isolation_provider: Set a unique name for spawned containers

Set a unique name for spawned containers, based on the ID of the
provided document. This ID is not globally unique, as it has few bits of
entropy.  However, since we only want to avoid collisions within a
single Dangerzone invocation, and since we can't support multiple
containers running in parallel, this ID will suffice.

dangerzone/isolation_provider/container.py

@@ -129,6 +129,14 @@ class Container(IsolationProvider):
 
         return installed
 
+    def doc_to_pixels_container_name(self, document: Document) -> str:
+        """Unique container name for the doc-to-pixels phase."""
+        return f"dangerzone-doc-to-pixels-{document.id}"
+
+    def pixels_to_pdf_container_name(self, document: Document) -> str:
+        """Unique container name for the pixels-to-pdf phase."""
+        return f"dangerzone-pixels-to-pdf-{document.id}"
+
     def assert_field_type(self, val: Any, _type: object) -> None:
         # XXX: Use a stricter check than isinstance because `bool` is a subclass of
         # `int`.
@@ -172,6 +180,7 @@ class Container(IsolationProvider):
     def exec_container(
         self,
         command: List[str],
+        name: str,
         extra_args: List[str] = [],
     ) -> subprocess.Popen:
         container_runtime = self.get_runtime()
@@ -187,6 +196,7 @@ class Container(IsolationProvider):
         security_args += ["--cap-drop", "all"]
         user_args = ["-u", "dangerzone"]
         enable_stdin = ["-i"]
+        set_name = ["--name", name]
 
         prevent_leakage_args = ["--rm"]
 
@@ -196,6 +206,7 @@ class Container(IsolationProvider):
             + security_args
             + prevent_leakage_args
             + enable_stdin
+            + set_name
             + extra_args
             + [self.CONTAINER_NAME]
             + command
@@ -222,7 +233,8 @@ class Container(IsolationProvider):
             f"OCR_LANGUAGE={ocr_lang}",
         ]
 
-        pixels_to_pdf_proc = self.exec_container(command, extra_args)
+        name = self.pixels_to_pdf_container_name(document)
+        pixels_to_pdf_proc = self.exec_container(command, name, extra_args)
         if pixels_to_pdf_proc.stdout:
             for line in pixels_to_pdf_proc.stdout:
                 self.parse_progress_trusted(document, line.decode())
@@ -258,7 +270,8 @@ class Container(IsolationProvider):
             "-m",
             "dangerzone.conversion.doc_to_pixels",
         ]
-        return self.exec_container(command)
+        name = self.doc_to_pixels_container_name(document)
+        return self.exec_container(command, name=name)
 
     def get_max_parallel_conversions(self) -> int:
         # FIXME hardcoded 1 until length conversions are better handled