Why do I get a 404 error when I send a POST request to the server?

Question

Python

My task is to send a request to the server with two parameters login and password and parse the response in JSON format, which it will return to me.

I have a custom script running on the server:

import sqlite3
from flask import Flask, jsonify, request, abort
import json

app = Flask('__name__')

def register(login, password, data=""):
    insert_data = (login, password, data)
    conn = sqlite3.connect("users.db")
    cursor = conn.cursor()

    x = cursor.execute(" SELECT * FROM users WHERE login=?", (login,)).fetchall()

    if not x:
        cursor.execute("INSERT INTO users VALUES (?,?,?)", insert_data)
        conn.commit()
        return "OK"
    return "Username is registered"

def login(login, password):
    insert_data = (login, password)
    conn = sqlite3.connect("users.db")
    cursor = conn.cursor()

    x = cursor.execute(" SELECT data FROM users WHERE login=? AND password=?", (login,password)).fetchone()

    if not x:
        return "Login or password is incorrect"
    return {"status": "logged in", "data": x[0]}

def delete(login, password):
    insert_data = (login, password)
    conn = sqlite3.connect("users.db")
    cursor = conn.cursor()

    x = cursor.execute(" SELECT data FROM users WHERE login=? AND password=?", (login,password)).fetchone()

    if not x:
        return "Login or password is incorrect"
    x = cursor.execute(" DELETE FROM users WHERE login=? AND password=?", (login,password)).fetchone()
    conn.commit()
    return "user deleted"

#=======================================================================================

@app.route('/register', methods=['POST'])
def write_reg():
    if not request.json:
        print(request.json)
        abort(404)

    user = {"login": request.json["login"],
              "password": request.json["password"],
              "data": request.json.get("data") or ""}
    return register(**user), 201

@app.route('/login', methods=['POST'])
def write_log():
    if not request.json:
        print(request.json)
        abort(404)

    user = {"login": request.json["login"],
              "password": request.json["password"]}
    return login(**user), 201

@app.route('/delete', methods=['POST'])
def write_del():
    if not request.json:
        print(request.json)
        abort(404)

    user = {"login": request.json["login"],
              "password": request.json["password"]}
    return delete(**user), 201

@app.errorhandler(404)
def not_found(error):
    return jsonify({'error': 'Not enought data'}), 404

if __name__ == '__main__':
    app.run(host='0.0.0.0',debug=True, threaded=True, port=5123)

I send a POST request like this:

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url + "?" + Data);

request.Method = "POST";
request.Accept = "application/json";
request.UserAgent = "Mozilla/5.0....";

HttpWebResponse response = (HttpWebResponse)request.GetResponse();
StreamReader reader = new StreamReader(response.GetResponseStream());
StringBuilder output = new StringBuilder();
output.Append(reader.ReadToEnd());
response.Close();

And I get a 404 error:

System.Net.WebException: "Удаленный сервер возвратил ошибку: (404) Не найден."

Tell me, what's the matter? When sending a similar request through the console using httpie, everything goes fine and the response is returned:

HTTP/1.0 201 CREATED
Content-Length: 43
Content-Type: application/json
Date: Mon, 07 Sep 2020 09:49:10 GMT
Server: Werkzeug/0.16.0 Python/3.7.7

{
    "data": "",
    "status": "logged in"
}

Answer 1

404 rushes at

if not request.json:
        print(request.json)
        abort(404)

Let's omit the question, why is 404 thrown here, although it should be 400 in meaning.
And in order not to throw 404, you need to add a json body to the request like this:

var httpClient = new HttpClient();
var request = new
{
  login = "admin",
  password = "12345"
};
var jsonString = JsonSerializer.Serialize(request);
var response = await httpClient.PostAsync(url, new StringContent(jsonString))
var contentString = await response.Content.ReadAsStringAsync();
var result = JsonDocument.Parse(contentString);

Answer 2

In general, for a POST request, it would be necessary to fill the RequestStream itself with JSON data. You are sending an empty request.