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consumer.py
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consumer.py
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from __future__ import annotations
import asyncio
import json
from memphis.exceptions import MemphisError
from memphis.utils import default_error_handler, get_internal_name
from memphis.message import Message
class Consumer:
MAX_BATCH_SIZE = 5000
def __init__(
self,
connection,
station_name: str,
consumer_name,
consumer_group,
pull_interval_ms: int,
batch_size: int,
batch_max_time_to_wait_ms: int,
max_ack_time_ms: int,
max_msg_deliveries: int = 10,
error_callback=None,
start_consume_from_sequence: int = 1,
last_messages: int = -1,
):
self.connection = connection
self.station_name = station_name.lower()
self.consumer_name = consumer_name.lower()
self.consumer_group = consumer_group.lower()
self.pull_interval_ms = pull_interval_ms
self.batch_size = batch_size
self.batch_max_time_to_wait_ms = batch_max_time_to_wait_ms
self.max_ack_time_ms = max_ack_time_ms
self.max_msg_deliveries = max_msg_deliveries
self.ping_consumer_interval_ms = 30000
if error_callback is None:
error_callback = default_error_handler
self.t_ping = asyncio.create_task(self.__ping_consumer(error_callback))
self.start_consume_from_sequence = start_consume_from_sequence
self.last_messages = last_messages
self.context = {}
self.dls_messages = []
self.dls_current_index = 0
self.dls_callback_func = None
self.t_dls = asyncio.create_task(self.__consume_dls())
self.t_consume = None
def set_context(self, context):
"""Set a context (dict) that will be passed to each message handler call."""
self.context = context
def consume(self, callback):
"""Consume events."""
self.dls_callback_func = callback
self.t_consume = asyncio.create_task(self.__consume(callback))
async def __consume(self, callback):
subject = get_internal_name(self.station_name)
consumer_group = get_internal_name(self.consumer_group)
self.psub = await self.connection.broker_connection.pull_subscribe(
subject + ".final", durable=consumer_group
)
while True:
if self.connection.is_connection_active and self.pull_interval_ms:
try:
memphis_messages = []
msgs = await self.psub.fetch(self.batch_size)
for msg in msgs:
memphis_messages.append(
Message(msg, self.connection, self.consumer_group)
)
await callback(memphis_messages, None, self.context)
await asyncio.sleep(self.pull_interval_ms / 1000)
except asyncio.TimeoutError:
await callback(
[], MemphisError("Memphis: TimeoutError"), self.context
)
continue
except Exception as e:
if self.connection.is_connection_active:
raise MemphisError(str(e)) from e
return
else:
break
async def __consume_dls(self):
subject = get_internal_name(self.station_name)
consumer_group = get_internal_name(self.consumer_group)
try:
subscription_name = "$memphis_dls_" + subject + "_" + consumer_group
self.consumer_dls = await self.connection.broker_manager.subscribe(
subscription_name, subscription_name
)
async for msg in self.consumer_dls.messages:
index_to_insert = self.dls_current_index
if index_to_insert >= 10000:
index_to_insert %= 10000
self.dls_messages.insert(
index_to_insert, Message(
msg, self.connection, self.consumer_group)
)
self.dls_current_index += 1
if self.dls_callback_func != None:
await self.dls_callback_func(
[Message(msg, self.connection, self.consumer_group)],
None,
self.context,
)
except Exception as e:
if self.dls_callback_func != None:
await self.dls_callback_func([], MemphisError(str(e)), self.context)
return
async def fetch(self, batch_size: int = 10):
"""
Fetch a batch of messages.
Returns a list of Message objects. If the connection is
not active or no messages are recieved before timing out,
an empty list is returned.
Example:
import asyncio
from memphis import Memphis
async def main(/, host, username, password, station):
memphis = Memphis()
await memphis.connect(host=host,
username=username,
password=password)
consumer = await memphis.consumer(station_name=station,
consumer_name="test-consumer",
consumer_group="test-consumer-group")
while True:
batch = await consumer.fetch()
print("Recieved {} messages".format(len(batch)))
for msg in batch:
serialized_record = msg.get_data()
print("Message:", serialized_record)
await memphis.close()
if __name__ == '__main__':
asyncio.run(main(host=host,
username=username,
password=password,
station=station))
"""
messages = []
if self.connection.is_connection_active:
try:
if batch_size > self.MAX_BATCH_SIZE:
raise MemphisError(
f"Batch size can not be greater than {self.MAX_BATCH_SIZE}")
self.batch_size = batch_size
if len(self.dls_messages) > 0:
if len(self.dls_messages) <= batch_size:
messages = self.dls_messages
self.dls_messages = []
self.dls_current_index = 0
else:
messages = self.dls_messages[0:batch_size]
del self.dls_messages[0:batch_size]
self.dls_current_index -= len(messages)
return messages
durable_name = ""
if self.consumer_group != "":
durable_name = get_internal_name(self.consumer_group)
else:
durable_name = get_internal_name(self.consumer_name)
subject = get_internal_name(self.station_name)
self.psub = await self.connection.broker_connection.pull_subscribe(
subject + ".final", durable=durable_name
)
msgs = await self.psub.fetch(batch_size)
for msg in msgs:
messages.append(
Message(msg, self.connection, self.consumer_group))
return messages
except Exception as e:
if "timeout" not in str(e).lower():
raise MemphisError(str(e)) from e
return messages
async def __ping_consumer(self, callback):
while True:
try:
await asyncio.sleep(self.ping_consumer_interval_ms / 1000)
consumer_group = get_internal_name(self.consumer_group)
await self.connection.broker_connection.consumer_info(
self.station_name, consumer_group, timeout=30
)
except Exception as e:
callback(MemphisError(str(e)))
async def destroy(self):
"""Destroy the consumer."""
if self.t_consume is not None:
self.t_consume.cancel()
if self.t_dls is not None:
self.t_dls.cancel()
if self.t_ping is not None:
self.t_ping.cancel()
self.pull_interval_ms = None
try:
destroy_consumer_req = {
"name": self.consumer_name,
"station_name": self.station_name,
"username": self.connection.username
}
consumer_name = json.dumps(
destroy_consumer_req, indent=2).encode("utf-8")
res = await self.connection.broker_manager.request(
"$memphis_consumer_destructions", consumer_name, timeout=5
)
error = res.data.decode("utf-8")
if error != "" and not "not exist" in error:
raise MemphisError(error)
self.dls_messages.clear()
internal_station_name = get_internal_name(self.station_name)
map_key = internal_station_name + "_" + self.consumer_name.lower()
del self.connection.consumers_map[map_key]
except Exception as e:
raise MemphisError(str(e)) from e