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pdfstreamparser.py
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pdfstreamparser.py
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#!/usr/bin/env python3
import re, sys
from sly import Lexer, Parser
# ========================================================================== class PdfStreamSyntax
class PdfStreamSyntax:
'''see PDF Ref. sec. 4.1; order is important: BT should preceed B, for example'''
white_spaces_raw = r"\x00\t\n\x0c\r\x20"
white_spaces = "\x00\t\n\x0c\r\x20"
delimiters_raw = r'\(\)<>\[\]{}/%'
marked_content = r'MP|DP|BMC|BDC|EMC'
compatibility_section = r'BX|EX'
xobjects = r'Do'
type3_fonts = r'd0|d1'
shading_patterns = r'sh'
general_graphics_state = r'w|J|j|M|d|ri|i|gs'
special_graphics_state = r'q|Q|cm'
color = r'CS|cs|SCN|SC|scn|sc|G|g|RG|rg|K|k'
path_construction = r'm|l|c|v|y|h|re'
path_painting = r'S|s|F|f\*|f|B\*|B|b\*|b|n'
clipping_paths = r'W\*|W'
text_state = r'Tc|Tw|Tz|TL|Tf|Tr|Ts'
text_positioning = r'Td|TD|Tm|T\*'
text_showing = r'Tj|TJ|\'|\"'
indirect_reference = r'R'
operator = '|'.join([marked_content,compatibility_section,xobjects,
type3_fonts,shading_patterns,
general_graphics_state,special_graphics_state,color,
path_construction,path_painting,clipping_paths,
text_state,text_positioning,text_showing,indirect_reference])
# ========================================================================== class PdfStreamLexer
class PdfStreamLexer(Lexer):
'''A lexer for pdf content streams'''
# Set of token names. This is always required
tokens = {INLINE_IMAGE_STREAM,
HSTRING, FLOAT, INTEGER,
BOOLEAN, NULL, NAME_OBJ,
LBRACKET, RBRACKET, LANGLE, RANGLE, LPAREN,
BT, ET, BI, OPERATOR, ERROR}
# ignore (single) chars
ignore = PdfStreamSyntax.white_spaces
# ignored patterns
ignore_comment = r'%.*'
# Text object
BT,ET = r'BT',r'ET'
# Inline image start
BI = r'BI'
# Inline image stream: PDF Ref 1.7 sec. 4.8; '(.|\n)' -- match across multiple lines, '*?' -- non-greedy matching
INLINE_IMAGE_STREAM=r'\bID\s(.|\n)*?EI\s'
# LSTRING = r"(?<!\\)\(.*?(?<!\\)\)"
HSTRING = r"<[0-9a-fA-F\n]*>"
FLOAT = r"[+\-]?(\d+\.\d*|\d*\.\d+)"
INTEGER = r"[+\-]?\d+"
BOOLEAN = r'true|false'
NULL = r'null'
NAME_OBJ = r"/[^" + PdfStreamSyntax.delimiters_raw + PdfStreamSyntax.white_spaces_raw + r"]+"
LBRACKET,RBRACKET = r"\[",r"\]"
LANGLE,RANGLE = r"<<",r">>"
# If '(' is found switch to a special lexer state
@_(r"\(")
def LPAREN(self,t):
self.push_state(PdfLiteralStringLexer)
return t
def error(self, t):
print(f'lexing error: illegal character {t.value[0]} at index {self.index}', file=sys.stderr)
self.index += 1
return t
OPERATOR = PdfStreamSyntax.operator
# ========================================================================== class PdfLiteralStringLexer
class PdfLiteralStringLexer(Lexer):
'''A special lexer for pdf literal strings'''
# Set of token names. This is always required
tokens = {LS_ESCAPED, LS_LPAREN, LS_RPAREN, LS_CHAR}
LS_ESCAPED = r"\\([nrtbf\(\)\\]|[0-7]{3})"
LS_LPAREN, LS_RPAREN = r"\(", r"\)" # This will only match unescaped parens; escaped are matched by LS_ESCAPED
LS_CHAR = r"(.|\n)" # Everything else, including linefeeds
# LS_CHAR = r"([^\\\(\)]|\n)+" # Everything else, including linefeeds
def LS_LPAREN(self,t):
self.push_state(PdfLiteralStringLexer)
return t
def LS_RPAREN(self,t):
self.pop_state()
return t
# ========================================================================== class PdfStreamParser
class PdfStreamParser(Parser):
tokens = PdfStreamLexer.tokens.union(PdfLiteralStringLexer.tokens)
start = "stream"
# Stream
@_('[ chunks ]')
def stream(self, p): return p.chunks if p.chunks else []
@_('chunk { chunk }')
def chunks(self, p): return [p.chunk0] + p.chunk1
# Chunk
@_('error_token','command','text_object','inline_image')
def chunk(self, p): return p[0]
# ERROR token (from lexer)
# this is different from error() func below which is called when illegal parsing state occurs
@_('ERROR')
def error_token(self, p): raise ValueError(f'ERROR token: {[p[0]]}')
# Command
@_('[ operands ] OPERATOR')
def command(self, p): return [p.OPERATOR, p.operands if p.operands else []]
# Text object
@_('BT stream ET')
def text_object(self, p): return ['BT',[], p.stream]
# Inline image
@_('BI [ pairs ] INLINE_IMAGE_STREAM')
def inline_image(self, p): return ['BI',[dict(p.pairs) if p.pairs else {}, p.INLINE_IMAGE_STREAM]]
# Operands
@_('operand { operand }')
def operands(self, p): return [p.operand0] + p.operand1
@_('scalar', 'array', 'dict', 'lstring')
def operand(self, p): return p[0]
# Scalars
@_('BOOLEAN','NULL','NAME_OBJ','FLOAT','INTEGER')
def scalar(self, p): return p[0]
@_('HSTRING')
def scalar(self, p): return re.sub('\n','',p[0])
# Arrays & dicts
@_('LBRACKET [ operands ] RBRACKET')
def array(self, p): return p.operands if p.operands else []
@_('LANGLE [ pairs ] RANGLE')
def dict(self, p): return dict(p.pairs) if p.pairs else {}
# Literal strings
@_('left_paren [ ls_internals ] LS_RPAREN')
def lstring(self, p): return '(' + (''.join(p.ls_internals) if p.ls_internals else '') + ')'
@_('LPAREN','LS_LPAREN')
def left_paren(self, p): return p[0]
@_('ls_internal { ls_internal }')
def ls_internals(self, p): return [p.ls_internal0] + p.ls_internal1
@_('LS_ESCAPED', 'LS_CHAR', 'lstring')
def ls_internal(self, p): return p[0]
# Pairs
@_('pair { pair }')
def pairs(self, p): return [p.pair0] + p.pair1
@_('operand operand')
def pair (self, p): return [p.operand0, p.operand1]
# Error
def error(self, p):
raise ValueError("parsing error at token %s" % str(p))
# ========================================================================== class PdfStream
class PdfStream:
'''The class provides (static) functions:
stream_to_tree()
tree_to_stream()
pass_only_text()
pass_only_vector_graphics_and_images()
for translation between the pdf stream and pdf stream tree representations.
'''
def stream_to_tree(stream:str, textOnly:bool=False, vectorGraphicsAndImagesOnly=False, XObject=None):
'''
Parse stream and return the resulting parsed PDF stream tree.
If textOnly==True only the text and state operators are parsed, i.e. the bare minimum that allows to
to extract full text–related information from the stream.
'''
assert isinstance(stream, str)
lexer, parser = PdfStreamLexer(), PdfStreamParser()
tokens = lexer.tokenize(stream)
if textOnly:
tokens = PdfStream.pass_only_text(tokens,XObject)
if vectorGraphicsAndImagesOnly:
tokens = PdfStream.pass_only_vector_graphics_and_images(tokens,XObject)
tree = parser.parse(tokens)
return tree
def pass_only_text(tokens, XObject=None):
'''
Pass the tokens in the entire BT/ET blocks and everything else except images & vector graphics,
'''
# N.B. sometimes Tf is present outside the BT/ET block!
path_construction = ['m', 'l', 'c', 'v', 'y', 'h', 're']
path_painting = ['S', 's', 'f', 'F', 'f*', 'B', 'B*', 'b', 'b*', 'n']
clipping_paths = ['W','W*']
vector_graphics = path_construction + path_painting + clipping_paths
isText,isInlineImage = False,False
args = []
for tok in tokens:
if tok.type == 'BT': isText = True; yield tok
elif tok.type == 'ET': isText = False; yield tok
elif tok.type == 'BI': isInlineImage = True
elif tok.type == 'INLINE_IMAGE_STREAM': isInlineImage = False
elif isText: yield tok
elif isInlineImage: pass
elif tok.type == 'OPERATOR':
if tok.value not in vector_graphics and tok.value != 'Do' or tok.value == 'Do' and \
not (XObject != None and args[0].value in XObject and XObject[args[0].value].Subtype == '/Image'):
for arg in args: yield arg
yield tok
args = []
else:
args.append(tok)
def pass_only_vector_graphics_and_images(tokens,XObject=None):
'''
Pass all tokens except the BT/ET blocks
'''
isText = False
args = []
for tok in tokens:
if tok.type == 'BT': isText = True
elif tok.type == 'ET': isText = False
elif not isText:
if tok.type == 'OPERATOR':
for arg in args: yield arg
yield tok
args = []
else:
args.append(tok)
def tree_to_stream(tree:list):
'''
Turn the parsed PDF stream tree back to PDF stream.
'''
pair = {'BT':'ET'}
s = ''
for leaf in tree:
# print(f'leaf: {leaf}')
cmd,args = leaf[0],leaf[1]
if cmd == 'BI': # inline image streams; note: BI's dict should be output without the outermost brackets
s += 'BI ' + \
' '.join(f'{PdfStream.obj_to_stream(k)} {PdfStream.obj_to_stream(args[0][k])}' for k in args[0]) \
+ '\n' + args[1]
else:
s += ' '.join(f'{PdfStream.obj_to_stream(arg)}' for arg in args)+' '+cmd+'\n' if len(args) != 0 else cmd+'\n'
kids = leaf[2] if len(leaf) == 3 else None
if kids != None:
s += PdfStream.tree_to_stream(kids)
s += pair[cmd]+'\n'
return s
def obj_to_stream(obj):
'''
Converts objects to string representation in accordance with the PDF syntax.
The floats are printed in a fixed point format with 10 decimal points accuracy with no trailing zeros.
'''
if isinstance(obj,dict):
return '<<' + ' '.join([PdfStream.obj_to_stream(key) + ' ' + PdfStream.obj_to_stream(obj[key]) for key in obj]) + '>>'
elif isinstance(obj,list):
return '[' + ' '.join([PdfStream.obj_to_stream(element) for element in obj]) + ']'
elif isinstance(obj,float):
return f'{obj:.10f}'.rstrip('0').rstrip('.')
else:
return f'{obj}'