Iteratively encode JSON responses to avoid blocking the reactor. (#8013)

pull/8111/head
Patrick Cloke 2020-08-18 08:49:59 -04:00 committed by GitHub
parent 25e55d2598
commit 2f4d60a5ba
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5 changed files with 94 additions and 13 deletions

1
changelog.d/8013.feature Normal file
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@ -0,0 +1 @@
Iteratively encode JSON to avoid blocking the reactor.

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@ -22,12 +22,13 @@ import types
import urllib
from http import HTTPStatus
from io import BytesIO
from typing import Any, Callable, Dict, Tuple, Union
from typing import Any, Callable, Dict, Iterator, List, Tuple, Union
import jinja2
from canonicaljson import encode_canonical_json, encode_pretty_printed_json
from canonicaljson import iterencode_canonical_json, iterencode_pretty_printed_json
from zope.interface import implementer
from twisted.internet import defer
from twisted.internet import defer, interfaces
from twisted.python import failure
from twisted.web import resource
from twisted.web.server import NOT_DONE_YET, Request
@ -499,6 +500,78 @@ class RootOptionsRedirectResource(OptionsResource, RootRedirect):
pass
@implementer(interfaces.IPullProducer)
class _ByteProducer:
"""
Iteratively write bytes to the request.
"""
# The minimum number of bytes for each chunk. Note that the last chunk will
# usually be smaller than this.
min_chunk_size = 1024
def __init__(
self, request: Request, iterator: Iterator[bytes],
):
self._request = request
self._iterator = iterator
def start(self) -> None:
self._request.registerProducer(self, False)
def _send_data(self, data: List[bytes]) -> None:
"""
Send a list of strings as a response to the request.
"""
if not data:
return
self._request.write(b"".join(data))
def resumeProducing(self) -> None:
# We've stopped producing in the meantime (note that this might be
# re-entrant after calling write).
if not self._request:
return
# Get the next chunk and write it to the request.
#
# The output of the JSON encoder is coalesced until min_chunk_size is
# reached. (This is because JSON encoders produce a very small output
# per iteration.)
#
# Note that buffer stores a list of bytes (instead of appending to
# bytes) to hopefully avoid many allocations.
buffer = []
buffered_bytes = 0
while buffered_bytes < self.min_chunk_size:
try:
data = next(self._iterator)
buffer.append(data)
buffered_bytes += len(data)
except StopIteration:
# The entire JSON object has been serialized, write any
# remaining data, finalize the producer and the request, and
# clean-up any references.
self._send_data(buffer)
self._request.unregisterProducer()
self._request.finish()
self.stopProducing()
return
self._send_data(buffer)
def stopProducing(self) -> None:
self._request = None
def _encode_json_bytes(json_object: Any) -> Iterator[bytes]:
"""
Encode an object into JSON. Returns an iterator of bytes.
"""
for chunk in json_encoder.iterencode(json_object):
yield chunk.encode("utf-8")
def respond_with_json(
request: Request,
code: int,
@ -533,15 +606,23 @@ def respond_with_json(
return None
if pretty_print:
json_bytes = encode_pretty_printed_json(json_object) + b"\n"
encoder = iterencode_pretty_printed_json
else:
if canonical_json or synapse.events.USE_FROZEN_DICTS:
# canonicaljson already encodes to bytes
json_bytes = encode_canonical_json(json_object)
encoder = iterencode_canonical_json
else:
json_bytes = json_encoder.encode(json_object).encode("utf-8")
encoder = _encode_json_bytes
return respond_with_json_bytes(request, code, json_bytes, send_cors=send_cors)
request.setResponseCode(code)
request.setHeader(b"Content-Type", b"application/json")
request.setHeader(b"Cache-Control", b"no-cache, no-store, must-revalidate")
if send_cors:
set_cors_headers(request)
producer = _ByteProducer(request, encoder(json_object))
producer.start()
return NOT_DONE_YET
def respond_with_json_bytes(

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@ -43,7 +43,7 @@ REQUIREMENTS = [
"jsonschema>=2.5.1",
"frozendict>=1",
"unpaddedbase64>=1.1.0",
"canonicaljson>=1.2.0",
"canonicaljson>=1.3.0",
# we use the type definitions added in signedjson 1.1.
"signedjson>=1.1.0",
"pynacl>=1.2.1",

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@ -15,12 +15,12 @@
import logging
from typing import Dict, Set
from canonicaljson import encode_canonical_json, json
from canonicaljson import json
from signedjson.sign import sign_json
from synapse.api.errors import Codes, SynapseError
from synapse.crypto.keyring import ServerKeyFetcher
from synapse.http.server import DirectServeJsonResource, respond_with_json_bytes
from synapse.http.server import DirectServeJsonResource, respond_with_json
from synapse.http.servlet import parse_integer, parse_json_object_from_request
logger = logging.getLogger(__name__)
@ -223,4 +223,4 @@ class RemoteKey(DirectServeJsonResource):
results = {"server_keys": signed_keys}
respond_with_json_bytes(request, 200, encode_canonical_json(results))
respond_with_json(request, 200, results, canonical_json=True)

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@ -178,7 +178,6 @@ class JsonResourceTests(unittest.TestCase):
self.assertEqual(channel.result["code"], b"200")
self.assertNotIn("body", channel.result)
self.assertEqual(channel.headers.getRawHeaders(b"Content-Length"), [b"15"])
class OptionsResourceTests(unittest.TestCase):