path: root/requests_cache/backends/sqlite.py

"""
.. image::
    ../_static/sqlite.png

`SQLite <https://www.sqlite.org/>`_ is a fast and lightweight SQL database engine that stores data
either in memory or in a single file on disk.

Despite its simplicity, SQLite is a powerful tool. For example, it's the primary storage system for
a number of common applications including Dropbox, Firefox, and Chrome. It's well suited for
caching, and requires no extra configuration or dependencies, which is why it's the default backend
for requests-cache.

Cache Files
^^^^^^^^^^^
The cache name will be used as the cache's filename and (optionally) its path. You can specify a
just a filename, optionally with a file extension, and it will be created in the current working
directory.

Relative Paths
~~~~~~~~~~~~~~

    >>> # Base filename only
    >>> session = CachedSession('http_cache')
    >>> print(session.cache.db_path)
    '<current working dir>/http_cache.sqlite'

    >>> # Filename with extension
    >>> session = CachedSession('http_cache.db')
    >>> print(session.cache.db_path)
    '<current working dir>/http_cache.db'

    >>> # Relative path with subdirectory
    >>> session = CachedSession('cache_dir/http_cache')
    >>> print(session.cache.db_path)
    '<current working dir>/cache_dir/http_cache.sqlite'

Absolute Paths
~~~~~~~~~~~~~~
You can also give an absolute path, including user paths (with `~`).

    >>> session = CachedSession('/home/user/.cache/http_cache')
    >>> print(session.cache.db_path)
    '/home/user/.cache/http_cache.sqlite'

    >>> session = CachedSession('~/.cache/http_cache')
    >>> print(session.cache.db_path)
    '/home/user/.cache/http_cache.sqlite'

.. note::
    Parent directories will always be created, if they don't already exist.

Special System Paths
~~~~~~~~~~~~~~~~~~~~
If you don't know exactly where you want to put your cache file, your **system's default temp
directory** or **cache directory** is a good choice.

Use a temp directory with the ``use_temp`` option:

    >>> session = CachedSession('http_cache', use_temp=True)
    >>> print(session.cache.db_path)
    '/tmp/http_cache.sqlite'

.. note::
    If the cache name is an absolute path, the ``use_temp`` option will be ignored. If it's a
    relative path, it will be relative to the temp directory.

If you want an easy cross-platform way to get the system cache directory, use the
`appdirs <https://github.com/ActiveState/appdirs>`_ library:

    >>> from appdirs import user_cache_dir
    >>> db_path = join(user_cache_dir('requests_cache'), 'http_cache')
    >>> session = CachedSession(db_path, use_temp=True)

In-Memory Caching
~~~~~~~~~~~~~~~~~
SQLite also supports `in-memory databases <https://www.sqlite.org/inmemorydb.html>`_.
You can enable this (in "shared" memory mode) with the ``use_memory`` option:

    >>> session = CachedSession('http_cache', use_memory=True)

Or specify a memory URI with additional options:

    >>> session = CachedSession(':file:memdb1?mode=memory')

Or just `:memory:`, if you are only using the cache from a single thread:

    >>> session = CachedSession(':memory:')

Performance
^^^^^^^^^^^
When working with average-sized HTTP responses (< 1MB) and using a modern SSD for file storage, you
can expect speeds of around:

* Write: 2-8ms
* Read: 0.2-0.6ms

Of course, this will vary based on hardware specs, response size, and other factors.

Concurrency
^^^^^^^^^^^
SQLite supports concurrent access, so it is safe to use from a multi-threaded and/or multi-process
application. It supports unlimited concurrent reads. Writes, however, are queued and run in serial,
so if you have a massively parallel application making large volumes of requests, you may want to
consider a different backend that's specifically made for that kind of workload, like
:py:class:`.RedisCache`.

Connection Options
^^^^^^^^^^^^^^^^^^
The SQLite backend accepts any keyword arguments for :py:func:`sqlite3.connect`. These can be passed
via :py:class:`.CachedSession`:

    >>> session = CachedSession('http_cache', timeout=30)

Or via :py:class:`.SQLiteCache`:

    >>> backend = SQLiteCache('http_cache', timeout=30)
    >>> session = CachedSession(backend=backend)

API Reference
^^^^^^^^^^^^^
.. automodsumm:: requests_cache.backends.sqlite
   :classes-only:
   :nosignatures:
"""
import sqlite3
import threading
from contextlib import contextmanager
from logging import getLogger
from os import makedirs, unlink
from os.path import abspath, basename, dirname, expanduser, isabs, isfile, join
from pathlib import Path
from tempfile import gettempdir
from typing import Collection, Iterable, Iterator, List, Tuple, Type, Union

from . import BaseCache, BaseStorage, get_valid_kwargs

MEMORY_URI = 'file::memory:?cache=shared'
SQLITE_MAX_VARIABLE_NUMBER = 999
logger = getLogger(__name__)


class SQLiteCache(BaseCache):
    """SQLite cache backend.

    Args:
        db_path: Database file path (expands user paths and creates parent dirs)
        use_temp: Store database in a temp directory (e.g., ``/tmp/http_cache.sqlite``)
        use_memory: Store database in memory instead of in a file
        fast_save: Significantly increases cache write performance, but with the possibility of data
            loss. See `pragma: synchronous <http://www.sqlite.org/pragma.html#pragma_synchronous>`_
            for details.
        kwargs: Additional keyword arguments for :py:func:`sqlite3.connect`
    """

    def __init__(self, db_path: Union[Path, str] = 'http_cache', **kwargs):
        super().__init__(**kwargs)
        self.responses = SQLitePickleDict(db_path, table_name='responses', **kwargs)
        self.redirects = SQLiteDict(db_path, table_name='redirects', **kwargs)

    def db_path(self) -> str:
        return self.responses.db_path

    def bulk_delete(self, keys):
        """Remove multiple responses and their associated redirects from the cache, with additional cleanup"""
        self.responses.bulk_delete(keys=keys)
        self.responses.vacuum()

        self.redirects.bulk_delete(keys=keys)
        self.redirects.bulk_delete(values=keys)
        self.redirects.vacuum()

    def clear(self):
        """Clear the cache. If this fails due to a corrupted cache or other I/O error, this will
        attempt to delete the cache file and re-initialize.
        """
        try:
            super().clear()
        except Exception:
            logger.exception('Failed to clear cache')
            if isfile(self.responses.db_path):
                unlink(self.responses.db_path)
            self.responses.init_db()
            self.redirects.init_db()


class SQLiteDict(BaseStorage):
    """A dictionary-like interface for SQLite"""

    def __init__(
        self,
        db_path,
        table_name='http_cache',
        fast_save=False,
        use_temp: bool = False,
        use_memory: bool = False,
        **kwargs,
    ):
        super().__init__(**kwargs)
        self.connection_kwargs = get_valid_kwargs(sqlite_template, kwargs)
        self.db_path = _get_db_path(db_path, use_temp, use_memory)
        self.fast_save = fast_save
        self.table_name = table_name

        self._lock = threading.RLock()
        self._can_commit = True
        self._local_context = threading.local()
        self.init_db()

    def init_db(self):
        """Initialize the database, if it hasn't already been"""
        self.close()
        with self._lock, self.connection() as con:
            con.execute(f'CREATE TABLE IF NOT EXISTS {self.table_name} (key PRIMARY KEY, value)')

    @contextmanager
    def connection(self, commit=False) -> Iterator[sqlite3.Connection]:
        """Get a thread-local database connection"""
        if not getattr(self._local_context, 'con', None):
            logger.debug(f'Opening connection to {self.db_path}:{self.table_name}')
            self._local_context.con = sqlite3.connect(self.db_path, **self.connection_kwargs)
            if self.fast_save:
                self._local_context.con.execute('PRAGMA synchronous = 0;')
        yield self._local_context.con
        if commit and self._can_commit:
            self._local_context.con.commit()

    def close(self):
        """Close any active connections"""
        if getattr(self._local_context, 'con', None):
            self._local_context.con.close()
            self._local_context.con = None

    @contextmanager
    def bulk_commit(self):
        """Context manager used to speed up insertion of a large number of records

        Example:

            >>> d1 = SQLiteDict('test')
            >>> with d1.bulk_commit():
            ...     for i in range(1000):
            ...         d1[i] = i * 2

        """
        self._can_commit = False
        try:
            yield
            if hasattr(self._local_context, 'con'):
                self._local_context.con.commit()
        finally:
            self._can_commit = True

    def __del__(self):
        self.close()

    def __delitem__(self, key):
        with self.connection(commit=True) as con:
            cur = con.execute(f'DELETE FROM {self.table_name} WHERE key=?', (key,))
        if not cur.rowcount:
            raise KeyError

    def __getitem__(self, key):
        with self.connection() as con:
            row = con.execute(f'SELECT value FROM {self.table_name} WHERE key=?', (key,)).fetchone()
        # raise error after the with block, otherwise the connection will be locked
        if not row:
            raise KeyError
        return row[0]

    def __setitem__(self, key, value):
        with self.connection(commit=True) as con:
            con.execute(
                f'INSERT OR REPLACE INTO {self.table_name} (key,value) VALUES (?,?)',
                (key, value),
            )

    def __iter__(self):
        with self.connection() as con:
            for row in con.execute(f'SELECT key FROM {self.table_name}'):
                yield row[0]

    def __len__(self):
        with self.connection() as con:
            return con.execute(f'SELECT COUNT(key) FROM  {self.table_name}').fetchone()[0]

    def bulk_delete(self, keys=None, values=None):
        """Delete multiple keys from the cache, without raising errors for any missing keys.
        Also supports deleting by value.
        """
        if not keys and not values:
            return

        column = 'key' if keys else 'value'
        with self.connection(commit=True) as con:
            # Split into small enough chunks for SQLite to handle
            for chunk in chunkify(keys or values):
                marks, args = _format_sequence(chunk)
                statement = f'DELETE FROM {self.table_name} WHERE {column} IN ({marks})'
                con.execute(statement, args)

    def clear(self):
        with self.connection(commit=True) as con:
            con.execute(f'DROP TABLE IF EXISTS {self.table_name}')
        self.init_db()
        self.vacuum()

    def vacuum(self):
        with self.connection(commit=True) as con:
            con.execute('VACUUM')


class SQLitePickleDict(SQLiteDict):
    """Same as :class:`SQLiteDict`, but serializes values before saving"""

    def __setitem__(self, key, value):
        serialized_value = self.serializer.dumps(value)
        if isinstance(serialized_value, bytes):
            serialized_value = sqlite3.Binary(serialized_value)
        super().__setitem__(key, serialized_value)

    def __getitem__(self, key):
        return self.serializer.loads(super().__getitem__(key))


def chunkify(iterable: Iterable, max_size=SQLITE_MAX_VARIABLE_NUMBER) -> Iterator[List]:
    """Split an iterable into chunks of a max size"""
    iterable = list(iterable)
    for index in range(0, len(iterable), max_size):
        yield iterable[index : index + max_size]


def _format_sequence(values: Collection) -> Tuple[str, List]:
    """Get SQL parameter marks for a sequence-based query, and ensure value is a sequence"""
    if not isinstance(values, Iterable):
        values = [values]
    return ','.join(['?'] * len(values)), list(values)


def _get_db_path(db_path: Union[Path, str], use_temp: bool, use_memory: bool) -> str:
    """Get resolved path for database file"""
    db_path = str(db_path)
    # Use an in-memory database, if specified
    if use_memory:
        return MEMORY_URI
    elif ':memory:' in db_path or 'mode=memory' in db_path:
        return db_path

    # Save to a temp directory, if specified
    if use_temp and not isabs(db_path):
        db_path = join(gettempdir(), db_path)

    # Expand relative and user paths (~/*), and add file extension if not specified
    db_path = abspath(expanduser(db_path))
    if '.' not in basename(db_path):
        db_path += '.sqlite'

    # Make sure parent dirs exist
    makedirs(dirname(db_path), exist_ok=True)
    return db_path


def sqlite_template(
    timeout: float = 5.0,
    detect_types: int = 0,
    isolation_level: str = None,
    check_same_thread: bool = True,
    factory: Type = None,
    cached_statements: int = 100,
    uri: bool = False,
):
    """Template function to get an accurate signature for the builtin :py:func:`sqlite3.connect`"""