NestJS Validate Headers using class-transform example

Question

I am trying to validate that the headers of the request contain some specific data, and I am using NestJS. I found this information. While this is what I want to do, and it looks proper, the ClassType reference does not exist, and I am not sure what to use instead.

From the example, the decorator is referring to.

request-header.decorator.ts

import { createParamDecorator, ExecutionContext } from '@nestjs/commom'
import { plainToClass } from 'class-transformer';
// The import below fails
import { ClassType } from 'class-transformer/ClassTransformer';
import { validateOrReject } from 'class-validator';

export const RequestHeader = createParamDecorator(
  async (value:  ClassType<unknown>, ctx: ExecutionContext) => {

    // extract headers
    const headers = ctx.switchToHttp().getRequest().headers;

    // Convert headers to DTO object
    const dto = plainToClass(value, headers, { excludeExtraneousValues: true });
    
    // Validate 
    await validateOrReject(dto);

    // return header dto object 
    return dto;
  },
);

Jackie McDoniel · Accepted Answer · 2021-03-31 18:30:41Z

3

Rather than passing the type through a decorator like this, I'd suggest making a custom decorator and setting the validateCustomDecorators option for the ValidationPipe to true. The decorator would look something like

const Header = createParamDecorator((data: unknown, context: ExecutionContext) => {
  const req = context.switchToHttp().getRequest();
  if (data) {
    return req.headers[data];
  }
  return req.headers;
});

And now instead of @Header() from @nestjs/common you can you @Header() from this file and get the ValidationPipe to run after applying the appropriate type metadata

answered Mar 31, 2021 at 18:30

Jackie McDoniel

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9 Comments

Steven Scott Over a year ago

I get an error on the return req.headers[data]; which is stating that the Type 'unknown' cannot be used as an index type.ts(2538)

Jackie McDoniel Over a year ago

Probably need to add some type/data checking in the if (data). Something like if (data && typeof data === 'string') and it should be okay.

Steven Scott Over a year ago

Sorry, new to NestJS, and the use of decorators is giving me some grief as they are not a straight flow through in the debugger. I am using the ` @RequestHeader HeaderInfo:SVSHeadersDTO` and that is then giving me an additonal error

error TS1237: The return type of a parameter decorator function must be either 'void' or 'any'.       Unable to resolve signature of parameter decorator when called as an expression.      44   @RequestHeader HeaderInfo:SVSHeadersDTO          ~~~~~~~~~~~~~~

Steven Scott Over a year ago

Let me accept your answer as I believe it is correct, as I assumed it would look something like that, since I have worked with the headers and the .getRequest()/.getResponse() in interceptors. I will have to make a bigger question around it all, as I need to introduce a custom validator as well.

Jackie McDoniel Over a year ago

Try using @RequestHeader() as a function, because the decorators are technically decorator factories (meaning they're a function that return the thing)

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