Is it possible to alter RPC context data through an interceptor?

Question

Is it possible to alter RPC context data through an interceptor?

Is it possible to adjust the request payload in an RPC-based context, as opposed to HTTP-based contexts like this method? This question arises within the context of modifying a message payload received from Kafka in NestJS microservices setup where messages are encoded using Avro.

// code snippet depicting message decoding
const rpcContext = context.switchToRpc().getContext();
const kafkaMessageBuffer: Buffer = context.switchToRpc().getData();
const decodedMessage = await this.schemaRegistry.decode(kafkaMessageBuffer);

// Attempting to replace the buffer value with the decoded data
rpcContext.args[0]['value'] = decodedMessage;

The above approach encounters obstacles due to the fact that args is protected and cannot be modified.

Are there alternative methods to globally decode all Kafka messages?

Possible alternatives include:

Developing a custom pipe to transform data in the controller:
- ```
@Payload(AvroTransformPipe) message: CustomerMessage
```
Manual decoding of messages in the controller before forwarding them to services

typescript apache-kafka nestjs

Answer 1

Answer №1

I encountered a similar issue and found a workaround in the global interceptor by dynamically executing the method without utilizing next.handle():

const rpcHost: RpcArgumentsHost = context.switchToRpc();
const dataWrapper = rpcHost.getData();
const user = dataWrapper.user;
const data = dataWrapper.data;

const instance = app.get(context.getClass());

const resultPromise: Promise<any> =
  instance[context.getHandler().name](data);

return from(resultPromise);

Answer 2

I encountered a similar issue and found a workaround in the global interceptor by dynamically executing the method without utilizing next.handle():

const rpcHost: RpcArgumentsHost = context.switchToRpc();
const dataWrapper = rpcHost.getData();
const user = dataWrapper.user;
const data = dataWrapper.data;

const instance = app.get(context.getClass());

const resultPromise: Promise<any> =
  instance[context.getHandler().name](data);

return from(resultPromise);

Answer 3

Answer №2

After some consideration, I decided to implement a Global Pipe.

transform(value: any, metadata: ArgumentMetadata): any {
  if (metadata.type !== 'body') {
    return value;
  }

  return value instanceof Buffer ? this.schemaRegistry.decode(value) : null;
}

While this approach is functional, it has its limitations. It will impact every decorator due to the metadata.type check, and targeting a specific decorator like @Payload() can be challenging. Additionally, in a Hybrid application with HTTP endpoints, this solution may present some challenges.

Answer 4

After some consideration, I decided to implement a Global Pipe.

transform(value: any, metadata: ArgumentMetadata): any {
  if (metadata.type !== 'body') {
    return value;
  }

  return value instanceof Buffer ? this.schemaRegistry.decode(value) : null;
}

While this approach is functional, it has its limitations. It will impact every decorator due to the metadata.type check, and targeting a specific decorator like @Payload() can be challenging. Additionally, in a Hybrid application with HTTP endpoints, this solution may present some challenges.

Is it possible to alter RPC context data through an interceptor?

Answer №1

Answer №2

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