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Easy Django based gRPC service

Project description

django-grpc

CircleCI

Easy way to launch gRPC server with access to Django ORM and other handy stuff. gRPC calls are much faster that traditional HTTP requests because communicate over persistent connection and are compressed. Underlying gRPC library is written in C which makes it work faster than any RESTful framework where a lot of time is spent on serialization/deserialization.

Note that you need this project only if you want to use Django functionality in gRPC service. For pure python implementation read this

  • Supported Python: 3.4+
  • Supported Django: 2.X and 3.X

Installation

pip install django-grpc

Update settings.py

INSTALLED_APPS = [
    # ...
    'django_grpc',
]

GRPCSERVER = {
    'servicers': ['dotted.path.to.callback.eg.grpc_hook'],  # see `grpc_hook()` below
    'interceptors': ['dotted.path.to.interceptor_class',],  # optional, interceprots are similar to middleware in Django
    'maximum_concurrent_rpcs': None,
    'options': [("grpc.max_receive_message_length", 1024 * 1024 * 100)],  # optional, list of key-value pairs to configure the channel. The full list of available channel arguments: https://grpc.github.io/grpc/core/group__grpc__arg__keys.html
    'credentials': [{
        'private_key': 'private_key.pem',
        'certificate_chain': 'certificate_chain.pem'
    }]    # required only if SSL/TLS support is required to be enabled
}

The callback that initializes "servicer" must look like following:

import my_pb2
import my_pb2_grpc

def grpc_hook(server):
    my_pb2_grpc.add_MYServicer_to_server(MYServicer(), server)

...
class MYServicer(my_pb2_grpc.MYServicer):

    def GetPage(self, request, context):
        response = my_pb2.PageResponse(title="Demo object")
        return response

Usage

python manage.py grpcserver

For developer's convenience add --autoreload flag during development.

Signals

The package uses Django signals to allow decoupled applications get notified when some actions occur:

  • django_grpc.signals.grpc_request_started - sent before gRPC server begins processing a request
  • django_grpc.signals.grpc_request_finished - sent when gRPC server finishes delivering response to the client
  • django_grpc.signals.grpc_got_request_exception - this signal is sent whenever RPC encounters an exception while processing an incoming request.

Note that signal names are similar to Django's built-in signals, but have "grpc_" prefix.

Serializers

There is an easy way to serialize django model to gRPC message using django_grpc.serializers.serialize_model.

Helpers

Ratelimits

You can limit number of requests to your procedures by using decorator django_grpc.helpers.ratelimit.ratelimit.

from tests.sampleapp import helloworld_pb2_grpc, helloworld_pb2
from django_grpc.helpers import ratelimit


class Greeter(helloworld_pb2_grpc.GreeterServicer):
    
    @ratelimit(max_calls=10, time_period=60)
    def SayHello(self, request, context):
        return helloworld_pb2.HelloReply(message='Hello, %s!' % request.name)

When limit is reached for given time period decorator will abort with status grpc.StatusCode.RESOURCE_EXHAUSTED

As storage for state of calls Django's cache framework is used. By default "default" cache system is used but you can specify any other in settings RATELIMIT_USE_CACHE

Advanced usage

Using groups

@ratelimit(max_calls=10, time_period=60, group="main")
def foo(request, context):
    ...

@ratelimit(max_calls=5, time_period=60, group="main")
def bar(request, context):
    ...

foo and bar will share the same counter because they are in the same group

Using keys

@ratelimit(max_calls=5, time_period=10, keys=["request:dot.path.to.field"])
@ratelimit(max_calls=5, time_period=10, keys=["metadata:user-agent"])
@ratelimit(max_calls=5, time_period=10, keys=[lambda request, context: context.peer()])

Right now 3 type of keys are supported with prefixes "request:", "metadata:" and as callable.

  • "request:" allows to extract request's field value by doted path
  • "metadata:" allows to extract metadata from context.invocation_metadata()
  • callable function that takes request and context and returns string

NOTE: if value of key is empty string it still will be considered a valid value and can cause sharing of ratelimits between different RPCs in the same group

TIP: To use the same configuration for different RPCs use dict variable

MAIN_GROUP = {"max_calls": 5, "time_period": 60, "group": "main"}

@ratelimit(**MAIN_GROUP)
def foo(request, context):
   ...

@ratelimit(**MAIN_GROUP)
def bar(request, context):
   ...

Testing

Test your RPCs just like regular python methods which return some structure or generator. You need to provide them with only 2 parameters: request (protobuf structure or generator) and context (use FakeServicerContext from the example below).

Fake Context

You can pass instance of django_grpc_testtools.context.FakeServicerContext to your gRPC method to verify how it works with context (aborts, metadata and etc.).

import grpc
from django_grpc_testtools.context import FakeServicerContext
from tests.sampleapp.servicer import Greeter
from tests.sampleapp.helloworld_pb2 import HelloRequest

servicer = Greeter()
context = FakeServicerContext()
request = HelloRequest(name='Tester')

# To check metadata set by RPC 
response = servicer.SayHello(request, context)
assert context.get_trailing_metadata("Header1") == '...'

# To check status code
try:
    servicer.SayHello(request, context) 
except Exception:
    pass

assert context.abort_status == grpc.StatusCode.INVALID_ARGUMENT
assert context.abort_message == 'Cannot say hello to John'

In addition to standard gRPC context methods, FakeServicerContext provides:

  • .set_invocation_metadata() allows to simulate metadata from client to server.
  • .get_trailing_metadata() to get metadata set by your server
  • .abort_status and .abort_message to check if .abort() was called

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