How do you handle file upload validation with ParseFilePipe and custom file validators in NestJS?

Q: How do you handle file upload validation with ParseFilePipe and custom file validators in NestJS?

// Built-in validators @Post('upload') @UseInterceptors(FileInterceptor('file')) uploadFile( @UploadedFile( new ParseFilePipe({ validators: [ new MaxFileSizeValidator({ maxSize: 5 * 1024 * 1024 }), // 5 MB new FileTypeValidator({ fileType: /^image\/(jpeg|png|webp)$/ }), ], errorHttpStatusCode: HttpStatus.UNPROCESSABLE_ENTITY, fileIsRequired: true, }), ) file: Express.Multer.File, ) {} // Custom validator — check image dimensions export class MaxDimensionsValidator extends FileValidator { constructor(private maxWidth: number, private maxHeight: number) { super({}); } async isValid(file: Express.Multer.File): Promise { const { width, height } = await getImageDimensions(file.buffer); return width <= this.maxWidth && height <= this.maxHeight; } buildErrorMessage(): string { return `Image must not exceed ${this.maxWidth}x${this.maxHeight} pixels`; } } // Usage with custom validator new ParseFilePipe({ validators: [ new MaxFileSizeValidator({ maxSize: 2_000_000 }), new MaxDimensionsValidator(1920, 1080), ], }) MaxFileSizeValidator checks file.size in bytes — multiply MB by 1024 * 1024. FileTypeValidator accepts a regex matched against file.mimetype — not the file extension. Custom FileValidator extends the abstract base class and implements isValid() and buildErrorMessage(). isValid() can be async — useful for reading file headers or dimensions from the buffer. errorHttpStatusCode defaults to 400 — use HttpStatus.UNPROCESSABLE_ENTITY (422) for semantic correctness. fileIsRequired: false makes the pipe pass through when no file is provided.

Difficulty: 5/10

ParseFilePipe, custom validators, NestJS file upload

NestJS provides ParseFilePipe with built-in MaxFileSizeValidator and FileTypeValidator. Custom validators extend the abstract FileValidator class and implement isValid() and buildErrorMessage(). Pass an array of validator instances to ParseFilePipe's validators option.

ParseFilePipe with built-in and custom validators

File validation design notes:

1
MaxFileSizeValidator checks file.size in bytes — multiply MB by 1024 * 1024.
2

How do you handle file upload validation with ParseFilePipe and custom file validators in NestJS?

Difficulty: 5/10

ParseFilePipe, custom validators, NestJS file upload

NestJS provides ParseFilePipe with built-in MaxFileSizeValidator and FileTypeValidator. Custom validators extend the abstract FileValidator class and implement isValid() and buildErrorMessage(). Pass an array of validator instances to ParseFilePipe's validators option.

ParseFilePipe with built-in and custom validators

File validation design notes:

1
MaxFileSizeValidator checks file.size in bytes — multiply MB by 1024 * 1024.
2

How do you handle file upload validation with ParseFilePipe and custom file validators in NestJS?

NestJS provides ParseFilePipe with built-in MaxFileSizeValidator and FileTypeValidator. Custom validators extend the abstract FileValidator class and implement isValid() and buildErrorMessage(). Pass an array of validator instances to ParseFilePipe's validators option.

How do you handle file upload validation with ParseFilePipe and custom file validators in NestJS?

NestJS provides ParseFilePipe with built-in MaxFileSizeValidator and FileTypeValidator. Custom validators extend the abstract FileValidator class and implement isValid() and buildErrorMessage(). Pass an array of validator instances to ParseFilePipe's validators option.

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