Getting started with the Dapr Python gRPC service extension

How to get up and running with the Dapr Python gRPC extension

The Dapr Python SDK provides a built in gRPC server extension, dapr.ext.grpc, for creating Dapr services.

Installation

You can download and install the Dapr gRPC server extension with:


pip install dapr-ext-grpc


pip3 install dapr-ext-grpc-dev

Examples

The App object can be used to create a server.

Listen for service invocation requests

The InvokeMethodReqest and InvokeMethodResponse objects can be used to handle incoming requests.

A simple service that will listen and respond to requests will look like:

from dapr.ext.grpc import App, InvokeMethodRequest, InvokeMethodResponse

app = App()

@app.method(name='my-method')
def mymethod(request: InvokeMethodRequest) -> InvokeMethodResponse:
    print(request.metadata, flush=True)
    print(request.text(), flush=True)

    return InvokeMethodResponse(b'INVOKE_RECEIVED', "text/plain; charset=UTF-8")

app.run(50051)

A full sample can be found here.

Subscribe to a topic

When subscribing to a topic, you can instruct dapr whether the event delivered has been accepted, or whether it should be dropped, or retried later.

from typing import Optional
from cloudevents.sdk.event import v1
from dapr.ext.grpc import App
from dapr.clients.grpc._response import TopicEventResponse

app = App()

# Default subscription for a topic
@app.subscribe(pubsub_name='pubsub', topic='TOPIC_A')
def mytopic(event: v1.Event) -> Optional[TopicEventResponse]:
    print(event.Data(),flush=True)
    # Returning None (or not doing a return explicitly) is equivalent
    # to returning a TopicEventResponse("success").
    # You can also return TopicEventResponse("retry") for dapr to log
    # the message and retry delivery later, or TopicEventResponse("drop")
    # for it to drop the message
    return TopicEventResponse("success")

# Specific handler using Pub/Sub routing
@app.subscribe(pubsub_name='pubsub', topic='TOPIC_A',
               rule=Rule("event.type == \"important\"", 1))
def mytopic_important(event: v1.Event) -> None:
    print(event.Data(),flush=True)

# Handler with disabled topic validation
@app.subscribe(pubsub_name='pubsub-mqtt', topic='topic/#', disable_topic_validation=True,)
def mytopic_wildcard(event: v1.Event) -> None:
    print(event.Data(),flush=True)

app.run(50051)

A full sample can be found here.

Setup input binding trigger

from dapr.ext.grpc import App, BindingRequest

app = App()

@app.binding('kafkaBinding')
def binding(request: BindingRequest):
    print(request.text(), flush=True)

app.run(50051)

A full sample can be found here.