Request Files

Request Files

🎯 What You'll Learn

- How to receive uploaded files using File and UploadFile classes

- Understanding the difference between File (bytes) and UploadFile

- Handling file metadata like filename and content type

- Implementing secure file upload endpoints

📚 Theory

You can define files to be uploaded by the client using File. FastAPI provides two main ways to handle file uploads:

1. File() - Receives files as bytes, storing the entire content in memory

2. UploadFile - Provides a file-like object with metadata and streaming capabilities

Why Two Different Approaches?

- File() as bytes: Good for small files, simple to use, entire content loaded into memory

- UploadFile: Better for larger files, provides metadata, supports streaming, more memory efficient

Import File Classes

First, import File and UploadFile from fastapi:

[Code Example]

🔧 Key Concepts

File as Bytes

When you declare a parameter with File(), FastAPI reads the entire file and provides it as bytes:

[Code Example]

UploadFile Class

For more control and better performance with larger files, use UploadFile:

[Code Example]

UploadFile Attributes

UploadFile provides useful metadata and methods:

- filename: Original filename (if provided by client)

- content_type: MIME type (e.g., "text/plain", "image/jpeg")

- file: File-like object for reading content

- read(): Read entire file content

- seek(): Move file pointer position

- close(): Close the file

Multiple Files

You can also receive multiple files:

[Code Example]

Form Data Requirement

Files are sent as "form data" (multipart/form-data), which requires the python-multipart package to be installed.

💡 Best Practices

- Use UploadFile for files larger than a few KB to avoid memory issues

- Always validate file types and sizes for security

- Check file.content_type to ensure acceptable file formats

- Use file.filename cautiously - sanitize before saving to disk

- Consider file size limits to prevent abuse

- Handle file upload errors gracefully

🚫 Common Pitfalls

- Using File() for large files: Can cause memory issues - use UploadFile instead

- Not validating file types: Security risk - always check content_type

- Trusting filename: Sanitize filenames before saving to prevent path traversal

- Missing python-multipart: File uploads won't work without this package

- Not handling upload errors: Always implement proper error handling

🔗 Additional Resources

- FastAPI Request Files Documentation

- Python Multipart Package

- File Upload Security Best Practices