MaxFileSizeValidator

Kind: Class

Source: packages/common/pipes/file/max-file-size.validator.ts

Part of: Common

Defines the built-in MaxSize File Validator

MaxFileSizeValidator is a built-in file validator that checks whether an uploaded file is smaller than a configured maximum size. It is typically used with NestJS ParseFilePipe to reject oversized uploads before they reach application logic.

Extends: FileValidator

Methods

Where it refuses work

• MaxFileSizeValidator stops the work with an early return when errorMessage.
• MaxFileSizeValidator stops the work with an early return when message.
• MaxFileSizeValidator stops the work with an early return when file?.size.
• MaxFileSizeValidator stops the work with an early return when !this.validationOptions || !file.

Diagram

mermaid
graph LR
  A[Incoming uploaded file] --> B[ParseFilePipe]
  B --> C[MaxFileSizeValidator]
  C --> D{file.size < maxSize?}
  D -->|Yes| E[Continue request handling]
  D -->|No| F[buildErrorMessage()]
  F --> G[Return validation error]

Usage

ts
import {
  Controller,
  MaxFileSizeValidator,
  ParseFilePipe,
  Post,
  UploadedFile,
  UseInterceptors,
} from '@nestjs/common';
import { FileInterceptor } from '@nestjs/platform-express';

@Controller('uploads')
export class UploadController {
  @Post()
  @UseInterceptors(FileInterceptor('file'))
  uploadFile(
    @UploadedFile(
      new ParseFilePipe({
        validators: [
          new MaxFileSizeValidator({
            maxSize: 5 * 1024 * 1024, // 5 MB
          }),
        ],
      }),
    )
    file: Express.Multer.File,
  ) {
    return {
      filename: file.originalname,
      size: file.size,
    };
  }
}

AI Coding Instructions

• Instantiate MaxFileSizeValidator with a maxSize value in bytes; use clear constants for readable size limits.
• Add the validator to ParseFilePipe alongside other validators such as FileTypeValidator.
• Ensure the upload interceptor, such as FileInterceptor, runs before attempting to validate the uploaded file.
• Do not rely on client-provided file metadata alone; configure upload limits and storage settings as additional protection.
• Use buildErrorMessage() behavior consistently when extending or composing file-validation error handling.