[cookies] open cookie databases in read-only mode

bypasses the need to copy the entire database file
might solve #4195

gallery_dl/cookies.py

@@ -47,7 +47,7 @@ def load_cookies(cookiejar, browser_specification):
 
 def load_cookies_firefox(cookiejar, profile=None, container=None, domain=None):
     path, container_id = _firefox_cookies_database(profile, container)
-    with DatabaseCopy(path) as db:
+    with DatabaseConnection(path) as db:
 
         sql = ("SELECT name, value, host, path, isSecure, expiry "
                "FROM moz_cookies")
@@ -100,7 +100,7 @@ def load_cookies_chrome(cookiejar, browser_name, profile=None,
     path = _chrome_cookies_database(profile, config)
     _log_debug("Extracting cookies from %s", path)
 
-    with DatabaseCopy(path) as db:
+    with DatabaseConnection(path) as db:
         db.text_factory = bytes
         decryptor = get_cookie_decryptor(
             config["directory"], config["keyring"], keyring)
@@ -814,7 +814,7 @@ class DataParser:
         self.skip_to(len(self._data), description)
 
 
-class DatabaseCopy():
+class DatabaseConnection():
 
     def __init__(self, path):
         self.path = path
@@ -822,13 +822,26 @@ class DatabaseCopy():
         self.directory = None
 
     def __enter__(self):
+        try:
+            # https://www.sqlite.org/uri.html#the_uri_path
+            path = self.path.replace("?", "%3f").replace("#", "%23")
+            if util.WINDOWS:
+                path = "/" + os.path.abspath(path)
+
+            uri = "file:{}?mode=ro&immutable=1".format(path)
+            self.database = sqlite3.connect(
+                uri, uri=True, isolation_level=None, check_same_thread=False)
+            return self.database
+        except Exception:
+            _log_debug("Falling back to temporary database copy")
+
         try:
             self.directory = tempfile.TemporaryDirectory(prefix="gallery-dl-")
             path_copy = os.path.join(self.directory.name, "copy.sqlite")
             shutil.copyfile(self.path, path_copy)
-            self.database = db = sqlite3.connect(
+            self.database = sqlite3.connect(
                 path_copy, isolation_level=None, check_same_thread=False)
-            return db
+            return self.database
         except BaseException:
             if self.directory:
                 self.directory.cleanup()
@@ -836,7 +849,8 @@ class DatabaseCopy():
 
     def __exit__(self, exc, value, tb):
         self.database.close()
-        self.directory.cleanup()
+        if self.directory:
+            self.directory.cleanup()
 
 
 def Popen_communicate(*args):