path: root/server/user_session.py

# coding=utf-8
import traceback

import uuid
import threading  # multiprocessing.managers.BaseManager uses threading to serve incoming requests
import hashlib
import base64
import random
import db
import server
from errors.session import NoSuchSession, AuthenticationFailed, PasswordChangeFailed, UserExists, SignupFailed, NotLoggedIn
import psycopg2.extras
import datetime
import logging
import time

__all__ = ['get_session_by_id', 'UserSession']

sessions = {}  # maps session IDs to session objects

module_access_lock = threading.Lock()  # use this lock to access the sessions dictionary

_user_session_access_update_keys = {
    'login', 'get_sid', 'get_uid', 'get_settings', 'update_settings',
    'load_language_session', 'end_language_session', 'current_language_session',
    'current_solution', 'update_solution', 'change_password'
}

_user_session_restricted_keys = {
    'get_uid', 'get_settings', 'update_settings',
    'load_language_session', 'end_language_session', 'current_language_session',
    'current_solution', 'update_solution', 'change_password'
}


class UserSession(object):
    """Abstracts a user session.
    When first created, the session represents an unauthenticated user.
    As such only get_sid() and last_access are permitted, any other
    action is refused.
    To authenticate the session, call the login() or signup() method.
    """
    def __init__(self):
        self._access_lock = threading.Lock()
        self.sid = uuid.uuid4().hex
        self.uid = None
        self.username = None
        self._lang_session = None
        self.settings = {}
        self.last_access = int(time.time())  # resolution: 1 second
        with module_access_lock:
            sessions[self.sid] = self

    def __getattribute__(self, item):
        """Update the last access time on every access to select methods/properties."""
        if item in _user_session_access_update_keys:
            self.last_access = int(time.time())
        if (item in _user_session_restricted_keys) and (self.uid is None):  # be very careful! this works because 'uid' is not in _user_session_access_update_keys, otherwise we'd have an endless loop
            raise NotLoggedIn('The user in session ' + self.sid + ' is not logged in')
        return super(UserSession, self).__getattribute__(item)

    def login(self, username, password):
        with self._access_lock:
            now = datetime.datetime.utcnow()
            conn = db.get_connection()
            try:
                cur = conn.cursor()
                try:
                    cur.execute('select id, password, name, email, date_joined, gui_lang, robot_address from codeq_user where username = %s', (username,))
                    row = cur.fetchone()
                    if row is None:
                        raise AuthenticationFailed('No such user: {}'.format(username))
                    if verify_password(password, row[1]):
                        cur.execute('update codeq_user set last_login = %s  where id = %s', (str(now), row[0],))
                        self.uid = row[0]
                        self.username = username
                        self.settings = {'gui_lang': row[5], 'robot_address': row[6]}
                        return row[2], row[3], row[4], now
                    else:
                        raise AuthenticationFailed('Password mismatch')
                finally:
                    cur.close()
            finally:
                conn.commit()
                db.return_connection(conn)

    def signup(self, username, name, email, password, lang):
        with self._access_lock:
            now = datetime.datetime.utcnow()
            conn = db.get_connection()
            try:
                cur = conn.cursor()
                try:
                    cur.execute('select id from codeq_user where username = %s', (username,))
                    row = cur.fetchone()
                    if row:
                        raise UserExists('User exists')
                    else:
                        cur.execute('insert into codeq_user (username, password, name, email, is_admin, is_active, date_joined, last_login, gui_lang) values (%s, %s, %s, %s, %s, %s, %s, %s, %s) returning id', (username, encrypt_password(password), name, email, False, True, str(now), str(now), lang))
                        row = cur.fetchone()
                        if row is None:
                            raise SignupFailed('Sign-up failed')
                        self.uid = row[0]
                        self.username = username
                        self.settings = {'gui_lang': lang}
                finally:
                    cur.close()
            finally:
                conn.commit()
                db.return_connection(conn)

    def destroy(self):
        """Destroys the session."""
        with module_access_lock:
            del sessions[self.sid]
        with self._access_lock:
            lang_session = self._lang_session
            self._lang_session = None
            uid = self.uid
            sid = self.sid
            username = self.username
        if lang_session is not None:  # do not handle the language session holding the lock: we may deadlock if the callee calls the caller
            lang_session.destroy()
        logging.debug('User session destroyed: username={0}, uid={1}, sid={2}'.format(username, uid, sid))
        # TODO: add any cleanups as features are added!

    def get_sid(self):
        return self.sid

    def get_uid(self):
        with self._access_lock:
            return self.uid

    def get_settings(self):
        with self._access_lock:  # settings are mutable, so we need a locked access
            return self.settings

    def update_settings(self, new_settings):
        with self._access_lock:
            self.settings.update(new_settings)
            conn = db.get_connection()
            try:
                cur = conn.cursor()
                try:
                    cur.execute("update codeq_user set gui_lang = %s, robot_address = %s where id = %s", (self.settings['gui_lang'], self.settings['robot_address'], self.uid))
                finally:
                    cur.close()
            finally:
                conn.commit()
                db.return_connection(conn)

    def load_language_session(self, problem_id):
        with self._access_lock:
            if self._lang_session is not None:
                self._lang_session.destroy()
                self._lang_session = None
            conn = db.get_connection()
            try:
                cur = conn.cursor()
                try:
                    cur.execute("select l.identifier, g.identifier, p.identifier from problem p inner join language l on l.id = p.language_id inner join problem_group g on g.id = p.problem_group_id where p.id = %s", (problem_id,))
                    row = cur.fetchone()
                    if not row:
                        return None
                    language_identifier = row[0]
                    group_identifier = row[1]
                    problem_identifier = row[2]
                    handler = server.language_session_handlers.get(language_identifier)
                    if not handler:
                        return None
                    self._lang_session = handler(self, problem_id, language_identifier, group_identifier, problem_identifier)
                    return self._lang_session
                finally:
                    cur.close()
            finally:
                conn.commit()
                db.return_connection(conn)

    def end_language_session(self):
        with self._access_lock:
            if self._lang_session is not None:
                self._lang_session.destroy()
                self._lang_session = None

    def current_language_session(self):
        with self._access_lock:
            return self._lang_session

    def current_solution(self, problem_id):
        with self._access_lock:
            uid = self.uid
        conn = db.get_connection()
        try:
            cur = conn.cursor()
            try:
                result = {}
                cur.execute("select content from solution where problem_id = %s and codeq_user_id = %s", (problem_id, uid))
                row = cur.fetchone()
                if row:
                    result['solution'] = row[0] or ''
                else:
                    result['solution'] = ''
                return result
            finally:
                cur.close()
        finally:
            conn.commit()
            db.return_connection(conn)

    def update_solution(self, problem_id, trace, solution):
        if (trace is None) and (solution is None):
            return
        with self._access_lock:
            uid = self.uid
            conn = db.get_connection()
            try:
                cur = conn.cursor()
                try:
                    # TODO: convert to upsert with postgresql 9.5 to eliminate the small window where it's possible for more than one concurrent insert to execute
                    cur.execute('select id, trace, content from solution where codeq_user_id = %s and problem_id = %s for update', (uid, problem_id))
                    row = cur.fetchone()
                    if row:
                        if row[1]:
                            new_trace = row[1]
                            if trace:
                                new_trace.extend(trace)
                        else:
                            new_trace = trace
                        new_solution = row[2] if solution is None else solution
                        cur.execute('update solution set content = %s, trace = %s where id = %s', (new_solution, psycopg2.extras.Json(new_trace), row[0]))
                    else:
                        # this is the first entry
                        cur.execute('insert into solution (done, content, problem_id, codeq_user_id, trace) values (%s, %s, %s, %s, %s)', (False, solution, problem_id, uid, psycopg2.extras.Json(trace)))
                finally:
                    cur.close()
                conn.commit()
            except:
                conn.rollback()
                raise
            finally:
                db.return_connection(conn)

    def change_password(self, password):
        uid = self.get_uid()
        conn = db.get_connection()
        try:
            cur = conn.cursor()
            try:
                cur.execute('update codeq_user set password = %s  where id = %s', (encrypt_password(password), uid))
                affected = cur.rowcount
                if affected is None:
                    raise PasswordChangeFailed('Password change failed')
            finally:
                cur.close()
        finally:
            conn.commit()
            db.return_connection(conn)


    def get_stat(self):
        uid = self.get_uid()
        conn = db.get_connection()
        try:
            cur = conn.cursor()
            try:
                cur.execute("""select * from(
               (SELECT
                  distinct
                  l.identifier as language,
                  pg.id as problem_group_id,
                  pg.identifier as problem_group,
                  count(distinct p.id) as all,
                  count(CASE s.done WHEN true THEN true END) as done,
                  count(CASE s.done WHEN false THEN true END) as in_progress
                FROM problem p
                  INNER JOIN language l ON p.language_id = l.id
                  INNER JOIN problem_group pg ON p.problem_group_id = pg.id
                  LEFT JOIN solution s ON s.problem_id = p.id AND s.codeq_user_id = %s
                GROUP BY l.identifier, pg.id, pg.identifier)
               UNION ALL
               (SELECT
                  distinct
                  l.identifier as language,
                  0 as problem_group_id,
                  null as problem_group,
                  count(distinct p.id) as all,
                  count(CASE s.done WHEN true THEN true END) as done,
                  count(CASE s.done WHEN false THEN true END) as in_progress
                FROM problem p
                  INNER JOIN language l ON p.language_id = l.id
                  LEFT JOIN solution s ON s.problem_id = p.id AND s.codeq_user_id = %s
                GROUP BY l.identifier)
             ) as u
            ORDER BY u.language, problem_group_id""", (uid, uid,))
                #return cur.fetchall()
                columns = ('language', 'problem_group_id', 'problem_group', 'problems_count', 'done', 'in_progress')
                results = []
                for row in cur.fetchall():
                    results.append(dict(zip(columns, row)))
                return results
            finally:
                cur.close()
        finally:
            conn.commit()
            db.return_connection(conn)


    def send(self, json_obj):
        """Sends a message to the user.

        This method may be used only for messages that are not replies to requests.
        For replies use the reply() method on the Request object.
        :param json_obj: a dict representing the json message
        :return: None
        """
        json_obj['sid'] = self.sid
        server.handlers.send(None, self.sid, json_obj)

    def __del__(self):
        #  no locking needed if GC is removing us, as there cannot be any concurrent access by definition
        if hasattr(self, '_lang_session') and (self._lang_session is not None):
            self._lang_session.destroy()
            self._lang_session = None
        # TODO: add any cleanups as features are added!


def get_session_by_id(sid):
    with module_access_lock:
        s = sessions.get(sid, None)
        if s is None:
            raise NoSuchSession('There is no session with SID {}'.format(sid))
        return s


def verify_password(plain_password, encrypted_password):
    elts = encrypted_password.split('$')
    if len(elts) != 4:
        return False
    if elts[0] != 'pbkdf2_sha256':
        return False
    try:
        rounds = int(elts[1])
    except:
        return False
    enc = hashlib.pbkdf2_hmac('sha256', plain_password.encode('utf-8'), elts[2].encode('utf-8'), rounds)
    return base64.b64encode(enc).decode('utf-8') == elts[3]


_salt_chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'
_salt_chars_len = len(_salt_chars)


def encrypt_password(plain_password):
    rounds = 20000
    chosen_chars = []
    for i in range(0, 12):
        chosen_chars.append(_salt_chars[random.randrange(0, _salt_chars_len)])
    salt = ''.join(chosen_chars)
    enc = hashlib.pbkdf2_hmac('sha256', plain_password.encode('utf-8'), salt.encode('utf-8'), rounds)
    return '{0}${1}${2}${3}'.format('pbkdf2_sha256', rounds, salt, base64.b64encode(enc).decode('utf-8'))

random.seed()


# a session timeout timer
def _session_cleaner():
    try:
        while True:
            try:
                with module_access_lock:
                    s = dict(sessions)  # make a copy of the collection of sessions, because it's a bad idea to iterate over a collection that is modified as we go, and we must not hold the module lock or else we deadlock
                now = int(time.time())
                for sid, session in s.items():
                    try:
                        if (now - session.last_access) > 3600:  # a session is considered stale if there's no activity for at least an hour
                            logging.info('Expiring session: {}'.format(sid))
                            session.destroy()
                            server.handlers.send(None, sid, {'sid': sid, 'type': 'session_expire'})  # inform the frontend via system (meta) protocol of the session expiry
                    except Exception as e:
                        logging.critical('Error while checking last access or pruning the session {0}: {1}'.format(sid, str(e)))
                        logging.critical(traceback.format_exc())
            except Exception as e:
                logging.critical('Error while pruning stale sessions: ' + str(e))
                logging.critical(traceback.format_exc())
            time.sleep(60)  # one minute interval between prune runs
    finally:
        logging.critical('The session cleaner thread terminated!')

_session_cleaner_thread = threading.Thread(target=_session_cleaner)
_session_cleaner_thread.daemon = True
_session_cleaner_thread.start()