Add mysqldb module

This contains common code to connect to MariaDB with Python's
mysqlclient library.

1 files changed, 93 insertions, 0 deletions

diff --git a/gn_libs/mysqldb.py b/gn_libs/mysqldb.py
new file mode 100644
index 0000000..f0bc651
--- /dev/null
+++ b/gn_libs/mysqldb.py
@@ -0,0 +1,93 @@
+"""This exte"""
+import logging
+import contextlib
+from urllib.parse import urlparse
+from typing import Any, Iterator, Protocol, Callable
+
+import MySQLdb as mdb
+
+
+_logger = logging.getLogger(__file__)
+
+
+def __check_true__(val: str) -> bool:
+    """Check whether the variable 'val' has the string value `true`."""
+    return val.strip().lower() == "true"
+
+
+def __parse_db_opts__(opts: str) -> dict:
+    """Parse database options into their appropriate values.
+
+    This assumes use of python-mysqlclient library."""
+    allowed_opts = (
+        "unix_socket", "connect_timeout", "compress", "named_pipe",
+        "init_command", "read_default_file", "read_default_group",
+        "cursorclass", "use_unicode", "charset", "collation", "auth_plugin",
+        "sql_mode", "client_flag", "multi_statements", "ssl_mode", "ssl",
+        "local_infile", "autocommit", "binary_prefix")
+    conversion_fns: dict[str, Callable] = {
+        **{opt: str for opt in allowed_opts},
+        "connect_timeout": int,
+        "compress": __check_true__,
+        "use_unicode": __check_true__,
+        # "cursorclass": __load_cursor_class__
+        "client_flag": int,
+        "multi_statements": __check_true__,
+        # "ssl": __parse_ssl_options__,
+        "local_infile": __check_true__,
+        "autocommit": __check_true__,
+        "binary_prefix": __check_true__
+    }
+    queries = tuple(filter(bool, opts.split("&")))
+    if len(queries) > 0:
+        keyvals: tuple[tuple[str, ...], ...] = tuple(
+            tuple(item.strip() for item in query.split("="))
+            for query in queries)
+        def __check_opt__(opt):
+            assert opt in allowed_opts, (
+                f"Invalid database connection option ({opt}) provided.")
+            return opt
+        return {
+            __check_opt__(key): conversion_fns[key](val)
+            for key, val in keyvals
+        }
+    return {}
+
+
+def parse_db_url(sql_uri: str) -> dict:
+    """Parse the `sql_uri` variable into a dict of connection parameters."""
+    parsed_db = urlparse(sql_uri)
+    return {
+        "host": parsed_db.hostname,
+        "port": parsed_db.port or 3306,
+        "user": parsed_db.username,
+        "password": parsed_db.password,
+        "database": parsed_db.path.strip("/").strip(),
+        **__parse_db_opts__(parsed_db.query)
+    }
+
+
+class Connection(Protocol):
+    """Type Annotation for MySQLdb's connection object"""
+
+    def commit(self):
+        """Finish a transaction and commit the changes."""
+
+    def rollback(self):
+        """Cancel the current transaction and roll back the changes."""
+
+    def cursor(self, *args, **kwargs) -> Any:
+        """A cursor in which queries may be performed"""
+
+@contextlib.contextmanager
+def database_connection(sql_uri: str, logger: logging.Logger = _logger) -> Iterator[Connection]:
+    """Connect to MySQL database."""
+    connection = mdb.connect(**parse_db_url(sql_uri))
+    try:
+        yield connection
+    except mdb.Error as _mbde:
+        logger.error("DB error encountered", exc_info=True)
+        connection.rollback()
+    finally:
+        connection.commit()
+        connection.close()