From 89debe60cf9ed24ba1f52a9e34464cc2a7fcf3d9 Mon Sep 17 00:00:00 2001
From: stefan6419846 <96178532+stefan6419846@users.noreply.github.com>
Date: Thu, 28 Sep 2023 08:46:46 +0200
Subject: [PATCH] BUG: Avoid isolating the graphics state multiple times (fixes
 #2219)

---
 pypdf/generic/_data_structures.py | 21 +++++++++++++
 tests/test_page.py                | 51 +++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)

diff --git a/pypdf/generic/_data_structures.py b/pypdf/generic/_data_structures.py
index 88a17d85a..ed1d06336 100644
--- a/pypdf/generic/_data_structures.py
+++ b/pypdf/generic/_data_structures.py
@@ -1023,6 +1023,8 @@ def __init__(
                 super().set_data(b_(stream_data))
             self.forced_encoding = forced_encoding
 
+        self._has_isolated_graphics_state: Optional[bool] = None
+
     def clone(
         self,
         pdf_dest: Any,
@@ -1229,12 +1231,31 @@ def operations(self, operations: List[Tuple[Any, Any]]) -> None:
         self._operations = operations
         self._data = b""
 
+    @property
+    def has_isolated_graphics_state(self) -> bool:
+        if self._has_isolated_graphics_state is None:
+            if self._operations:
+                self._has_isolated_graphics_state = self._operations[0] == "q" and self._operations[-1] == "Q"
+            elif self._data:
+                # Check for the character with the linebreak as inserted by `isolate_graphics_state`.
+                self._has_isolated_graphics_state = self._data[:2] == b"q\n" and self._data[-2:] == b"Q\n"
+            else:
+                # Empty stream.
+                self._has_isolated_graphics_state = True
+
+        return self._has_isolated_graphics_state
+
     def isolate_graphics_state(self) -> None:
+        if self.has_isolated_graphics_state:
+            # No need to isolate again.
+            return
+
         if self._operations:
             self._operations.insert(0, ([], "q"))
             self._operations.append(([], "Q"))
         elif self._data:
             self._data = b"q\n" + b_(self._data) + b"Q\n"
+        self._has_isolated_graphics_state = True
 
     # This overrides the parent method:
     def write_to_stream(
diff --git a/tests/test_page.py b/tests/test_page.py
index 1d6c49443..530821e37 100644
--- a/tests/test_page.py
+++ b/tests/test_page.py
@@ -1288,3 +1288,54 @@ def test_get_contents_from_nullobject():
     p = writer.add_blank_page(100, 100)
     p[NameObject("/Contents")] = writer._add_object(NullObject())
     p.get_contents()
+
+
+@pytest.mark.enable_socket()
+def test_has_isolated_graphics_state():
+    # Real example.
+    url = "https://github.com/py-pdf/pypdf/files/12428859/out1.pdf"
+    name = "isolate-graphics-state.pdf"
+    page = PdfReader(BytesIO(get_data_from_url(url, name=name))).pages[0]
+    content_stream = page.get_contents()
+    assert content_stream is not None
+
+    assert content_stream.has_isolated_graphics_state is False
+    content_stream.isolate_graphics_state()
+    assert content_stream.has_isolated_graphics_state is True
+
+    # Empty stream handling.
+    content_stream = ContentStream(stream=None, pdf="dummy.pdf")
+    assert content_stream.has_isolated_graphics_state is True
+
+    # Handling of string-based checks.
+    content_stream = ContentStream(stream=None, pdf="dummy.pdf")
+    content_stream.set_data(b"q\n 841.680 0 0 595.200 0.000 0.000 cm\n/Im0 Do\nQ\n\n \n")
+    assert content_stream.has_isolated_graphics_state is False
+
+    content_stream = ContentStream(stream=None, pdf="dummy.pdf")
+    content_stream.set_data(b"q\n 841.680 0 0 595.200 0.000 0.000 cm\n/Im0 Do\nQ\n")
+    assert content_stream.has_isolated_graphics_state is True
+
+    # Dummy example to test caching.
+    content_stream = ContentStream(stream=None, pdf="dummy.pdf")
+    assert content_stream._has_isolated_graphics_state is None
+    content_stream._has_isolated_graphics_state = True
+    assert content_stream.has_isolated_graphics_state is True
+    content_stream._has_isolated_graphics_state = False
+    assert content_stream.has_isolated_graphics_state is False
+
+
+@pytest.mark.enable_socket()
+def test_isolate_graphics_state():
+    url = "https://github.com/py-pdf/pypdf/files/12428859/out1.pdf"
+    name = "isolate-graphics-state.pdf"
+    page = PdfReader(BytesIO(get_data_from_url(url, name=name))).pages[0]
+    content_stream = page.get_contents()
+    assert content_stream is not None
+
+    # This page is not considered isolated at the beginning due to the final characters.
+    assert content_stream._data == b"q\n 841.680 0 0 595.200 0.000 0.000 cm\n/Im0 Do\nQ\n\n \n"
+    content_stream.isolate_graphics_state()
+    assert content_stream._data == b"q\nq\n 841.680 0 0 595.200 0.000 0.000 cm\n/Im0 Do\nQ\n\n \nQ\n"
+    content_stream.isolate_graphics_state()
+    assert content_stream._data == b"q\nq\n 841.680 0 0 595.200 0.000 0.000 cm\n/Im0 Do\nQ\n\n \nQ\n"