File download responses in FastAPI

Introduction

File download responses let your web app send files to users so they can save or open them on their device.

When you want users to download reports or documents from your app.

When providing images or videos for users to save.

When letting users download generated files like PDFs or CSVs.

When sharing software or data files through your API.

When allowing users to export their data from your app.

Syntax

FastAPI

from fastapi import FastAPI
from fastapi.responses import FileResponse

app = FastAPI()

@app.get("/download")
async def download_file():
    return FileResponse("path/to/file.txt", media_type="text/plain", filename="file.txt")

FileResponse sends a file from your server to the user.

The filename parameter sets the name the user sees when saving.

Examples

Sends a PDF file named monthly_report.pdf for download.

FastAPI

return FileResponse("files/report.pdf", media_type="application/pdf", filename="monthly_report.pdf")

Sends a JPEG image named vacation.jpg for download.

FastAPI

return FileResponse("images/photo.jpg", media_type="image/jpeg", filename="vacation.jpg")

Sends a CSV file named data_export.csv for download.

FastAPI

return FileResponse("data/export.csv", media_type="text/csv", filename="data_export.csv")

Sample Program

This FastAPI app has one route /download-text. When you visit it, the server sends the file example.txt for download with the same name.

FastAPI

from fastapi import FastAPI
from fastapi.responses import FileResponse

app = FastAPI()

@app.get("/download-text")
async def download_text_file():
    # This will send the file 'example.txt' located in the current folder
    return FileResponse("example.txt", media_type="text/plain", filename="example.txt")

Important Notes

Make sure the file path is correct and the file exists on the server.

Use the correct media_type so browsers handle the file properly.

FileResponse streams the file efficiently without loading it all into memory.

Summary

File download responses let users save files from your FastAPI app.

Use FileResponse with the file path, media type, and filename.

Always check file paths and use correct media types for best results.