# IFile

**Kind:** Interface

**Source:** [`packages/common/pipes/file/interfaces/file.interface.ts`](https://github.com/nestjs/nest/blob/master/packages/common/pipes/file/interfaces/file.interface.ts#L1)

**Part of:** [Common](subsystem-packages-common)

`IFile` defines the normalized shape of a file handled by the common file pipe utilities. It stores the file MIME type, byte size, and in-memory `Buffer` content so validation and downstream processing can work with a consistent payload.

## Properties

| Property | Type |
|---|---|
| `mimetype` | `string` |
| `size` | `number` |
| `buffer` | `Buffer` |

## Diagram

```mermaid
graph LR
  Upload[Incoming file upload] --> IFile[IFile]
  IFile --> Mime[mimetype: string]
  IFile --> Size[size: number]
  IFile --> Content[buffer: Buffer]
  IFile --> Validation[File validation pipes]
  Validation --> Processing[Application file processing]
```

## Usage

```ts
import { IFile } from '@common/pipes/file/interfaces/file.interface';

function validateImage(file: IFile): void {
  if (!file.mimetype.startsWith('image/')) {
    throw new Error('Only image files are allowed.');
  }

  if (file.size > 5 * 1024 * 1024) {
    throw new Error('File must not exceed 5 MB.');
  }
}

const file: IFile = {
  mimetype: 'image/png',
  size: 1024,
  buffer: Buffer.from('image-content'),
};

validateImage(file);
```

## AI Coding Instructions

- Treat `buffer` as the authoritative in-memory file content; do not assume a filesystem path or stream is available.
- Validate `mimetype` and `size` before processing or persisting file data.
- Keep `size` aligned with the byte length of `buffer` when constructing `IFile` objects manually.
- Use this interface at file-pipe boundaries to normalize upload-provider-specific file objects.