dangerzone/isolation_provider/base.py

@@ -94,6 +94,8 @@ class IsolationProvider(ABC):
             self.proc_stderr = subprocess.PIPE
         else:
             self.proc_stderr = subprocess.DEVNULL
+        # Store the proc stderr in memory
+        self.stderr = BytesIO()
 
     def should_capture_stderr(self) -> bool:
         return self.debug or getattr(sys, "dangerzone_dev", False)
@@ -333,10 +335,8 @@ class IsolationProvider(ABC):
         timeout_force: int = TIMEOUT_FORCE,
     ) -> Iterator[subprocess.Popen]:
         """Start a conversion process, pass it to the caller, and then clean it up."""
-        # Store the proc stderr in memory
-        stderr = BytesIO()
         p = self.start_doc_to_pixels_proc(document)
-        stderr_thread = self.start_stderr_thread(p, stderr)
+        stderr_thread = self.start_stderr_thread(p)
 
         if platform.system() != "Windows":
             assert os.getpgid(p.pid) != os.getpgid(
@@ -357,7 +357,7 @@ class IsolationProvider(ABC):
                 # Wait for the thread to complete. If it's still alive, mention it in the debug log.
                 stderr_thread.join(timeout=1)
 
-                debug_bytes = stderr.getvalue()
+                debug_bytes = self.stderr.getvalue()
                 debug_log = read_debug_text(debug_bytes)[:MAX_CONVERSION_LOG_CHARS]
 
                 incomplete = "(incomplete)\n" if stderr_thread.is_alive() else ""
@@ -371,14 +371,14 @@ class IsolationProvider(ABC):
                 )
 
     def start_stderr_thread(
-        self, process: subprocess.Popen, stderr: IO[bytes]
+        self, process: subprocess.Popen
     ) -> Optional[threading.Thread]:
         """Start a thread to read stderr from the process"""
 
         def _stream_stderr(process_stderr: IO[bytes]) -> None:
             try:
                 for line in process_stderr:
-                    stderr.write(line)
+                    self.stderr.write(line)
             except (ValueError, IOError) as e:
                 log.debug(f"Stderr stream closed: {e}")
 

dangerzone/isolation_provider/container.py

@@ -154,7 +154,7 @@ class Container(IsolationProvider):
             args,
             stdin=subprocess.PIPE,
             stdout=subprocess.PIPE,
-            stderr=self.proc_stderr,
+            stderr=subprocess.PIPE,
             startupinfo=startupinfo,
             # Start the conversion process in a new session, so that we can later on
             # kill the process group, without killing the controlling script.

dangerzone/logic.py

@@ -1,6 +1,7 @@
 import concurrent.futures
 import json
 import logging
+from io import StringIO
 from typing import Callable, List, Optional
 
 import colorama