index.js

const grpc = require("@grpc/grpc-js");
const protobufjs = require("protobufjs");
const protoLoader = require("@grpc/proto-loader");
const fs = require("fs");

const MOCK_SERVER_ADDRESS = "127.0.0.1:50051";
const MOCKED_JSON_FILE = "./mock-response.json";
const protoDirectory = "./proto";

const mockedData = JSON.parse(fs.readFileSync(MOCKED_JSON_FILE));

const protoFiles = fs.readdirSync(protoDirectory);

const options = {
  keepCase: true,
  longs: String,
  enums: String,
  defaults: true,
  oneofs: true,
};

const server = new grpc.Server();

protoFiles.forEach((eachService) => {
  const fullProtoAddress = `${protoDirectory}/${eachService}`;

  const loadedProtoFile = protoLoader.loadSync(fullProtoAddress);

  const service = grpc.loadPackageDefinition(loadedProtoFile, options);

  const jsonProto = protobufjs.loadSync(fullProtoAddress).toJSON().nested;

  const serviceName = Object.keys(jsonProto)[0];

  const serviceMethods = jsonProto[serviceName].methods;

  if (!serviceMethods) return;

  server.addService(
    service[serviceName].service,
    (() => {
      const services = [];
      for (const method in serviceMethods) {
        const responseTypeName = serviceMethods[method].responseType;
        services[method] = (_, res) => {
          res(null, mockedData[responseTypeName] || {});
        };
      }
      return services;
    })()
  );
  console.log("Loaded ", eachService);
});

server.bindAsync(
  MOCK_SERVER_ADDRESS,
  grpc.ServerCredentials.createInsecure(),
  (error, port) => {
    console.log(`Server running at ${MOCK_SERVER_ADDRESS}`);
    server.start();
  }
);