How To Test Grpc Using Postman

How to Test gRPC using Postman

gRPC is a modern high-performance Remote Procedure Call (RPC) framework that is gaining popularity for building microservices. It uses Protocol Buffers for defining the structure of data exchanged between services. While gRPC comes with its own command-line tool for testing, Postman offers a user-friendly interface that can be more convenient, especially for complex scenarios.

This guide will walk you through the process of testing gRPC services using Postman, covering the essential steps, along with practical examples and code snippets.

Prerequisites

Before you begin, ensure you have the following set up:

Postman: Install the latest version of Postman from https://www.postman.com/.
gRPC Server: You need a running gRPC server. For this example, let’s work with a simple gRPC server written in Python using the grpcio library.

Setting Up a gRPC Server

For illustrative purposes, let’s create a basic gRPC server in Python.

1. Define a Protocol Buffer (.proto) File

Create a file named greet.proto:

syntax = "proto3";

package greet;

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

message HelloRequest {
  string name = 1;
}

message HelloReply {
  string message = 1;
}

2. Generate Python Code

Use the Protocol Buffer compiler (protoc) to generate Python code from the .proto file:

protoc --python_out=. greet.proto

3. Implement the Server Logic

Create a Python file named server.py:

import grpc
import greet_pb2
import greet_pb2_grpc

class GreeterServicer(greet_pb2_grpc.GreeterServicer):
    def SayHello(self, request, context):
        return greet_pb2.HelloReply(message='Hello, {}!'.format(request.name))

def serve():
    server = grpc.server(futures.ThreadPoolExecutor(max_workers=10))
    greet_pb2_grpc.add_GreeterServicer_to_server(GreeterServicer(), server)
    server.add_insecure_port('[::]:50051')
    server.start()
    server.wait_for_termination()

if __name__ == '__main__':
    serve()

4. Run the Server

Execute the Python script:

python server.py

This will start a gRPC server listening on port 50051.

Testing with Postman

Now, let’s use Postman to interact with this gRPC Server.

1. Install the gRPC Plugin

In Postman, go to Manage Plugins and search for “gRPC.” Install the gRPC Plugin by Postman Labs.

2. Create a New Request

Open Postman and create a new request.

3. Choose gRPC Protocol

Under the “Authorization” tab, select “gRPC.”

4. Configure gRPC Settings

In the “gRPC Settings,” specify the following:

Address: The address of your gRPC Server (e.g., localhost:50051).
Method: The desired gRPC method (e.g., greet.Greeter/SayHello).
Request Body: Here you will define the request message in JSON format.

Example Request Body for `SayHello`:

{
  "name": "Postman"
}

5. Send the Request

Click the “Send” button.

6. View the Response

Postman will display the response from your gRPC server. The response will be in JSON format, aligning with the defined structure in the Protocol Buffer definition.

In the case of the SayHello example, you should see a response like this:

{
  "message": "Hello, Postman!"
}

Testing Other gRPC Methods

The process for testing other gRPC methods is very similar. You simply need to:

Change the “Method” field in Postman to the name of the desired method.
Modify the request body to match the expected input message for that method.

Testing gRPC with Different Request Types

Postman’s gRPC plugin enhances testing by supporting various request types for gRPC calls:

Unary Requests

For simple requests that return a single response, use the standard gRPC method selection in Postman, as illustrated in the previous example.

Server Streaming Requests

These requests result in the server continuously streaming responses. To accommodate server streaming in Postman, you can use the special “gRPC-Stream” method type. This option allows the server to send back data in multiple chunks.

Example Request (Server streaming method):

Method: greet.Greeter/SayHelloStream
Request Body: (Optional)
  {
     "name": "Postman"
  }

The response will be streamed, and you can view each message segment in Postman.

Client Streaming Requests

In these requests, the client sends a stream of messages to the server. Postman can simulate this using the “Client Streaming” option for the request type. This option allows you to send multiple data chunks with the request.

Example Request (Client streaming method):

Method: greet.Greeter/SayHelloStreamClient
Request Body: (Optional)
  {
      "name": "Postman"
  }

Postman will present a “Send Chunk” option, enabling you to submit multiple pieces of data before sending the complete request.

Bidirectional Streaming Requests

These requests involve both the client and server sending streams of messages simultaneously. While Postman provides a visual interface for client and server streaming, bidirectional streaming currently lacks direct support within the plugin. To test bidirectional streaming, you would need to use a different tool or custom scripting to manually manage the client and server streams.