"""

Copyright (c) Microsoft Corporation.

Licensed under the MIT license.

This module defines the Connection class, which is used to manage a connection to a database.

The class provides methods to establish a connection, create cursors, commit transactions,

roll back transactions, and close the connection.

Resource Management:

- All cursors created from this connection are tracked internally.

- When close() is called on the connection, all open cursors are automatically closed.

- Do not use any cursor after the connection is closed; doing so will raise an exception.

- Cursors are also cleaned up automatically when no longer referenced, to prevent memory leaks.

"""

import weakref

import re

import codecs

from mssql_python.cursor import Cursor

from mssql_python.helpers import add_driver_to_connection_str, sanitize_connection_string, sanitize_user_input, log

from mssql_python import ddbc_bindings

from mssql_python.pooling import PoolingManager

from mssql_python.exceptions import InterfaceError, ProgrammingError

from mssql_python.auth import process_connection_string

from mssql_python.constants import ConstantsDDBC

# Add SQL_WMETADATA constant for metadata decoding configuration

SQL_WMETADATA = -99 # Special flag for column name decoding

# UTF-16 encoding variants that should use SQL_WCHAR by default

UTF16_ENCODINGS = frozenset([

'utf-16',

'utf-16le',

'utf-16be'

])

def _validate_encoding(encoding: str) -> bool:

"""

Cached encoding validation using codecs.lookup().

Args:

encoding (str): The encoding name to validate.

Returns:

bool: True if encoding is valid, False otherwise.

Note:

Uses LRU cache to avoid repeated expensive codecs.lookup() calls.

Cache size is limited to 128 entries which should cover most use cases.

"""

try:

codecs.lookup(encoding)

return True

except LookupError:

return False

# Import all DB-API 2.0 exception classes for Connection attributes

from mssql_python.exceptions import (

Warning,

Error,

InterfaceError,

DatabaseError,

DataError,

OperationalError,

IntegrityError,

InternalError,

ProgrammingError,

NotSupportedError,

)

class Connection:

"""

A class to manage a connection to a database, compliant with DB-API 2.0 specifications.

This class provides methods to establish a connection to a database, create cursors,

commit transactions, roll back transactions, and close the connection. It is designed

to be used in a context where database operations are required, such as executing queries

and fetching results.

The Connection class supports the Python context manager protocol (with statement).

When used as a context manager, it will automatically close the connection when

exiting the context, ensuring proper resource cleanup.

Example usage:

with connect(connection_string) as conn:

cursor = conn.cursor()

cursor.execute("INSERT INTO table VALUES (?)", [value])

# Connection is automatically closed when exiting the with block

For long-lived connections, use without context manager:

conn = connect(connection_string)

try:

# Multiple operations...

finally:

conn.close()

Methods:

__init__(database: str) -> None:

connect_to_db() -> None:

cursor() -> Cursor:

commit() -> None:

rollback() -> None:

close() -> None:

__enter__() -> Connection:

__exit__() -> None:

setencoding(encoding=None, ctype=None) -> None:

setdecoding(sqltype, encoding=None, ctype=None) -> None:

getdecoding(sqltype) -> dict:

"""

# DB-API 2.0 Exception attributes

# These allow users to catch exceptions using connection.Error, connection.ProgrammingError, etc.

Warning = Warning

Error = Error

InterfaceError = InterfaceError

DatabaseError = DatabaseError

DataError = DataError

OperationalError = OperationalError

IntegrityError = IntegrityError

InternalError = InternalError

ProgrammingError = ProgrammingError

NotSupportedError = NotSupportedError

def __init__(self, connection_str: str = "", autocommit: bool = False, attrs_before: dict = None, **kwargs) -> None:

"""

Initialize the connection object with the specified connection string and parameters.

Args:

- connection_str (str): The connection string to connect to.

- autocommit (bool): If True, causes a commit to be performed after each SQL statement.

**kwargs: Additional key/value pairs for the connection string.

Not including below properties since we are driver doesn't support this:

Returns:

None

Raises:

ValueError: If the connection string is invalid or connection fails.

This method sets up the initial state for the connection object,

preparing it for further operations such as connecting to the

database, executing queries, etc.

"""

self.connection_str = self._construct_connection_string(

connection_str, **kwargs

)

self._attrs_before = attrs_before or {}

# Initialize encoding settings with defaults for Python 3

# Python 3 only has str (which is Unicode), so we use utf-16le by default

self._encoding_settings = {

'encoding': 'utf-16le',

'ctype': ConstantsDDBC.SQL_WCHAR.value

}

# Initialize decoding settings with Python 3 defaults

self._decoding_settings = {

ConstantsDDBC.SQL_CHAR.value: {

'encoding': 'utf-8',

'ctype': ConstantsDDBC.SQL_CHAR.value

},

ConstantsDDBC.SQL_WCHAR.value: {

'encoding': 'utf-16le',

'ctype': ConstantsDDBC.SQL_WCHAR.value

},

SQL_WMETADATA: {

'encoding': 'utf-16le',

'ctype': ConstantsDDBC.SQL_WCHAR.value

}

}

# Check if the connection string contains authentication parameters

# This is important for processing the connection string correctly.

# If authentication is specified, it will be processed to handle

# different authentication types like interactive, device code, etc.

if re.search(r"authentication", self.connection_str, re.IGNORECASE):

connection_result = process_connection_string(self.connection_str)

self.connection_str = connection_result[0]

if connection_result[1]:

self._attrs_before.update(connection_result[1])

self._closed = False

# Using WeakSet which automatically removes cursors when they are no longer in use

# It is a set that holds weak references to its elements.

# When an object is only weakly referenced, it can be garbage collected even if it's still in the set.

# It prevents memory leaks by ensuring that cursors are cleaned up when no longer in use without requiring explicit deletion.

# TODO: Think and implement scenarios for multi-threaded access to cursors

self._cursors = weakref.WeakSet()

# Auto-enable pooling if user never called

if not PoolingManager.is_initialized():

PoolingManager.enable()

self._pooling = PoolingManager.is_enabled()

self._conn = ddbc_bindings.Connection(self.connection_str, self._pooling, self._attrs_before)

self.setautocommit(autocommit)

def _construct_connection_string(self, connection_str: str = "", **kwargs) -> str:

"""

Construct the connection string by concatenating the connection string

with key/value pairs from kwargs.

Args:

connection_str (str): The base connection string.

**kwargs: Additional key/value pairs for the connection string.

Returns:

str: The constructed connection string.

"""

# Add the driver attribute to the connection string

conn_str = add_driver_to_connection_str(connection_str)

# Add additional key-value pairs to the connection string

for key, value in kwargs.items():

if key.lower() == "host" or key.lower() == "server":

key = "Server"

elif key.lower() == "user" or key.lower() == "uid":

key = "Uid"

elif key.lower() == "password" or key.lower() == "pwd":

key = "Pwd"

elif key.lower() == "database":

key = "Database"

elif key.lower() == "encrypt":

key = "Encrypt"

elif key.lower() == "trust_server_certificate":

key = "TrustServerCertificate"

else:

continue

conn_str += f"{key}={value};"

log('info', "Final connection string: %s", sanitize_connection_string(conn_str))

return conn_str

@property

def autocommit(self) -> bool:

"""

Return the current autocommit mode of the connection.

Returns:

bool: True if autocommit is enabled, False otherwise.

"""

return self._conn.get_autocommit()

@autocommit.setter

def autocommit(self, value: bool) -> None:

"""

Set the autocommit mode of the connection.

Args:

value (bool): True to enable autocommit, False to disable it.

Returns:

None

"""

self.setautocommit(value)

log('info', "Autocommit mode set to %s.", value)

def setautocommit(self, value: bool = False) -> None:

"""

Set the autocommit mode of the connection.

Args:

value (bool): True to enable autocommit, False to disable it.

Returns:

None

Raises:

DatabaseError: If there is an error while setting the autocommit mode.

"""

self._conn.set_autocommit(value)

def setencoding(self, encoding=None, ctype=None):

"""

Sets the text encoding for SQL statements and text parameters.

Since Python 3 only has str (which is Unicode), this method configures

how text is encoded when sending to the database.

Args:

encoding (str, optional): The encoding to use. This must be a valid Python

encoding that converts text to bytes. If None, defaults to 'utf-16le'.

ctype (int, optional): The C data type to use when passing data:

SQL_CHAR or SQL_WCHAR. If not provided, SQL_WCHAR is used for

UTF-16 variants (see UTF16_ENCODINGS constant). SQL_CHAR is used for all other encodings.

Returns:

None

Raises:

ProgrammingError: If the encoding is not valid or not supported.

InterfaceError: If the connection is closed.

Example:

# For databases that only communicate with UTF-8

cnxn.setencoding(encoding='utf-8')

# For explicitly using SQL_CHAR

cnxn.setencoding(encoding='utf-8', ctype=mssql_python.SQL_CHAR)

"""

if self._closed:

raise InterfaceError(

driver_error="Connection is closed",

ddbc_error="Connection is closed",

)

# Set default encoding if not provided

if encoding is None:

encoding = 'utf-16le'

# Validate encoding using cached validation for better performance

if not _validate_encoding(encoding):

# Log the sanitized encoding for security

log('warning', "Invalid encoding attempted: %s", sanitize_user_input(str(encoding)))

raise ProgrammingError(

driver_error=f"Unsupported encoding: {encoding}",

ddbc_error=f"The encoding '{encoding}' is not supported by Python",

)

# Normalize encoding to casefold for more robust Unicode handling

encoding = encoding.casefold()

# Set default ctype based on encoding if not provided

if ctype is None:

if encoding in UTF16_ENCODINGS:

ctype = ConstantsDDBC.SQL_WCHAR.value

else:

ctype = ConstantsDDBC.SQL_CHAR.value

# Validate ctype

valid_ctypes = [ConstantsDDBC.SQL_CHAR.value, ConstantsDDBC.SQL_WCHAR.value]

if ctype not in valid_ctypes:

# Log the sanitized ctype for security

log('warning', "Invalid ctype attempted: %s", sanitize_user_input(str(ctype)))

raise ProgrammingError(

driver_error=f"Invalid ctype: {ctype}",

ddbc_error=f"ctype must be SQL_CHAR ({ConstantsDDBC.SQL_CHAR.value}) or SQL_WCHAR ({ConstantsDDBC.SQL_WCHAR.value})",

)

# Store the encoding settings

self._encoding_settings = {

'encoding': encoding,

'ctype': ctype

}

# Log with sanitized values for security

log('info', "Text encoding set to %s with ctype %s",

sanitize_user_input(encoding), sanitize_user_input(str(ctype)))

def getencoding(self):

"""

Gets the current text encoding settings.

Returns:

dict: A dictionary containing 'encoding' and 'ctype' keys.

Raises:

InterfaceError: If the connection is closed.

Example:

settings = cnxn.getencoding()

print(f"Current encoding: {settings['encoding']}")

print(f"Current ctype: {settings['ctype']}")

"""

if self._closed:

raise InterfaceError(

driver_error="Connection is closed",

ddbc_error="Connection is closed",

)

return self._encoding_settings.copy()

def setdecoding(self, sqltype, encoding=None, ctype=None):

"""

Sets the text decoding used when reading SQL_CHAR and SQL_WCHAR from the database.

This method configures how text data is decoded when reading from the database.

In Python 3, all text is Unicode (str), so this primarily affects the encoding

used to decode bytes from the database.

Args:

sqltype (int): The SQL type being configured: SQL_CHAR, SQL_WCHAR, or SQL_WMETADATA.

SQL_WMETADATA is a special flag for configuring column name decoding.

encoding (str, optional): The Python encoding to use when decoding the data.

If None, uses default encoding based on sqltype.

ctype (int, optional): The C data type to request from SQLGetData:

SQL_CHAR or SQL_WCHAR. If None, uses default based on encoding.

Returns:

None

Raises:

ProgrammingError: If the sqltype, encoding, or ctype is invalid.

InterfaceError: If the connection is closed.

Example:

# Configure SQL_CHAR to use UTF-8 decoding

cnxn.setdecoding(mssql_python.SQL_CHAR, encoding='utf-8')

# Configure column metadata decoding

cnxn.setdecoding(mssql_python.SQL_WMETADATA, encoding='utf-16le')

# Use explicit ctype

cnxn.setdecoding(mssql_python.SQL_WCHAR, encoding='utf-16le', ctype=mssql_python.SQL_WCHAR)

"""

if self._closed:

raise InterfaceError(

driver_error="Connection is closed",

ddbc_error="Connection is closed",

)

# Validate sqltype

valid_sqltypes = [

ConstantsDDBC.SQL_CHAR.value,

ConstantsDDBC.SQL_WCHAR.value,

SQL_WMETADATA

]

if sqltype not in valid_sqltypes:

log('warning', "Invalid sqltype attempted: %s", sanitize_user_input(str(sqltype)))

raise ProgrammingError(

driver_error=f"Invalid sqltype: {sqltype}",

ddbc_error=f"sqltype must be SQL_CHAR ({ConstantsDDBC.SQL_CHAR.value}), SQL_WCHAR ({ConstantsDDBC.SQL_WCHAR.value}), or SQL_WMETADATA ({SQL_WMETADATA})",

)

# Set default encoding based on sqltype if not provided

if encoding is None:

if sqltype == ConstantsDDBC.SQL_CHAR.value:

encoding = 'utf-8' # Default for SQL_CHAR in Python 3

else: # SQL_WCHAR or SQL_WMETADATA

encoding = 'utf-16le' # Default for SQL_WCHAR in Python 3

# Validate encoding using cached validation for better performance

if not _validate_encoding(encoding):

log('warning', "Invalid encoding attempted: %s", sanitize_user_input(str(encoding)))

raise ProgrammingError(

driver_error=f"Unsupported encoding: {encoding}",

ddbc_error=f"The encoding '{encoding}' is not supported by Python",

)

# Normalize encoding to lowercase for consistency

encoding = encoding.lower()

# Set default ctype based on encoding if not provided

if ctype is None:

if encoding in UTF16_ENCODINGS:

ctype = ConstantsDDBC.SQL_WCHAR.value

else:

ctype = ConstantsDDBC.SQL_CHAR.value

# Validate ctype

valid_ctypes = [ConstantsDDBC.SQL_CHAR.value, ConstantsDDBC.SQL_WCHAR.value]

if ctype not in valid_ctypes:

log('warning', "Invalid ctype attempted: %s", sanitize_user_input(str(ctype)))

raise ProgrammingError(

driver_error=f"Invalid ctype: {ctype}",

ddbc_error=f"ctype must be SQL_CHAR ({ConstantsDDBC.SQL_CHAR.value}) or SQL_WCHAR ({ConstantsDDBC.SQL_WCHAR.value})",

)

# Store the decoding settings for the specified sqltype

self._decoding_settings[sqltype] = {

'encoding': encoding,

'ctype': ctype

}

# Log with sanitized values for security

sqltype_name = {

ConstantsDDBC.SQL_CHAR.value: "SQL_CHAR",

ConstantsDDBC.SQL_WCHAR.value: "SQL_WCHAR",

SQL_WMETADATA: "SQL_WMETADATA"

}.get(sqltype, str(sqltype))

log('info', "Text decoding set for %s to %s with ctype %s",

sqltype_name, sanitize_user_input(encoding), sanitize_user_input(str(ctype)))

def getdecoding(self, sqltype):

"""

Gets the current text decoding settings for the specified SQL type.

Args:

sqltype (int): The SQL type to get settings for: SQL_CHAR, SQL_WCHAR, or SQL_WMETADATA.

Returns:

dict: A dictionary containing 'encoding' and 'ctype' keys for the specified sqltype.

Raises:

ProgrammingError: If the sqltype is invalid.

InterfaceError: If the connection is closed.

Example:

settings = cnxn.getdecoding(mssql_python.SQL_CHAR)

print(f"SQL_CHAR encoding: {settings['encoding']}")

print(f"SQL_CHAR ctype: {settings['ctype']}")

"""

if self._closed:

raise InterfaceError(

driver_error="Connection is closed",

ddbc_error="Connection is closed",

)

# Validate sqltype

valid_sqltypes = [

ConstantsDDBC.SQL_CHAR.value,

ConstantsDDBC.SQL_WCHAR.value,

SQL_WMETADATA

]

if sqltype not in valid_sqltypes:

raise ProgrammingError(

driver_error=f"Invalid sqltype: {sqltype}",

ddbc_error=f"sqltype must be SQL_CHAR ({ConstantsDDBC.SQL_CHAR.value}), SQL_WCHAR ({ConstantsDDBC.SQL_WCHAR.value}), or SQL_WMETADATA ({SQL_WMETADATA})",

)

return self._decoding_settings[sqltype].copy()

def cursor(self) -> Cursor:

"""

Return a new Cursor object using the connection.

This method creates and returns a new cursor object that can be used to

execute SQL queries and fetch results. The cursor is associated with the

current connection and allows interaction with the database.

Returns:

Cursor: A new cursor object for executing SQL queries.

Raises:

DatabaseError: If there is an error while creating the cursor.

InterfaceError: If there is an error related to the database interface.

"""

"""Return a new Cursor object using the connection."""

if self._closed:

# raise InterfaceError

raise InterfaceError(

driver_error="Cannot create cursor on closed connection",

ddbc_error="Cannot create cursor on closed connection",

)

cursor = Cursor(self)

self._cursors.add(cursor) # Track the cursor

return cursor

def commit(self) -> None:

"""

Commit the current transaction.

This method commits the current transaction to the database, making all

changes made during the transaction permanent. It should be called after

executing a series of SQL statements that modify the database to ensure

that the changes are saved.

Raises:

DatabaseError: If there is an error while committing the transaction.

"""

# Commit the current transaction

self._conn.commit()

log('info', "Transaction committed successfully.")

def rollback(self) -> None:

"""

Roll back the current transaction.

This method rolls back the current transaction, undoing all changes made

during the transaction. It should be called if an error occurs during the

transaction or if the changes should not be saved.

Raises:

DatabaseError: If there is an error while rolling back the transaction.

"""

# Roll back the current transaction

self._conn.rollback()

log('info', "Transaction rolled back successfully.")

def close(self) -> None:

"""

Close the connection now (rather than whenever .__del__() is called).

This method closes the connection to the database, releasing any resources

associated with it. After calling this method, the connection object should

not be used for any further operations. The same applies to all cursor objects

trying to use the connection. Note that closing a connection without committing

the changes first will cause an implicit rollback to be performed.

Raises:

DatabaseError: If there is an error while closing the connection.

"""

# Close the connection

if self._closed:

return

# Close all cursors first, but don't let one failure stop the others

if hasattr(self, '_cursors'):

# Convert to list to avoid modification during iteration

cursors_to_close = list(self._cursors)

close_errors = []

for cursor in cursors_to_close:

try:

if not cursor.closed:

cursor.close()

except Exception as e:

# Collect errors but continue closing other cursors

close_errors.append(f"Error closing cursor: {e}")

log('warning', f"Error closing cursor: {e}")

# If there were errors closing cursors, log them but continue

if close_errors:

log('warning', f"Encountered {len(close_errors)} errors while closing cursors")

# Clear the cursor set explicitly to release any internal references

self._cursors.clear()

# Close the connection even if cursor cleanup had issues

try:

if self._conn:

if not self.autocommit:

# If autocommit is disabled, rollback any uncommitted changes

# This is important to ensure no partial transactions remain

# For autocommit True, this is not necessary as each statement is committed immediately

log('info', "Rolling back uncommitted changes before closing connection.")

self._conn.rollback()

# TODO: Check potential race conditions in case of multithreaded scenarios

# Close the connection

self._conn.close()

self._conn = None

except Exception as e:

log('error', f"Error closing database connection: {e}")

# Re-raise the connection close error as it's more critical

raise

finally:

# Always mark as closed, even if there were errors

self._closed = True

log('info', "Connection closed successfully.")

def __enter__(self) -> 'Connection':

"""

Enter the context manager.

This method enables the Connection to be used with the 'with' statement.

When entering the context, it simply returns the connection object itself.

Returns:

Connection: The connection object itself.

Example:

with connect(connection_string) as conn:

cursor = conn.cursor()

cursor.execute("INSERT INTO table VALUES (?)", [value])

# Transaction will be committed automatically when exiting

"""

log('info', "Entering connection context manager.")

return self

def __exit__(self, *args) -> None:

"""

Exit the context manager.

Closes the connection when exiting the context, ensuring proper resource cleanup.

This follows the modern standard used by most database libraries.

"""

if not self._closed:

self.close()

def __del__(self):

"""

Destructor to ensure the connection is closed when the connection object is no longer needed.

This is a safety net to ensure resources are cleaned up

even if close() was not called explicitly.

"""

if "_closed" not in self.__dict__ or not self._closed:

try:

self.close()

except Exception as e:

# Dont raise exceptions from __del__ to avoid issues during garbage collection

log('error', f"Error during connection cleanup: {e}")