Let your client and server talk over function calls under JSON-RPC 2.0 spec.
npm install --save json-rpc-2.0
The example uses HTTP for communication protocol, but it can be anything.
const express = require("express");
const bodyParser = require("body-parser");
const { JSONRPCServer } = require("json-rpc-2.0");
const server = new JSONRPCServer();
// First parameter is a method name.
// Second parameter is a method itself.
// A method takes JSON-RPC params and returns a result.
// It can also return a promise of the result.
server.addMethod("echo", ({ text }) => text);
server.addMethod("log", ({ message }) => console.log(message));
const app = express();
app.use(bodyParser.json());
app.post("/json-rpc", (req, res) => {
const jsonRPCRequest = req.body;
// server.receive takes a JSON-RPC request and returns a promise of a JSON-RPC response.
// It can also receive an array of requests, in which case it may return an array of responses.
// Alternatively, you can use server.receiveJSON, which takes JSON string as is (in this case req.body).
server.receive(jsonRPCRequest).then((jsonRPCResponse) => {
if (jsonRPCResponse) {
res.json(jsonRPCResponse);
} else {
// If response is absent, it was a JSON-RPC notification method.
// Respond with no content status (204).
res.sendStatus(204);
}
});
});
app.listen(80);To hook authentication into the API, inject custom params:
const server = new JSONRPCServer();
// The method can also take a custom parameter as the second parameter.
// Use this to inject whatever information that method needs outside the regular JSON-RPC request.
server.addMethod("echo", ({ text }, { userID }) => `${userID} said ${text}`);
app.post("/json-rpc", (req, res) => {
const jsonRPCRequest = req.body;
const userID = getUserID(req);
// server.receive takes an optional second parameter.
// The parameter will be injected to the JSON-RPC method as the second parameter.
server.receive(jsonRPCRequest, { userID }).then((jsonRPCResponse) => {
if (jsonRPCResponse) {
res.json(jsonRPCResponse);
} else {
res.sendStatus(204);
}
});
});
const getUserID = (req) => {
// Do whatever to get user ID out of the request
};Use middleware to intercept request and response:
const server = new JSONRPCServer();
// next will call the next middleware
const logMiddleware = (next, request, serverParams) => {
console.log(`Received ${JSON.stringify(request)}`);
return next(request, serverParams).then((response) => {
console.log(`Responding ${JSON.stringify(response)}`);
return response;
});
};
const exceptionMiddleware = async (next, request, serverParams) => {
try {
return await next(request, serverParams);
} catch (error) {
if (error.code) {
return createJSONRPCErrorResponse(request.id, error.code, error.message);
} else {
throw error;
}
}
};
// Middleware will be called in the same order they are applied
server.applyMiddleware(logMiddleware, exceptionMiddleware);Optionally, you can pass options to JSONRPCServer constructor:
new JSONRPCServer({
errorListener: (message: string, data: unknown): void => {
// Listen to error here. By default, it will use console.warn to log errors.
},
});import { JSONRPCClient } from "json-rpc-2.0";
// JSONRPCClient needs to know how to send a JSON-RPC request.
// Tell it by passing a function to its constructor. The function must take a JSON-RPC request and send it.
const client = new JSONRPCClient((jsonRPCRequest) =>
fetch("http://localhost/json-rpc", {
method: "POST",
headers: {
"content-type": "application/json",
},
body: JSON.stringify(jsonRPCRequest),
}).then((response) => {
if (response.status === 200) {
// Use client.receive when you received a JSON-RPC response.
return response
.json()
.then((jsonRPCResponse) => client.receive(jsonRPCResponse));
} else if (jsonRPCRequest.id !== undefined) {
return Promise.reject(new Error(response.statusText));
}
})
);
// Use client.request to make a JSON-RPC request call.
// The function returns a promise of the result.
client
.request("echo", { text: "Hello, World!" })
.then((result) => console.log(result));
// Use client.notify to make a JSON-RPC notification call.
// By definition, JSON-RPC notification does not respond.
client.notify("log", { message: "Hello, World!" });Just like JSONRPCServer, you can inject custom params to JSONRPCClient too:
const client = new JSONRPCClient(
// It can also take a custom parameter as the second parameter.
(jsonRPCRequest, { token }) =>
fetch("http://localhost/json-rpc", {
method: "POST",
headers: {
"content-type": "application/json",
authorization: `Bearer ${token}`, // Use the passed token
},
body: JSON.stringify(jsonRPCRequest),
}).then((response) => {
// ...
})
);
// Pass the custom params as the third argument.
client.request("echo", { text: "Hello, World!" }, { token: "foo's token" });
client.notify("log", { message: "Hello, World!" }, { token: "foo's token" });Sometimes you don't want to wait for the response indefinitely. You can use timeout to automatically fail the request after certain delay:
const client = new JSONRPCClient(/* ... */);
client
.timeout(10 * 1000) // Automatically fails if it didn't get a response within 10 sec
.request("echo", { text: "Hello, World!" });
// Create a custom error response
const createTimeoutJSONRPCErrorResponse = (
id: JSONRPCID
): JSONRPCErrorResponse =>
createJSONRPCErrorResponse(id, 123, "Custom error message");
client
.timeout(10 * 1000, createTimeoutJSONRPCErrorResponse)
.request("echo", { text: "Hello, World!" });For bi-directional JSON-RPC, use JSONRPCServerAndClient.
const webSocket = new WebSocket("ws://localhost");
const serverAndClient = new JSONRPCServerAndClient(
new JSONRPCServer(),
new JSONRPCClient((request) => {
try {
webSocket.send(JSON.stringify(request));
return Promise.resolve();
} catch (error) {
return Promise.reject(error);
}
})
);
webSocket.onmessage = (event) => {
serverAndClient.receiveAndSend(JSON.parse(event.data.toString()));
};
// On close, make sure to reject all the pending requests to prevent hanging.
webSocket.onclose = (event) => {
serverAndClient.rejectAllPendingRequests(
`Connection is closed (${event.reason}).`
);
};
serverAndClient.addMethod("echo", ({ text }) => text);
serverAndClient
.request("add", { x: 1, y: 2 })
.then((result) => console.log(`1 + 2 = ${result}`));Optionally, you can pass options to JSONRPCServerAndClient constructor:
new JSONRPCServerAndClient(server, client, {
errorListener: (message: string, data: unknown): void => {
// Listen to error here. By default, it will use console.warn to log errors.
},
});To respond an error, reject with an Error. On the client side, the promise will be rejected with an Error object with the same message.
server.addMethod("fail", () =>
Promise.reject(new Error("This is an error message."))
);
client.request("fail").then(
() => console.log("This does not get called"),
(error) => console.error(error.message) // Outputs "This is an error message."
);If you want to return a custom error response, use JSONRPCErrorException:
import { JSONRPCErrorException } from "json-rpc-2.0";
const server = new JSONRPCServer();
server.addMethod("throws", () => {
const errorCode = 123;
const errorData = {
foo: "bar",
};
throw new JSONRPCErrorException(
"A human readable error message",
errorCode,
errorData
);
});Alternatively, use advanced APIs or implement mapErrorToJSONRPCErrorResponse:
import {
createJSONRPCErrorResponse,
JSONRPCErrorResponse,
JSONRPCID,
JSONRPCServer,
} from "json-rpc-2.0";
const server = new JSONRPCServer();
server.mapErrorToJSONRPCErrorResponse = (
id: JSONRPCID,
error: any
): JSONRPCErrorResponse => {
return createJSONRPCErrorResponse(
id,
error?.code || 0,
error?.message || "An unexpected error occurred",
// Optional 4th argument. It maps to error.data of the response.
{ foo: "bar" }
);
};Use the advanced APIs to handle raw JSON-RPC messages.
import { JSONRPC, JSONRPCResponse, JSONRPCServer } from "json-rpc-2.0";
const server = new JSONRPCServer();
// Advanced method takes a raw JSON-RPC request and returns a raw JSON-RPC response
server.addMethodAdvanced(
"doSomething",
(jsonRPCRequest: JSONRPCRequest): PromiseLike<JSONRPCResponse> => {
if (isValid(jsonRPCRequest.params)) {
return {
jsonrpc: JSONRPC,
id: jsonRPCRequest.id,
result: "Params are valid",
};
} else {
return {
jsonrpc: JSONRPC,
id: jsonRPCRequest.id,
error: {
code: -100,
message: "Params are invalid",
data: jsonRPCRequest.params,
},
};
}
}
);// You can remove the added method if needed
server.removeMethod("doSomething");import {
JSONRPC,
JSONRPCClient,
JSONRPCRequest,
JSONRPCResponse,
} from "json-rpc-2.0";
const send = () => {
// ...
};
let nextID: number = 0;
const createID = () => nextID++;
// To avoid conflict ID between basic and advanced method request, inject a custom ID factory function.
const client = new JSONRPCClient(send, createID);
const jsonRPCRequest: JSONRPCRequest = {
jsonrpc: JSONRPC,
id: createID(),
method: "doSomething",
params: {
foo: "foo",
bar: "bar",
},
};
// Advanced method takes a raw JSON-RPC request and returns a raw JSON-RPC response
// It can also send an array of requests, in which case it returns an array of responses.
client
.requestAdvanced(jsonRPCRequest)
.then((jsonRPCResponse: JSONRPCResponse) => {
if (jsonRPCResponse.error) {
console.log(
`Received an error with code ${jsonRPCResponse.error.code} and message ${jsonRPCResponse.error.message}`
);
} else {
doSomethingWithResult(jsonRPCResponse.result);
}
});To strongly type request and addMethod methods, use TypedJSONRPCClient, TypedJSONRPCServer and TypedJSONRPCServerAndClient interfaces.
import {
JSONRPCClient,
JSONRPCServer,
JSONRPCServerAndClient,
TypedJSONRPCClient,
TypedJSONRPCServer,
TypedJSONRPCServerAndClient,
} from "json-rpc-2.0";
// Use `type` instead of `interface`. In TypeScript, interface can be exnteded,
// so the type checker considers the possibility of the interface being extended,
// resulting in an error.
// Reference: https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#differences-between-type-aliases-and-interfaces
type Methods = {
echo(params: { message: string }): string;
sum(params: { x: number; y: number }): number;
};
const server: TypedJSONRPCServer<Methods> = new JSONRPCServer(/* ... */);
const client: TypedJSONRPCClient<Methods> = new JSONRPCClient(/* ... */);
// Types are infered from the Methods type
server.addMethod("echo", ({ message }) => message);
server.addMethod("sum", ({ x, y }) => x + y);
// These result in type error
// server.addMethod("ech0", ({ message }) => message); // typo in method name
// server.addMethod("echo", ({ messagE }) => messagE); // typo in param name
// server.addMethod("echo", ({ message }) => 123); // return type must be string
client
.request("echo", { message: "hello" })
.then((result) => console.log(result));
client.request("sum", { x: 1, y: 2 }).then((result) => console.log(result));
// These result in type error
// client.request("ech0", { message: "hello" }); // typo in method name
// client.request("echo", { messagE: "hello" }); // typo in param name
// client.request("echo", { message: 123 }); // message param must be string
// client
// .request("echo", { message: "hello" })
// .then((result: number) => console.log(result)); // return type must be string
// The same rule applies to TypedJSONRPCServerAndClient
type ServerAMethods = {
echo(params: { message: string }): string;
};
type ServerBMethods = {
sum(params: { x: number; y: number }): number;
};
const serverAndClientA: TypedJSONRPCServerAndClient<
ServerAMethods,
ServerBMethods
> = new JSONRPCServerAndClient(/* ... */);
const serverAndClientB: TypedJSONRPCServerAndClient<
ServerBMethods,
ServerAMethods
> = new JSONRPCServerAndClient(/* ... */);
serverAndClientA.addMethod("echo", ({ message }) => message);
serverAndClientB.addMethod("sum", ({ x, y }) => x + y);
serverAndClientA
.request("sum", { x: 1, y: 2 })
.then((result) => console.log(result));
serverAndClientB
.request("echo", { message: "hello" })
.then((result) => console.log(result));npm run build
npm test