Set TMPDIR in the environment to a unique directory for each browser

instance and delete it when the browser quits.

This is a workaround for an issue with geckodriver.  When the OpenWPM
extension is installed via `WebDriver.install_addon()`, geckodriver
makes a copy of the XPI file in TMPDIR.  However, geckodriver never
deletes that file.  So on a stateless crawl, you end up with one copy of
the XPI file for each site visited.

This workaround sets TMPDIR in the environment before creating the
geckodriver service, and then deletes the directory after
`driver.quit()` returns in `BrowserManager.run()`.  We use this
indirection because we don't have access to the name of the temporary
file, and it doesn't seem safe to just delete XPI files in /tmp.

openwpm/browser_manager.py

@@ -131,6 +131,33 @@ def launch_browser_manager(self) -> bool:
 
             crash_recovery = True
 
+        # Create a unique temporary directory that we can delete
+        # when we shut down.  Note that this doesn't force anything to
+        # use `tmpdir`, it just makes it available.
+        if self.browser_params.tmpdir is not None:
+            self.logger.debug(
+                "BROWSER %i: leftover temp directory %s?  Deleting it."
+                % (self.browser_params.browser_id, self.browser_params.tmpdir)
+            )
+            try:
+                shutil.rmtree(self.browser_params.tmpdir)
+            except Exception as e:
+                self.logger.debug(
+                    "BROWSER %i: error deleting %s: %s."
+                    % (
+                        self.browser_params.browser_id,
+                        self.browser_params.tmpdir,
+                        str(e),
+                    )
+                )
+        self.browser_params.tmpdir = Path(
+            tempfile.mkdtemp(prefix="openwpm_", dir=os.getenv("TMPDIR", default="/tmp"))
+        )
+        self.logger.debug(
+            "BROWSER %i: Using temp dir %s"
+            % (self.browser_params.browser_id, self.browser_params.tmpdir)
+        )
+
         self.logger.info("BROWSER %i: Launching browser..." % self.browser_id)
         self.is_fresh = not crash_recovery
 
@@ -332,14 +359,32 @@ def close_browser_manager(self, force: bool = False) -> None:
                     )
                     return
 
-            self.logger.debug(
-                "BROWSER %i: Browser manager closed successfully." % self.browser_id
-            )
+                self.logger.debug(
+                    "BROWSER %i: Browser manager closed successfully." % self.browser_id
+                )
             shutdown_complete = True
         finally:
             if not shutdown_complete:
                 self.kill_browser_manager()
 
+            # Delete the temporary directory used by geckodriver.
+            try:
+                self.logger.debug(
+                    "BROWSER %i: deleting temp dir %s"
+                    % (self.browser_params.browser_id, self.browser_params.tmpdir)
+                )
+                shutil.rmtree(self.browser_params.tmpdir)
+                self.browser_params.tmpdir = None
+            except Exception as e:
+                self.logger.warn(
+                    "BROWSER %i: failed to delete temp dir %s: %s"
+                    % (
+                        self.browser_params.browser_id,
+                        self.browser_params.tmpdir,
+                        str(e),
+                    )
+                )
+
     def execute_command_sequence(
         self,
         # Quoting to break cyclic import, see https://stackoverflow.com/a/39757388

openwpm/config.py

@@ -103,6 +103,7 @@ class BrowserParams(DataClassJsonMixin):
         default=Path(tempfile.gettempdir()),
         metadata=DCJConfig(encoder=path_to_str, decoder=str_to_path),
     )
+
     """
     The tmp_profile_dir defaults to the OS's temporary file folder (typically /tmp) and is where the generated 
     browser profiles and residual files are stored.
@@ -139,6 +140,18 @@ class BrowserParams(DataClassJsonMixin):
 
     """
 
+    tmpdir: Optional[Path] = field(
+        default=None,
+        metadata=DCJConfig(encoder=path_to_str, decoder=str_to_path),
+    )
+    """
+    The temporary directory used by `geckodriver`.  This is configured in
+    `BrowserManager.run` and then deleted when the browser is finished.  We do
+    this because it seems that `geckodriver` doesn't clean up its temporary
+    files (in particular, a copy of the extension XPI file), so we need to do
+    so ourselves.
+    """
+
     recovery_tar: Optional[Path] = None
     donottrack: bool = False
     tracking_protection: bool = False

openwpm/deploy_browsers/deploy_firefox.py

@@ -140,6 +140,14 @@ def deploy_firefox(
     # Launch the webdriver
     status_queue.put(("STATUS", "Launch Attempted", None))
 
+    # Use browser_params.tmpdir as the temporary directory.  This is so that
+    # geckodriver makes its copy of the extension XPI file in tmpdir, so
+    # we can delete it later and not have it left behind.  I make a shallow
+    # copy of `os.environ` because I'm a little nervous about modifying the
+    # OpenWPM process' environment.
+    env = os.environ.copy()
+    env["TMPDIR"] = str(browser_params.tmpdir)
+
     fo.binary_location = firefox_binary_path
     geckodriver_path = subprocess.check_output(
         "which geckodriver", encoding="utf-8", shell=True
@@ -149,6 +157,7 @@ def deploy_firefox(
         service=Service(
             executable_path=geckodriver_path,
             log_output=open(webdriver_interceptor.fifo, "w"),
+            env=env,
         ),
     )