connection.py

import asyncio
import copy
import enum
import inspect
import os
import socket
import ssl
import sys
import threading
import weakref
from itertools import chain
from types import MappingProxyType
from typing import (
    Any,
    Callable,
    Iterable,
    List,
    Mapping,
    Optional,
    Set,
    Tuple,
    Type,
    TypeVar,
    Union,
)
from urllib.parse import ParseResult, parse_qs, unquote, urlparse

if sys.version_info.major >= 3 and sys.version_info.minor >= 11:
    from asyncio import timeout as async_timeout
else:
    from async_timeout import timeout as async_timeout


from redis.asyncio.retry import Retry
from redis.backoff import NoBackoff
from redis.compat import Protocol, TypedDict
from redis.credentials import CredentialProvider, UsernamePasswordCredentialProvider
from redis.exceptions import (
    AuthenticationError,
    AuthenticationWrongNumberOfArgsError,
    BusyLoadingError,
    ChildDeadlockedError,
    ConnectionError,
    DataError,
    ExecAbortError,
    InvalidResponse,
    ModuleError,
    NoPermissionError,
    NoScriptError,
    ReadOnlyError,
    RedisError,
    ResponseError,
    TimeoutError,
)
from redis.typing import EncodableT, EncodedT
from redis.utils import HIREDIS_AVAILABLE, str_if_bytes

hiredis = None
if HIREDIS_AVAILABLE:
    import hiredis

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"
)
# user send an AUTH cmd to a server without authorization configured
NO_AUTH_SET_ERROR = {
    # Redis >= 6.0
    "AUTH <password> called without any password "
    "configured for the default user. Are you sure "
    "your configuration is correct?": AuthenticationError,
    # Redis < 6.0
    "Client sent AUTH, but no password is set": AuthenticationError,
}


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, str):
            return value.encode(self.encoding, self.encoding_errors)
        if isinstance(value, (bytes, memoryview)):
            return value
        if isinstance(value, (int, float)):
            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."
                )
            return repr(value).encode()
        # a value we don't know how to deal with. throw an error
        typename = value.__class__.__name__
        raise DataError(
            f"Invalid input of type: {typename!r}. "
            "Convert to a bytes, string, int or float first."
        )

    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, bytes):
                return value.decode(self.encoding, self.encoding_errors)
            if isinstance(value, memoryview):
                return value.tobytes().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", "_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,  # noqa: E501
            # some Redis server versions report invalid command syntax
            # in uppercase
            "wrong number of arguments for 'AUTH' command": AuthenticationWrongNumberOfArgsError,  # noqa: E501
            MODULE_LOAD_ERROR: ModuleError,
            MODULE_EXPORTS_DATA_TYPES_ERROR: ModuleError,
            NO_SUCH_MODULE_ERROR: ModuleError,
            MODULE_UNLOAD_NOT_POSSIBLE_ERROR: ModuleError,
            **NO_AUTH_SET_ERROR,
        },
        "WRONGPASS": AuthenticationError,
        "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._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 = self.EXCEPTION_CLASSES[error_code]
            if isinstance(exception_class, dict):
                exception_class = exception_class.get(response, ResponseError)
            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_destructive(self) -> bool:
        raise NotImplementedError()

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


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

    __slots__ = BaseParser.__slots__ + ("encoder", "_buffer", "_pos", "_chunks")

    def __init__(self, socket_read_size: int):
        super().__init__(socket_read_size)
        self.encoder: Optional[Encoder] = None
        self._buffer = b""
        self._chunks = []
        self._pos = 0

    def _clear(self):
        self._buffer = b""
        self._chunks.clear()

    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.encoder = connection.encoder

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

    async def can_read_destructive(self) -> bool:
        if self._buffer:
            return True
        if self._stream is None:
            raise RedisError("Buffer is closed.")
        try:
            async with async_timeout(0):
                return await self._stream.read(1)
        except asyncio.TimeoutError:
            return False

    async def read_response(self, disable_decoding: bool = False):
        if self._chunks:
            # augment parsing buffer with previously read data
            self._buffer += b"".join(self._chunks)
            self._chunks.clear()
        self._pos = 0
        response = await self._read_response(disable_decoding=disable_decoding)
        # Successfully parsing a response allows us to clear our parsing buffer
        self._clear()
        return response

    async def _read_response(
        self, disable_decoding: bool = False
    ) -> Union[EncodableT, ResponseError, None]:
        if not self._stream or not self.encoder:
            raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)
        raw = await self._readline()
        response: Any
        byte, response = raw[:1], raw[1:]

        # 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):
                self._clear()  # Successful parse
                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":":
            return int(response)
        # bulk response
        elif byte == b"$" and response == b"-1":
            return None
        elif byte == b"$":
            response = await self._read(int(response))
        # multi-bulk response
        elif byte == b"*" and response == b"-1":
            return None
        elif byte == b"*":
            response = [
                (await self._read_response(disable_decoding))
                for _ in range(int(response))  # noqa
            ]
        else:
            raise InvalidResponse(f"Protocol Error: {raw!r}")

        if disable_decoding is False:
            response = self.encoder.decode(response)
        return response

    async def _read(self, length: int) -> bytes:
        """
        Read `length` bytes of data.  These are assumed to be followed
        by a '\r\n' terminator which is subsequently discarded.
        """
        want = length + 2
        end = self._pos + want
        if len(self._buffer) >= end:
            result = self._buffer[self._pos : end - 2]
        else:
            tail = self._buffer[self._pos :]
            try:
                data = await self._stream.readexactly(want - len(tail))
            except asyncio.IncompleteReadError as error:
                raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR) from error
            result = (tail + data)[:-2]
            self._chunks.append(data)
        self._pos += want
        return result

    async def _readline(self) -> bytes:
        """
        read an unknown number of bytes up to the next '\r\n'
        line separator, which is discarded.
        """
        found = self._buffer.find(b"\r\n", self._pos)
        if found >= 0:
            result = self._buffer[self._pos : found]
        else:
            tail = self._buffer[self._pos :]
            data = await self._stream.readline()
            if not data.endswith(b"\r\n"):
                raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)
            result = (tail + data)[:-2]
            self._chunks.append(data)
        self._pos += len(result) + 2
        return result


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

    __slots__ = BaseParser.__slots__ + ("_reader", "_connected")

    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._connected: bool = False

    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._connected = True

    def on_disconnect(self):
        self._connected = False

    async def can_read_destructive(self):
        if not self._connected:
            raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)
        if self._reader.gets():
            return True
        try:
            async with async_timeout(0):
                return await self.read_from_socket()
        except asyncio.TimeoutError:
            return False

    async def read_from_socket(self):
        buffer = await self._stream.read(self._read_size)
        if not buffer or not isinstance(buffer, bytes):
            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

    async def read_response(
        self, disable_decoding: bool = False
    ) -> Union[EncodableT, List[EncodableT]]:
        # If `on_disconnect()` has been called, prohibit any more reads
        # even if they could happen because data might be present.
        # We still allow reads in progress to finish
        if not self._connected:
            raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR) from None

        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]
        return 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",
        "credential_provider",
        "password",
        "socket_timeout",
        "socket_connect_timeout",
        "socket_keepalive",
        "socket_keepalive_options",
        "socket_type",
        "redis_connect_func",
        "retry_on_timeout",
        "retry_on_error",
        "health_check_interval",
        "next_health_check",
        "last_active_at",
        "encoder",
        "ssl_context",
        "_reader",
        "_writer",
        "_parser",
        "_connect_callbacks",
        "_buffer_cutoff",
        "_lock",
        "_socket_read_size",
        "__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,
        retry_on_error: Union[list, _Sentinel] = SENTINEL,
        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,
        retry: Optional[Retry] = None,
        redis_connect_func: Optional[ConnectCallbackT] = None,
        encoder_class: Type[Encoder] = Encoder,
        credential_provider: Optional[CredentialProvider] = None,
    ):
        if (username or password) and credential_provider is not None:
            raise DataError(
                "'username' and 'password' cannot be passed along with 'credential_"
                "provider'. Please provide only one of the following arguments: \n"
                "1. 'password' and (optional) 'username'\n"
                "2. 'credential_provider'"
            )
        self.pid = os.getpid()
        self.host = host
        self.port = int(port)
        self.db = db
        self.client_name = client_name
        self.credential_provider = credential_provider
        self.password = password
        self.username = username
        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
        if retry_on_error is SENTINEL:
            retry_on_error = []
        if retry_on_timeout:
            retry_on_error.append(TimeoutError)
            retry_on_error.append(socket.timeout)
            retry_on_error.append(asyncio.TimeoutError)
        self.retry_on_error = retry_on_error
        if retry or retry_on_error:
            if not retry:
                self.retry = Retry(NoBackoff(), 1)
            else:
                # deep-copy the Retry object as it is mutable
                self.retry = copy.deepcopy(retry)
            # Update the retry's supported errors with the specified errors
            self.retry.update_supported_errors(retry_on_error)
        else:
            self.retry = Retry(NoBackoff(), 0)
        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.redis_connect_func = redis_connect_func
        self._reader: Optional[asyncio.StreamReader] = None
        self._writer: Optional[asyncio.StreamWriter] = None
        self._socket_read_size = socket_read_size
        self.set_parser(parser_class)
        self._connect_callbacks: List[weakref.WeakMethod[ConnectCallbackT]] = []
        self._buffer_cutoff = 6000

    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_running_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 self._reader is not None and self._writer is not None

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

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

    def set_parser(self, parser_class: Type[BaseParser]) -> None:
        """
        Creates a new instance of parser_class with socket size:
        _socket_read_size and assigns it to the parser for the connection
        :param parser_class: The required parser class
        """
        self._parser = parser_class(socket_read_size=self._socket_read_size)

    async def connect(self):
        """Connects to the Redis server if not already connected"""
        if self.is_connected:
            return
        try:
            await self.retry.call_with_retry(
                lambda: self._connect(), lambda error: self.disconnect()
            )
        except asyncio.CancelledError:
            raise  # in 3.7 and earlier, this is an Exception, not BaseException
        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:
            if not self.redis_connect_func:
                # Use the default on_connect function
                await self.on_connect()
            else:
                # Use the passed function redis_connect_func
                await self.redis_connect_func(self) if asyncio.iscoroutinefunction(
                    self.redis_connect_func
                ) else self.redis_connect_func(self)
        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 ref in self._connect_callbacks:
            callback = ref()
            task = callback(self)
            if task and inspect.isawaitable(task):
                await task

    async def _connect(self):
        """Create a TCP socket connection"""
        async with async_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:
            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 not exception.args:
            # asyncio has a bug where on Connection reset by peer, the
            # exception is not instanciated, so args is empty. This is the
            # workaround.
            # See: https://github.com/redis/redis-py/issues/2237
            # See: https://github.com/python/cpython/issues/94061
            return (
                f"Error connecting to {self.host}:{self.port}. Connection reset by peer"
            )
        elif 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) -> None:
        """Initialize the connection, authenticate and select a database"""
        self._parser.on_connect(self)

        # if credential provider or username and/or password are set, authenticate
        if self.credential_provider or (self.username or self.password):
            cred_provider = (
                self.credential_provider
                or UsernamePasswordCredentialProvider(self.username, self.password)
            )
            auth_args = cred_provider.get_credentials()
            # 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", auth_args[-1], 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, nowait: bool = False) -> None:
        """Disconnects from the Redis server"""
        try:
            async with async_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]
                        # wait for close to finish, except when handling errors and
                        # forcefully disconnecting.
                        if not nowait:
                            await self._writer.wait_closed()  # type: ignore[union-attr]
                except OSError:
                    pass
                finally:
                    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 _send_ping(self):
        """Send PING, expect PONG in return"""
        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")

    async def _ping_failed(self, error):
        """Function to call when PING fails"""
        await self.disconnect()

    async def check_health(self):
        """Check the health of the connection with a PING/PONG"""
        if (
            self.health_check_interval
            and asyncio.get_running_loop().time() > self.next_health_check
        ):
            await self.retry.call_with_retry(self._send_ping, self._ping_failed)

    async def _send_packed_command(self, command: Iterable[bytes]) -> None:
        self._writer.writelines(command)
        await self._writer.drain()

    async def send_packed_command(
        self, command: Union[bytes, str, Iterable[bytes]], check_health: bool = True
    ) -> None:
        if not self.is_connected:
            await self.connect()
        elif check_health:
            await self.check_health()

        try:
            if isinstance(command, str):
                command = command.encode()
            if isinstance(command, bytes):
                command = [command]
            if self.socket_timeout:
                await asyncio.wait_for(
                    self._send_packed_command(command), self.socket_timeout
                )
            else:
                self._writer.writelines(command)
                await self._writer.drain()
        except asyncio.TimeoutError:
            await self.disconnect(nowait=True)
            raise TimeoutError("Timeout writing to socket") from None
        except OSError as e:
            await self.disconnect(nowait=True)
            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 Exception:
            await self.disconnect(nowait=True)
            raise

    async def send_command(self, *args: Any, **kwargs: Any) -> None:
        """Pack and send a command to the Redis server"""
        await self.send_packed_command(
            self.pack_command(*args), check_health=kwargs.get("check_health", True)
        )

    async def can_read_destructive(self):
        """Poll the socket to see if there's data that can be read."""
        try:
            return await self._parser.can_read_destructive()
        except OSError as e:
            await self.disconnect(nowait=True)
            raise ConnectionError(
                f"Error while reading from {self.host}:{self.port}: {e.args}"
            )

    async def read_response(
        self,
        disable_decoding: bool = False,
        timeout: Optional[float] = None,
    ):
        """Read the response from a previously sent command"""
        read_timeout = timeout if timeout is not None else self.socket_timeout
        try:
            if read_timeout is not None:
                async with async_timeout(read_timeout):
                    response = await self._parser.read_response(
                        disable_decoding=disable_decoding
                    )
            else:
                response = await self._parser.read_response(
                    disable_decoding=disable_decoding
                )
        except asyncio.TimeoutError:
            if timeout is not None:
                # user requested timeout, return None
                return None
            # it was a self.socket_timeout error.
            await self.disconnect(nowait=True)
            raise TimeoutError(f"Timeout reading from {self.host}:{self.port}")
        except OSError as e:
            await self.disconnect(nowait=True)
            raise ConnectionError(
                f"Error while reading from {self.host}:{self.port} : {e.args}"
            )
        except asyncio.CancelledError:
            # need this check for 3.7, where CancelledError
            # is subclass of Exception, not BaseException
            raise
        except Exception:
            await self.disconnect(nowait=True)
            raise

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

        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)
                ):
                    if pieces:
                        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_ca_data: 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,
            ca_data=ssl_ca_data,
            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 ca_data(self):
        return self.ssl_context.ca_data

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


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

    def __init__(
        self,
        keyfile: Optional[str] = None,
        certfile: Optional[str] = None,
        cert_reqs: Optional[str] = None,
        ca_certs: Optional[str] = None,
        ca_data: 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.ca_data = ca_data
        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 or self.ca_data:
                context.load_verify_locations(cafile=self.ca_certs, cadata=self.ca_data)
            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,
        retry_on_error: Union[list, _Sentinel] = SENTINEL,
        parser_class: Type[BaseParser] = DefaultParser,
        socket_read_size: int = 65536,
        health_check_interval: float = 0.0,
        client_name: str = None,
        retry: Optional[Retry] = None,
        redis_connect_func=None,
        credential_provider: Optional[CredentialProvider] = None,
    ):
        """
        Initialize a new UnixDomainSocketConnection.
        To specify a retry policy, first set `retry_on_timeout` to `True`
        then set `retry` to a valid `Retry` object
        """
        if (username or password) and credential_provider is not None:
            raise DataError(
                "'username' and 'password' cannot be passed along with 'credential_"
                "provider'. Please provide only one of the following arguments: \n"
                "1. 'password' and (optional) 'username'\n"
                "2. 'credential_provider'"
            )
        self.pid = os.getpid()
        self.path = path
        self.db = db
        self.client_name = client_name
        self.credential_provider = credential_provider
        self.password = password
        self.username = username
        self.socket_timeout = socket_timeout
        self.socket_connect_timeout = socket_connect_timeout or socket_timeout or None
        self.retry_on_timeout = retry_on_timeout
        if retry_on_error is SENTINEL:
            retry_on_error = []
        if retry_on_timeout:
            retry_on_error.append(TimeoutError)
        self.retry_on_error = retry_on_error
        if retry_on_error:
            if retry is None:
                self.retry = Retry(NoBackoff(), 1)
            else:
                # deep-copy the Retry object as it is mutable
                self.retry = copy.deepcopy(retry)
            # Update the retry's supported errors with the specified errors
            self.retry.update_supported_errors(retry_on_error)
        else:
            self.retry = Retry(NoBackoff(), 0)
        self.health_check_interval = health_check_interval
        self.next_health_check = -1
        self.redis_connect_func = redis_connect_func
        self.encoder = Encoder(encoding, encoding_errors, decode_responses)
        self._sock = None
        self._reader = None
        self._writer = None
        self._socket_read_size = socket_read_size
        self.set_parser(parser_class)
        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(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:
                    kwargs[name] = parser(value)
                except (TypeError, ValueError):
                    raise ValueError(f"Invalid value for `{name}` in connection URL.")
            else:
                kwargs[name] = value

    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@]/path/to/socket.sock?db=0[&password=password]

        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_destructive():
                    raise ConnectionError("Connection has data") from None
            except (ConnectionError, OSError):
                await connection.disconnect()
                await connection.connect()
                if await connection.can_read_destructive():
                    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

    def set_retry(self, retry: "Retry") -> None:
        for conn in self._available_connections:
            conn.retry = retry
        for conn in self._in_use_connections:
            conn.retry = retry


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

        >>> from redis.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(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_destructive():
                    raise ConnectionError("Connection has data") from None
            except (ConnectionError, OSError):
                await connection.disconnect()
                await connection.connect()
                if await connection.can_read_destructive():
                    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