File download responses in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this FastAPI file download endpoint?

Consider this FastAPI endpoint code. What will the client receive when accessing /download?

FastAPI

from fastapi import FastAPI
from fastapi.responses import FileResponse

app = FastAPI()

@app.get('/download')
async def download_file():
    return FileResponse('example.txt', media_type='text/plain', filename='example.txt')

A The server raises a FileNotFoundError because 'example.txt' is missing.

B The client downloads the file 'example.txt' with correct text content and filename.

C The client receives a JSON response with file metadata instead of the file content.

D The client receives an HTML page showing the file content inline.

💡 Hint

FileResponse sends the file content with headers to trigger download.

FileResponse streams the file content with the specified media type and sets headers so the browser downloads it with the given filename.

📝 Syntax

intermediate

Which option correctly sets a custom filename for download in FastAPI?

You want the client to download a file named 'report.pdf' regardless of the actual file name on disk. Which code snippet achieves this?

FastAPI

from fastapi.responses import FileResponse

# Assume 'files/12345.pdf' exists

@app.get('/get-report')
async def get_report():
    # Fill in the return statement

A return FileResponse('files/12345.pdf', filename='report.pdf')

B return FileResponse('files/12345.pdf', media_type='application/pdf')

C return FileResponse('files/12345.pdf', headers={'Content-Disposition': 'attachment; filename=report.pdf'})

D return FileResponse('files/12345.pdf', filename='files/12345.pdf')

💡 Hint

Use the filename parameter to set the download name.

The filename parameter in FileResponse sets the name the client sees when downloading, overriding the actual file path name.

🔧 Debug

advanced

Why does this FastAPI file download endpoint cause a 500 Internal Server Error?

Analyze the code below. Why does the server return a 500 error when the endpoint is called?

FastAPI

from fastapi import FastAPI
from fastapi.responses import FileResponse

app = FastAPI()

@app.get('/download')
async def download():
    file_path = 'static/report.pdf'
    return FileResponse(path=file_path, media_type='application/pdf', filename='report.pdf')

A The file 'static/report.pdf' does not exist or path is incorrect, causing FileNotFoundError.

B The media_type 'application/pdf' is invalid and causes a runtime error.

C The filename parameter must be omitted to avoid errors.

D The endpoint must be synchronous, async causes the error.

💡 Hint

Check if the file path is correct and file exists on the server.

FileResponse raises an error if the file path does not exist, causing a 500 error. The media_type and filename are valid, and async is allowed.

❓ state_output

advanced

What headers are set by FastAPI's FileResponse for file downloads?

Given this endpoint, which HTTP header ensures the browser downloads the file instead of displaying it inline?

FastAPI

from fastapi import FastAPI
from fastapi.responses import FileResponse

app = FastAPI()

@app.get('/file')
async def file():
    return FileResponse('data.csv', media_type='text/csv', filename='data.csv')

A Cache-Control: no-cache

B Content-Type: application/octet-stream

C Content-Encoding: gzip

D Content-Disposition: attachment; filename="data.csv"

💡 Hint

Look for the header that controls download behavior in browsers.

FileResponse sets the Content-Disposition header with 'attachment' and filename to prompt download. Other headers control content type or caching but not download behavior.

🧠 Conceptual

expert

How does FastAPI's FileResponse handle large files efficiently?

FastAPI's FileResponse is used to send large files to clients. How does it avoid loading the entire file into memory at once?

A It compresses the file fully before sending to reduce memory usage.

B It reads the entire file into memory and then sends it in one response.

C It streams the file in chunks using Python's file iterator, sending data progressively.

D It converts the file to base64 string and sends it as JSON.

💡 Hint

Think about how servers send big files without freezing or crashing.

FileResponse uses Python's file streaming to send data in chunks, which is memory efficient and allows clients to start receiving data immediately.