NestJS: How to automatically log @MessagePattern's input data with another decorator?

Question

I have a Controller, which is called by external microservices using the ClientProxy.send<>() method, which sends a command that is recognized by the accompanying @MessagePattern decorator and executes that Controller function:

@Controller()
export class DataController {

  @CustomLogger()
  @MessagePattern({ cmd: 'storeData' })
  storeData(
    owner: string,
    dataType: string,
  ): void {

  }
}

Now, every time this Controller is called, I want to log exactly which command was called. I could simply hardcode Logger.log('storeData') in the storeData() function and do that for every next function, but is it possible to log the input of the @MessagePattern() with another decorator automatically, like for example with @CustomLogger which I would define myself? And if so, how?

Answer 1

It is possible to combine decorators with applyDecorators().

In your case you could create a LogMessage Decorator like this:

// LogMessage.ts
const LogMessage = (cmd: string) => {
  const logger = new Logger('MessageLogger');
  return (target: any, propertyKey: string, descriptor: PropertyDescriptor) => {
    const targetFunc = descriptor.value;
    descriptor.value = function (...args: any[]) {
      logger.log(`Message: ${cmd}`);
      targetFunc.apply(this, args);
    };
    return descriptor;
  };
};

export default LogMessage;

and combine it with MessagePattern inside a new decorator MessagePatternWithLog:

// MessagePatternWithLog.ts
const MessagePatternWithLog = ({cmd: string}) => {
  return applyDecorators(LogMessage(cmd), MessagePattern({cmd}));
};

export default MessagePatternWithLog;

After that you can use it like every other Decorator:

@Controller()
export class DataController {

  @MessagePatternWithLog({cmd: 'storeData'})
  storeData(
    owner: string,
    dataType: string,
  ): void {

  }
}

This code is not tested but derived from a working example.