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Project description

:hibiscus: Petal - Flask, for gRPC services.

Petal reduces the boilerplate required to write and maintain gRPC based services whilst ensuring your service code is always in sync with your definitions. It aims to be a somewhat opinionated gRPC framework. This is very, very early code.

Installation and features

pip install petal

Right now:

  • Define your service methods as simple Python functions
  • Ensure they are up to date with service definitions by utilizing type annotations
  • Build your proto definitions and run your app with a petal command
  • Share compiled protobuf definitions as Python packages.
  • Streaming requests and responses

Future features:

  • Autoreloading during development
  • Structured logging
  • Some form of plugin architecture
  • Distributed tracing
  • A testing client
  • AsyncIO support

Hello world example:

from petal import Service
from example.protobuf.greeter_pb2 import HelloReply, HelloRequest

service = Service(__name__)

def say_hello(request: HelloRequest) -> HelloReply:
    return HelloReply(message=f'Hello {}')

Tutorial: Creating a petal app

Lets create a Hello World Petal app. First lets define an entirely useless service. Place the file below in hello_world/protobuf/service.proto:

syntax = "proto3";
package hello_world.protobuf.service;

service HelloWorld {
  rpc SayHello (HelloRequest) returns (HelloReply) {}

message HelloRequest {

message HelloReply {

Then run petal build hello_world.

Next, write our service definitions. Create a hello_world/ file and add some imports:

from petal import Service
from hello_world.protobuf.service_pb2 import HelloReply, HelloRequest

service = Service(__name__)

This imports the request and response types our service will need. Next we need to fill in the SayHello method:

def say_hello(request: HelloRequest) -> HelloReply:
    return HelloReply()

And finally, run the service by executing petal run hello_world.

Now if we modify the service by adding a new method:

message HelloAgain {}

service HelloWorld {
  rpc SayHelloAgain (HelloRequest) returns (HelloAgain) {}

And run petal build hello_world && petal run hello_world, we get an error:

$ petal run hello_world
Error: Cannot find a suitable method for GRPC method SayHelloAgain
Please ensure one exists in your service code, or use service.grpc(name=NAME) to define one.

Petal is ensuring we have the correct Python methods defined for all our service functions. We can fix this by defining one:

from hello_world.protobuf.service_pb2 import HelloAgain

def say_hello_again(request: HelloRequest) -> HelloAgain:
    return HelloAgain()

Now running petal serve hello_world will work.

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