A Guide to Building a Python RPC Server Using Flask

Introduction

Remote Procedure Call (RPC) is a communication protocol that allows a client application to call a function or method on a remote server. RPC is widely used in distributed systems for inter-process communication. Python is a powerful programming language for building applications, and Flask is a popular web framework for building web applications in Python. In this blog post, we will guide you on how to build a Python RPC server using Flask.

• Step 1: Install Flask
• Step 2: Create a Flask app
• Step 3: Add a JSON-RPC endpoint
• Step 4: Define JSON-RPC functions
• Step 5: Test the JSON-RPC server
• Conclusion

Step 1: Install Flask

The first step is to install Flask. You can install Flask using pip, which is the package installer for Python.

pip install flask

Step 2: Create a Flask app

The next step is to create a Flask app. You can create a Flask app by creating a Python file and importing Flask. The following code creates a simple Flask app:

from flask import Flask

app = Flask(__name__)

@app.route('/')
def index():
    return 'Hello, world!'

The above code creates a Flask app and defines a route for the root URL. When a client sends a GET request to the root URL, the server will return 'Hello, world!'.

Step 3: Add a JSON-RPC endpoint

The next step is to add a JSON-RPC endpoint to the Flask app. JSON-RPC is a lightweight remote procedure call protocol that uses JSON to encode messages. You can use the jsonrpcserver package to add a JSON-RPC endpoint to Flask. The jsonrpcserver package provides a decorator @app.route_jsonrpc that you can use to define a JSON-RPC endpoint.

from flask import Flask
from jsonrpcserver import dispatch, result

app = Flask(__name__)

@app.route('/')
def index():
    return 'Hello, world!'

@app.route_jsonrpc('/rpc')
def rpc(request):
    response = dispatch(request.data)
    return result(response)

The above code defines a JSON-RPC endpoint at the URL /rpc. When a client sends a JSON-RPC request to the URL /rpc, the server will dispatch the request to the appropriate function and return the result in a JSON-RPC response.

Step 4: Define JSON-RPC functions

The next step is to define the JSON-RPC functions that the client can call. You can define JSON-RPC functions as Python functions and use the @dispatch decorator from the jsonrpcserver package to register the functions with the JSON-RPC server.

from flask import Flask
from jsonrpcserver import dispatch, result
from jsonrpcserver.exceptions import InvalidParams

app = Flask(__name__)

@app.route('/')
def index():
    return 'Hello, world!'

@app.route_jsonrpc('/rpc')
def rpc(request):
    response = dispatch(request.data)
    return result(response)

@dispatch
def add(a: int, b: int) -> int:
    return a + b

@dispatch
def subtract(a: int, b: int) -> int:
    return a - b

@dispatch
def multiply(a: int, b: int) -> int:
    return a * b

@dispatch
def divide(a: int, b: int) -> float:
    if b == 0:
        raise InvalidParams('division by zero')
    return a / b

The above code defines four JSON-RPC functions: add, subtract, multiply, and divide. Each function takes two integer arguments and returns an integer or float.

Step 5: Test the JSON-RPC server

The final step is to test the JSON-RPC server. You can test the server by sending JSON-RPC requests to the URL /rpc. You can use any JSON-RPC client to send requests to the server. In the following example, we will use the jsonrpcclient package to send requests to the server.

import jsonrpcclient

url = 'http://localhost:5000/rpc'

result = jsonrpcclient.request(url, 'add', a=2, b=3)
print(result)  # Output: 5

result = jsonrpcclient.request(url, 'subtract', a=5, b=3)
print(result)  # Output: 2

result = jsonrpcclient.request(url, 'multiply', a=2, b=3)
print(result)  # Output: 6

result = jsonrpcclient.request(url, 'divide', a=6, b=3)
print(result)  # Output: 2.0

result = jsonrpcclient.request(url, 'divide', a=6, b=0)
print(result)  # Output: {'code': -32602, 'message': 'Invalid params', 'data': 'division by zero'}

The above code sends five JSON-RPC requests to the server and prints the results. The first four requests call the add, subtract, multiply, and divide functions, respectively. The last request calls the divide function with a zero value for the b argument, which raises an InvalidParams exception.

Conclusion

In this blog post, we have shown you how to build a Python RPC server using Flask. We have used the jsonrpcserver package to add a JSON-RPC endpoint to Flask and define JSON-RPC functions. We have also shown you how to test the server using the jsonrpcclient package. With this knowledge, you can build powerful distributed systems that can communicate seamlessly across networks.

Any comments or suggestions? Let me know.