fastify-file-interceptor/fastify-file-interceptor/src/multer/interceptor/file-fields-fastify-interceptor.ts

This library for Nestjs using FastifyAdapter it rely on library fastify-multer and express multer

import {
  CallHandler,
  ExecutionContext,
  Inject,
  mixin,
  NestInterceptor,
  Optional,
  Type,
} from "@nestjs/common";
import { Observable } from "rxjs";
import FastifyMulter from "fastify-multer";
import { Options, Multer, Field } from "multer";
import { MULTER_MODULE_OPTIONS } from "../constant/multer-module-option";
import { transformException } from "../utils/multer-utils";

type MulterInstance = any;
export function FileFieldsFastifyInterceptor(
  fields: ReadonlyArray<Field>,
  localOptions?: Options
): Type<NestInterceptor> {
  class MixinInterceptor implements NestInterceptor {
    protected multer: MulterInstance;

    constructor(
      @Optional()
      @Inject(MULTER_MODULE_OPTIONS)
      options: Multer
    ) {
      this.multer = (FastifyMulter as any)({ ...options, ...localOptions });
    }

    async intercept(
      context: ExecutionContext,
      next: CallHandler
    ): Promise<Observable<any>> {
      const ctx = context.switchToHttp();

      await new Promise<void>((resolve, reject) =>
        this.multer.fields(fields)(
          ctx.getRequest(),
          ctx.getResponse(),
          (err: any) => {
            if (err) {
              const error = transformException(err);
              return reject(error);
            }
            resolve();
          }
        )
      );

      return next.handle();
    }
  }
  const Interceptor = mixin(MixinInterceptor);
  return Interceptor as Type<NestInterceptor>;
}