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import asyncio
import base64
import binascii
import collections
import hashlib
import itertools
import random
import string
import time
import types
import aioredis
import msgpack
from channels.exceptions import ChannelFull
from channels.layers import BaseChannelLayer
def _wrap_close(loop, pool):
"""
Decorate an event loop's close method with our own.
"""
original_impl = loop.close
def _wrapper(self, *args, **kwargs):
# If the event loop was closed, there's nothing we can do anymore.
if not self.is_closed():
self.run_until_complete(pool.close_loop(self))
# Restore the original close() implementation after we're done.
self.close = original_impl
return self.close(*args, **kwargs)
loop.close = types.MethodType(_wrapper, loop)
class ConnectionPool:
"""
Connection pool manager for the channel layer.
It manages a set of connections for the given host specification and
taking into account asyncio event loops.
"""
def __init__(self, host):
self.host = host
self.conn_map = {}
self.in_use = {}
def _ensure_loop(self, loop):
"""
Get connection list for the specified loop.
"""
if loop is None:
loop = asyncio.get_event_loop()
if loop not in self.conn_map:
# Swap the loop's close method with our own so we get
# a chance to do some cleanup.
_wrap_close(loop, self)
self.conn_map[loop] = []
return self.conn_map[loop], loop
async def pop(self, loop=None):
"""
Get a connection for the given identifier and loop.
"""
conns, loop = self._ensure_loop(loop)
if not conns:
conns.append(await aioredis.create_redis(**self.host, loop=loop))
conn = conns.pop()
self.in_use[conn] = loop
return conn
def push(self, conn):
"""
Return a connection to the pool.
"""
loop = self.in_use[conn]
del self.in_use[conn]
if loop is not None:
conns, _ = self._ensure_loop(loop)
conns.append(conn)
def conn_error(self, conn):
"""
Handle a connection that produced an error.
"""
conn.close()
del self.in_use[conn]
def reset(self):
"""
Clear all connections from the pool.
"""
self.conn_map = {}
self.in_use = {}
async def close_loop(self, loop):
"""
Close all connections owned by the pool on the given loop.
"""
if loop in self.conn_map:
for conn in self.conn_map[loop]:
conn.close()
await conn.wait_closed()
del self.conn_map[loop]
for k, v in self.in_use.items():
if v is loop:
self.in_use[k] = None
async def close(self):
"""
Close all connections owned by the pool.
"""
conn_map = self.conn_map
in_use = self.in_use
self.reset()
for conns in conn_map.values():
for conn in conns:
conn.close()
await conn.wait_closed()
for conn in in_use:
conn.close()
await conn.wait_closed()
class ChannelLock:
"""
Helper class for per-channel locking.
Once a lock is released and has no waiters, it will also be deleted,
to mitigate multi-event loop problems.
"""
def __init__(self):
self.locks = collections.defaultdict(asyncio.Lock)
self.wait_counts = collections.defaultdict(int)
async def acquire(self, channel):
"""
Acquire the lock for the given channel.
"""
self.wait_counts[channel] += 1
return await self.locks[channel].acquire()
def locked(self, channel):
"""
Return ``True`` if the lock for the given channel is acquired.
"""
return self.locks[channel].locked()
def release(self, channel):
"""
Release the lock for the given channel.
"""
self.locks[channel].release()
self.wait_counts[channel] -= 1
if self.wait_counts[channel] < 1:
del self.locks[channel]
del self.wait_counts[channel]
class UnsupportedRedis(Exception):
pass
class RedisChannelLayer(BaseChannelLayer):
"""
Redis channel layer.
It routes all messages into remote Redis server. Support for
sharding among different Redis installations and message
encryption are provided.
"""
brpop_timeout = 5
def __init__(
self,
hosts=None,
prefix="asgi:",
expiry=60,
group_expiry=86400,
capacity=100,
channel_capacity=None,
symmetric_encryption_keys=None,
):
# Store basic information
self.expiry = expiry
self.group_expiry = group_expiry
self.capacity = capacity
self.channel_capacity = self.compile_capacities(channel_capacity or {})
self.prefix = prefix
assert isinstance(self.prefix, str), "Prefix must be unicode"
# Configure the host objects
self.hosts = self.decode_hosts(hosts)
self.ring_size = len(self.hosts)
# Cached redis connection pools and the event loop they are from
self.pools = [ConnectionPool(host) for host in self.hosts]
# Normal channels choose a host index by cycling through the available hosts
self._receive_index_generator = itertools.cycle(range(len(self.hosts)))
self._send_index_generator = itertools.cycle(range(len(self.hosts)))
# Decide on a unique client prefix to use in ! sections
# TODO: ensure uniqueness better, e.g. Redis keys with SETNX
self.client_prefix = "".join(
random.choice(string.ascii_letters) for i in range(8)
)
# Set up any encryption objects
self._setup_encryption(symmetric_encryption_keys)
# Number of coroutines trying to receive right now
self.receive_count = 0
# The receive lock
self.receive_lock = None
# Event loop they are trying to receive on
self.receive_event_loop = None
# Buffered messages by process-local channel name
self.receive_buffer = collections.defaultdict(asyncio.Queue)
# Detached channel cleanup tasks
self.receive_cleaners = []
# Per-channel cleanup locks to prevent a receive starting and moving
# a message back into the main queue before its cleanup has completed
self.receive_clean_locks = ChannelLock()
def decode_hosts(self, hosts):
"""
Takes the value of the "hosts" argument passed to the class and returns
a list of kwargs to use for the Redis connection constructor.
"""
# If no hosts were provided, return a default value
if not hosts:
return [{"address": ("localhost", 6379)}]
# If they provided just a string, scold them.
if isinstance(hosts, (str, bytes)):
raise ValueError(
"You must pass a list of Redis hosts, even if there is only one."
)
# Decode each hosts entry into a kwargs dict
result = []
for entry in hosts:
if isinstance(entry, dict):
result.append(entry)
else:
result.append({"address": entry})
return result
def _setup_encryption(self, symmetric_encryption_keys):
# See if we can do encryption if they asked
if symmetric_encryption_keys:
if isinstance(symmetric_encryption_keys, (str, bytes)):
raise ValueError(
"symmetric_encryption_keys must be a list of possible keys"
)
try:
from cryptography.fernet import MultiFernet
except ImportError:
raise ValueError(
"Cannot run with encryption without 'cryptography' installed."
)
sub_fernets = [self.make_fernet(key) for key in symmetric_encryption_keys]
self.crypter = MultiFernet(sub_fernets)
else:
self.crypter = None
### Channel layer API ###
extensions = ["groups", "flush"]
async def send(self, channel, message):
"""
Send a message onto a (general or specific) channel.
"""
# Typecheck
assert isinstance(message, dict), "message is not a dict"
assert self.valid_channel_name(channel), "Channel name not valid"
# Make sure the message does not contain reserved keys
assert "__asgi_channel__" not in message
# If it's a process-local channel, strip off local part and stick full name in message
channel_non_local_name = channel
if "!" in channel:
message = dict(message.items())
message["__asgi_channel__"] = channel
channel_non_local_name = self.non_local_name(channel)
# Write out message into expiring key (avoids big items in list)
channel_key = self.prefix + channel_non_local_name
# Pick a connection to the right server - consistent for specific
# channels, random for general channels
if "!" in channel:
index = self.consistent_hash(channel)
else:
index = next(self._send_index_generator)
async with self.connection(index) as connection:
# Check the length of the list before send
# This can allow the list to leak slightly over capacity, but that's fine.
if await connection.llen(channel_key) >= self.get_capacity(channel):
raise ChannelFull()
# Push onto the list then set it to expire in case it's not consumed
await connection.lpush(channel_key, self.serialize(message))
await connection.expire(channel_key, int(self.expiry))
def _backup_channel_name(self, channel):
"""
Construct the key used as a backup queue for the given channel.
"""
return channel + "$inflight"
async def _brpop_with_clean(self, index, channel, timeout):
"""
Perform a Redis BRPOP and manage the backup processing queue.
In case of cancellation, make sure the message is not lost.
"""
# The script will pop messages from the processing queue and push them in front
# of the main message queue in the proper order; BRPOP must *not* be called
# because that would deadlock the server
cleanup_script = """
local backed_up = redis.call('LRANGE', ARGV[2], 0, -1)
for i = #backed_up, 1, -1 do
redis.call('LPUSH', ARGV[1], backed_up[i])
end
redis.call('DEL', ARGV[2])
"""
backup_queue = self._backup_channel_name(channel)
async with self.connection(index) as connection:
# Cancellation here doesn't matter, we're not doing anything destructive
# and the script executes atomically...
await connection.eval(cleanup_script, keys=[], args=[channel, backup_queue])
# ...and it doesn't matter here either, the message will be safe in the backup.
return await connection.brpoplpush(channel, backup_queue, timeout=timeout)
async def _clean_receive_backup(self, index, channel):
"""
Pop the oldest message off the channel backup queue.
The result isn't interesting as it was already processed.
"""
async with self.connection(index) as connection:
await connection.brpop(self._backup_channel_name(channel))
async def receive(self, channel):
"""
Receive the first message that arrives on the channel.
If more than one coroutine waits on the same channel, the first waiter
will be given the message when it arrives.
"""
# Make sure the channel name is valid then get the non-local part
# and thus its index
assert self.valid_channel_name(channel)
if "!" in channel:
real_channel = self.non_local_name(channel)
assert real_channel.endswith(
self.client_prefix + "!"
), "Wrong client prefix"
# Enter receiving section
loop = asyncio.get_event_loop()
self.receive_count += 1
try:
if self.receive_count == 1:
# If we're the first coroutine in, create the receive lock!
self.receive_lock = asyncio.Lock()
self.receive_event_loop = loop
else:
# Otherwise, check our event loop matches
if self.receive_event_loop != loop:
raise RuntimeError(
"Two event loops are trying to receive() on one channel layer at once!"
)
# Wait for our message to appear
message = None
while self.receive_buffer[channel].empty():
tasks = [
self.receive_lock.acquire(),
self.receive_buffer[channel].get(),
]
tasks = [asyncio.ensure_future(task) for task in tasks]
try:
done, pending = await asyncio.wait(
tasks, return_when=asyncio.FIRST_COMPLETED
)
for task in pending:
# Cancel all pending tasks.
task.cancel()
except asyncio.CancelledError:
# Ensure all tasks are cancelled if we are cancelled.
# Also see: https://bugs.python.org/issue23859
del self.receive_buffer[channel]
for task in tasks:
if not task.cancel():
assert task.done()
if task.result() is True:
self.receive_lock.release()
raise
message, token, exception = None, None, None
for task in done:
try:
result = task.result()
except Exception as error: # NOQA
# We should not propagate exceptions immediately as otherwise this may cause
# the lock to be held and never be released.
exception = error
continue
if result is True:
token = result
else:
assert isinstance(result, dict)
message = result
if message or exception:
if token:
# We will not be receving as we already have the message.
self.receive_lock.release()
if exception:
raise exception
else:
break
else:
assert token
# We hold the receive lock, receive and then release it.
try:
# There is no interruption point from when the message is
# unpacked in receive_single to when we get back here, so
# the following lines are essentially atomic.
message_channel, message = await self.receive_single(
real_channel
)
if type(message_channel) is list:
for chan in message_channel:
self.receive_buffer[chan].put_nowait(message)
else:
self.receive_buffer[message_channel].put_nowait(message)
message = None
except:
del self.receive_buffer[channel]
raise
finally:
self.receive_lock.release()
# We know there's a message available, because there
# couldn't have been any interruption between empty() and here
if message is None:
message = self.receive_buffer[channel].get_nowait()
if self.receive_buffer[channel].empty():
del self.receive_buffer[channel]
return message
finally:
self.receive_count -= 1
# If we were the last out, drop the receive lock
if self.receive_count == 0:
assert not self.receive_lock.locked()
self.receive_lock = None
self.receive_event_loop = None
else:
# Do a plain direct receive
return (await self.receive_single(channel))[1]
async def receive_single(self, channel):
"""
Receives a single message off of the channel and returns it.
"""
# Check channel name
assert self.valid_channel_name(channel, receive=True), "Channel name invalid"
# Work out the connection to use
if "!" in channel:
assert channel.endswith("!")
index = self.consistent_hash(channel)
else:
index = next(self._receive_index_generator)
channel_key = self.prefix + channel
content = None
await self.receive_clean_locks.acquire(channel_key)
try:
while content is None:
# Nothing is lost here by cancellations, messages will still
# be in the backup queue.
content = await self._brpop_with_clean(
index, channel_key, timeout=self.brpop_timeout
)
# Fire off a task to clean the message from its backup queue.
# Per-channel locking isn't needed, because the backup is a queue
# and additionally, we don't care about the order; all processed
# messages need to be removed, no matter if the current one is
# removed after the next one.
# NOTE: Duplicate messages will be received eventually if any
# of these cleaners are cancelled.
cleaner = asyncio.ensure_future(
self._clean_receive_backup(index, channel_key)
)
self.receive_cleaners.append(cleaner)
def _cleanup_done(cleaner):
self.receive_cleaners.remove(cleaner)
self.receive_clean_locks.release(channel_key)
cleaner.add_done_callback(_cleanup_done)
except Exception:
self.receive_clean_locks.release(channel_key)
raise
# Message decode
message = self.deserialize(content)
# TODO: message expiry?
# If there is a full channel name stored in the message, unpack it.
if "__asgi_channel__" in message:
channel = message["__asgi_channel__"]
del message["__asgi_channel__"]
return channel, message
async def new_channel(self, prefix="specific"):
"""
Returns a new channel name that can be used by something in our
process as a specific channel.
"""
# TODO: Guarantee uniqueness better?
return "%s.%s!%s" % (
prefix,
self.client_prefix,
"".join(random.choice(string.ascii_letters) for i in range(12)),
)
### Flush extension ###
async def flush(self):
"""
Deletes all messages and groups on all shards.
"""
# Make sure all channel cleaners have finished before removing
# keys from under their feet.
await self.wait_received()
# Lua deletion script
delete_prefix = """
local keys = redis.call('keys', ARGV[1])
for i=1,#keys,5000 do
redis.call('del', unpack(keys, i, math.min(i+4999, #keys)))
end
"""
# Go through each connection and remove all with prefix
for i in range(self.ring_size):
async with self.connection(i) as connection:
await connection.eval(delete_prefix, keys=[], args=[self.prefix + "*"])
# Now clear the pools as well
await self.close_pools()
async def close_pools(self):
"""
Close all connections in the event loop pools.
"""
# Flush all cleaners, in case somebody just wanted to close the
# pools without flushing first.
await self.wait_received()
for pool in self.pools:
await pool.close()
async def wait_received(self):
"""
Wait for all channel cleanup functions to finish.
"""
if self.receive_cleaners:
await asyncio.wait(self.receive_cleaners[:])
### Groups extension ###
async def group_add(self, group, channel):
"""
Adds the channel name to a group.
"""
# Check the inputs
assert self.valid_group_name(group), "Group name not valid"
assert self.valid_channel_name(channel), "Channel name not valid"
# Get a connection to the right shard
group_key = self._group_key(group)
async with self.connection(self.consistent_hash(group)) as connection:
# Add to group sorted set with creation time as timestamp
await connection.zadd(group_key, time.time(), channel)
# Set expiration to be group_expiry, since everything in
# it at this point is guaranteed to expire before that
await connection.expire(group_key, self.group_expiry)
async def group_discard(self, group, channel):
"""
Removes the channel from the named group if it is in the group;
does nothing otherwise (does not error)
"""
assert self.valid_group_name(group), "Group name not valid"
assert self.valid_channel_name(channel), "Channel name not valid"
key = self._group_key(group)
async with self.connection(self.consistent_hash(group)) as connection:
await connection.zrem(key, channel)
async def group_send(self, group, message):
"""
Sends a message to the entire group.
"""
assert self.valid_group_name(group), "Group name not valid"
# Retrieve list of all channel names
key = self._group_key(group)
async with self.connection(self.consistent_hash(group)) as connection:
# Discard old channels based on group_expiry
await connection.zremrangebyscore(
key, min=0, max=int(time.time()) - self.group_expiry
)
channel_names = [
x.decode("utf8") for x in await connection.zrange(key, 0, -1)
]
connection_to_channel_keys, channel_keys_to_message, channel_keys_to_capacity = self._map_channel_keys_to_connection(
channel_names, message
)
for connection_index, channel_redis_keys in connection_to_channel_keys.items():
# Create a LUA script specific for this connection.
# Make sure to use the message specific to this channel, it is
# stored in channel_to_message dict and contains the
# __asgi_channel__ key.
group_send_lua = (
"""
for i=1,#KEYS do
if redis.call('LLEN', KEYS[i]) < tonumber(ARGV[i + #KEYS]) then
redis.call('LPUSH', KEYS[i], ARGV[i])
redis.call('EXPIRE', KEYS[i], %d)
end
end
"""
% self.expiry
)
# We need to filter the messages to keep those related to the connection
args = [
channel_keys_to_message[channel_key]
for channel_key in channel_redis_keys
]
# We need to send the capacity for each channel
args += [
channel_keys_to_capacity[channel_key]
for channel_key in channel_redis_keys
]
# channel_keys does not contain a single redis key more than once
async with self.connection(connection_index) as connection:
await connection.eval(
group_send_lua, keys=channel_redis_keys, args=args
)
def _map_channel_to_connection(self, channel_names, message):
"""
For a list of channel names, bucket each one to a dict keyed by the
connection index
Also for each channel create a message specific to that channel, adding
the __asgi_channel__ key to the message
We also return a mapping from channel names to their corresponding Redis
keys, and a mapping of channels to their capacity
"""
connection_to_channels = collections.defaultdict(list)
channel_to_message = dict()
channel_to_capacity = dict()
channel_to_key = dict()
for channel in channel_names:
channel_non_local_name = channel
if "!" in channel:
message = dict(message.items())
message["__asgi_channel__"] = channel
channel_non_local_name = self.non_local_name(channel)
channel_key = self.prefix + channel_non_local_name
idx = self.consistent_hash(channel_non_local_name)
connection_to_channels[idx].append(channel_key)
channel_to_capacity[channel] = self.get_capacity(channel)
channel_to_message[channel] = self.serialize(message)
# We build a
channel_to_key[channel] = channel_key
return (
connection_to_channels,
channel_to_message,
channel_to_capacity,
channel_to_key,
)
def _map_channel_keys_to_connection(self, channel_names, message):
"""
For a list of channel names, GET
1. list of their redis keys bucket each one to a dict keyed by the connection index
2. for each unique channel redis key create a serialized message specific to that redis key, by adding
the list of channels mapped to that redis key in __asgi_channel__ key to the message
3. returns a mapping of redis channels keys to their capacity
"""
# Connection dict keyed by index to list of redis keys mapped on that index
connection_to_channel_keys = collections.defaultdict(list)
# Message dict maps redis key to the message that needs to be send on that key
channel_key_to_message = dict()
# Channel key mapped to its capacity
channel_key_to_capacity = dict()
# For each channel
for channel in channel_names:
channel_non_local_name = channel
if "!" in channel:
channel_non_local_name = self.non_local_name(channel)
# Get its redis key
channel_key = self.prefix + channel_non_local_name
# Have we come across the same redis key?
if channel_key not in channel_key_to_message.keys():
# If not, fill the corresponding dicts
message = dict(message.items())
message["__asgi_channel__"] = [channel]
channel_key_to_message[channel_key] = message
channel_key_to_capacity[channel_key] = self.get_capacity(channel)
idx = self.consistent_hash(channel_non_local_name)
connection_to_channel_keys[idx].append(channel_key)
else:
# Yes, Append the channel in message dict
channel_key_to_message[channel_key]["__asgi_channel__"].append(channel)
# Now that we know what message needs to be send on a redis key we serialize it
for key in channel_key_to_message.keys():
# Serialize the message stored for each redis key
channel_key_to_message[key] = self.serialize(channel_key_to_message[key])
return (
connection_to_channel_keys,
channel_key_to_message,
channel_key_to_capacity,
)
def _group_key(self, group):
"""
Common function to make the storage key for the group.
"""
return ("%s:group:%s" % (self.prefix, group)).encode("utf8")
### Serialization ###
def serialize(self, message):
"""
Serializes message to a byte string.
"""
value = msgpack.packb(message, use_bin_type=True)
if self.crypter:
value = self.crypter.encrypt(value)
return value
def deserialize(self, message):
"""
Deserializes from a byte string.
"""
if self.crypter:
message = self.crypter.decrypt(message, self.expiry + 10)
return msgpack.unpackb(message, raw=False)
### Internal functions ###
def consistent_hash(self, value):
"""
Maps the value to a node value between 0 and 4095
using CRC, then down to one of the ring nodes.
"""
if isinstance(value, str):
value = value.encode("utf8")
bigval = binascii.crc32(value) & 0xFFF
ring_divisor = 4096 / float(self.ring_size)
return int(bigval / ring_divisor)
def make_fernet(self, key):
"""
Given a single encryption key, returns a Fernet instance using it.
"""
from cryptography.fernet import Fernet
if isinstance(key, str):
key = key.encode("utf8")
formatted_key = base64.urlsafe_b64encode(hashlib.sha256(key).digest())
return Fernet(formatted_key)
def __str__(self):
return "%s(hosts=%s)" % (self.__class__.__name__, self.hosts)
### Connection handling ###
def connection(self, index):
"""
Returns the correct connection for the index given.
Lazily instantiates pools.
"""
# Catch bad indexes
if not 0 <= index < self.ring_size:
raise ValueError(
"There are only %s hosts - you asked for %s!" % (self.ring_size, index)
)
# Make a context manager
return self.ConnectionContextManager(self.pools[index])
class ConnectionContextManager:
"""
Async context manager for connections
"""
def __init__(self, pool):
self.pool = pool
async def __aenter__(self):
self.conn = await self.pool.pop()
return self.conn
async def __aexit__(self, exc_type, exc, tb):
if exc:
self.pool.conn_error(self.conn)
else:
self.pool.push(self.conn)
self.conn = None