How to Download Files After POSTing Data using FastAPI?

Downloading Files After POSTing Data using FastAPI

When developing web applications that need to receive user input, process it, and then provide a file for download, the ability to properly facilitate this exchange is crucial. FastAPI provides a robust framework for building such applications, and this guide will explore how to effectively download a file after processing POSTed data.

Implementing the Function

First, define an endpoint in your FastAPI application to handle the file download request. This endpoint will receive the file path and return the file as a response. A sample implementation using the FastAPI FileResponse class:

<code class="python">from fastapi import FastAPI, FileResponse, Request
from fastapi.responses import FileResponse

app = FastAPI()

@app.post('/download-file')
async def download_file(request: Request, user_id: int = Form(...)):
    file_path = 'path/to/file.mp3'
    return FileResponse(file_path, media_type='audio/mp3', filename='output.mp3')</code>

In this code, the file_path variable should be replaced with the actual path to the file that needs to be downloaded. The media_type and filename parameters specify the type of file and the name under which it will be downloaded.

Using HTML to Trigger the Download

After defining the endpoint, incorporate an HTML form into your frontend that triggers a POST request to the /download-file endpoint and provides the necessary user_id parameter:

<code class="html"><form action="/download-file" method="post">
    <input type="text" name="user_id" placeholder="Enter user ID">
    <input type="submit" value="Download File">
</form></code>

When the form is submitted, a POST request with the specified user_id will be sent to the /download-file endpoint, which will then process the request and return the file for download.

Handling Large File Downloads

If the file to be downloaded is particularly large, consider using the StreamingResponse class in FastAPI:

<code class="python">from fastapi import FastAPI, Response, StreamingResponse

@app.post('/stream-large-file')
async def download_large_file(request: Request, user_id: int = Form(...)):
    file_path = 'path/to/large_file.mp3'
    async def iter_file():
        with open(file_path, 'rb') as f:
            while chunk := f.read(1024):
                yield chunk
    return StreamingResponse(iter_file(), media_type='audio/mp3', filename='output.mp3')</code>

Here, the iter_file function reads the file in chunks to reduce memory consumption and facilitates the streaming of the file.

Conclusion

By following the steps outlined above, you can create FastAPI applications that seamlessly handle file downloads after POST operations. This empowers your applications to offer download functionality, enriching the user experience and making it easier to access generated files.

The above is the detailed content of How to Download Files After POSTing Data using FastAPI?. For more information, please follow other related articles on the PHP Chinese website!