Building Your Service Provider

Since a lot of logic you will write in this section is similar or the same to UC code you just written, this section will only focus on SP-specific functionality

  • Paste the following code into src/index.ts
import WebSocket, { MessageEvent } from "ws";

var ourAddress:          string;
var websocketConnection: any;

async function main() {
    var port = '1978' 
    var localClientUrl = "ws://" + port;

    // Set up and handle websocket connection to our desktop client.
    websocketConnection = await connectWebsocket(localClientUrl).then(function (c) {
        return c;
    }).catch(function (err) {
        console.log("Websocket connection error. Is the client running with <pre>--connection-type WebSocket</pre> on port " + port + "?");

    websocketConnection.onmessage = function (e : any) {


// Handle any messages that come back down the websocket. 
function handleResponse(responseMessageEvent : MessageEvent) {

    try {
            let response = JSON.parse(;
        if (response.type == "error") {
            console.log("\x1b[91mAn error occured: " + response.message + "\x1b[0m")
        } else if (response.type == "selfAddress") {
            ourAddress = response.address;
            console.log("\x1b[94mOur address is: " + ourAddress + "\x1b[0m")
        } else if (response.type == "received") {
            let messageContent = JSON.parse(response.message)

            console.log('\x1b[93mRecieved : \x1b[0m');
            console.log('\x1b[92mName : ' + + '\x1b[0m');
            console.log('\x1b[92mService : ' + messageContent.service + '\x1b[0m');
            console.log('\x1b[92mComment : ' + messageContent.comment + '\x1b[0m');

            console.log('\x1b[93mSending response back to client... \x1b[0m')

    } catch (_) {
        console.log('something went wrong in handleResponse')

function sendMessageToMixnet(senderTag: string) {

    // Place each of the form values into a single object to be sent.
    const messageContentToSend = {
        text: 'We recieved your request - this reply sent to you anonymously with SURBs',
        fromAddress : ourAddress
    const message = {
        type: "reply",
        message: JSON.stringify(messageContentToSend),
    	senderTag: senderTag
    // Send our message object via out via our websocket connection.

// Send a message to the mixnet client, asking what our own address is. 
function sendSelfAddressRequest() {
    var selfAddress = {
        type: "selfAddress"

// Function that connects our application to the mixnet Websocket. We want to call this first in our main function.
function connectWebsocket(url : string) {
    return new Promise(function (resolve, reject) {
        var server = new WebSocket(url);
        console.log('connecting to Mixnet Websocket (Nym Client)...')
        server.onopen = function () {
        server.onerror = function (err) {



main() is still the function in charge of initializing and executing your application. Note that the SP’s client is running on port 1978. This is so we don’t have a conflict with the client we have running for the UC part of our tutorial code!

handleResponse() works in a similar manner as the function with the same name in simple-service-provider/user-client/src/index.ts. This implementation logs to the console instead of passing messages to a UI.

The \x1b prefix you see in console.log adds colour to console ouput. The number that you see following the [ and preceeding m is the colour code that can be compared here. Its a nice and quick way of styling our terminal output.

When the SP receives a message from the mixnet, sendMessageToMixnet() sends a response back to notify the the user that the SP recieved their request successfully.

Connecting to your Nym Client

Remember to init and run this client using port 1978 to avoid port clashes.

  • Refresh your browser window. You should see a successful response, including a Nym address, in your console:
> service-provider@1.0.0 start:dev
> nodemon

[nodemon] 2.0.20
[nodemon] to restart at any time, enter `rs`
[nodemon] watching path(s): src/**/*
[nodemon] watching extensions: ts,js
[nodemon] starting `ts-node ./src/index.ts`
connecting to Mixnet Websocket (Nym Client)...
Our address is: 6V5eEguz4rUsfntVLKQuD2ymgdY5iDKCV2GY2EH3CxG4.AKdk22atwRaVkN2PLEDsWUKKDc3ieNm1avKqVGgmJx8s@FQon7UwF5knbUr2jf6jHhmNLbJnMreck1eUcVH59kxYE

Set Service Address in User Client

The final step of this tutorial is to update our User Client code with the address of the now-running Service Provider so it can send it a message.

Copy the SP’s Nym address from your console and set it as the value of the targetAddress variable on line 2 of simple-service-provider/user-client/src/index.ts.

var targetAddress: string = '6V5eEguz4rUsfntVLKQuD2ymgdY5iDKCV2GY2EH3CxG4.AKdk22atwRaVkN2PLEDsWUKKDc3ieNm1avKqVGgmJx8s@FQon7UwF5knbUr2jf6jHhmNLbJnMreck1eUcVH59kxYE';