Bad request the browser (or proxy) sent a request that this server could not understand - simple solution when encountering the error

Question

I get the error message:

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

Has anyone ever faced this problem? How to troubleshoot the “bad request the browser (or proxy) sent a request that this server could not understand..” The problem appears when I try to operate the following program:

<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>

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)

lyytutoria · Accepted Answer

The cause: This error happened due to BadRequestKeyError accessed to a key which did not exist within request.form.

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

Solution: You have to key uploaded files under request.files dictionary but not under request.form. You also have to delete the loop as the value keyed under u_img is an instance 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')

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Bad request the browser (or proxy) sent a request that this server could not understand – simple solution when encountering the error