 1):
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target_page, target_x, target_y = target
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target = (target_page,) + matrices[target_page].transform_point(
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target_x, target_y)
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bookmark = {
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'Count': 0, 'First': None, 'Last': None, 'Prev': None,
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'Next': None, 'Parent': last_id_by_depth[depth - 1],
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'label': label, 'target': target}
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if depth > len(last_by_depth) - 1:
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last_by_depth[depth - 1]['First'] = bookmark_id
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else:
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# The bookmark is sibling of last_id_by_depth[depth]
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bookmark['Prev'] = last_id_by_depth[depth]
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last_by_depth[depth]['Next'] = bookmark_id
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# Remove the bookmarks with a depth higher than the current one
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del last_by_depth[depth:]
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del last_id_by_depth[depth:]
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for i in range(depth):
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last_by_depth[i]['Count'] += 1
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last_by_depth[depth - 1]['Last'] = bookmark_id
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last_by_depth.append(bookmark)
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last_id_by_depth.append(bookmark_id)
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bookmark_list.append(bookmark)
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return bookmark_root, bookmark_list, links
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def write_pdf_metadata(document, fileobj):
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"""Append to a seekable file-like object to add PDF metadata."""
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pdf = PDFFile(fileobj)
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bookmark_root_id = pdf.next_object_number()
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bookmark_root, bookmarks, links = prepare_metadata(
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document, bookmark_root_id)
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if bookmarks:
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pdf.extend_dict(pdf.catalog, pdf_format(
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'/Outlines {0} 0 R /PageMode /UseOutlines', bookmark_root_id))
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pdf.write_new_object(pdf_format(
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'<< /Type /Outlines /Count {0} /First {1} 0 R /Last {2} 0 R\n>>',
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bookmark_root['Count'],
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bookmark_root['First'],
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bookmark_root['Last']))
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for bookmark in bookmarks:
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content = [pdf_format('<< /Title {0!P}\n', bookmark['label'])]
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content.append(pdf_format(
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'/A << /Type /Action /S /GoTo '
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'/D [{0} /XYZ {1:f} {2:f} 0] >>\n',
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*bookmark['target']))
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if bookmark['Count']:
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content.append(pdf_format('/Count {0}\n', bookmark['Count']))
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for key in ['Parent', 'Prev', 'Next', 'First', 'Last']:
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if bookmark[key]:
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content.append(pdf_format(
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'/{0} {1} 0 R\n', key, bookmark[key]))
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content.append(b'>>')
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pdf.write_new_object(b''.join(content))
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for page, page_links in zip(pdf.pages, links):
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annotations = []
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for is_internal, target, rectangle in page_links:
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content = [pdf_format(
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'<< /Type /Annot /Subtype /Link '
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'/Rect [{0:f} {1:f} {2:f} {3:f}] /Border [0 0 0]\n',
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*rectangle)]
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if is_internal == 'internal':
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content.append(pdf_format(
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'/A << /Type /Action /S /GoTo '
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'/D [{0} /XYZ {1:f} {2:f} 0] >>\n',
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*target))
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else:
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content.append(pdf_format(
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'/A << /Type /Action /S /URI /URI ({0}) >>\n',
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iri_to_uri(target)))
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content.append(b'>>')
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annotations.append(pdf.write_new_object(b''.join(content)))
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if annotations:
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pdf.extend_dict(page, pdf_format(
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'/Annots [{0}]', ' '.join(
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'{0} 0 R'.format(n) for n in annotations)))
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pdf.overwrite_object(pdf.info.object_number, pdf_format(
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'<< /Producer {producer!P} >>',
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producer=VERSION_STRING))
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pdf.finish()
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