Flask - Bad Request The browser (or proxy) sent a request that this server could not understand

Question

I'm trying to do a file upload & enter data task into my MongoDB using flask but I had this error when I filled my form & upload the image:

Bad Request The browser (or proxy) sent a request that this server could not understand.

my HTML code

    <form class="form-check form-control" method="post" enctype="multipart/form-data" action="{{ url_for('index') }}">      
          <label>Full Name*</label></td>
          <input name="u_name" type="text" class="text-info my-input" required="required" />
          <label>Email*</label>
          <input name="u_email" type="email" class="text-info my-input" required="required" />
          <label>Password*</label>
          <input name="u_pass" type="password" class="text-info my-input" required="required" />
          <label>Your Image*</label>
          <input name="u_img" type="file" class="text-info" required="required" /></td>
          <input name="btn_submit" type="submit" class="btn-info" />
    </form>

& my python code:

from flask import Flask, render_template, request, url_for
from flask_pymongo import PyMongo
import os
app = Flask(__name__)
app.config['MONGO_DBNAME'] = 'flask_assignment'
app.config['MONGO_URI'] = 'mongodb://<user>:<pass>@<host>:<port>/<database>'
mongo = PyMongo(app)
app_root = os.path.dirname(os.path.abspath(__file__))


@app.route('/', methods=['GET', 'POST'])
def index():
    target = os.path.join(app_root, 'static/img/')
    if not os.path.isdir(target):
        os.mkdir(target)
    if request.method == 'POST':
        name = request.form['u_name']
        password = request.form['u_pass']
        email = request.form['u_email']
        file_name = ''
        for file in request.form['u_img']:
            file_name = file.filename
            destination = '/'.join([target, file_name])
            file.save(destination)
        mongo.db.employee_entry.insert({'name': name, 'password': password, 'email': email, 'img_name': file_name})
        return render_template('index.html')
    else:
        return render_template('index.html')

app.run(debug=True)

Answer 1

The error there is resulting from a BadRequestKeyError because of access to a key that doesn't exist in request.form.

ipdb> request.form['u_img']
*** BadRequestKeyError: 400 Bad Request: The browser (or proxy) sent a request that this server could not understand.

Uploaded files are keyed under request.files and not request.form dictionary. Also, you need to lose the loop because the value keyed under u_img is an instance of FileStorage and not iterable.

@app.route('/', methods=['GET', 'POST'])
def index():
    target = os.path.join(app_root, 'static/img/')
    if not os.path.isdir(target):
        os.makedirs(target)
    if request.method == 'POST':
        ...
        file = request.files['u_img']
        file_name = file.filename or ''
        destination = '/'.join([target, file_name])
        file.save(destination)
        ...
    return render_template('index.html')