nestjs-cls

What is nestjs-cls?

The 'nestjs-cls' package provides a way to manage context-local storage in NestJS applications. It allows you to store and retrieve data that is scoped to the current request, making it useful for tasks like logging, tracing, and managing user sessions.

What are nestjs-cls's main functionalities?

Context Management

This feature allows you to set and get values within the context of a request. The 'ClsService' is used to manage context-local storage, making it easy to store and retrieve data that is specific to the current request.

const { ClsService } = require('nestjs-cls');

@Injectable()
export class MyService {
  constructor(private readonly cls: ClsService) {}

  doSomething() {
    this.cls.set('key', 'value');
    const value = this.cls.get('key');
    console.log(value); // Outputs: 'value'
  }
}

Middleware Integration

This feature demonstrates how to integrate 'ClsMiddleware' into your NestJS application. By applying this middleware, you ensure that context-local storage is available for all routes, making it easy to manage request-specific data throughout your application.

const { ClsMiddleware } = require('nestjs-cls');

@Module({
  providers: [ClsMiddleware],
})
export class AppModule {
  configure(consumer: MiddlewareConsumer) {
    consumer
      .apply(ClsMiddleware)
      .forRoutes('*');
  }
}

Async Context Management

This feature shows how to manage context-local storage in asynchronous operations. The 'run' method of 'ClsService' ensures that the context is preserved across asynchronous boundaries, allowing you to set and get values within async functions.

const { ClsService } = require('nestjs-cls');

@Injectable()
export class MyService {
  constructor(private readonly cls: ClsService) {}

  async doSomethingAsync() {
    await this.cls.run(async () => {
      this.cls.set('key', 'value');
      const value = this.cls.get('key');
      console.log(value); // Outputs: 'value'
    });
  }
}

Other packages similar to nestjs-cls

cls-hooked

The 'cls-hooked' package provides a way to manage context-local storage using Node.js async_hooks. It is a lower-level library compared to 'nestjs-cls' and requires more manual setup, but it offers similar functionality for managing request-specific data.

async-local-storage

The 'async-local-storage' package is another library for managing context-local storage in Node.js applications. It provides a simple API for storing and retrieving data that is scoped to the current request, similar to 'nestjs-cls', but without the NestJS-specific integrations.

continuation-local-storage

The 'continuation-local-storage' package offers context-local storage using the continuation-local-storage API. It is an older library and has been largely replaced by 'cls-hooked', but it still provides similar functionality for managing request-specific data.

README

NestJS CLS

A continuation-local storage module compatible with NestJS's dependency injection.

Continuous-local storage allows to store state and propagate it throughout callbacks and promise chains. It allows storing data throughout the lifetime of a web request or any other asynchronous duration. It is similar to thread-local storage in other languages.

Some common use cases for CLS include:

• Request ID tracing for logging purposes
• Making the Tenant ID available everywhere in multi-tenant apps
• Globally setting the authentication level for the request

Most of these are theoretically solvable using request-scoped providers or passing the context as a parameter, but these solutions are often clunky and come with a whole lot of other issues. Thus this package was born.

Note: For versions < 1.2, this package used cls-hooked as a peer dependency, now it uses AsyncLocalStorage from Node's async_hooks directly. The API stays the same for now but I'll consider making it more friendly for version 2.

Outline

• Install
• Quick Start
• How it works
• Setting up the CLS context
  • Using a Middleware
  • Using a Guard
  • Using an Interceptor
• API
• Options
• Request ID
• Additional CLS Setup
• Breaking out of DI
• Security considerations
• Compatibility considerations
  • REST
  • GraphQL
  • Others
• Namespaces (experimental)

Install

npm install nestjs-cls
# or
yarn add nestjs-cls

Note: This module requires additional peer deps, like the nestjs core and common libraries, but it is assumed those are already installed.

Quick Start

Below is an example of storing the client's IP address in an interceptor and retrieving it in a service without explicitly passing it along.

Note: This example assumes you are using HTTP and therefore can use middleware. For usage with non-HTTP transports, keep reading.

// app.module.ts
@Module({
    imports: [
        // Register the ClsModule and automatically mount the ClsMiddleware
        ClsModule.register({
            global: true,
            middleware: { mount: true }
        }),
    ],
    providers: [AppService],
    controllers: [AppController],
})
export class TestHttpApp {}


/* user-ip.interceptor.ts */
@Injectable()
export class UserIpInterceptor implements NestInterceptor {
    constructor(
        // Inject the ClsService into the interceptor to get
        // access to the current shared cls context.
        private readonly cls: ClsService
    )

    intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
        // Extract the client's ip address from the request...
        const request = context.switchToHttp().getRequest();
        cosnt userIp = req.connection.remoteAddress;
        // ...and store it to the cls context.
        this.cls.set('ip', userIp);
        return next.handle();
    }
}


/* app.controller.ts */

// By mounting the interceptor on the controller, it gets access
// to the same shared cls context that the ClsMiddleware set up.
@UseInterceptors(UserIpInterceptor)
@Injectable()
export class AppController {
    constructor(private readonly appService: AppService) {}

    @Get('/hello')
    hello() {
        return this.appService.sayHello();
    }
}


/* app.service.ts */
@Injectable()
export class AppService {
    constructor(
        // Inject ClsService to be able to retireve data from the cls context.
        private readonly cls: ClsService
    ) {}

    sayHello() {
        // Here we can extract the value of 'ip' that was
        // put into the cls context in the interceptor.
        return 'Hello ' + this.cls.get<string>('ip') + '!';
    }
}

How it works

Continuation-local storage provides a common space for storing and retrieving data throughout the life of a function/callback call chain. In NestJS, this allows for sharing request data across the lifetime of a single request - without the need for request-scoped providers. It also makes it easy to track and log request ids throughout the whole application.

To make CLS work, it is required to set up the CLS context first. This is done by calling cls.run() (or cls.enter(), see Security considerations for more info) somewhere in the app. Once that is set up, anything that is called within the same callback chain has access to the same storage with cls.set() and cls.get().

Setting up the CLS context

This package provides three methods of setting up the CLS context for incoming requests. This is mainly due to the fact that different underlying platforms are compatible with some of these methods - see Compatibility considerations.

For HTTP transports, the context can be preferably set up in a ClsMiddleware. For all other platforms, or cases where the ClsMiddleware is not applicable, this package also provides a ClsGuard and ClsInterceptor. While both of these also work with HTTP, they come with some caveats, see below.

Using a Middleware (HTTP Only)

Since in NestJS, HTTP middleware is the first thing to run when a request arrives, it is an ideal place to initialise the cls context. This package provides ClsMidmidleware that can be mounted to all (or selected) routes inside which the context is set up before the next() call.

All you have to do is mount it to routes in which you want to use CLS, or pass middleware: { mount: true } to the ClsModule.register options which automatically mounts it to all routes.

Once that is set up, the ClsService will have access to a common storage in all Guards, Interceptors, Pipes, Controllers, Services and Exception Filters that are called within that route.

Manually mounting the middleware

Sometimes, you might want to only use CLS on certain routes. In that case, you can bind the ClsMiddleware manually in the module:

export class AppModule implements NestModule {
    configure(consumer: MiddlewareConsumer) {
        apply(ClsMiddleware).forRoutes(AppController);
    }
}

Sometimes, however, that won't be enough, because the middleware could be mounted too late and you won't be able to use it in other middlewares (as is the case of GQL resolvers). In that case, you can mount it directly in the bootstrap method:

function bootstrap() {
    const app = await NestFactory.create(AppModule);
    // create and mount the middleware manually here
    app.use(
        new ClsMiddleware({
            /* useEnterWith: true */
        }).use,
    );
    await app.listen(3000);
}

Please note: If you bind the middleware using app.use(), it will not respect middleware settings passed to ClsModule.register(), so you will have to provide them yourself in the constructor.

Using a Guard

The ClsGuard can be also used set up the CLS context. While it is not a "guard" per-se, it's the second best place to set up the CLS context, since after a middleware, it is the first piece of code that the request hits.

To use it, pass its configuration to the guard property to the ClsModule.register options:

ClsModule.register({
    guard: { generateId: true, mount: true }
}),

If you need any other guards to use the ClsService, it's preferable mount ClsGuard manually as the first guard in the root module:

@Module({
    //...
    providers: [
        {
            provide: APP_GUARD,
            useClass: ClsGuard,
        },
    ],
})
export class AppModule {}

Please note: since the ClsGuard uses the AsyncLocalStorage#enterWith method, using the ClsGuard comes with some security considerations!

Using an Interceptor

Another place to initiate the CLS context is an ClsInterceptor, which, unlike the ClsGuard uses AsyncLocalStorage#run method to wrap the following code, which is considered safer than enterWith.

To use it, pass its configuration to the interceptor property to the ClsModule.register options:

ClsModule.register({
    interceptor: { generateId: true, mount: true }
}),

Or mount it manually as APP_INTERCEPTOR, should you need it.

Please note: Since Nest's Interceptors run after Guards, that means using this method makes CLS unavailable in Guards (and in case of REST Controllers, also in Exception Filters).

API

The injectable ClsService provides the following API to manipulate the cls context:

• set<T>(key: string, value: T): T
  Set a value on the CLS context.
• get<T>(key: string): T
  Retrieve a value from the CLS context by key.
• getId(): string;
  Retrieve the request ID (a shorthand for cls.get(CLS_ID))
• getStore(): any
  Retrieve the object containing all properties of the current CLS context.
• enter(): void;
  Run any following code in a shared CLS context.
• enterWith(store: any): void;
  Run any following code in a shared CLS context (while supplying the default contents).
• run(callback: () => T): T;
  Run the callback in a shared CLS context.
• runWith(store: any, callback: () => T): T;
  Run the callback in a shared CLS context (while supplying the default contents).
• isActive(): boolean
  Whether the current code runs within an active CLS context.

Options

The ClsModule.register() method takes the following ClsModuleOptions:

• namespaceName: string
  The name of the cls namespace. This is the namespace that will be used by the ClsService and ClsMiddleware (most of the time you will not need to touch this setting)
• global: boolean (default false)
  Whether to make the module global, so you do not have to import ClsModule.forFeature() in other modules.
• middleware: ClsMiddlewareOptions
  An object with additional options for the ClsMiddleware, see below
• guard: ClsGuardOptions
  An object with additional options for the ClsGuard, see below
• interceptor: ClsInterceptorOptions
  An object with additional options for the ClsInterceptor, see below

Important: the middleware, guard and interceptor options are mutually exclusive - do not use more than one of them, otherwise the context will get overridden with the one that runs after.

All of the Cls{Middleware,Guard,Interceptor}Options take the following parameters (either in ClsModuleOptions or directly when instantiating them manually):

• mount: boolean (default false)
  Whether to automatically mount the middleware/guard/interceptor to every route (not applicable when instantiating manually)
• generateId: bolean (default false)
  Whether to automatically generate request IDs.
• idGenerator: (req: Request | ExecutionContext) => string | Promise<string> An optional function for generating the request ID. It takes the Request object (or the ExecutionContext in case of a Guard or Interceptor) as an argument and (synchronously or asynchronously) returns a string. The default implementation uses Math.random() to generate a string of 8 characters.
• setup: (cls: ClsService, req: Request) => void | Promise<void>; Function that executes after the CLS context has been initialised. It can be used to put additional variables in the CLS context.

The ClsMiddlewareOptions additionally takes the following parameters:

• saveReq: boolean (default true)
  Whether to store the Request object to the context. It will be available under the CLS_REQ key.
• saveRes: boolean (default false)
  Whether to store the Response object to the context. It will be available under the CLS_RES key
• useEnterWith: boolean (default false)
  Set to true to set up the context using a call to AsyncLocalStorage#enterWith instead of wrapping the next() call with the safer AsyncLocalStorage#run. Most of the time this should not be necessary, but some frameworks are known to lose the context with run.

Request ID

Because of a shared storage, CLS is an ideal tool for tracking request (correlation) IDs for the purpose of logging. This package provides an option to automatically generate request IDs in the middleware/guard/interceptor, if you pass { generateId: true } to its options. By default, the generated ID is a string based on Math.random(), but you can provide a custom function in the idGenerator option.

This function receives the Request (or ExecutionContext in case a ClsGuard is used) as the first parameter, which can be used in the generation process and should return (or resolve with) a string ID that will be stored in the CLS for later use.

Below is an example of retrieving the request ID from the request header with a fallback to an autogenerated one.

ClsModule.register({
    middleware: {
        mount: true,
        generateId: true
        idGenerator: (req: Request) =>
            req.headers['X-Request-Id'] ?? uuid();
    }
})

The ID is stored under the CLS_ID constant in the context. ClsService provides a shorthand method getId to quickly retrieve it anywhere. It can be for example used in a custom logger:

// my.logger.ts
@Injectable()
class MyLogger {
    constructor(private readonly cls: ClsService) {}

    log(message: string) {
        console.log(`<${this.cls.getId()}> ${message}`);
    }

    // [...]
}

// my.service.ts
@Injectable()
class MyService {
    constructor(private readonly logger: MyLogger);

    hello() {
        this.logger.log('Hello');
        // -> logs for ex.: "<44c2d8ff-49a6-4244-869f-75a2df11517a> Hello"
    }
}

Additional CLS Setup

The CLS middleware/guard/interceptor provide some default functionality, but sometimes you might want to store more things in the context by default. This can be of course done in a custom enhancer bound after, but for this scenario the options expose the setup function, which will be executed in the middleware/guard after the CLS context is set up.

The function receives the ClsService instance and the Request (or ExecutionContext) object, and can be asynchronous.

ClsModule.register({
    middleware: {
        mount: true,
        setup: (cls, req) => {
            // put some additional default info in the CLS
            cls.set('TENANT_ID', req.params('tenant_id'));
            cls.set('AUTH', { authenticated: false });
        },
    },
});

Breaking out of DI

While this package aims to be compatible with NestJS's DI, it is also possible to access the CLS context outside of it. For that, it provides the static ClsServiceManager class that exposes the getClsService() method.

function helper() {
    const cls = ClsServiceManager.getClsService();
    // you now have access to the shared storage
    console.log(cls.getId());
}

Please note: Only use this feature where absolutely necessary. Using this technique instead of dependency injection will make it difficult to mock the ClsService and your code will become harder to test.

Security considerations

It is often discussed whether AsyncLocalStorage is safe to use for concurrent requests (because of a possible context leak) and whether the context could be lost throughout the duration of a request.

The ClsMiddleware by default uses the safe run() method, so it should not leak context, however, that only works for REST Controllers.

GraphQL Resolvers, cause the context to be lost and therefore require using the less safe enterWith() method. The same applies to using ClsGuard to set up the context, since there's no callback to wrap with the run() call, the only way to set up context in a guard is to use enterWith() (the context would be not available outside of the guard otherwise).

This has a consequence that should be taken into account:

When the enterWith method is used, any consequent requests get access to the context of the previous one until the request hits the enterWith call.

That means, when using ClsMiddleware with the useEnterWith option, or ClsGuard to set up context, be sure to mount them as early in the request lifetime as possible and do not use any other enhancers that rely on ClsService before them. For ClsGuard, that means you should probably manually mount it in AppModule if you require any other guard to run after it.

The ClsInterceptor only uses the safe run() method.

Compatibility considerations

The table below outlines the compatibility with some platforms:

	REST	GQL	Others
ClsMiddleware	✔	must be mounted manually and use useEnterWith: true	✖
ClsGuard (uses enterWith)	✔	✔	?
ClsInterceptor (context inaccessible in Guards)	context also inaccessible in Exception Filters	✔	?

REST

This package is 100% compatible with Nest-supported REST controllers and the preferred way is to use the ClsMiddleware with the mount option.

Tested with:

• ✔ Express
• ✔ Fastify

GraphQL

For GraphQL, the ClsMiddleware needs to be mounted manually with app.use(...) in order to correctly set up the context for resolvers. Additionally, you have to pass useEnterWith: true to the ClsMiddleware options, because the context gets lost otherwise due to an issue with CLS and Apollo (sadly, the same is true for Mercurius). This method is functionally identical to just using the ClsGuard.

Alternatively, you can use the ClsInterceptor, which uses the safer AsyncLocalStorage#run (thanks to andreialecu), but remember that using it makes CLS unavailable in Guards.

Tested with:

• ✔ Apollo (Express)
• ✔ Mercurius (Fastify)

Others

Use the ClsGuard or ClsInterceptor to set up context with any other platform. This is still experimental, as there are no test and I can't guarantee it will work with your platform of choice.

If you decide to try this package with a platform that is not listed here, please let me know so I can add the compatibility notice.

Namespaces (experimental)

Warning: Namespace support is currently experimental and has no tests. While the API is mostly stable now, it can still change any time.

The default CLS namespace that the ClsService provides should be enough for most application, but should you need it, this package provides a way to use multiple CLS namespaces in order to be fully compatible with cls-hooked.

Note: Since cls-hooked was ditched in version 1.2, it is no longer necessary to strive for compatibility with it. Still, the namespace support was there and there's no reason to remove it.

To use custom namespace provider, use ClsModule.forFeature('my-namespace').

@Module({
    imports: [ClsModule.forFeature('hello-namespace')],
    providers: [HelloService],
    controllers: [HelloController],
})
export class HelloModule {}

This creates a namespaces ClsService provider that you can inject using @InjectCls

@Injectable()
class HelloService {
    constructor(
        @InjectCls('hello-namespace')
        private readonly myCls: ClsService,
    ) {}

    sayHello() {
        return this.myCls.get('hi');
    }
}

Note: @InjectCls('x') is equivalent to @Inject(getNamespaceToken('x')). If you don't pass an argument to @InjectCls(), the default ClsService will be injected and is equivalent to omitting the decorator altogether.

@Injectable()
export class HelloController {
    constructor(
        @InjectCls('hello-namespace')
        private readonly myCls: ClsService,
        private readonly helloService: HelloService,
    );

    @Get('/hello')
    hello2() {
        // seting up cls context manually
        return this.myCls.run(() => {
            this.myCls.set('hi', 'Hello');
            return this.helloService.sayHello();
        });
    }
}