ENH: Robustify parsing for Object streams in XRef rebuilding (#2818)

Closes #2817.

pypdf/_reader.py

@@ -77,6 +77,7 @@
  NullObject,
  NumberObject,
  PdfObject,
+ StreamObject,
  TextStringObject,
  read_object,
 )
@@ -316,8 +317,6 @@ def _get_object_from_stream(
  obj_stm: EncodedStreamObject = IndirectObject(stmnum, 0, self).get_object() # type: ignore
  # This is an xref to a stream, so its type better be a stream
  assert cast(str, obj_stm["/Type"]) == "/ObjStm"
- # /N is the number of indirect objects in the stream
- assert idx < obj_stm["/N"]
  stream_data = BytesIO(obj_stm.get_data())
  for i in range(obj_stm["/N"]): # type: ignore
  read_non_whitespace(stream_data)
@@ -999,6 +998,41 @@ def _rebuild_xref_table(self, stream: StreamType) -> None:
  if generation not in self.xref:
  self.xref[generation] = {}
  self.xref[generation][idnum] = m.start(1)
+
+ logger_warning("parsing for Object Streams", __name__)
+ for g in self.xref:
+ for i in self.xref[g]:
+ # get_object in manual
+ stream.seek(self.xref[g][i], 0)
+ try:
+ _ = self.read_object_header(stream)
+ o = cast(StreamObject, read_object(stream, self))
+ if o.get("/Type", "") != "/ObjStm":
+ continue
+ strm = BytesIO(o.get_data())
+ cpt = 0
+ while True:
+ s = read_until_whitespace(strm)
+ if not s.isdigit():
+ break
+ _i = int(s)
+ skip_over_whitespace(strm)
+ strm.seek(-1, 1)
+ s = read_until_whitespace(strm)
+ if not s.isdigit(): # pragma: no cover
+ break # pragma: no cover
+ _o = int(s)
+ self.xref_objStm[_i] = (i, _o)
+ cpt += 1
+ if cpt != o.get("/N"): # pragma: no cover
+ logger_warning( # pragma: no cover
+ f"found {cpt} objects within Object({i},{g})"
+ f" whereas {o.get('/N')} expected",
+ __name__,
+ )
+ except Exception: # could be of many cause
+ pass
+
  stream.seek(0, 0)
  for m in re.finditer(rb"[\r\n \t][ \t]*trailer[\r\n \t]*(<<)", f_):
  stream.seek(m.start(1), 0)

tests/test_filters.py

@@ -5,7 +5,6 @@
 from io import BytesIO
 from itertools import product as cartesian_product
 from pathlib import Path
-from unittest.mock import patch
 
 import pytest
 from PIL import Image
@@ -225,14 +224,11 @@ def test_ccitt_fax_decode():
 
 
 @pytest.mark.enable_socket()
-@patch("pypdf._reader.logger_warning")
-def test_decompress_zlib_error(mock_logger_warning):
+def test_decompress_zlib_error(caplog):
  reader = PdfReader(BytesIO(get_data_from_url(name="tika-952445.pdf")))
  for page in reader.pages:
  page.extract_text()
- mock_logger_warning.assert_called_with(
- "incorrect startxref pointer(3)", "pypdf._reader"
- )
+ assert "incorrect startxref pointer(3)" in caplog.text
 
 
 @pytest.mark.enable_socket()

tests/test_reader.py

@@ -276,14 +276,22 @@ def test_get_images(src, expected_images):
  False,
  0,
  False,
- ["startxref on same line as offset", "incorrect startxref pointer(1)"],
+ [
+ "startxref on same line as offset",
+ "incorrect startxref pointer(1)",
+ "parsing for Object Streams",
+ ],
  ), # error on startxref, but no strict => xref rebuilt,no fail
  (
  False,
  True,
  0,
  False,
- ["startxref on same line as offset", "incorrect startxref pointer(1)"],
+ [
+ "startxref on same line as offset",
+ "incorrect startxref pointer(1)",
+ "parsing for Object Streams",
+ ],
  ),
  ],
 )
@@ -344,7 +352,10 @@ def test_issue297(caplog):
  assert caplog.text == ""
  assert "Broken xref table" in exc.value.args[0]
  reader = PdfReader(path, strict=False)
- assert normalize_warnings(caplog.text) == ["incorrect startxref pointer(1)"]
+ assert normalize_warnings(caplog.text) == [
+ "incorrect startxref pointer(1)",
+ "parsing for Object Streams",
+ ]
  reader.pages[0]
 
 
@@ -898,23 +909,28 @@ def test_form_topname_with_and_without_acroform(caplog):
 def test_extract_text_xref_issue_2(caplog):
  # pdf/0264cf510015b2a4b395a15cb23c001e.pdf
  url = "https://corpora.tika.apache.org/base/docs/govdocs1/981/981961.pdf"
- msg = "incorrect startxref pointer(2)"
+ msg = [
+ "incorrect startxref pointer(2)",
+ "parsing for Object Streams",
+ ]
  reader = PdfReader(BytesIO(get_data_from_url(url, name="tika-981961.pdf")))
  for page in reader.pages:
  page.extract_text()
- assert normalize_warnings(caplog.text) == [msg]
+ assert normalize_warnings(caplog.text) == msg
 
 
 @pytest.mark.enable_socket()
 @pytest.mark.slow()
 def test_extract_text_xref_issue_3(caplog):
  # pdf/0264cf510015b2a4b395a15cb23c001e.pdf
  url = "https://corpora.tika.apache.org/base/docs/govdocs1/977/977774.pdf"
- msg = "incorrect startxref pointer(3)"
+ msg = [
+ "incorrect startxref pointer(3)",
+ ]
  reader = PdfReader(BytesIO(get_data_from_url(url, name="tika-977774.pdf")))
  for page in reader.pages:
  page.extract_text()
- assert normalize_warnings(caplog.text) == [msg]
+ assert normalize_warnings(caplog.text) == msg
 
 
 @pytest.mark.enable_socket()
@@ -1589,3 +1605,15 @@ def test_iss2761():
  reader = PdfReader(BytesIO(get_data_from_url(url, name=name)), strict=False)
  with pytest.raises(PdfReadError):
  reader.pages[0].extract_text()
+
+
+@pytest.mark.enable_socket()
+def test_iss2817():
+ """Test for rebuiling Xref_ObjStm"""
+ url = "https://github.com/user-attachments/files/16764070/crash-7e1356f1179b4198337f282304cb611aea26a199.pdf"
+ name = "iss2817.pdf"
+ reader = PdfReader(BytesIO(get_data_from_url(url, name=name)))
+ assert (
+ reader.pages[0]["/Annots"][0].get_object()["/Contents"]
+ == "A\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0 B"
+ )