Reimplemented communication with the client side.

 * Implemented a node web server supporting asynchronous websocket and long-polling communication with clients.
 * Implemented TCP communication between python middleware and node web server.

5 files changed, 608 insertions, 1 deletions

diff --git a/server/__init__.py b/server/__init__.py
index 284c162..861a7df 100644
--- a/server/__init__.py
+++ b/server/__init__.py
@@ -3,9 +3,14 @@
 import multiprocessing.managers
 from . import user_session
 from . import prolog_session
+from . import python_session
+from . import socket
 import server.problems
 
-__all__ = ['user_session', 'prolog_session', 'problems', 'start']
+__all__ = ['socket', 'handlers', 'user_session', 'prolog_session', 'python_session', 'problems', 'start']
+
+
+# TODO: everything below is deprecated, remove it
 
 class Codeq(object):
     _method_to_typeid_ = {
diff --git a/server/handlers.py b/server/handlers.py
new file mode 100644
index 0000000..e9cf7c8
--- /dev/null
+++ b/server/handlers.py
@@ -0,0 +1,302 @@
+# coding=utf-8
+
+from concurrent.futures import ThreadPoolExecutor
+import traceback
+from errors.session import *
+import server
+
+
+class CodeqService(object):
+    """Base class for all CodeQ services.
+    """
+    session_is_optional = False
+
+    def process(self, request):
+        pass
+
+
+class ProblemList(CodeqService):
+    """List all available problems to the client.
+    """
+    session_is_optional = True
+
+    def process(self, request):
+        request.reply({'code': 0, 'message': 'ok', 'problems': server.problems.list_problems()})
+
+
+class Login(CodeqService):
+    """Logs in a client, creating a new session.
+    """
+    session_is_optional = True
+
+    def process(self, request):
+        js = request.data
+        username = js.get('username')
+        password = js.get('password')
+        if username is None:
+            request.reply({'code': 1, 'message': 'Username was not provided'})
+        elif password is None:
+            request.reply({'code': 2, 'message': 'Password was not provided'})
+        else:
+            try:
+                session = server.user_session.authenticate_and_create_session(username, password)
+            except AuthenticationFailed:
+                request.reply({'code': 3, 'message': 'Username or password do not match'})
+            else:
+                if request.session:
+                    request.session.destroy()
+                request.reply({'code': 0, 'message': 'OK', 'sid':session.get_sid()})
+
+
+class Activity(CodeqService):
+    def process(self, request):
+        js = request.data
+        trace = js.get('trace')
+        solution = js.get('solution')
+        problem_id = js.get('problem_id')
+        if (trace is not None) or (solution is not None):
+            # we have something to do
+            if problem_id is None:
+                request.reply({'code': 1, 'message': 'Problem ID is missing'})
+            else:
+                request.session.update_solution(problem_id, trace, solution)
+                request.end()  # no feedback, just acknowledge the reception
+
+
+class Query(CodeqService):
+    def process(self, request):
+        js = request.data
+        step = js.get('step')
+        if step is None:
+            request.reply({'code': 1, 'message': '"step" is not set'})
+        else:
+            problem_id = js.get('problem_id')
+            if problem_id is None:
+                request.reply({'code': 4, 'message': 'Problem ID not given'})
+            else:
+                session = request.session
+                trace = js.get('trace')
+                prolog = session.get_prolog()
+                program = None
+                if step == 'run':
+                    program = js.get('program')
+                    query = js.get('query')
+                    if program is None:
+                        result = {'code': 2, 'message': 'No program specified'}
+                    elif query is None:
+                        result = {'code': 3, 'message': 'No query specified'}
+                    else:
+                        messages, status, have_more = prolog.run_for_user(session.get_uid(), problem_id, program, query)
+                        result = {'code': 0, 'message': 'ok', 'terminal': {'messages': messages, 'status': status, 'have_more': have_more}}
+                elif step == 'next':
+                    messages, status, have_more = prolog.step()
+                    result = {'code': 0, 'message': 'ok', 'terminal': {'messages': messages, 'status': status, 'have_more': have_more}}
+                elif step == 'end':
+                    messages, status, have_more = prolog.end()
+                    result = {'code': 0, 'message': 'ok', 'terminal': {'messages': messages, 'status': status, 'have_more': have_more}}
+                else:
+                    result = {'code': 5, 'message': 'Unknown prolog step: {0}'.format(step)}
+                if program or trace:
+                    session.update_solution(problem_id, trace, program)
+                request.reply(result)
+
+
+# Pull stdout/stderr from the session's Python interpreter. TODO: convert to async handling
+class PythonPull(CodeqService):
+    def process(self, request):
+        python = request.session.get_python()
+        output = python.pull()
+        request.reply({'code': 0, 'message': 'ok', 'terminal': {'text': output if output else ''}})
+
+
+# Push stdin to the session's Python interpreter. TODO: convert to async handling
+class PythonPush(CodeqService):
+    def process(self, request):
+        text = request.data.get('text')
+        if text is None:
+            request.reply({'code': 1, 'message': 'No input specified'})
+        else:
+            python = request.session.get_python()
+            python.push(text)
+            request.reply({'code': 0, 'message': 'ok'})
+
+
+class Hint(CodeqService):
+    def process(self, request):
+        js = request.data
+        language = js.get('language')
+        problem_id = js.get('problem_id')
+        program = js.get('program')
+
+        if problem_id is None:
+            request.reply({'code': 1, 'message': 'No problem ID specified'})
+        elif program is None:
+            request.reply({'code': 2, 'message': 'No program specified'})
+        else:
+            session = request.session
+            lang_session = None
+            if language == 'prolog':
+                lang_session = session.get_prolog()
+            elif language == 'python':
+                lang_session = session.get_python()
+
+            if lang_session is None:
+                request.reply({'code': 3, 'message': 'Unknown language specified'})
+            else:
+                hints = lang_session.hint(session.get_sid(), problem_id, program)
+                request.reply({'code': 0, 'message': 'ok', 'hints': hints})
+
+
+class Test(CodeqService):
+    def process(self, request):
+        js = request.data
+        language = js.get('language')
+        problem_id = js.get('problem_id')
+        program = js.get('program')
+
+        if problem_id is None:
+            request.reply({'code': 1, 'message': 'No problem ID specified'})
+        elif program is None:
+            request.reply({'code': 2, 'message': 'No program specified'})
+        else:
+            session = request.session
+            lang_session = None
+            if language == 'prolog':
+                lang_session = session.get_prolog()
+            elif language == 'python':
+                lang_session = session.get_python()
+
+            if lang_session is None:
+                request.reply({'code': 3, 'message': 'Unknown language specified'})
+            else:
+                hints = lang_session.test(session.get_sid(), problem_id, program)
+                request.reply({'code': 0, 'message': 'ok', 'hints': hints})
+
+
+class GetProblem(CodeqService):
+    def process(self, request):
+        js = request.data
+        language = js.get('language')
+        problem_group = js.get('problem_group')
+        problem = js.get('problem')
+        if language is None:
+            request.reply({'code': 1, 'message': 'Language identifier not given'})
+        elif problem_group is None:
+            request.reply({'code': 2, 'message': 'Problem group identifier not given'})
+        elif problem is None:
+            request.reply({'code': 3, 'message': 'Problem identifier not given'})
+        else:
+            request.reply({'code': 0, 'message': 'ok', 'data': request.session.get_problem_data(language, problem_group, problem)})
+
+
+# maps actions to their handlers
+incoming_handlers = {
+    'list_problems': ProblemList(),
+    'login': Login(),
+    'get_problem': GetProblem(),
+    'logout': None,
+    'activity': Activity(),
+    'query': Query(),
+    'hint': Hint(),
+    'test': Test()
+}
+
+
+class Request(object):
+    def __init__(self, tid, original_sid, session, data):
+        """Creates a new request
+
+        :param tid: communicator-level transaction ID (global relative to the specific communicator where it originated)
+        :param original_sid: session ID, optional
+        :param session: the actual session with the original_sid, if it exists; the processor may swap it for a new session
+        :param data: the request data from the client
+        :return: new instance
+        """
+        self._tid = tid
+        self._original_sid = original_sid
+        self.session = session
+        self.data = data
+        self.is_finished = False
+
+    def reply(self, data):
+        """Reply to this request.
+
+        :param data: the dictionary representing the reply, that will be converted to JSON
+        :return: None
+        """
+        if data is None:
+            self.end()
+        if self._original_sid is not None:
+            sid = data.get('sid')
+            if sid is None:
+                data['sid'] = self._original_sid
+            elif sid != self._original_sid:
+                data['sid'] = self._original_sid
+                data['new_sid'] = sid
+        # it is important to reply with the same tid and sid parameters as were in the request, so message accounting doesn't get confused
+        send(self._tid, self._original_sid, data)
+        self.is_finished = True
+
+    def end(self):
+        """Conclude the request, without sending a response.
+
+        This is to acknowledge that the response has been received.
+        :return: None
+        """
+        send(self._tid, self._original_sid, None)
+        self.is_finished = True
+
+
+########## low-level machinery, subject to change to support more than the single socket communicator ##########
+
+_executor = ThreadPoolExecutor(max_workers=100)
+
+def _invoke_handler(handler, request):
+    try:
+        print('Worker thread processing data={}'.format(str(request.data)))
+        handler.process(request)
+        if not request.is_finished:
+            print('ERROR: the request was not concluded!')
+            request.reply({'code': -1, 'message': 'Request processing did not provide a reply'})
+        print('Processing finished')
+    except Exception as e:
+        print('ERROR: data processing failed: ' + str(e))
+        traceback.print_exc()
+        request.reply({'code': -1, 'message': 'Internal error: ' + str(e)})
+
+def serve_request(json_obj):
+    if not isinstance(json_obj, dict):
+        raise RequestProcessingError('Require a request represented as a dict, instead got: ' + str(type(json_obj)))
+    tid = json_obj.get('tid')  # session ID and transaction ID uniquely identify a transaction
+    sid = json_obj.get('sid')
+    action = json_obj.get('action')
+    if action is None:
+        raise RequestProcessingError('Request does not contain an action')
+    if not isinstance(action, str):
+        raise RequestProcessingError('Requested action must be a string, got: ' + str(type(action)))
+    handler = incoming_handlers.get(action)
+    if handler is None:
+        raise RequestProcessingError('No handler for ' + action)
+    print("Attempting to serve action={}".format(action))
+    session = None
+    if sid is None:
+        if not handler.session_is_optional:
+            raise RequestProcessingError('Request is missing a session-ID')
+    else:
+        del json_obj['sid']
+        try:
+            session = server.user_session.get_session_by_id(sid)
+        except NoSuchSession:
+            if not handler.session_is_optional:
+                raise RequestProcessingError('This user session has expired. Please log-in again.')
+    _executor.submit(_invoke_handler, handler, Request(tid, sid, session, json_obj))
+
+def send(tid, sid, json_obj):
+    # just a proxy function for now
+    print('Sending reply: {}'.format(str(json_obj)))
+    server.socket.sendPacket(tid, sid, json_obj)
+
+def stop():
+    global _executor
+    _executor.shutdown()
+    _executor = None
diff --git a/server/problems.py b/server/problems.py
index 02f0307..1c87345 100644
--- a/server/problems.py
+++ b/server/problems.py
@@ -19,6 +19,9 @@ def load_module(fullname):
             d = os.path.join(_path_prefix, *parts[:-1])
             ff = importlib.machinery.FileFinder(d, (importlib.machinery.SourceFileLoader, ['.py']))
             spec = ff.find_spec(fullname)
+            if spec is None:
+                print('ERROR: there is no problem module {0}'.format(fullname))
+                return None
             mod = type(sys)(fullname)
             mod.__loader__ = spec.loader
             mod.__package__ = spec.parent
diff --git a/server/socket.py b/server/socket.py
new file mode 100644
index 0000000..c248056
--- /dev/null
+++ b/server/socket.py
@@ -0,0 +1,286 @@
+# coding=utf-8
+
+import socket
+import selectors
+import json
+import threading
+import traceback
+from server.handlers import serve_request
+
+# TODO: add a whole lot of try..except blocks, and just make it overall error resistant
+# TODO: add logging
+
+_mapping_lock = threading.Lock()  # the lock guarding access to the two mappings below
+
+_sessions_to_socket = {}  # keyed by sid: what session is bound to what socket
+
+_transactions_to_socket = {}  # keyed by tid, used only when there is no sid available, so a request can be replied
+
+
+def processIncomingPacket(receiving_socket, packet):
+    print('Decocoding JSON: {}'.format(packet))
+    obj = json.loads(packet)
+    if obj.get('type') == 'connect':
+        return  # TODO: first packet is 'connect', providing the list of connected sessions to the peer
+    tid = obj.get('tid')  # transaction ID
+    if tid is None:
+        raise Exception('Transaction ID is missing from the request')
+    sid = obj.get('sid')  # session ID
+    _mapping_lock.acquire()
+    try:
+        if sid is None:
+            _transactions_to_socket[tid] = receiving_socket
+        else:
+            _sessions_to_socket[sid] = receiving_socket
+    finally:
+        _mapping_lock.release()
+    serve_request(obj)
+
+
+def sendPacket(tid, sid, json_obj):
+    if sid is None:
+        if tid is None:
+            raise Exception('Cannot send a message without a tid and/or a sid')
+        _mapping_lock.acquire()
+        try:
+            socket = _transactions_to_socket.get(tid)
+            del _transactions_to_socket[tid]  # this mapping is not relevant anymore
+        finally:
+            _mapping_lock.release()
+        if socket is None:
+            raise Exception('Cannot send in transaction, it is not registered: ' + tid)
+    else:
+        _mapping_lock.acquire()
+        try:
+            socket = _sessions_to_socket.get(sid)
+        finally:
+            _mapping_lock.release()
+        if socket is None:
+            raise Exception('Cannot send to session, it is not registered: ' + sid)
+    if json_obj is None:
+        # a special case: this is only an acknowledgment, so any request/response accounting can be cleared
+        json_obj = {}
+        if sid is not None:
+            json_obj['sid'] = sid
+    if tid is not None:
+        json_obj['tid'] = tid
+    socket.send(json_obj)
+
+
+class SocketHandler(object):
+
+    def read(self):
+        pass
+
+    def destroy(self):
+        pass
+
+
+class ServerSocket(SocketHandler):
+
+    def __init__(self, communication, hostname='localhost', port=19732):
+        self.communication = communication
+        server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        server_socket.bind((hostname, port))
+        server_socket.listen(5)
+        server_socket.setblocking(False)
+        self.socket = server_socket
+
+    def read(self):
+        conn, addr = self.socket.accept()
+        self.communication.add_socket(JsonClientSocket(self.communication, conn, addr))
+
+    def destroy(self):
+        self.communication.remove_socket(self)
+        try:
+            self.socket.close()
+        except:
+            pass
+
+
+class JsonClientSocket(SocketHandler):
+
+    def __init__(self, communication, socket, address):
+        self.communication = communication
+        self.socket = socket
+        self.address = address
+        socket.setblocking(False)
+        self.status = 0  # registering
+        self.receiving_header = True
+        self.buffer = []
+        self.received_length = 0  # the cumulative length of strings in buffer
+        self.body_length = 0  # the length of the next packet, given in the header
+        self._read_lock = threading.Lock()
+        self._write_lock = threading.Lock()
+
+    def read(self):
+        lock = self._read_lock
+        lock.acquire()
+        try:
+            data = self.socket.recv(8192)
+            if not data:
+                self.destroy()
+            else:
+                # packet decode loop
+                data = data.decode('utf-8')
+                print("received: {}".format(data))
+                offset = 0
+                N = len(data)
+                while (offset < N):
+                    if self.receiving_header:
+                        i = data.find(':', offset)
+                        if i < 0:
+                            self.buffer.append(data[offset:])
+                            break
+                        if len(self.buffer) == 0:
+                            self.body_length = int(data[offset:i])
+                        else:
+                            self.buffer.append(data[offset:i])
+                            self.body_length = int(''.join(self.buffer))
+                            self.buffer.clear()
+                        offset = i + 1
+                        self.receiving_header = False
+                        continue
+                    elif (self.received_length + N - offset) <= self.body_length:
+                        if self.received_length == 0:
+                            # an optimized case
+                            s = data[offset:offset+self.body_length]
+                            offset += len(s)
+                        else:
+                            s = data[offset:offset+self.body_length - self.received_length]  # TODO: is this correct?
+                            offset += len(s)
+                            self.buffer.append(s)
+                            s = ''.join(self.buffer)
+                            self.buffer.clear()
+                            self.received_length = 0
+                        self.receiving_header = True
+                        try:
+                            processIncomingPacket(self, s)
+                        except Exception as e:
+                            # any exception that propagates to here means a possible protocol error, we have to disconnect
+                            traceback.print_exc()
+                            self.destroy()
+                            return
+                    else:
+                        # incomplete packet body, buffer it until the next time
+                        s = data[offset:]
+                        self.buffer.append(s)
+                        self.received_length += len(s)
+                        break
+        finally:
+            lock.release()
+
+    def destroy(self):
+        self.communication.remove_socket(self)
+        try:
+            self.socket.close()
+        except:
+            pass
+            # TODO: unregister from any internal mechanisms
+
+    def send(self, json_obj):
+        js = json.dumps(json_obj)
+        m = str(len(js)) + u':' + js
+        bytes = m.encode('utf-8')
+        lock = self._write_lock
+        lock.acquire()
+        try:
+            self.socket.sendall(bytes)
+        finally:
+            lock.release()
+
+
+class Communication(SocketHandler):
+    def __init__(self):
+        # the selector to register sockets with, the serve_forever() uses it to handle any incoming data
+        self._selector = selectors.DefaultSelector()  # to wait until at least on socket is readable
+        self._lock = threading.Lock()  # the access lock, because of multi-threading
+        self._remove_queue = []  # what sockets to remove
+        self._add_queue = []  # what sockets to add
+        notifier, receiver = socket.socketpair()  # the notification mechanism for the serving thread, using the selector
+        receiver.setblocking(False)
+        self._notifier = notifier
+        self._receiver = receiver
+        self._registered_handlers = set()
+        self._not_signalled = True
+        self._destroying = False
+
+    def serve_forever(self):
+        self._selector.register(self._receiver, selectors.EVENT_READ, self)
+        while True:
+            events = self._selector.select()
+            for key, mask in events:
+                if mask & selectors.EVENT_READ:
+                    key.data.read()
+
+    def add_socket(self, socket_handler):
+        lock = self._lock
+        lock.acquire()
+        try:
+            self._add_queue.append(socket_handler)
+            self._signal()
+        finally:
+            lock.release()
+
+    def remove_socket(self, socket_handler):
+        lock = self._lock
+        lock.acquire()
+        try:
+            self._remove_queue.append(socket_handler)
+            self._signal()
+        finally:
+            lock.release()
+
+    def _signal(self):  # invoke holding the lock
+        if self._not_signalled:
+            self._notifier.send(b'1')
+            self._not_signalled = False
+
+    def read(self):
+        # we have been invoked to process some new additions and/or removals
+        lock = self._lock
+        lock.acquire()
+        try:
+            self._receiver.recv(1024)  # clear the queue
+            self._not_signalled = True
+            selector = self._selector
+            for handler in self._remove_queue:
+                selector.unregister(handler.socket)
+                self._registered_handlers.remove(handler)
+            self._remove_queue.clear()
+            for handler in self._add_queue:
+                selector.register(handler.socket, selectors.EVENT_READ, handler)
+                self._registered_handlers.add(handler)
+            self._add_queue.clear()
+            if self._destroying:
+                self._notifier.close()
+                self._receiver.close()
+                self._selector.close()
+        finally:
+            lock.release()
+
+    def destroy(self):
+        lock = self._lock
+        # make a copy of handlers, because as we're destroying them each will invoke remove_socket(), and for that the lock must be available and the iterating set must not change
+        lock.acquire()
+        try:
+            handlers = set(self._registered_handlers)
+        finally:
+            lock.release()
+        for handler in handlers:
+            handler.destroy()  # destroy them all, even the server socket
+        # this is where everything is destroyed but us, so what follows is self-destruct
+        lock.acquire()
+        try:
+            self._destroying = True
+            self._signal()
+        finally:
+            lock.release()
+
+
+def serve_forever():
+    communication = Communication()
+    server = ServerSocket(communication)
+    communication.add_socket(server)
+    communication.serve_forever()
diff --git a/server/user_session.py b/server/user_session.py
index f21102c..5eec743 100644
--- a/server/user_session.py
+++ b/server/user_session.py
@@ -8,6 +8,7 @@ import random
 from . import prolog_session
 from . import python_session
 from . import problems
+from . import handlers
 import db
 from errors.session import NoSuchSession, AuthenticationFailed
 import psycopg2.extras
@@ -128,6 +129,16 @@ class UserSession(object):
         finally:
             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
+        """
+        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, 'prolog_session') and (self.prolog_session is not None):