Reworked session handling.

 * All requests have a session ID, except for the initial create_session system messages.
 * User session can be in an authenticated or anonymous state.
 * In anonymous state it is not possible to perform user actions.
 * Logout has been implemented.
 * Sessions timeout and are cleared after a period of inactivity (1 hour).
 * Bugfixed the lang setting handling.
 * Renamed get_problem -> get_current_solution, return only the user's current solution, not the whole problem data.

1 files changed, 155 insertions, 110 deletions

diff --git a/server/user_session.py b/server/user_session.py
index 5618c90..cf5e120 100644
--- a/server/user_session.py
+++ b/server/user_session.py
@@ -1,4 +1,5 @@
 # coding=utf-8
+import traceback
 
 import uuid
 import threading  # multiprocessing.managers.BaseManager uses threading to serve incoming requests
@@ -7,64 +8,145 @@ import base64
 import random
 import db
 import server
-from errors.session import NoSuchSession, AuthenticationFailed, PasswordChangeFailed, UserExists, SignupFailed
+from errors.session import NoSuchSession, AuthenticationFailed, PasswordChangeFailed, UserExists, SignupFailed, NotLoggedIn
 import psycopg2.extras
 import datetime
+import logging
+import time
 
-__all__ = ['get_session_by_id', 'get_or_create_session', 'UserSession']
+__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.
-    Only public methods are available to the outside world due to the use of multiprocessing managers.
-    Therefore prefix any private methods with an underscore (_).
-    No properties are accessible; use getters and setters instead.
-    Values are passed by value instead of by reference (deep copy!).
+    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, uid, username, settings):
+    def __init__(self):
         self._access_lock = threading.Lock()
         self.sid = uuid.uuid4().hex
-        self.uid = uid
-        self.username = username
+        self.uid = None
+        self.username = None
         self._lang_session = None
-        self.settings = settings
+        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.now()
+            conn = db.get_connection()
+            try:
+                cur = conn.cursor()
+                try:
+                    cur.execute('select id, password, gui_lang 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 = {'lang': row[2]}
+                    else:
+                        raise AuthenticationFailed('Password mismatch')
+                finally:
+                    cur.close()
+            finally:
+                conn.commit()
+                db.return_connection(conn)
+
+    def signup(self, username, password, lang):
+        with self._access_lock:
+            now = datetime.datetime.now()
+            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), None ,'', 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 = {'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:
-            with module_access_lock:
-                del sessions[self.sid]
-            if self._lang_session is not None:
-                self._lang_session.destroy()
-                self._lang_session = None
-            # TODO: add any cleanups as features are added!
+            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):
-        return self.uid
+        with self._access_lock:
+            return self.uid
 
     def get_settings(self):
-        return self.settings
-
-    def update_settings(self, newSettings):
-        self.settings.update(newSettings)
+        with self._access_lock:  # settings are mutable, so we need a locked access
+            return self.settings
 
-    def write_settings_to_db(self):
-        conn = db.get_connection()
-        try:
-            cur = conn.cursor()
+    def update_settings(self, new_settings):
+        with self._access_lock:
+            self.settings.update(new_settings)
+            conn = db.get_connection()
             try:
-                cur.execute("UPDATE codeq_user SET gui_lang='" + self.settings['lang'] + "' WHERE id="+str(self.uid))
+                cur = conn.cursor()
+                try:
+                    cur.execute("update codeq_user set gui_lang = %s where id = %s", (self.settings['lang'], self.uid))
+                finally:
+                    cur.close()
             finally:
-                cur.close()
-        finally:
-            conn.commit()
-            db.return_connection(conn)
+                conn.commit()
+                db.return_connection(conn)
 
     def load_language_session(self, problem_id):
         with self._access_lock:
@@ -103,31 +185,18 @@ class UserSession(object):
         with self._access_lock:
             return self._lang_session
 
-    def get_problem_data(self, language, problem_group, problem):
-        mod = server.problems.load_problem(language, problem_group, problem, 'sl')
-        mod_language = server.problems.load_language(language, 'sl')
-
-        # Get generic and problem-specific hints.
-        hint = dict(mod_language.hint)
-        hint.update(mod.hint)
-        plan = mod.plan if hasattr(mod, 'plan') else []
-
+    def current_solution(self, problem_id):
+        with self._access_lock:
+            uid = self.uid
         conn = db.get_connection()
         try:
             cur = conn.cursor()
             try:
-                cur.execute("select l.id, l.name, g.id, g.name, p.id, p.name 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 l.identifier = %s and g.identifier = %s and p.identifier = %s", (language, problem_group, problem))
-                row = cur.fetchone()
-                problem_id = row[4]
-                result = {
-                    'language': {'id': row[0], 'identifier': language, 'name': row[1]},
-                    'problem_group': {'id': row[2], 'identifier': problem_group, 'name': row[3]},
-                    'problem': {'id': problem_id, 'identifier': problem, 'name': row[5], 'slug': mod.slug, 'description': mod.description, 'hint': hint, 'plan': plan}
-                }
-                cur.execute("select content from solution where problem_id = %s and codeq_user_id = %s", (problem_id, self.uid))
+                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]
+                    result['solution'] = row[0] or ''
                 else:
                     result['solution'] = ''
                 return result
@@ -140,12 +209,13 @@ class UserSession(object):
     def update_solution(self, problem_id, trace, solution):
         if (trace is None) and (solution is None):
             return
+        uid = self.get_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', (self.uid, problem_id))
+                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]:
@@ -158,7 +228,7 @@ class UserSession(object):
                     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, self.uid, psycopg2.extras.Json(trace)))
+                    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()
@@ -169,11 +239,12 @@ class UserSession(object):
             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), self.uid,))
+                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')
@@ -183,7 +254,6 @@ class UserSession(object):
             conn.commit()
             db.return_connection(conn)
 
-
     def send(self, json_obj):
         """Sends a message to the user.
 
@@ -202,6 +272,7 @@ class UserSession(object):
             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)
@@ -209,62 +280,6 @@ def get_session_by_id(sid):
             raise NoSuchSession('There is no session with SID {}'.format(sid))
         return s
 
-def get_or_create_session(uid, username, sid=None, lan=None):
-    with module_access_lock:
-        if sid is not None:
-            s = sessions.get(sid)
-            if s is not None:
-                return s
-        settings = {}
-        if lan is not None:
-            #settings['lan'] or settings['lang'] ????
-            settings['lan'] = lan
-        s = UserSession(uid, username, settings)
-        sessions[s.sid] = s
-        return s
-
-def authenticate_and_create_session(username, password):
-    now = datetime.datetime.now()
-    conn = db.get_connection()
-    try:
-        cur = conn.cursor()
-        try:
-            cur.execute('select id, password, gui_lang 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],))
-                return get_or_create_session(row[0], username, None, row[2])
-            raise AuthenticationFailed('Password mismatch')
-        finally:
-            cur.close()
-    finally:
-        conn.commit()
-        db.return_connection(conn)
-
-
-def signup(username, password):
-    now = datetime.datetime.now()
-    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),None ,'', False, True, str(now), str(now), None ))
-                affected = cur.rowcount
-                if affected is None:
-                    raise SignupFailed('Signn up failed')
-        finally:
-            cur.close()
-    finally:
-        conn.commit()
-        db.return_connection(conn)
-
 
 def verify_password(plain_password, encrypted_password):
     elts = encrypted_password.split('$')
@@ -279,8 +294,11 @@ def verify_password(plain_password, encrypted_password):
     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 = []
@@ -292,4 +310,31 @@ def encrypt_password(plain_password):
 
 random.seed()
 
-# TODO: add a session timeout timer
+
+# 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()