Validation methods in Google App Engine

validate.py

##########

import re
import hmac
import random
from hashlib import sha256

from base_handler import BaseHandler

from google.appengine.ext import db
from google.appengine.api import memcache

##########

"""
validate module for validating usernames, passwords and emails for Sign Up feature.
"""

def valid_user(user):
	USER_RE = re.compile("^[a-zA-Z0-9_-]{3,20}$")
	if len(user)>=6:
		return USER_RE.match(user)

def valid_pw(pw):
	PW_RE = re.compile("^.{3,20}$")
	if len(pw)>=6:
		return PW_RE.match(pw)

def valid_email(email):
	EMAIL_RE = re.compile("^[\S]+@[\S]+\.[\S]+$")
	if len(email)>=6:
		return EMAIL_RE.match(email)

def make_salt():
    """
    Generates 16-character salt for encrypting passwords.
    Encryption done with SHA256 via HMAC.
    """
    ALPHABET = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
    chars = []
    for i in range(16):
        chars.append(random.choice(ALPHABET))
    return ''.join(chars)

def make_cookie(uid, pw):
    cookie = uid + '|' + pw
    return cookie


class SafeLogin(BaseHandler):

    def valid_login(self):
        """
        Cookies are in a string separated by a pipe
        >>> cookie = make_cookie('maverick', 'hashed_pw_here')
        >>> cookie
        'maverick|hashed_pw_here'
        >>> valid_cookie(cookie)
        True
    
        Checks the browser's cookie and extract password.
        Matches with memcache-stored (sometimes, but RARELY DB-stored) password.
        Checks with DB if memcache dies down
    
        Returns a Boolean value of user's login cookie
        """
        
        cookie = self.request.cookies.get('login')
    
        # Checks if cookie is present
        if cookie:
            
            cookie = cookie.split('|')
    
            # Checks if cookie contains pipe
            if len(cookie) == 2:
    
                username = cookie[0]
                cookie_pw = cookie[1]
    
                # This value in cache should be set on login
                # Gets this value each page refresh
                db_pw = memcache.get('login_' + username)
    
                if db_pw is not None:
                    
                    if cookie_pw == db_pw:
                        return True
    
                else:
                    # THIS IS RARE
                    # It means that the cache died down and DB query needs to be done
                    # Queries and set memcache
                    sql = "SELECT * FROM User WHERE username = '{0}'".format(
                          username)
                    query = db.GqlQuery(sql).get()

                    if cookie_pw == query.pw:
                        memcache.set('login_' + username, query.pw)
                        return True

                    else:
                        return False
    
            else:
                return False
    
        else:
            return False