Handling File Uploads and Request Files in FastAPI

Creating a FastAPI application to handle file uploads and request files involves several steps. I’ll guide you through the process in four steps, providing production-level code examples along the way.

Step 1: Set Up Your FastAPI Application

First, you need to create a FastAPI application and set up your project structure. We’ll use FastAPI’s File and UploadFile classes to handle file uploads and request files.

# main.py
from fastapi.responses import JSONResponse
from typing import Annotated
from fastapi import FastAPI, File, UploadFile

app = FastAPI()

# Step 2: Define an endpoint to upload files
@app.post("/uploadfile/")
async def upload_file(file: UploadFile):
    # Step 3: Handle file upload and processing
    # Here, you can save, process, or analyze the uploaded file
    # For simplicity, we'll just return the file details
    return {"filename": file.filename}

# Step 4: Define an endpoint to download files (request files)
@app.get("/downloadfile/")
async def download_file(filename: str):
    # You can implement code to fetch and return the requested file
    # For now, we'll just return a placeholder response
    return JSONResponse(content={"message": f"Requested file: {filename}"})


@app.post('/files/')
async def create_files(file: Annotated[bytes, File()]):
    return {
        "file_size": len(file)
    }


@app.post('/upload_files/')
async def create_upload_files(files: list[UploadFile] = File(...)):
    images = []
    for file in files:
        images.append({
            "filename": file.filename,
            "bytes": str(file.file.read())[:30]
        })
    return {
        "images": images
    }

Step 2: Define an Endpoint to Upload Files

In this step, we create an endpoint that allows clients to upload files. We use the UploadFile class from FastAPI to handle file uploads.

Step 3: Handle File Upload and Processing

Inside the upload_file function, you can process the uploaded file as needed. For example, you can save it to a storage system, analyze its content, or perform any required operations. In this example, we simply return the filename as a confirmation.

Step 4: Define an Endpoint to Download Files (Request Files)

To allow clients to request files, create another endpoint (/downloadfile/) that accepts a filename as a query parameter. In this step, we'll keep it simple by returning a placeholder response. In a production application, you would fetch and return the requested file.

To run this FastAPI application, make sure you have FastAPI and Uvicorn installed:

pip install fastapi uvicorn

Now, you can start your FastAPI application using Uvicorn:

uvicorn main:app --reload

Your FastAPI application is now ready to handle file uploads and requests for files. Clients can use the /uploadfile/ endpoint to upload files, and the /downloadfile/ endpoint to request files.

Remember that this is a basic example, and in a production environment, you should implement proper error handling, file validation, and security measures. Additionally, consider using a storage system (e.g., Amazon S3, Google Cloud Storage) for storing and serving files, rather than directly manipulating them on the server.

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