Assume I want to upload a file to a web server. Maybe even a rather big file (e.g. 30 MB). It's done with a typical file upload form (see minimal example below).
Now networks are not perfect. I see those types of errors being possible:
- Bitflips can happen
- packages can get lost
- the order in which packages arrive might not be the order in which they were sent
- a package could be received twice
Reading the TCP wiki article, I see
At the lower levels of the protocol stack, due to network congestion, traffic load balancing, or unpredictable network behaviour, IP packets may be lost, duplicated, or delivered out of order. TCP detects these problems, requests re-transmission of lost data, rearranges out-of-order data and even helps minimize network congestion to reduce the occurrence of the other problems. If the data still remains undelivered, the source is notified of this failure. Once the TCP receiver has reassembled the sequence of octets originally transmitted, it passes them to the receiving application. Thus, TCP abstracts the application's communication from the underlying networking details.
Reading that, the only reason I can see why a downloaded file might be broken is (1) something went wrong after it was downloaded or (2) the connection was interrupted.
Do I miss something? Why do sites that offer Linux images often also provide an MD5 hash? Is the integrity of a file upload/download over HTTPS (and thus also over TCP) guaranteed or not?
Minimal File Upload Example
HTML:
<!DOCTYPE html>
<html>
<head><title>Upload a file</title></head>
<body>
<form method="post" enctype="multipart/form-data">
<input name="file" type="file" />
<input type="submit"/>
</form>
</body>
</html>
Python/Flask:
"""
Prerequesites:
$ pip install flask
$ mkdir uploads
"""
import os
from flask import Flask, flash, request, redirect, url_for
from werkzeug.utils import secure_filename
app = Flask(__name__)
app.config["UPLOAD_FOLDER"] = "uploads"
@app.route("/", methods=["GET", "POST"])
def upload_file():
if request.method == "POST":
# check if the post request has the file part
if "file" not in request.files:
flash("No file part")
return redirect(request.url)
file = request.files["file"]
# if user does not select file, browser also
# submit an empty part without filename
if file.filename == "":
flash("No selected file")
return redirect(request.url)
filename = secure_filename(file.filename)
file.save(os.path.join(app.config["UPLOAD_FOLDER"], filename))
return redirect(url_for("upload_file", filename=filename))
else:
return """<!DOCTYPE html>
<html>
<head><title>Upload a file</title></head>
<body>
<form method="post" enctype="multipart/form-data">
<input name="file" type="file" />
<input type="submit"/>
</form>
</body>
</html>"""
return "upload handled"
if __name__ == "__main__":
app.run()
question from:
https://stackoverflow.com/questions/65875755/is-the-integrity-of-file-uploads-downloads-guaranteed-by-tcp-https 与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
