connection.py

import asyncio
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 typing import (
    Any,
    Iterable,
    List,
    Mapping,
    Optional,
    Set,
    Tuple,
    Type,
    TypeVar,
    Union,
)
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."

SENTINEL = object()
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 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__
            raise DataError(
                f"Invalid input of type: {typename!r}. "
                "Convert to a bytes, string, int or float first."
            )
        if isinstance(value, str):
            return value.encode(self.encoding, self.encoding_errors)
        return value

    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 = 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(self, timeout: float) -> bool:
        raise NotImplementedError()

    async def read_response(self) -> Union[EncodableT, ResponseError, None]:
        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: float,
    ):
        self._stream = stream_reader
        self.socket_read_size = socket_read_size
        self.socket_timeout = socket_timeout
        self._buffer = 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: int = None,
        timeout: Optional[float] = SENTINEL,  # type: ignore
        raise_on_timeout: bool = True,
    ) -> bool:
        buf = self._buffer
        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)

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

    def close(self):
        try:
            self.purge()
            self._buffer.close()
        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
        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:
            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")

    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._next_response = ...
        self._reader: Optional[hiredis.Reader] = None
        self._socket_timeout: Optional[float] = None

    def on_connect(self, connection: "Connection"):
        self._stream = connection._reader
        kwargs = {
            "protocolError": InvalidResponse,
            "replyError": self.parse_error,
        }
        if connection.encoder.decode_responses:
            kwargs.update(
                encoding=connection.encoder.encoding,
                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: Optional[float] = SENTINEL, raise_on_timeout: bool = True
    ):
        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) -> EncodableT:
        if not self._stream or not self._reader:
            self.on_disconnect()
            raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR) from None

        # _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]
        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",
        "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",
        "__dict__",
    )

    def __init__(
        self,
        *,
        host: str = "localhost",
        port: Union[str, int] = 6379,
        db: Union[str, int] = 0,
        password: str = None,
        socket_timeout: float = None,
        socket_connect_timeout: float = None,
        socket_keepalive: bool = False,
        socket_keepalive_options: dict = 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: int = 0,
        client_name: str = None,
        username: 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 = -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

    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:
            if self.username:
                auth_args = (self.username, self.password or "")
            else:
                auth_args = (self.password,)
            # 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()
                        # py3.6 doesn't have this method
                        if hasattr(self._writer, "wait_closed"):
                            await self._writer.wait_closed()
                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: Union[bytes, str, Iterable[Union[bytes, str]]]
    ):
        self._writer.writelines(command)
        await self._writer.drain()

    async def send_packed_command(
        self,
        command: Union[bytes, str, Iterable[Union[bytes, str]]],
        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 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 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.
        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: str = None,
        ssl_certfile: str = None,
        ssl_cert_reqs: str = "required",
        ssl_ca_certs: str = None,
        ssl_check_hostname: bool = False,
        **kwargs,
    ):
        super().__init__(**kwargs)
        self.ssl_context = 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: str = None,
        certfile: str = None,
        cert_reqs: str = None,
        ca_certs: 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 = 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: str = None,
        password: str = None,
        socket_timeout: float = None,
        socket_connect_timeout: 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) -> 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 = {
    "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


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

    for name, value in parse_qs(parsed.query).items():
        if value and len(value) > 0:
            value = unquote(value[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")


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: 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 = 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