0.3.0-beta.0 • Public • Published

    Testchain Client

    GitHub License NPM



    The client is to be used along with the staxx which is a docker container containing all testchain functionality. Requires docker and docker-compose

    git clone https://github.com/makerdao/staxx.git
    cd ./staxx
    make docker-deps      # will download required docker images 
    make run-dev          # will take a minute or two 

    The data folder which docker will work out of is /tmp which will store chain and snapshot data under /tmp/chains and /tmp/snapshots respectively.

    NOTE - The backendgateway takes approximately 5 minutes to download and organise all maker contracts from their various github repositories. By observing the undetached process of the docker-compose up command, it will be evident to the user when they are loaded.


    The client can be installed locally as follows:

    git clone https://github.com/makerdao/testchain-client.git
    cd ./testchain-client
    yarn install

    To build the project, simply run yarn build, or to build on file changes, yarn build:watch.

    If you want to install the library directly from npm:

    yarn add @makerdao/testchain-client


    To include the library:

    import { Client, Event } from '@makerdao/testchain-client';

    The client can then be setup as follows:

    const client = new Client(
      '', // <REST_API_ENDPOINT>
      'ws://' // <WS_API_ENDPOINT>
    client.init().then(() => {
      console.log('Client initialised');

    The client takes two url parameters as shown above, the first being the REST endpoint which is used for retrieving chain and snapshot data. The second being a websocket endpoint for performing chain functions and listening to system events. These events are declared as constants in the Event import.

    The user must use the init() function on the client in order to setup the endpoint connections correctly. It also automatically opens the 'api' channel on the websocket connection.


    The rest api is accessed by calling functions on client.api and is not to be confused with the aformentioned 'api' channel used by the websocket connection. All functions are asynchronous.

    • listAllChains() - returns a list of all the chains in existence.

    • listAllSnapshots(chainType) - returns a list of all snapshots for each chaintype, ganache or geth

    • getChain(id) - finds the chain with id and returns it's details including it's passed configuration data, it's account information and other chain information.

    • downloadSnapshotUrl(id) - returns the download snapshot url endpoint.

    • getBlockNumber(id) - will perform a json-rpc request to chain of id and return the current block number. This can be useful for debugging purposes.

    • mineBlock(id) - if the chainType is ganache, a useful json-rpc command is included called evm_mine which is used to increment the blocknumber. This too is also useful for debugging purposes.


    await client.api.getChain(id);


    This section lists the chain functions the client provides to interact with the websocket api. This is done over a websocket connection and we will examine in the next section how to intercept and monitor events coming from them.

    As previously mentioned, when the client is initialised, it automatically opens the 'api' channel. We use this channel to create our chains instances by passing an options object as a parameter.


        testchain: {
            config: {
                type: 'geth,
                accounts: 3,
                block_mine_time: 0,
                clean_on_stop: false, // Because we have to test restart
            deps: []

    To create the chain instance:


    In order to interact with the created chain instance we must first extract the chain's id. When we create a chain instance, we are also creating a websocket channel specific to that chain. Using that id, which we use as a parameter to other functions, we can then find/create that channel.

    To extract the id we make use of some of the event functionality that is explained in the next section

    client.create({ ...options });
    client.once('api', Event.CHAIN_CREATED).then(console.log);
    // prints
        eventName: 'phx_reply',
        payload: {
            status: 'ok',
            response: {
                id: '7177259706074024037'

    Once the id is extracted, the other functions are easily used.

    To stop a running chain:


    To restart a stopped chain:


    To take a snapshot of the current chains state:

    client.takeSnapshot(id, description);

    Taking a snapshot will stop the chain; if the chain was created with the config option clean_on_stop: true, the chain will be removed when stopped. Therefore, takeSnapshot can only be used with chains that have been created with clean_on_stop: false.

    To restore a snapshot of a previous chain state:

    client.restoreSnapshot(id, snapshotId);

    The snapshotId parameter refers to the id of the snapshot we wish to restore. If the chain which initially created the snapshot no longer exists, this will create a new chain instance using the snapshot.

    To remove a chain instance permanently:


    This returns a promise and will stop a chain instance first before deleting it


    As noted in the import of the client, we also imported the Event object. This lists all events which can be listened to after performing websocket api functions.

    The source file for all of these events is located under src/core/constants.js. Many of these constants refer to the same string event but by abstracting them to be more human-readable, gives better clarity.

    The client uses the zen-observable library to transform all websocket data into an observable object. An observable object is an asynchronous data stream and can be subscribed to at any time. We use this object and the event constants to observe the websocket channel's behaviour and extract information as it comes down this stream.


    To subscribe to a chain's data stream, we call the stream() function which returns the observable object for that channel.

    const chainStream = client.stream(id); // Specify the chain by it's id
    const obs = chainStream.subscribe(
        ({ eventName, payload }) => {
            // do something

    In the above example, the Observable is assigned to our chainStream constant. subscribe() takes a callback function as an argument and is executed on an effective infinite loop for each incoming event fired from the backend on each channel. This callback is where all incoming data is passed and where a user should expect to find the chain events and returning data. The client has bootstrapped the value eventName to make it easier for the user to specify a target event.


    The once() function builds around this subscription model and wraps a promise based on the next incoming event, returning the payload. This is especially useful around functions like create() and takeSnapshot() which return data after being executed.

    client.once('api', Event.CHAIN_STARTED).then(console.log);
    // prints
        eventName: 'started',
        payload: {
            ws_url: 'ws://ex-testchain.local:8552',
            rpc_url: 'http://ex-testchain.local:8552',
            network_id: 999,
            id: '12449877630527910658',
            gas_limit: 9000000000000,
            coinbase: '0xf84174a9fb743c6df671bc391acab4a5bcafeefe',
            accounts: [ ... ]

    The above awaits on a promise which resolves on the Event.CHAIN_STARTED event firing on the api channel with that payload data.


    Where we wish to observe and wait on multiple events to be fired, we can use sequenceEvents(). This will return a promise which when resolved produces an object of the fired events and the returned payloads.

    // prints
        started: {
            ws_url: 'ws://ex-testchain.local:8571',
            rpc_url: 'http://ex-testchain.local:8571',
            network_id: 999,
            id: '11957893023697223559',
            gas_limit: 9000000000000,
            coinbase: '0x3a92149876fb55d685a15caea45979526a4b2242',
            accounts: [ ... ]
        status_changed: {
            data: 'active'
        ready: {}


    on() is similar to once() in that it will look to target an individual event coming from a specific chain channel. The difference however is that on() gives the user finer control in terms of what event and payload they wish to listen for. once() will resolve its promise with the next event on the stream that matches its event parameter.

    The on() function takes three parameters, the chain id we wish to listen on, the event we wish to listen for on that chain channel, and a callback which fires on that event firing.

    That callback contains the payload for that event and a function off() which is used to unsubscribe from the on() when satisfied.


    A good example of this is in the delete() function where a promise is returned. We use the on() function to resolve said promise when the correct payload is returned signifying that it has been deleted.

    return new Promise(resolve => {
      this.on('api', Event.CHAIN_DELETED, (payload, off) => {
        const { response } = payload;
        if (response.message && response.message === 'Chain removed') {
          // do something now that chain has been deleted


    In order to observe the stream visually, the client uses debug.js to extend logging functionality to the console.

    When testing, prepend the cli arg with an environement variable DEBUG=log* which will print out all socket and channel events information.

    • log:api:* will print all api events only
    • log:chain:* will print all channel events only
    • log:* will print all socket events only


    The testchain client is MIT licensed.




    npm i @makerdao/testchain-client

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