connection.py

import asyncio
import enum
import errno
import inspect
import io
import os
import socket
import ssl
import threading
import warnings
from distutils.version import StrictVersion
from itertools import chain
from types import MappingProxyType
from typing import (
    Any,
    Callable,
    Iterable,
    List,
    Mapping,
    Optional,
    Set,
    Tuple,
    Type,
    TypeVar,
    Union,
    cast,
)
from urllib.parse import ParseResult, parse_qs, unquote, urlparse

import async_timeout

from .compat import Protocol, TypedDict
from .exceptions import (
    AuthenticationError,
    AuthenticationWrongNumberOfArgsError,
    BusyLoadingError,
    ChildDeadlockedError,
    ConnectionError,
    DataError,
    ExecAbortError,
    InvalidResponse,
    ModuleError,
    NoPermissionError,
    NoScriptError,
    ReadOnlyError,
    RedisError,
    ResponseError,
    TimeoutError,
)
from .utils import str_if_bytes

NONBLOCKING_EXCEPTION_ERROR_NUMBERS = {
    BlockingIOError: errno.EWOULDBLOCK,
    ssl.SSLWantReadError: 2,
    ssl.SSLWantWriteError: 2,
    ssl.SSLError: 2,
}

NONBLOCKING_EXCEPTIONS = tuple(NONBLOCKING_EXCEPTION_ERROR_NUMBERS.keys())

try:
    import hiredis

except (ImportError, ModuleNotFoundError):
    HIREDIS_AVAILABLE = False
else:
    HIREDIS_AVAILABLE = True
    hiredis_version = StrictVersion(hiredis.__version__)
    if hiredis_version < StrictVersion("1.0.0"):
        warnings.warn(
            "aioredis supports hiredis @ 1.0.0 or higher. "
            f"You have hiredis @ {hiredis.__version__}. "
            "Pure-python parser will be used instead."
        )
        HIREDIS_AVAILABLE = False

SYM_STAR = b"*"
SYM_DOLLAR = b"$"
SYM_CRLF = b"\r\n"
SYM_LF = b"\n"
SYM_EMPTY = b""

SERVER_CLOSED_CONNECTION_ERROR = "Connection closed by server."


class _Sentinel(enum.Enum):
    sentinel = object()


SENTINEL = _Sentinel.sentinel
MODULE_LOAD_ERROR = "Error loading the extension. Please check the server logs."
NO_SUCH_MODULE_ERROR = "Error unloading module: no such module with that name"
MODULE_UNLOAD_NOT_POSSIBLE_ERROR = "Error unloading module: operation not possible."
MODULE_EXPORTS_DATA_TYPES_ERROR = (
    "Error unloading module: the module "
    "exports one or more module-side data "
    "types, can't unload"
)

EncodedT = Union[bytes, memoryview]
DecodedT = Union[str, int, float]
EncodableT = Union[EncodedT, DecodedT]


class _HiredisReaderArgs(TypedDict, total=False):
    protocolError: Callable[[str], Exception]
    replyError: Callable[[str], Exception]
    encoding: Optional[str]
    errors: Optional[str]


class Encoder:
    """Encode strings to bytes-like and decode bytes-like to strings"""

    __slots__ = "encoding", "encoding_errors", "decode_responses"

    def __init__(self, encoding: str, encoding_errors: str, decode_responses: bool):
        self.encoding = encoding
        self.encoding_errors = encoding_errors
        self.decode_responses = decode_responses

    def encode(self, value: EncodableT) -> EncodedT:
        """Return a bytestring or bytes-like representation of the value"""
        if isinstance(value, (bytes, memoryview)):
            return value
        if isinstance(value, bool):
            # special case bool since it is a subclass of int
            raise DataError(
                "Invalid input of type: 'bool'. "
                "Convert to a bytes, string, int or float first."
            )
        if isinstance(value, (int, float)):
            return repr(value).encode()
        if not isinstance(value, str):
            # a value we don't know how to deal with. throw an error
            typename = value.__class__.__name__  # type: ignore[unreachable]
            raise DataError(
                f"Invalid input of type: {typename!r}. "
                "Convert to a bytes, string, int or float first."
            )
        return value.encode(self.encoding, self.encoding_errors)

    def decode(self, value: EncodableT, force=False) -> EncodableT:
        """Return a unicode string from the bytes-like representation"""
        if self.decode_responses or force:
            if isinstance(value, memoryview):
                return value.tobytes().decode(self.encoding, self.encoding_errors)
            if isinstance(value, bytes):
                return value.decode(self.encoding, self.encoding_errors)
        return value


ExceptionMappingT = Mapping[str, Union[Type[Exception], Mapping[str, Type[Exception]]]]


class BaseParser:
    """Plain Python parsing class"""

    __slots__ = "_stream", "_buffer", "_read_size"

    EXCEPTION_CLASSES: ExceptionMappingT = {
        "ERR": {
            "max number of clients reached": ConnectionError,
            "Client sent AUTH, but no password is set": AuthenticationError,
            "invalid password": AuthenticationError,
            # some Redis server versions report invalid command syntax
            # in lowercase
            "wrong number of arguments for 'auth' command": AuthenticationWrongNumberOfArgsError,
            # some Redis server versions report invalid command syntax
            # in uppercase
            "wrong number of arguments for 'AUTH' command": AuthenticationWrongNumberOfArgsError,
            MODULE_LOAD_ERROR: ModuleError,
            MODULE_EXPORTS_DATA_TYPES_ERROR: ModuleError,
            NO_SUCH_MODULE_ERROR: ModuleError,
            MODULE_UNLOAD_NOT_POSSIBLE_ERROR: ModuleError,
        },
        "EXECABORT": ExecAbortError,
        "LOADING": BusyLoadingError,
        "NOSCRIPT": NoScriptError,
        "READONLY": ReadOnlyError,
        "NOAUTH": AuthenticationError,
        "NOPERM": NoPermissionError,
    }

    def __init__(self, socket_read_size: int):
        self._stream: Optional[asyncio.StreamReader] = None
        self._buffer: Optional[SocketBuffer] = None
        self._read_size = socket_read_size

    def __del__(self):
        try:
            self.on_disconnect()
        except Exception:
            pass

    def parse_error(self, response: str) -> ResponseError:
        """Parse an error response"""
        error_code = response.split(" ")[0]
        if error_code in self.EXCEPTION_CLASSES:
            response = response[len(error_code) + 1 :]
            exception_class_or_dict = self.EXCEPTION_CLASSES[error_code]
            if isinstance(exception_class_or_dict, dict):
                exception_class = exception_class_or_dict.get(response, ResponseError)
            else:
                exception_class = exception_class_or_dict
            return exception_class(response)
        return ResponseError(response)

    def on_disconnect(self):
        raise NotImplementedError()

    def on_connect(self, connection: "Connection"):
        raise NotImplementedError()

    async def can_read(self, timeout: float) -> bool:
        raise NotImplementedError()

    async def read_response(
        self,
    ) -> Union[EncodableT, ResponseError, None, List[EncodableT]]:
        raise NotImplementedError()


class SocketBuffer:
    """Async-friendly re-impl of redis-py's SocketBuffer.

    TODO: We're currently passing through two buffers,
        the asyncio.StreamReader and this. I imagine we can reduce the layers here
        while maintaining compliance with prior art.
    """

    def __init__(
        self,
        stream_reader: asyncio.StreamReader,
        socket_read_size: int,
        socket_timeout: Optional[float],
    ):
        self._stream: Optional[asyncio.StreamReader] = stream_reader
        self.socket_read_size = socket_read_size
        self.socket_timeout = socket_timeout
        self._buffer: Optional[io.BytesIO] = io.BytesIO()
        # number of bytes written to the buffer from the socket
        self.bytes_written = 0
        # number of bytes read from the buffer
        self.bytes_read = 0

    @property
    def length(self):
        return self.bytes_written - self.bytes_read

    async def _read_from_socket(
        self,
        length: Optional[int] = None,
        timeout: Union[float, None, _Sentinel] = SENTINEL,
        raise_on_timeout: bool = True,
    ) -> bool:
        buf = self._buffer
        if buf is None or self._stream is None:
            raise RedisError("Buffer is closed.")
        buf.seek(self.bytes_written)
        marker = 0
        timeout = timeout if timeout is not SENTINEL else self.socket_timeout

        try:
            while True:
                async with async_timeout.timeout(timeout):
                    data = await self._stream.read(self.socket_read_size)
                # an empty string indicates the server shutdown the socket
                if isinstance(data, bytes) and len(data) == 0:
                    raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)
                buf.write(data)
                data_length = len(data)
                self.bytes_written += data_length
                marker += data_length

                if length is not None and length > marker:
                    continue
                return True
        except (socket.timeout, asyncio.TimeoutError):
            if raise_on_timeout:
                raise TimeoutError("Timeout reading from socket")
            return False
        except NONBLOCKING_EXCEPTIONS as ex:
            # if we're in nonblocking mode and the recv raises a
            # blocking error, simply return False indicating that
            # there's no data to be read. otherwise raise the
            # original exception.
            allowed = NONBLOCKING_EXCEPTION_ERROR_NUMBERS.get(ex.__class__, -1)
            if not raise_on_timeout and ex.errno == allowed:
                return False
            raise ConnectionError(f"Error while reading from socket: {ex.args}")

    async def can_read(self, timeout: float) -> bool:
        return bool(self.length) or await self._read_from_socket(
            timeout=timeout, raise_on_timeout=False
        )

    async def read(self, length: int) -> bytes:
        length = length + 2  # make sure to read the \r\n terminator
        # make sure we've read enough data from the socket
        if length > self.length:
            await self._read_from_socket(length - self.length)

        if self._buffer is None:
            raise RedisError("Buffer is closed.")

        self._buffer.seek(self.bytes_read)
        data = self._buffer.read(length)
        self.bytes_read += len(data)

        # purge the buffer when we've consumed it all so it doesn't
        # grow forever
        if self.bytes_read == self.bytes_written:
            self.purge()

        return data[:-2]

    async def readline(self) -> bytes:
        buf = self._buffer
        if buf is None:
            raise RedisError("Buffer is closed.")

        buf.seek(self.bytes_read)
        data = buf.readline()
        while not data.endswith(SYM_CRLF):
            # there's more data in the socket that we need
            await self._read_from_socket()
            buf.seek(self.bytes_read)
            data = buf.readline()

        self.bytes_read += len(data)

        # purge the buffer when we've consumed it all so it doesn't
        # grow forever
        if self.bytes_read == self.bytes_written:
            self.purge()

        return data[:-2]

    def purge(self):
        if self._buffer is None:
            raise RedisError("Buffer is closed.")

        self._buffer.seek(0)
        self._buffer.truncate()
        self.bytes_written = 0
        self.bytes_read = 0

    def close(self):
        try:
            self.purge()
            self._buffer.close()  # type: ignore[union-attr]
        except Exception:
            # issue #633 suggests the purge/close somehow raised a
            # BadFileDescriptor error. Perhaps the client ran out of
            # memory or something else? It's probably OK to ignore
            # any error being raised from purge/close since we're
            # removing the reference to the instance below.
            pass
        self._buffer = None
        self._stream = None


class PythonParser(BaseParser):
    """Plain Python parsing class"""

    __slots__ = BaseParser.__slots__ + ("encoder",)

    def __init__(self, socket_read_size: int):
        super().__init__(socket_read_size)
        self.encoder: Optional[Encoder] = None

    def on_connect(self, connection: "Connection"):
        """Called when the stream connects"""
        self._stream = connection._reader
        if self._stream is None:
            raise RedisError("Buffer is closed.")

        self._buffer = SocketBuffer(
            self._stream, self._read_size, connection.socket_timeout
        )
        self.encoder = connection.encoder

    def on_disconnect(self):
        """Called when the stream disconnects"""
        if self._stream is not None:
            self._stream = None
        if self._buffer is not None:
            self._buffer.close()
            self._buffer = None
        self.encoder = None

    async def can_read(self, timeout: float):
        return self._buffer and bool(await self._buffer.can_read(timeout))

    async def read_response(self) -> Union[EncodableT, ResponseError, None]:
        if not self._buffer or not self.encoder:
            raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)
        raw = await self._buffer.readline()
        if not raw:
            raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)
        response: Any
        byte, response = raw[:1], raw[1:]

        if byte not in (b"-", b"+", b":", b"$", b"*"):
            raise InvalidResponse(f"Protocol Error: {raw!r}")

        # server returned an error
        if byte == b"-":
            response = response.decode("utf-8", errors="replace")
            error = self.parse_error(response)
            # if the error is a ConnectionError, raise immediately so the user
            # is notified
            if isinstance(error, ConnectionError):
                raise error
            # otherwise, we're dealing with a ResponseError that might belong
            # inside a pipeline response. the connection's read_response()
            # and/or the pipeline's execute() will raise this error if
            # necessary, so just return the exception instance here.
            return error
        # single value
        elif byte == b"+":
            pass
        # int value
        elif byte == b":":
            response = int(response)
        # bulk response
        elif byte == b"$":
            length = int(response)
            if length == -1:
                return None
            response = await self._buffer.read(length)
        # multi-bulk response
        elif byte == b"*":
            length = int(response)
            if length == -1:
                return None
            response = [(await self.read_response()) for _ in range(length)]
        if isinstance(response, bytes):
            response = self.encoder.decode(response)
        return response


class HiredisParser(BaseParser):
    """Parser class for connections using Hiredis"""

    __slots__ = BaseParser.__slots__ + ("_next_response", "_reader", "_socket_timeout")

    _next_response: bool

    def __init__(self, socket_read_size: int):
        if not HIREDIS_AVAILABLE:
            raise RedisError("Hiredis is not available.")
        super().__init__(socket_read_size=socket_read_size)
        self._reader: Optional[hiredis.Reader] = None
        self._socket_timeout: Optional[float] = None

    def on_connect(self, connection: "Connection"):
        self._stream = connection._reader
        kwargs: _HiredisReaderArgs = {
            "protocolError": InvalidResponse,
            "replyError": self.parse_error,
        }
        if connection.encoder.decode_responses:
            kwargs["encoding"] = connection.encoder.encoding
            kwargs["errors"] = connection.encoder.encoding_errors

        self._reader = hiredis.Reader(**kwargs)
        self._next_response = False
        self._socket_timeout = connection.socket_timeout

    def on_disconnect(self):
        self._stream = None
        self._reader = None
        self._next_response = False

    async def can_read(self, timeout: float):
        if not self._reader:
            raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)

        if self._next_response is False:
            self._next_response = self._reader.gets()
        if self._next_response is False:
            return await self.read_from_socket(timeout=timeout, raise_on_timeout=False)
        return True

    async def read_from_socket(
        self,
        timeout: Union[float, None, _Sentinel] = SENTINEL,
        raise_on_timeout: bool = True,
    ):
        if self._stream is None or self._reader is None:
            raise RedisError("Parser already closed.")

        timeout = self._socket_timeout if timeout is SENTINEL else timeout
        try:
            async with async_timeout.timeout(timeout):
                buffer = await self._stream.read(self._read_size)
            if not isinstance(buffer, bytes) or len(buffer) == 0:
                raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR) from None
            self._reader.feed(buffer)
            # data was read from the socket and added to the buffer.
            # return True to indicate that data was read.
            return True
        except asyncio.CancelledError:
            raise
        except (socket.timeout, asyncio.TimeoutError):
            if raise_on_timeout:
                raise TimeoutError("Timeout reading from socket") from None
            return False
        except NONBLOCKING_EXCEPTIONS as ex:
            # if we're in nonblocking mode and the recv raises a
            # blocking error, simply return False indicating that
            # there's no data to be read. otherwise raise the
            # original exception.
            allowed = NONBLOCKING_EXCEPTION_ERROR_NUMBERS.get(ex.__class__, -1)
            if not raise_on_timeout and ex.errno == allowed:
                return False
            raise ConnectionError(f"Error while reading from socket: {ex.args}")

    async def read_response(self) -> Union[EncodableT, List[EncodableT]]:
        if not self._stream or not self._reader:
            self.on_disconnect()
            raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR) from None

        response: Union[
            EncodableT, ConnectionError, List[Union[EncodableT, ConnectionError]]
        ]
        # _next_response might be cached from a can_read() call
        if self._next_response is not False:
            response = self._next_response
            self._next_response = False
            return response

        response = self._reader.gets()
        while response is False:
            await self.read_from_socket()
            response = self._reader.gets()

        # if the response is a ConnectionError or the response is a list and
        # the first item is a ConnectionError, raise it as something bad
        # happened
        if isinstance(response, ConnectionError):
            raise response
        elif (
            isinstance(response, list)
            and response
            and isinstance(response[0], ConnectionError)
        ):
            raise response[0]
        # cast as there won't be a ConnectionError here.
        return cast(Union[EncodableT, List[EncodableT]], response)


DefaultParser: Type[Union[PythonParser, HiredisParser]]
if HIREDIS_AVAILABLE:
    DefaultParser = HiredisParser
else:
    DefaultParser = PythonParser


class ConnectCallbackProtocol(Protocol):
    def __call__(self, connection: "Connection"):
        ...


class AsyncConnectCallbackProtocol(Protocol):
    async def __call__(self, connection: "Connection"):
        ...


ConnectCallbackT = Union[ConnectCallbackProtocol, AsyncConnectCallbackProtocol]


class Connection:
    """Manages TCP communication to and from a Redis server"""

    __slots__ = (
        "pid",
        "host",
        "port",
        "db",
        "username",
        "client_name",
        "password",
        "socket_timeout",
        "socket_connect_timeout",
        "socket_keepalive",
        "socket_keepalive_options",
        "socket_type",
        "retry_on_timeout",
        "health_check_interval",
        "next_health_check",
        "last_active_at",
        "encoder",
        "ssl_context",
        "_reader",
        "_writer",
        "_parser",
        "_connect_callbacks",
        "_buffer_cutoff",
        "_lock",
        "__dict__",
    )

    def __init__(
        self,
        *,
        host: str = "localhost",
        port: Union[str, int] = 6379,
        db: Union[str, int] = 0,
        password: Optional[str] = None,
        socket_timeout: Optional[float] = None,
        socket_connect_timeout: Optional[float] = None,
        socket_keepalive: bool = False,
        socket_keepalive_options: Optional[Mapping[int, Union[int, bytes]]] = None,
        socket_type: int = 0,
        retry_on_timeout: bool = False,
        encoding: str = "utf-8",
        encoding_errors: str = "strict",
        decode_responses: bool = False,
        parser_class: Type[BaseParser] = DefaultParser,
        socket_read_size: int = 65536,
        health_check_interval: float = 0,
        client_name: Optional[str] = None,
        username: Optional[str] = None,
        encoder_class: Type[Encoder] = Encoder,
    ):
        self.pid = os.getpid()
        self.host = host
        self.port = int(port)
        self.db = db
        self.username = username
        self.client_name = client_name
        self.password = password
        self.socket_timeout = socket_timeout
        self.socket_connect_timeout = socket_connect_timeout or socket_timeout or None
        self.socket_keepalive = socket_keepalive
        self.socket_keepalive_options = socket_keepalive_options or {}
        self.socket_type = socket_type
        self.retry_on_timeout = retry_on_timeout
        self.health_check_interval = health_check_interval
        self.next_health_check: float = -1
        self.ssl_context: Optional[RedisSSLContext] = None
        self.encoder = encoder_class(encoding, encoding_errors, decode_responses)
        self._reader: Optional[asyncio.StreamReader] = None
        self._writer: Optional[asyncio.StreamWriter] = None
        self._parser = parser_class(
            socket_read_size=socket_read_size,
        )
        self._connect_callbacks: List[ConnectCallbackT] = []
        self._buffer_cutoff = 6000
        self._lock = asyncio.Lock()

    def __repr__(self):
        repr_args = ",".join((f"{k}={v}" for k, v in self.repr_pieces()))
        return f"{self.__class__.__name__}<{repr_args}>"

    def repr_pieces(self):
        pieces = [("host", self.host), ("port", self.port), ("db", self.db)]
        if self.client_name:
            pieces.append(("client_name", self.client_name))
        return pieces

    def __del__(self):
        try:
            if self.is_connected:
                loop = asyncio.get_event_loop()
                coro = self.disconnect()
                if loop.is_running():
                    loop.create_task(coro)
                else:
                    loop.run_until_complete(coro)
        except Exception:
            pass

    @property
    def is_connected(self):
        return bool(self._reader and self._writer)

    def register_connect_callback(self, callback):
        self._connect_callbacks.append(callback)

    def clear_connect_callbacks(self):
        self._connect_callbacks = []

    async def connect(self):
        """Connects to the Redis server if not already connected"""
        if self.is_connected:
            return
        try:
            await self._connect()
        except asyncio.CancelledError:
            raise
        except (socket.timeout, asyncio.TimeoutError):
            raise TimeoutError("Timeout connecting to server")
        except OSError as e:
            raise ConnectionError(self._error_message(e))
        except Exception as exc:
            raise ConnectionError(exc) from exc

        try:
            await self.on_connect()
        except RedisError:
            # clean up after any error in on_connect
            await self.disconnect()
            raise

        # run any user callbacks. right now the only internal callback
        # is for pubsub channel/pattern resubscription
        for callback in self._connect_callbacks:
            task = callback(self)
            if task and inspect.isawaitable(task):
                await task

    async def _connect(self):
        """Create a TCP socket connection"""
        async with async_timeout.timeout(self.socket_connect_timeout):
            reader, writer = await asyncio.open_connection(
                host=self.host,
                port=self.port,
                ssl=self.ssl_context.get() if self.ssl_context else None,
            )
        self._reader = reader
        self._writer = writer
        sock = writer.transport.get_extra_info("socket")
        if sock is not None:
            sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
            try:
                # TCP_KEEPALIVE
                if self.socket_keepalive:
                    sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
                    for k, v in self.socket_keepalive_options.items():
                        sock.setsockopt(socket.SOL_TCP, k, v)

            except (OSError, TypeError):
                # `socket_keepalive_options` might contain invalid options
                # causing an error. Do not leave the connection open.
                writer.close()
                raise

    def _error_message(self, exception):
        # args for socket.error can either be (errno, "message")
        # or just "message"
        if len(exception.args) == 1:
            return f"Error connecting to {self.host}:{self.port}. {exception.args[0]}."
        else:
            return (
                f"Error {exception.args[0]} connecting to {self.host}:{self.port}. "
                f"{exception.args[0]}."
            )

    async def on_connect(self):
        """Initialize the connection, authenticate and select a database"""
        self._parser.on_connect(self)

        # if username and/or password are set, authenticate
        if self.username or self.password:
            auth_args: Union[Tuple[str], Tuple[str, str]]
            if self.username:
                auth_args = (self.username, self.password or "")
            else:
                # Mypy bug: https://github.com/python/mypy/issues/10944
                auth_args = (self.password or "",)
            # avoid checking health here -- PING will fail if we try
            # to check the health prior to the AUTH
            await self.send_command("AUTH", *auth_args, check_health=False)

            try:
                auth_response = await self.read_response()
            except AuthenticationWrongNumberOfArgsError:
                # a username and password were specified but the Redis
                # server seems to be < 6.0.0 which expects a single password
                # arg. retry auth with just the password.
                # https://github.com/andymccurdy/redis-py/issues/1274
                await self.send_command("AUTH", self.password, check_health=False)
                auth_response = await self.read_response()

            if str_if_bytes(auth_response) != "OK":
                raise AuthenticationError("Invalid Username or Password")

        # if a client_name is given, set it
        if self.client_name:
            await self.send_command("CLIENT", "SETNAME", self.client_name)
            if str_if_bytes(await self.read_response()) != "OK":
                raise ConnectionError("Error setting client name")

        # if a database is specified, switch to it
        if self.db:
            await self.send_command("SELECT", self.db)
            if str_if_bytes(await self.read_response()) != "OK":
                raise ConnectionError("Invalid Database")

    async def disconnect(self):
        """Disconnects from the Redis server"""
        try:
            async with async_timeout.timeout(self.socket_connect_timeout):
                self._parser.on_disconnect()
                if not self.is_connected:
                    return
                try:
                    if os.getpid() == self.pid:
                        self._writer.close()  # type: ignore[union-attr]
                        # py3.6 doesn't have this method
                        if hasattr(self._writer, "wait_closed"):
                            await self._writer.wait_closed()  # type: ignore[union-attr]
                except OSError:
                    pass
                self._reader = None
                self._writer = None
        except asyncio.TimeoutError:
            raise TimeoutError(
                f"Timed out closing connection after {self.socket_connect_timeout}"
            ) from None

    async def check_health(self):
        """Check the health of the connection with a PING/PONG"""
        if (
            self.health_check_interval
            and asyncio.get_event_loop().time() > self.next_health_check
        ):
            try:
                await self.send_command("PING", check_health=False)
                if str_if_bytes(await self.read_response()) != "PONG":
                    raise ConnectionError("Bad response from PING health check")
            except (ConnectionError, TimeoutError) as err:
                await self.disconnect()
                try:
                    await self.send_command("PING", check_health=False)
                    if str_if_bytes(await self.read_response()) != "PONG":
                        raise ConnectionError(
                            "Bad response from PING health check"
                        ) from None
                except BaseException as err2:
                    raise err2 from err

    async def _send_packed_command(self, command: Iterable[bytes]) -> None:
        if self._writer is None:
            raise RedisError("Connection already closed.")

        self._writer.writelines(command)
        await self._writer.drain()

    async def send_packed_command(
        self,
        command: Union[bytes, str, Iterable[bytes]],
        check_health: bool = True,
    ):
        """Send an already packed command to the Redis server"""
        if not self._writer:
            await self.connect()
        # guard against health check recursion
        if check_health:
            await self.check_health()
        try:
            if isinstance(command, str):
                command = command.encode()
            if isinstance(command, bytes):
                command = [command]
            await asyncio.wait_for(
                self._send_packed_command(command),
                self.socket_timeout,
            )
        except asyncio.TimeoutError:
            await self.disconnect()
            raise TimeoutError("Timeout writing to socket") from None
        except OSError as e:
            await self.disconnect()
            if len(e.args) == 1:
                err_no, errmsg = "UNKNOWN", e.args[0]
            else:
                err_no = e.args[0]
                errmsg = e.args[1]
            raise ConnectionError(
                f"Error {err_no} while writing to socket. {errmsg}."
            ) from e
        except BaseException:
            await self.disconnect()
            raise

    async def send_command(self, *args, **kwargs):
        """Pack and send a command to the Redis server"""
        if not self.is_connected:
            await self.connect()
        await self.send_packed_command(
            self.pack_command(*args), check_health=kwargs.get("check_health", True)
        )

    async def can_read(self, timeout: float = 0):
        """Poll the socket to see if there's data that can be read."""
        if not self.is_connected:
            await self.connect()
        return await self._parser.can_read(timeout)

    async def read_response(self):
        """Read the response from a previously sent command"""
        try:
            async with self._lock:
                async with async_timeout.timeout(self.socket_timeout):
                    response = await self._parser.read_response()
        except asyncio.TimeoutError:
            await self.disconnect()
            raise TimeoutError(f"Timeout reading from {self.host}:{self.port}")
        except OSError as e:
            await self.disconnect()
            raise ConnectionError(
                f"Error while reading from {self.host}:{self.port} : {e.args}"
            )
        except BaseException:
            await self.disconnect()
            raise

        if self.health_check_interval:
            self.next_health_check = (
                asyncio.get_event_loop().time() + self.health_check_interval
            )

        if isinstance(response, ResponseError):
            raise response from None
        return response

    def pack_command(self, *args: EncodableT) -> List[bytes]:
        """Pack a series of arguments into the Redis protocol"""
        output = []
        # the client might have included 1 or more literal arguments in
        # the command name, e.g., 'CONFIG GET'. The Redis server expects these
        # arguments to be sent separately, so split the first argument
        # manually. These arguments should be bytestrings so that they are
        # not encoded.
        assert not isinstance(args[0], float)
        if isinstance(args[0], str):
            args = tuple(args[0].encode().split()) + args[1:]
        elif b" " in args[0]:
            args = tuple(args[0].split()) + args[1:]

        buff = SYM_EMPTY.join((SYM_STAR, str(len(args)).encode(), SYM_CRLF))

        buffer_cutoff = self._buffer_cutoff
        for arg in map(self.encoder.encode, args):
            # to avoid large string mallocs, chunk the command into the
            # output list if we're sending large values or memoryviews
            arg_length = len(arg)
            if (
                len(buff) > buffer_cutoff
                or arg_length > buffer_cutoff
                or isinstance(arg, memoryview)
            ):
                buff = SYM_EMPTY.join(
                    (buff, SYM_DOLLAR, str(arg_length).encode(), SYM_CRLF)
                )
                output.append(buff)
                output.append(arg)
                buff = SYM_CRLF
            else:
                buff = SYM_EMPTY.join(
                    (
                        buff,
                        SYM_DOLLAR,
                        str(arg_length).encode(),
                        SYM_CRLF,
                        arg,
                        SYM_CRLF,
                    )
                )
        output.append(buff)
        return output

    def pack_commands(self, commands: Iterable[Iterable[EncodableT]]) -> List[bytes]:
        """Pack multiple commands into the Redis protocol"""
        output: List[bytes] = []
        pieces: List[bytes] = []
        buffer_length = 0
        buffer_cutoff = self._buffer_cutoff

        for cmd in commands:
            for chunk in self.pack_command(*cmd):
                chunklen = len(chunk)
                if (
                    buffer_length > buffer_cutoff
                    or chunklen > buffer_cutoff
                    or isinstance(chunk, memoryview)
                ):
                    output.append(SYM_EMPTY.join(pieces))
                    buffer_length = 0
                    pieces = []

                if chunklen > buffer_cutoff or isinstance(chunk, memoryview):
                    output.append(chunk)
                else:
                    pieces.append(chunk)
                    buffer_length += chunklen

        if pieces:
            output.append(SYM_EMPTY.join(pieces))
        return output


class SSLConnection(Connection):
    def __init__(
        self,
        ssl_keyfile: Optional[str] = None,
        ssl_certfile: Optional[str] = None,
        ssl_cert_reqs: str = "required",
        ssl_ca_certs: Optional[str] = None,
        ssl_check_hostname: bool = False,
        **kwargs,
    ):
        super().__init__(**kwargs)
        self.ssl_context: RedisSSLContext = RedisSSLContext(
            keyfile=ssl_keyfile,
            certfile=ssl_certfile,
            cert_reqs=ssl_cert_reqs,
            ca_certs=ssl_ca_certs,
            check_hostname=ssl_check_hostname,
        )

    @property
    def keyfile(self):
        return self.ssl_context.keyfile

    @property
    def certfile(self):
        return self.ssl_context.certfile

    @property
    def cert_reqs(self):
        return self.ssl_context.cert_reqs

    @property
    def ca_certs(self):
        return self.ssl_context.ca_certs

    @property
    def check_hostname(self):
        return self.ssl_context.check_hostname


class RedisSSLContext:
    __slots__ = (
        "keyfile",
        "certfile",
        "cert_reqs",
        "ca_certs",
        "context",
        "check_hostname",
    )

    def __init__(
        self,
        keyfile: Optional[str] = None,
        certfile: Optional[str] = None,
        cert_reqs: Optional[str] = None,
        ca_certs: Optional[str] = None,
        check_hostname: bool = False,
    ):
        self.keyfile = keyfile
        self.certfile = certfile
        if cert_reqs is None:
            self.cert_reqs = ssl.CERT_NONE
        elif isinstance(cert_reqs, str):
            CERT_REQS = {
                "none": ssl.CERT_NONE,
                "optional": ssl.CERT_OPTIONAL,
                "required": ssl.CERT_REQUIRED,
            }
            if cert_reqs not in CERT_REQS:
                raise RedisError(
                    f"Invalid SSL Certificate Requirements Flag: {cert_reqs}"
                )
            self.cert_reqs = CERT_REQS[cert_reqs]
        self.ca_certs = ca_certs
        self.check_hostname = check_hostname
        self.context: Optional[ssl.SSLContext] = None

    def get(self) -> ssl.SSLContext:
        if not self.context:
            context = ssl.create_default_context()
            context.check_hostname = self.check_hostname
            context.verify_mode = self.cert_reqs
            if self.certfile and self.keyfile:
                context.load_cert_chain(certfile=self.certfile, keyfile=self.keyfile)
            if self.ca_certs:
                context.load_verify_locations(self.ca_certs)
            self.context = context
        return self.context


class UnixDomainSocketConnection(Connection):  # lgtm [py/missing-call-to-init]
    def __init__(
        self,
        *,
        path: str = "",
        db: Union[str, int] = 0,
        username: Optional[str] = None,
        password: Optional[str] = None,
        socket_timeout: Optional[float] = None,
        socket_connect_timeout: Optional[float] = None,
        encoding: str = "utf-8",
        encoding_errors: str = "strict",
        decode_responses: bool = False,
        retry_on_timeout: bool = False,
        parser_class: Type[BaseParser] = DefaultParser,
        socket_read_size: int = 65536,
        health_check_interval: float = 0.0,
        client_name=None,
    ):
        self.pid = os.getpid()
        self.path = path
        self.db = db
        self.username = username
        self.client_name = client_name
        self.password = password
        self.socket_timeout = socket_timeout
        self.socket_connect_timeout = socket_connect_timeout or socket_timeout or None
        self.retry_on_timeout = retry_on_timeout
        self.health_check_interval = health_check_interval
        self.next_health_check = -1
        self.encoder = Encoder(encoding, encoding_errors, decode_responses)
        self._sock = None
        self._reader = None
        self._writer = None
        self._parser = parser_class(socket_read_size=socket_read_size)
        self._connect_callbacks = []
        self._buffer_cutoff = 6000

    def repr_pieces(self) -> Iterable[Tuple[str, Union[str, int]]]:
        pieces = [
            ("path", self.path),
            ("db", self.db),
        ]
        if self.client_name:
            pieces.append(("client_name", self.client_name))
        return pieces

    async def _connect(self):
        async with async_timeout.timeout(self.socket_connect_timeout):
            reader, writer = await asyncio.open_unix_connection(path=self.path)
        self._reader = reader
        self._writer = writer
        await self.on_connect()

    def _error_message(self, exception):
        # args for socket.error can either be (errno, "message")
        # or just "message"
        if len(exception.args) == 1:
            return f"Error connecting to unix socket: {self.path}. {exception.args[0]}."
        else:
            return (
                f"Error {exception.args[0]} connecting to unix socket: "
                f"{self.path}. {exception.args[1]}."
            )


FALSE_STRINGS = ("0", "F", "FALSE", "N", "NO")


def to_bool(value) -> Optional[bool]:
    if value is None or value == "":
        return None
    if isinstance(value, str) and value.upper() in FALSE_STRINGS:
        return False
    return bool(value)


URL_QUERY_ARGUMENT_PARSERS: Mapping[str, Callable[..., object]] = MappingProxyType(
    {
        "db": int,
        "socket_timeout": float,
        "socket_connect_timeout": float,
        "socket_keepalive": to_bool,
        "retry_on_timeout": to_bool,
        "max_connections": int,
        "health_check_interval": int,
        "ssl_check_hostname": to_bool,
    }
)


class ConnectKwargs(TypedDict, total=False):
    username: str
    password: str
    connection_class: Type[Connection]
    host: str
    port: int
    db: int
    path: str


def parse_url(url: str) -> ConnectKwargs:
    parsed: ParseResult = urlparse(url)
    kwargs: ConnectKwargs = {}

    for name, value_list in parse_qs(parsed.query).items():
        if value_list and len(value_list) > 0:
            value = unquote(value_list[0])
            parser = URL_QUERY_ARGUMENT_PARSERS.get(name)
            if parser:
                try:
                    # We can't type this.
                    kwargs[name] = parser(value)  # type: ignore[misc]
                except (TypeError, ValueError):
                    raise ValueError(f"Invalid value for `{name}` in connection URL.")
            else:
                kwargs[name] = value  # type: ignore[misc]

    if parsed.username:
        kwargs["username"] = unquote(parsed.username)
    if parsed.password:
        kwargs["password"] = unquote(parsed.password)

    # We only support redis://, rediss:// and unix:// schemes.
    if parsed.scheme == "unix":
        if parsed.path:
            kwargs["path"] = unquote(parsed.path)
        kwargs["connection_class"] = UnixDomainSocketConnection

    elif parsed.scheme in ("redis", "rediss"):
        if parsed.hostname:
            kwargs["host"] = unquote(parsed.hostname)
        if parsed.port:
            kwargs["port"] = int(parsed.port)

        # If there's a path argument, use it as the db argument if a
        # querystring value wasn't specified
        if parsed.path and "db" not in kwargs:
            try:
                kwargs["db"] = int(unquote(parsed.path).replace("/", ""))
            except (AttributeError, ValueError):
                pass

        if parsed.scheme == "rediss":
            kwargs["connection_class"] = SSLConnection
    else:
        valid_schemes = "redis://, rediss://, unix://"
        raise ValueError(
            f"Redis URL must specify one of the following schemes ({valid_schemes})"
        )

    return kwargs


_CP = TypeVar("_CP", bound="ConnectionPool")


class ConnectionPool:
    """
    Create a connection pool. ``If max_connections`` is set, then this
    object raises :py:class:`~redis.ConnectionError` when the pool's
    limit is reached.

    By default, TCP connections are created unless ``connection_class``
    is specified. Use :py:class:`~redis.UnixDomainSocketConnection` for
    unix sockets.

    Any additional keyword arguments are passed to the constructor of
    ``connection_class``.
    """

    @classmethod
    def from_url(cls: Type[_CP], url: str, **kwargs) -> _CP:
        """
        Return a connection pool configured from the given URL.

        For example::

            redis://[[username]:[password]]@localhost:6379/0
            rediss://[[username]:[password]]@localhost:6379/0
            unix://[[username]:[password]]@/path/to/socket.sock?db=0

        Three URL schemes are supported:

        - `redis://` creates a TCP socket connection. See more at:
          <https://www.iana.org/assignments/uri-schemes/prov/redis>
        - `rediss://` creates a SSL wrapped TCP socket connection. See more at:
          <https://www.iana.org/assignments/uri-schemes/prov/rediss>
        - ``unix://``: creates a Unix Domain Socket connection.

        The username, password, hostname, path and all querystring values
        are passed through urllib.parse.unquote in order to replace any
        percent-encoded values with their corresponding characters.

        There are several ways to specify a database number. The first value
        found will be used:
            1. A ``db`` querystring option, e.g. redis://localhost?db=0
            2. If using the redis:// or rediss:// schemes, the path argument
               of the url, e.g. redis://localhost/0
            3. A ``db`` keyword argument to this function.

        If none of these options are specified, the default db=0 is used.

        All querystring options are cast to their appropriate Python types.
        Boolean arguments can be specified with string values "True"/"False"
        or "Yes"/"No". Values that cannot be properly cast cause a
        ``ValueError`` to be raised. Once parsed, the querystring arguments
        and keyword arguments are passed to the ``ConnectionPool``'s
        class initializer. In the case of conflicting arguments, querystring
        arguments always win.
        """
        url_options = parse_url(url)
        kwargs.update(url_options)
        return cls(**kwargs)

    def __init__(
        self,
        connection_class: Type[Connection] = Connection,
        max_connections: Optional[int] = None,
        **connection_kwargs,
    ):
        max_connections = max_connections or 2 ** 31
        if not isinstance(max_connections, int) or max_connections < 0:
            raise ValueError('"max_connections" must be a positive integer')

        self.connection_class = connection_class
        self.connection_kwargs = connection_kwargs
        self.max_connections = max_connections

        # a lock to protect the critical section in _checkpid().
        # this lock is acquired when the process id changes, such as
        # after a fork. during this time, multiple threads in the child
        # process could attempt to acquire this lock. the first thread
        # to acquire the lock will reset the data structures and lock
        # object of this pool. subsequent threads acquiring this lock
        # will notice the first thread already did the work and simply
        # release the lock.
        self._fork_lock = threading.Lock()
        self._lock = asyncio.Lock()
        self._created_connections: int
        self._available_connections: List[Connection]
        self._in_use_connections: Set[Connection]
        self.reset()  # lgtm [py/init-calls-subclass]
        self.encoder_class = self.connection_kwargs.get("encoder_class", Encoder)

    def __repr__(self):
        return (
            f"{self.__class__.__name__}"
            f"<{self.connection_class(**self.connection_kwargs)!r}>"
        )

    def reset(self):
        self._lock = asyncio.Lock()
        self._created_connections = 0
        self._available_connections = []
        self._in_use_connections = set()

        # this must be the last operation in this method. while reset() is
        # called when holding _fork_lock, other threads in this process
        # can call _checkpid() which compares self.pid and os.getpid() without
        # holding any lock (for performance reasons). keeping this assignment
        # as the last operation ensures that those other threads will also
        # notice a pid difference and block waiting for the first thread to
        # release _fork_lock. when each of these threads eventually acquire
        # _fork_lock, they will notice that another thread already called
        # reset() and they will immediately release _fork_lock and continue on.
        self.pid = os.getpid()

    def _checkpid(self):
        # _checkpid() attempts to keep ConnectionPool fork-safe on modern
        # systems. this is called by all ConnectionPool methods that
        # manipulate the pool's state such as get_connection() and release().
        #
        # _checkpid() determines whether the process has forked by comparing
        # the current process id to the process id saved on the ConnectionPool
        # instance. if these values are the same, _checkpid() simply returns.
        #
        # when the process ids differ, _checkpid() assumes that the process
        # has forked and that we're now running in the child process. the child
        # process cannot use the parent's file descriptors (e.g., sockets).
        # therefore, when _checkpid() sees the process id change, it calls
        # reset() in order to reinitialize the child's ConnectionPool. this
        # will cause the child to make all new connection objects.
        #
        # _checkpid() is protected by self._fork_lock to ensure that multiple
        # threads in the child process do not call reset() multiple times.
        #
        # there is an extremely small chance this could fail in the following
        # scenario:
        #   1. process A calls _checkpid() for the first time and acquires
        #      self._fork_lock.
        #   2. while holding self._fork_lock, process A forks (the fork()
        #      could happen in a different thread owned by process A)
        #   3. process B (the forked child process) inherits the
        #      ConnectionPool's state from the parent. that state includes
        #      a locked _fork_lock. process B will not be notified when
        #      process A releases the _fork_lock and will thus never be
        #      able to acquire the _fork_lock.
        #
        # to mitigate this possible deadlock, _checkpid() will only wait 5
        # seconds to acquire _fork_lock. if _fork_lock cannot be acquired in
        # that time it is assumed that the child is deadlocked and a
        # redis.ChildDeadlockedError error is raised.
        if self.pid != os.getpid():
            acquired = self._fork_lock.acquire(timeout=5)
            if not acquired:
                raise ChildDeadlockedError
            # reset() the instance for the new process if another thread
            # hasn't already done so
            try:
                if self.pid != os.getpid():
                    self.reset()
            finally:
                self._fork_lock.release()

    async def get_connection(self, command_name, *keys, **options):
        """Get a connection from the pool"""
        self._checkpid()
        async with self._lock:
            try:
                connection = self._available_connections.pop()
            except IndexError:
                connection = self.make_connection()
            self._in_use_connections.add(connection)

        try:
            # ensure this connection is connected to Redis
            await connection.connect()
            # connections that the pool provides should be ready to send
            # a command. if not, the connection was either returned to the
            # pool before all data has been read or the socket has been
            # closed. either way, reconnect and verify everything is good.
            try:
                if await connection.can_read():
                    raise ConnectionError("Connection has data") from None
            except ConnectionError:
                await connection.disconnect()
                await connection.connect()
                if await connection.can_read():
                    raise ConnectionError("Connection not ready") from None
        except BaseException:
            # release the connection back to the pool so that we don't
            # leak it
            await self.release(connection)
            raise

        return connection

    def get_encoder(self):
        """Return an encoder based on encoding settings"""
        kwargs = self.connection_kwargs
        return self.encoder_class(
            encoding=kwargs.get("encoding", "utf-8"),
            encoding_errors=kwargs.get("encoding_errors", "strict"),
            decode_responses=kwargs.get("decode_responses", False),
        )

    def make_connection(self):
        """Create a new connection"""
        if self._created_connections >= self.max_connections:
            raise ConnectionError("Too many connections")
        self._created_connections += 1
        return self.connection_class(**self.connection_kwargs)

    async def release(self, connection: Connection):
        """Releases the connection back to the pool"""
        self._checkpid()
        async with self._lock:
            try:
                self._in_use_connections.remove(connection)
            except KeyError:
                # Gracefully fail when a connection is returned to this pool
                # that the pool doesn't actually own
                pass

            if self.owns_connection(connection):
                self._available_connections.append(connection)
            else:
                # pool doesn't own this connection. do not add it back
                # to the pool and decrement the count so that another
                # connection can take its place if needed
                self._created_connections -= 1
                await connection.disconnect()
                return

    def owns_connection(self, connection: Connection):
        return connection.pid == self.pid

    async def disconnect(self, inuse_connections: bool = True):
        """
        Disconnects connections in the pool

        If ``inuse_connections`` is True, disconnect connections that are
        current in use, potentially by other tasks. Otherwise only disconnect
        connections that are idle in the pool.
        """
        self._checkpid()
        async with self._lock:
            if inuse_connections:
                connections: Iterable[Connection] = chain(
                    self._available_connections, self._in_use_connections
                )
            else:
                connections = self._available_connections
            resp = await asyncio.gather(
                *(connection.disconnect() for connection in connections),
                return_exceptions=True,
            )
            exc = next((r for r in resp if isinstance(r, BaseException)), None)
            if exc:
                raise exc


class BlockingConnectionPool(ConnectionPool):
    """
    Thread-safe blocking connection pool::

        >>> from aioredis.client import Redis
        >>> client = Redis(connection_pool=BlockingConnectionPool())

    It performs the same function as the default
    :py:class:`~redis.ConnectionPool` implementation, in that,
    it maintains a pool of reusable connections that can be shared by
    multiple redis clients (safely across threads if required).

    The difference is that, in the event that a client tries to get a
    connection from the pool when all of connections are in use, rather than
    raising a :py:class:`~redis.ConnectionError` (as the default
    :py:class:`~redis.ConnectionPool` implementation does), it
    makes the client wait ("blocks") for a specified number of seconds until
    a connection becomes available.

    Use ``max_connections`` to increase / decrease the pool size::

        >>> pool = BlockingConnectionPool(max_connections=10)

    Use ``timeout`` to tell it either how many seconds to wait for a connection
    to become available, or to block forever:

        >>> # Block forever.
        >>> pool = BlockingConnectionPool(timeout=None)

        >>> # Raise a ``ConnectionError`` after five seconds if a connection is
        >>> # not available.
        >>> pool = BlockingConnectionPool(timeout=5)
    """

    def __init__(
        self,
        max_connections: int = 50,
        timeout: Optional[int] = 20,
        connection_class: Type[Connection] = Connection,
        queue_class: Type[asyncio.Queue] = asyncio.LifoQueue,
        **connection_kwargs,
    ):

        self.queue_class = queue_class
        self.timeout = timeout
        self._connections: List[Connection]
        super().__init__(
            connection_class=connection_class,
            max_connections=max_connections,
            **connection_kwargs,
        )

    def reset(self):
        # Create and fill up a thread safe queue with ``None`` values.
        self.pool = self.queue_class(self.max_connections)
        while True:
            try:
                self.pool.put_nowait(None)
            except asyncio.QueueFull:
                break

        # Keep a list of actual connection instances so that we can
        # disconnect them later.
        self._connections = []

        # this must be the last operation in this method. while reset() is
        # called when holding _fork_lock, other threads in this process
        # can call _checkpid() which compares self.pid and os.getpid() without
        # holding any lock (for performance reasons). keeping this assignment
        # as the last operation ensures that those other threads will also
        # notice a pid difference and block waiting for the first thread to
        # release _fork_lock. when each of these threads eventually acquire
        # _fork_lock, they will notice that another thread already called
        # reset() and they will immediately release _fork_lock and continue on.
        self.pid = os.getpid()

    def make_connection(self):
        """Make a fresh connection."""
        connection = self.connection_class(**self.connection_kwargs)
        self._connections.append(connection)
        return connection

    async def get_connection(self, command_name, *keys, **options):
        """
        Get a connection, blocking for ``self.timeout`` until a connection
        is available from the pool.

        If the connection returned is ``None`` then creates a new connection.
        Because we use a last-in first-out queue, the existing connections
        (having been returned to the pool after the initial ``None`` values
        were added) will be returned before ``None`` values. This means we only
        create new connections when we need to, i.e.: the actual number of
        connections will only increase in response to demand.
        """
        # Make sure we haven't changed process.
        self._checkpid()

        # Try and get a connection from the pool. If one isn't available within
        # self.timeout then raise a ``ConnectionError``.
        connection = None
        try:
            async with async_timeout.timeout(self.timeout):
                connection = await self.pool.get()
        except (asyncio.QueueEmpty, asyncio.TimeoutError):
            # Note that this is not caught by the redis client and will be
            # raised unless handled by application code. If you want never to
            raise ConnectionError("No connection available.")

        # If the ``connection`` is actually ``None`` then that's a cue to make
        # a new connection to add to the pool.
        if connection is None:
            connection = self.make_connection()

        try:
            # ensure this connection is connected to Redis
            await connection.connect()
            # connections that the pool provides should be ready to send
            # a command. if not, the connection was either returned to the
            # pool before all data has been read or the socket has been
            # closed. either way, reconnect and verify everything is good.
            try:
                if await connection.can_read():
                    raise ConnectionError("Connection has data") from None
            except ConnectionError:
                await connection.disconnect()
                await connection.connect()
                if await connection.can_read():
                    raise ConnectionError("Connection not ready") from None
        except BaseException:
            # release the connection back to the pool so that we don't leak it
            await self.release(connection)
            raise

        return connection

    async def release(self, connection: Connection):
        """Releases the connection back to the pool."""
        # Make sure we haven't changed process.
        self._checkpid()
        if not self.owns_connection(connection):
            # pool doesn't own this connection. do not add it back
            # to the pool. instead add a None value which is a placeholder
            # that will cause the pool to recreate the connection if
            # its needed.
            await connection.disconnect()
            self.pool.put_nowait(None)
            return

        # Put the connection back into the pool.
        try:
            self.pool.put_nowait(connection)
        except asyncio.QueueFull:
            # perhaps the pool has been reset() after a fork? regardless,
            # we don't want this connection
            pass

    async def disconnect(self, inuse_connections: bool = True):
        """Disconnects all connections in the pool."""
        self._checkpid()
        async with self._lock:
            resp = await asyncio.gather(
                *(connection.disconnect() for connection in self._connections),
                return_exceptions=True,
            )
            exc = next((r for r in resp if isinstance(r, BaseException)), None)
            if exc:
                raise exc