How to perform file upload in Sanic

After a long struggle I found the following code to be working

@app.route("/upload", methods=['POST'])
async def omo(request):
    from sanic import response
    import os
    import aiofiles
    if not os.path.exists(appConfig["upload"]):
        os.makedirs(appConfig["upload"])
    async with aiofiles.open(appConfig["upload"]+"/"+request.files["file"][0].name, 'wb') as f:
        await f.write(request.files["file"][0].body)
    f.close()

    return response.json(True)

Here's an example of file upload for a specific file type (this one is for pdf files)

from sanic import Sanic
from sanic.response import json
from pathlib import os
from datetime import datetime


app = Sanic()

config = {}
config["upload"] = "./tests/uploads"



@app.route("/upload", methods=['POST'])
def post_json(request):
    if not os.path.exists(config["upload"]):
        os.makedirs(config["upload"])
    test_file = request.files.get('file')
    file_parameters = {
        'body': test_file.body,
        'name': test_file.name,
        'type': test_file.type,
    }
    if file_parameters['name'].split('.')[-1] == 'pdf':
        file_path = f"{config['upload']}/{str(datetime.now())}.pdf"
        with open(file_path, 'wb') as f:
            f.write(file_parameters['body'])
        f.close()
        print('file wrote to disk')

        return json({ "received": True, "file_names": request.files.keys(), "success": True })
    else:
        return json({ "received": False, "file_names": request.files.keys(), "success": False, "status": "invalid file uploaded" })

For examples on other request types, refer official docs (https://sanic.readthedocs.io/en/latest/sanic/request_data.html)

The answers above are great. A few minor improvements:

(1) Since we are using Sanic, let's try to do the file io asynchronously:

async def write_file(path, body):
    async with aiofiles.open(path, 'wb') as f:
        await f.write(body)
    f.close()

(2) Make sure that the file isn't too large so as to crash your server:

def valid_file_size(file_body):
    if len(file_body) < 10485760:
        return True
    return False

(3) Check both the file name and file type for the proper type of file:

  def valid_file_type(file_name, file_type):
     file_name_type = file_name.split('.')[-1]
     if file_name_type == "pdf" and file_type == "application/pdf":
         return True
     return False

(4) Ensure the filename doesn't have dangerous/insecure characters. You can use the secure_filename function in werkzeug.utils: http://flask.pocoo.org/docs/0.12/patterns/fileuploads/

(5) This code brings it all together:

async def process_upload(request):
        # Create upload folder if doesn't exist
        if not os.path.exists(app.config.UPLOAD_DIR):
            os.makedirs(app.config.UPLOAD_DIR)

        # Ensure a file was sent
        upload_file = request.files.get('file_names')
        if not upload_file:
            return redirect("/?error=no_file")

        # Clean up the filename in case it creates security risks
        filename = secure_filename(upload_file.name)

        # Ensure the file is a valid type and size, and if so
        # write the file to disk and redirect back to main
        if not valid_file_type(upload_file.name, upload_file.type):
            return redirect('/?error=invalid_file_type')
        elif not valid_file_size(upload_file.body):
            return redirect('/?error=invalid_file_size')
        else:
            file_path = f"{app.config.UPLOAD_DIR}/{str(datetime.now())}.pdf"
            await write_file(file_path, upload_file.body)
            return redirect('/?error=none')

I created a blog post on how I handle file upload in Sanic. I added some file validation and also asynchronous file writing. I hope others find this helpful:

https://blog.fcast.co/2019/06/16/file-upload-handling-using-asynchronous-file-writing/