Mindconnect-NodeJS - Agent Development - Agent State Storage


The agents need to manage their state information over time. This state information consists of

  • agent secrets
  • agent configuration
  • agent mappings
  • history of agent secrets
  • list of uploaded files and corresponding eTags (so that agents can overwrite the files if necessary)

This information needs to be persisted over time.

The agents store the eTag of the file so that they can overwrite these files in the future. This will change once agents can read the eTags of the files.

Storage Provider - Default Implementation

The default implementation stores the state in the hidden .mc directory in the root directory of your project.

ls -la .mc

total 8
drwxr-xr-x 1 sn0wcat 1049089    0 May 17 17:41 .
drwxr-xr-x 1 sn0wcat 1049089    0 May 17 17:41 ..
-rw-r--r-- 1 sn0wcat 1049089 2814 May 17 17:41 8ed19ef5515542b4bb05842bfbd48f38.json

Storing the data using different storage provider

If you need to store the data in a different or more secure fashion you can provide your own implementation of the StorageProvider. You need to implement the following interface

 * Per default, the library stores the agent settings in the directory .mc
 * You can pass a class which implements a ConfigurationStorage in the constructor if you want to store
 * the settings somewhere else. (e.g. database, encrypted file system etc)
 * @export
 * @interface ConfigurationStorage
export interface IConfigurationStorage {
    GetConfig(config: IMindConnectConfiguration): IMindConnectConfiguration;
    SaveConfig(config: IMindConnectConfiguration): Promise<IMindConnectConfiguration>;

The GetConfig method should check if the config has changed and return no value so that the agent can be onboarded again

if (_.isEqual(json.content, configuration.content)) {
    return json;
} else {
    log("The configuration has changed we will onboard again.");


export class MySecureStorage implements IConfigurationStorage {
    private lock: AsyncLock;

    private encrypt(): string {
        //... your secure implementation

    private decrypt(): string {
        //... your secure implementation

    public GetConfig(configuration: IMindConnectConfiguration): IMindConnectConfiguration {
        try {
            const json = <IMindConnectConfiguration>(
                const result = fs.readFileSync (path.resolve(`${this._basePath}/${configuration.content.clientId}.bin`));
                return this.decrypt(result);
            if (_.isEqual(json.content, configuration.content)) {
                return json;
            } else {
                log("The configuration has changed we will onboard again.");
        } catch (err) {
            log(`There is no configuration stored yet for agent with id ${configuration.content.clientId}`);

        return configuration;

    public async SaveConfig(config: IMindConnectConfiguration): Promise<IMindConnectConfiguration> {
        const fileName = `${this._basePath}/${config.content.clientId}.bin`;
        return await this.lock.acquire(fileName, () => {
            const data = JSON.stringify(config);
            fs.writeFileSync(fileName, this.encrypt(data));
            return config;

    constructor(private _basePath: string) {
        if (!fs.existsSync(this._basePath)) {

        this.lock = new AsyncLock({});

Using your storage

You can pass the instance of your storage provider to the MindConnectAgent constructor.

const agent = new MindConnectAgent(configuration, undefined, new MySecureStorage());

Further Information

The content of the community tools and libraries documentation pages is licensed under the MIT License.
Siemens API Notice applies.
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