Separate the TCP and terse JSON formatting code. (#8587)

This should (theoretically) allow for using the TCP code with a different output type
and make it easier to use the JSON code with files / console.

changelog.d/8587.misc

@@ -0,0 +1 @@
+Re-organize the structured logging code to separate the TCP transport handling from the JSON formatting.

synapse/logging/_remote.py

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+# -*- coding: utf-8 -*-
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import sys
+import traceback
+from collections import deque
+from ipaddress import IPv4Address, IPv6Address, ip_address
+from math import floor
+from typing import Callable, Optional
+
+import attr
+from zope.interface import implementer
+
+from twisted.application.internet import ClientService
+from twisted.internet.defer import Deferred
+from twisted.internet.endpoints import (
+    HostnameEndpoint,
+    TCP4ClientEndpoint,
+    TCP6ClientEndpoint,
+)
+from twisted.internet.interfaces import IPushProducer, ITransport
+from twisted.internet.protocol import Factory, Protocol
+from twisted.logger import ILogObserver, Logger, LogLevel
+
+
+@attr.s
+@implementer(IPushProducer)
+class LogProducer:
+    """
+    An IPushProducer that writes logs from its buffer to its transport when it
+    is resumed.
+
+    Args:
+        buffer: Log buffer to read logs from.
+        transport: Transport to write to.
+        format_event: A callable to format the log entry to a string.
+    """
+
+    transport = attr.ib(type=ITransport)
+    format_event = attr.ib(type=Callable[[dict], str])
+    _buffer = attr.ib(type=deque)
+    _paused = attr.ib(default=False, type=bool, init=False)
+
+    def pauseProducing(self):
+        self._paused = True
+
+    def stopProducing(self):
+        self._paused = True
+        self._buffer = deque()
+
+    def resumeProducing(self):
+        self._paused = False
+
+        while self._paused is False and (self._buffer and self.transport.connected):
+            try:
+                # Request the next event and format it.
+                event = self._buffer.popleft()
+                msg = self.format_event(event)
+
+                # Send it as a new line over the transport.
+                self.transport.write(msg.encode("utf8"))
+            except Exception:
+                # Something has gone wrong writing to the transport -- log it
+                # and break out of the while.
+                traceback.print_exc(file=sys.__stderr__)
+                break
+
+
+@attr.s
+@implementer(ILogObserver)
+class TCPLogObserver:
+    """
+    An IObserver that writes JSON logs to a TCP target.
+
+    Args:
+        hs (HomeServer): The homeserver that is being logged for.
+        host: The host of the logging target.
+        port: The logging target's port.
+        format_event: A callable to format the log entry to a string.
+        maximum_buffer: The maximum buffer size.
+    """
+
+    hs = attr.ib()
+    host = attr.ib(type=str)
+    port = attr.ib(type=int)
+    format_event = attr.ib(type=Callable[[dict], str])
+    maximum_buffer = attr.ib(type=int)
+    _buffer = attr.ib(default=attr.Factory(deque), type=deque)
+    _connection_waiter = attr.ib(default=None, type=Optional[Deferred])
+    _logger = attr.ib(default=attr.Factory(Logger))
+    _producer = attr.ib(default=None, type=Optional[LogProducer])
+
+    def start(self) -> None:
+
+        # Connect without DNS lookups if it's a direct IP.
+        try:
+            ip = ip_address(self.host)
+            if isinstance(ip, IPv4Address):
+                endpoint = TCP4ClientEndpoint(
+                    self.hs.get_reactor(), self.host, self.port
+                )
+            elif isinstance(ip, IPv6Address):
+                endpoint = TCP6ClientEndpoint(
+                    self.hs.get_reactor(), self.host, self.port
+                )
+            else:
+                raise ValueError("Unknown IP address provided: %s" % (self.host,))
+        except ValueError:
+            endpoint = HostnameEndpoint(self.hs.get_reactor(), self.host, self.port)
+
+        factory = Factory.forProtocol(Protocol)
+        self._service = ClientService(endpoint, factory, clock=self.hs.get_reactor())
+        self._service.startService()
+        self._connect()
+
+    def stop(self):
+        self._service.stopService()
+
+    def _connect(self) -> None:
+        """
+        Triggers an attempt to connect then write to the remote if not already writing.
+        """
+        if self._connection_waiter:
+            return
+
+        self._connection_waiter = self._service.whenConnected(failAfterFailures=1)
+
+        @self._connection_waiter.addErrback
+        def fail(r):
+            r.printTraceback(file=sys.__stderr__)
+            self._connection_waiter = None
+            self._connect()
+
+        @self._connection_waiter.addCallback
+        def writer(r):
+            # We have a connection. If we already have a producer, and its
+            # transport is the same, just trigger a resumeProducing.
+            if self._producer and r.transport is self._producer.transport:
+                self._producer.resumeProducing()
+                self._connection_waiter = None
+                return
+
+            # If the producer is still producing, stop it.
+            if self._producer:
+                self._producer.stopProducing()
+
+            # Make a new producer and start it.
+            self._producer = LogProducer(
+                buffer=self._buffer,
+                transport=r.transport,
+                format_event=self.format_event,
+            )
+            r.transport.registerProducer(self._producer, True)
+            self._producer.resumeProducing()
+            self._connection_waiter = None
+
+    def _handle_pressure(self) -> None:
+        """
+        Handle backpressure by shedding events.
+
+        The buffer will, in this order, until the buffer is below the maximum:
+            - Shed DEBUG events
+            - Shed INFO events
+            - Shed the middle 50% of the events.
+        """
+        if len(self._buffer) <= self.maximum_buffer:
+            return
+
+        # Strip out DEBUGs
+        self._buffer = deque(
+            filter(lambda event: event["log_level"] != LogLevel.debug, self._buffer)
+        )
+
+        if len(self._buffer) <= self.maximum_buffer:
+            return
+
+        # Strip out INFOs
+        self._buffer = deque(
+            filter(lambda event: event["log_level"] != LogLevel.info, self._buffer)
+        )
+
+        if len(self._buffer) <= self.maximum_buffer:
+            return
+
+        # Cut the middle entries out
+        buffer_split = floor(self.maximum_buffer / 2)
+
+        old_buffer = self._buffer
+        self._buffer = deque()
+
+        for i in range(buffer_split):
+            self._buffer.append(old_buffer.popleft())
+
+        end_buffer = []
+        for i in range(buffer_split):
+            end_buffer.append(old_buffer.pop())
+
+        self._buffer.extend(reversed(end_buffer))
+
+    def __call__(self, event: dict) -> None:
+        self._buffer.append(event)
+
+        # Handle backpressure, if it exists.
+        try:
+            self._handle_pressure()
+        except Exception:
+            # If handling backpressure fails,clear the buffer and log the
+            # exception.
+            self._buffer.clear()
+            self._logger.failure("Failed clearing backpressure")
+
+        # Try and write immediately.
+        self._connect()