# Copyright 2016, Google Inc.
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#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
#     * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above
# copyright notice, this list of conditions and the following disclaimer
# in the documentation and/or other materials provided with the
# distribution.
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# contributors may be used to endorse or promote products derived from
# this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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"""Service-side implementation of gRPC Python."""

import collections
import enum
import logging
import threading
import time

import grpc
from grpc import _common
from grpc._cython import cygrpc
from grpc.framework.foundation import callable_util

_SHUTDOWN_TAG = 'shutdown'
_REQUEST_CALL_TAG = 'request_call'

_RECEIVE_CLOSE_ON_SERVER_TOKEN = 'receive_close_on_server'
_SEND_INITIAL_METADATA_TOKEN = 'send_initial_metadata'
_RECEIVE_MESSAGE_TOKEN = 'receive_message'
_SEND_MESSAGE_TOKEN = 'send_message'
_SEND_INITIAL_METADATA_AND_SEND_MESSAGE_TOKEN = (
    'send_initial_metadata * send_message')
_SEND_STATUS_FROM_SERVER_TOKEN = 'send_status_from_server'
_SEND_INITIAL_METADATA_AND_SEND_STATUS_FROM_SERVER_TOKEN = (
    'send_initial_metadata * send_status_from_server')

_OPEN = 'open'
_CLOSED = 'closed'
_CANCELLED = 'cancelled'

_EMPTY_FLAGS = 0
_EMPTY_METADATA = cygrpc.Metadata(())

_UNEXPECTED_EXIT_SERVER_GRACE = 1.0


def _serialized_request(request_event):
    return request_event.batch_operations[0].received_message.bytes()


def _application_code(code):
    cygrpc_code = _common.STATUS_CODE_TO_CYGRPC_STATUS_CODE.get(code)
    return cygrpc.StatusCode.unknown if cygrpc_code is None else cygrpc_code


def _completion_code(state):
    if state.code is None:
        return cygrpc.StatusCode.ok
    else:
        return _application_code(state.code)


def _abortion_code(state, code):
    if state.code is None:
        return code
    else:
        return _application_code(state.code)


def _details(state):
    return b'' if state.details is None else state.details


class _HandlerCallDetails(
        collections.namedtuple('_HandlerCallDetails', (
            'method', 'invocation_metadata',)), grpc.HandlerCallDetails):
    pass


class _RPCState(object):

    def __init__(self):
        self.condition = threading.Condition()
        self.due = set()
        self.request = None
        self.client = _OPEN
        self.initial_metadata_allowed = True
        self.disable_next_compression = False
        self.trailing_metadata = None
        self.code = None
        self.details = None
        self.statused = False
        self.rpc_errors = []
        self.callbacks = []


def _raise_rpc_error(state):
    rpc_error = grpc.RpcError()
    state.rpc_errors.append(rpc_error)
    raise rpc_error


def _possibly_finish_call(state, token):
    state.due.remove(token)
    if (state.client is _CANCELLED or state.statused) and not state.due:
        callbacks = state.callbacks
        state.callbacks = None
        return state, callbacks
    else:
        return None, ()


def _send_status_from_server(state, token):

    def send_status_from_server(unused_send_status_from_server_event):
        with state.condition:
            return _possibly_finish_call(state, token)

    return send_status_from_server


def _abort(state, call, code, details):
    if state.client is not _CANCELLED:
        effective_code = _abortion_code(state, code)
        effective_details = details if state.details is None else state.details
        if state.initial_metadata_allowed:
            operations = (cygrpc.operation_send_initial_metadata(
                _EMPTY_METADATA, _EMPTY_FLAGS),
                          cygrpc.operation_send_status_from_server(
                              _common.cygrpc_metadata(state.trailing_metadata),
                              effective_code, effective_details, _EMPTY_FLAGS),)
            token = _SEND_INITIAL_METADATA_AND_SEND_STATUS_FROM_SERVER_TOKEN
        else:
            operations = (cygrpc.operation_send_status_from_server(
                _common.cygrpc_metadata(state.trailing_metadata),
                effective_code, effective_details, _EMPTY_FLAGS),)
            token = _SEND_STATUS_FROM_SERVER_TOKEN
        call.start_server_batch(
            cygrpc.Operations(operations),
            _send_status_from_server(state, token))
        state.statused = True
        state.due.add(token)


def _receive_close_on_server(state):

    def receive_close_on_server(receive_close_on_server_event):
        with state.condition:
            if receive_close_on_server_event.batch_operations[
                    0].received_cancelled:
                state.client = _CANCELLED
            elif state.client is _OPEN:
                state.client = _CLOSED
            state.condition.notify_all()
            return _possibly_finish_call(state, _RECEIVE_CLOSE_ON_SERVER_TOKEN)

    return receive_close_on_server


def _receive_message(state, call, request_deserializer):

    def receive_message(receive_message_event):
        serialized_request = _serialized_request(receive_message_event)
        if serialized_request is None:
            with state.condition:
                if state.client is _OPEN:
                    state.client = _CLOSED
                state.condition.notify_all()
                return _possibly_finish_call(state, _RECEIVE_MESSAGE_TOKEN)
        else:
            request = _common.deserialize(serialized_request,
                                          request_deserializer)
            with state.condition:
                if request is None:
                    _abort(state, call, cygrpc.StatusCode.internal,
                           b'Exception deserializing request!')
                else:
                    state.request = request
                state.condition.notify_all()
                return _possibly_finish_call(state, _RECEIVE_MESSAGE_TOKEN)

    return receive_message


def _send_initial_metadata(state):

    def send_initial_metadata(unused_send_initial_metadata_event):
        with state.condition:
            return _possibly_finish_call(state, _SEND_INITIAL_METADATA_TOKEN)

    return send_initial_metadata


def _send_message(state, token):

    def send_message(unused_send_message_event):
        with state.condition:
            state.condition.notify_all()
            return _possibly_finish_call(state, token)

    return send_message


class _Context(grpc.ServicerContext):

    def __init__(self, rpc_event, state, request_deserializer):
        self._rpc_event = rpc_event
        self._state = state
        self._request_deserializer = request_deserializer

    def is_active(self):
        with self._state.condition:
            return self._state.client is not _CANCELLED and not self._state.statused

    def time_remaining(self):
        return max(
            float(self._rpc_event.request_call_details.deadline) - time.time(),
            0)

    def cancel(self):
        self._rpc_event.operation_call.cancel()

    def add_callback(self, callback):
        with self._state.condition:
            if self._state.callbacks is None:
                return False
            else:
                self._state.callbacks.append(callback)
                return True

    def disable_next_message_compression(self):
        with self._state.condition:
            self._state.disable_next_compression = True

    def invocation_metadata(self):
        return _common.application_metadata(self._rpc_event.request_metadata)

    def peer(self):
        return _common.decode(self._rpc_event.operation_call.peer())

    def send_initial_metadata(self, initial_metadata):
        with self._state.condition:
            if self._state.client is _CANCELLED:
                _raise_rpc_error(self._state)
            else:
                if self._state.initial_metadata_allowed:
                    operation = cygrpc.operation_send_initial_metadata(
                        _common.cygrpc_metadata(initial_metadata), _EMPTY_FLAGS)
                    self._rpc_event.operation_call.start_server_batch(
                        cygrpc.Operations((operation,)),
                        _send_initial_metadata(self._state))
                    self._state.initial_metadata_allowed = False
                    self._state.due.add(_SEND_INITIAL_METADATA_TOKEN)
                else:
                    raise ValueError('Initial metadata no longer allowed!')

    def set_trailing_metadata(self, trailing_metadata):
        with self._state.condition:
            self._state.trailing_metadata = _common.cygrpc_metadata(
                trailing_metadata)

    def set_code(self, code):
        with self._state.condition:
            self._state.code = code

    def set_details(self, details):
        with self._state.condition:
            self._state.details = _common.encode(details)


class _RequestIterator(object):

    def __init__(self, state, call, request_deserializer):
        self._state = state
        self._call = call
        self._request_deserializer = request_deserializer

    def _raise_or_start_receive_message(self):
        if self._state.client is _CANCELLED:
            _raise_rpc_error(self._state)
        elif self._state.client is _CLOSED or self._state.statused:
            raise StopIteration()
        else:
            self._call.start_server_batch(
                cygrpc.Operations(
                    (cygrpc.operation_receive_message(_EMPTY_FLAGS),)),
                _receive_message(self._state, self._call,
                                 self._request_deserializer))
            self._state.due.add(_RECEIVE_MESSAGE_TOKEN)

    def _look_for_request(self):
        if self._state.client is _CANCELLED:
            _raise_rpc_error(self._state)
        elif (self._state.request is None and
              _RECEIVE_MESSAGE_TOKEN not in self._state.due):
            raise StopIteration()
        else:
            request = self._state.request
            self._state.request = None
            return request

    def _next(self):
        with self._state.condition:
            self._raise_or_start_receive_message()
            while True:
                self._state.condition.wait()
                request = self._look_for_request()
                if request is not None:
                    return request

    def __iter__(self):
        return self

    def __next__(self):
        return self._next()

    def next(self):
        return self._next()


def _unary_request(rpc_event, state, request_deserializer):

    def unary_request():
        with state.condition:
            if state.client is _CANCELLED or state.statused:
                return None
            else:
                start_server_batch_result = rpc_event.operation_call.start_server_batch(
                    cygrpc.Operations(
                        (cygrpc.operation_receive_message(_EMPTY_FLAGS),)),
                    _receive_message(state, rpc_event.operation_call,
                                     request_deserializer))
                state.due.add(_RECEIVE_MESSAGE_TOKEN)
                while True:
                    state.condition.wait()
                    if state.request is None:
                        if state.client is _CLOSED:
                            details = '"{}" requires exactly one request message.'.format(
                                rpc_event.request_call_details.method)
                            _abort(state, rpc_event.operation_call,
                                   cygrpc.StatusCode.unimplemented,
                                   _common.encode(details))
                            return None
                        elif state.client is _CANCELLED:
                            return None
                    else:
                        request = state.request
                        state.request = None
                        return request

    return unary_request


def _call_behavior(rpc_event, state, behavior, argument, request_deserializer):
    context = _Context(rpc_event, state, request_deserializer)
    try:
        return behavior(argument, context), True
    except Exception as e:  # pylint: disable=broad-except
        with state.condition:
            if e not in state.rpc_errors:
                details = 'Exception calling application: {}'.format(e)
                logging.exception(details)
                _abort(state, rpc_event.operation_call,
                       cygrpc.StatusCode.unknown, _common.encode(details))
        return None, False


def _take_response_from_response_iterator(rpc_event, state, response_iterator):
    try:
        return next(response_iterator), True
    except StopIteration:
        return None, True
    except Exception as e:  # pylint: disable=broad-except
        with state.condition:
            if e not in state.rpc_errors:
                details = 'Exception iterating responses: {}'.format(e)
                logging.exception(details)
                _abort(state, rpc_event.operation_call,
                       cygrpc.StatusCode.unknown, _common.encode(details))
        return None, False


def _serialize_response(rpc_event, state, response, response_serializer):
    serialized_response = _common.serialize(response, response_serializer)
    if serialized_response is None:
        with state.condition:
            _abort(state, rpc_event.operation_call, cygrpc.StatusCode.internal,
                   b'Failed to serialize response!')
        return None
    else:
        return serialized_response


def _send_response(rpc_event, state, serialized_response):
    with state.condition:
        if state.client is _CANCELLED or state.statused:
            return False
        else:
            if state.initial_metadata_allowed:
                operations = (cygrpc.operation_send_initial_metadata(
                    _EMPTY_METADATA, _EMPTY_FLAGS),
                              cygrpc.operation_send_message(serialized_response,
                                                            _EMPTY_FLAGS),)
                state.initial_metadata_allowed = False
                token = _SEND_INITIAL_METADATA_AND_SEND_MESSAGE_TOKEN
            else:
                operations = (cygrpc.operation_send_message(serialized_response,
                                                            _EMPTY_FLAGS),)
                token = _SEND_MESSAGE_TOKEN
            rpc_event.operation_call.start_server_batch(
                cygrpc.Operations(operations), _send_message(state, token))
            state.due.add(token)
            while True:
                state.condition.wait()
                if token not in state.due:
                    return state.client is not _CANCELLED and not state.statused


def _status(rpc_event, state, serialized_response):
    with state.condition:
        if state.client is not _CANCELLED:
            trailing_metadata = _common.cygrpc_metadata(state.trailing_metadata)
            code = _completion_code(state)
            details = _details(state)
            operations = [
                cygrpc.operation_send_status_from_server(
                    trailing_metadata, code, details, _EMPTY_FLAGS),
            ]
            if state.initial_metadata_allowed:
                operations.append(
                    cygrpc.operation_send_initial_metadata(_EMPTY_METADATA,
                                                           _EMPTY_FLAGS))
            if serialized_response is not None:
                operations.append(
                    cygrpc.operation_send_message(serialized_response,
                                                  _EMPTY_FLAGS))
            rpc_event.operation_call.start_server_batch(
                cygrpc.Operations(operations),
                _send_status_from_server(state, _SEND_STATUS_FROM_SERVER_TOKEN))
            state.statused = True
            state.due.add(_SEND_STATUS_FROM_SERVER_TOKEN)


def _unary_response_in_pool(rpc_event, state, behavior, argument_thunk,
                            request_deserializer, response_serializer):
    argument = argument_thunk()
    if argument is not None:
        response, proceed = _call_behavior(rpc_event, state, behavior, argument,
                                           request_deserializer)
        if proceed:
            serialized_response = _serialize_response(
                rpc_event, state, response, response_serializer)
            if serialized_response is not None:
                _status(rpc_event, state, serialized_response)


def _stream_response_in_pool(rpc_event, state, behavior, argument_thunk,
                             request_deserializer, response_serializer):
    argument = argument_thunk()
    if argument is not None:
        response_iterator, proceed = _call_behavior(
            rpc_event, state, behavior, argument, request_deserializer)
        if proceed:
            while True:
                response, proceed = _take_response_from_response_iterator(
                    rpc_event, state, response_iterator)
                if proceed:
                    if response is None:
                        _status(rpc_event, state, None)
                        break
                    else:
                        serialized_response = _serialize_response(
                            rpc_event, state, response, response_serializer)
                        if serialized_response is not None:
                            proceed = _send_response(rpc_event, state,
                                                     serialized_response)
                            if not proceed:
                                break
                        else:
                            break
                else:
                    break


def _handle_unary_unary(rpc_event, state, method_handler, thread_pool):
    unary_request = _unary_request(rpc_event, state,
                                   method_handler.request_deserializer)
    thread_pool.submit(_unary_response_in_pool, rpc_event, state,
                       method_handler.unary_unary, unary_request,
                       method_handler.request_deserializer,
                       method_handler.response_serializer)


def _handle_unary_stream(rpc_event, state, method_handler, thread_pool):
    unary_request = _unary_request(rpc_event, state,
                                   method_handler.request_deserializer)
    thread_pool.submit(_stream_response_in_pool, rpc_event, state,
                       method_handler.unary_stream, unary_request,
                       method_handler.request_deserializer,
                       method_handler.response_serializer)


def _handle_stream_unary(rpc_event, state, method_handler, thread_pool):
    request_iterator = _RequestIterator(state, rpc_event.operation_call,
                                        method_handler.request_deserializer)
    thread_pool.submit(_unary_response_in_pool, rpc_event, state,
                       method_handler.stream_unary, lambda: request_iterator,
                       method_handler.request_deserializer,
                       method_handler.response_serializer)


def _handle_stream_stream(rpc_event, state, method_handler, thread_pool):
    request_iterator = _RequestIterator(state, rpc_event.operation_call,
                                        method_handler.request_deserializer)
    thread_pool.submit(_stream_response_in_pool, rpc_event, state,
                       method_handler.stream_stream, lambda: request_iterator,
                       method_handler.request_deserializer,
                       method_handler.response_serializer)


def _find_method_handler(rpc_event, generic_handlers):
    for generic_handler in generic_handlers:
        method_handler = generic_handler.service(
            _HandlerCallDetails(
                _common.decode(rpc_event.request_call_details.method),
                rpc_event.request_metadata))
        if method_handler is not None:
            return method_handler
    else:
        return None


def _handle_unrecognized_method(rpc_event):
    operations = (
        cygrpc.operation_send_initial_metadata(_EMPTY_METADATA, _EMPTY_FLAGS),
        cygrpc.operation_receive_close_on_server(_EMPTY_FLAGS),
        cygrpc.operation_send_status_from_server(
            _EMPTY_METADATA, cygrpc.StatusCode.unimplemented,
            b'Method not found!', _EMPTY_FLAGS),)
    rpc_state = _RPCState()
    rpc_event.operation_call.start_server_batch(
        operations, lambda ignored_event: (rpc_state, (),))
    return rpc_state


def _handle_with_method_handler(rpc_event, method_handler, thread_pool):
    state = _RPCState()
    with state.condition:
        rpc_event.operation_call.start_server_batch(
            cygrpc.Operations(
                (cygrpc.operation_receive_close_on_server(_EMPTY_FLAGS),)),
            _receive_close_on_server(state))
        state.due.add(_RECEIVE_CLOSE_ON_SERVER_TOKEN)
        if method_handler.request_streaming:
            if method_handler.response_streaming:
                _handle_stream_stream(rpc_event, state, method_handler,
                                      thread_pool)
            else:
                _handle_stream_unary(rpc_event, state, method_handler,
                                     thread_pool)
        else:
            if method_handler.response_streaming:
                _handle_unary_stream(rpc_event, state, method_handler,
                                     thread_pool)
            else:
                _handle_unary_unary(rpc_event, state, method_handler,
                                    thread_pool)
        return state


def _handle_call(rpc_event, generic_handlers, thread_pool):
    if not rpc_event.success:
        return None
    if rpc_event.request_call_details.method is not None:
        method_handler = _find_method_handler(rpc_event, generic_handlers)
        if method_handler is None:
            return _handle_unrecognized_method(rpc_event)
        else:
            return _handle_with_method_handler(rpc_event, method_handler,
                                               thread_pool)
    else:
        return None


@enum.unique
class _ServerStage(enum.Enum):
    STOPPED = 'stopped'
    STARTED = 'started'
    GRACE = 'grace'


class _ServerState(object):

    def __init__(self, completion_queue, server, generic_handlers, thread_pool):
        self.lock = threading.Lock()
        self.completion_queue = completion_queue
        self.server = server
        self.generic_handlers = list(generic_handlers)
        self.thread_pool = thread_pool
        self.stage = _ServerStage.STOPPED
        self.shutdown_events = None

        # TODO(https://github.com/grpc/grpc/issues/6597): eliminate these fields.
        self.rpc_states = set()
        self.due = set()


def _add_generic_handlers(state, generic_handlers):
    with state.lock:
        state.generic_handlers.extend(generic_handlers)


def _add_insecure_port(state, address):
    with state.lock:
        return state.server.add_http2_port(address)


def _add_secure_port(state, address, server_credentials):
    with state.lock:
        return state.server.add_http2_port(address,
                                           server_credentials._credentials)


def _request_call(state):
    state.server.request_call(state.completion_queue, state.completion_queue,
                              _REQUEST_CALL_TAG)
    state.due.add(_REQUEST_CALL_TAG)


# TODO(https://github.com/grpc/grpc/issues/6597): delete this function.
def _stop_serving(state):
    if not state.rpc_states and not state.due:
        for shutdown_event in state.shutdown_events:
            shutdown_event.set()
        state.stage = _ServerStage.STOPPED
        return True
    else:
        return False


def _serve(state):
    while True:
        event = state.completion_queue.poll()
        if event.tag is _SHUTDOWN_TAG:
            with state.lock:
                state.due.remove(_SHUTDOWN_TAG)
                if _stop_serving(state):
                    return
        elif event.tag is _REQUEST_CALL_TAG:
            with state.lock:
                state.due.remove(_REQUEST_CALL_TAG)
                rpc_state = _handle_call(event, state.generic_handlers,
                                         state.thread_pool)
                if rpc_state is not None:
                    state.rpc_states.add(rpc_state)
                if state.stage is _ServerStage.STARTED:
                    _request_call(state)
                elif _stop_serving(state):
                    return
        else:
            rpc_state, callbacks = event.tag(event)
            for callback in callbacks:
                callable_util.call_logging_exceptions(
                    callback, 'Exception calling callback!')
            if rpc_state is not None:
                with state.lock:
                    state.rpc_states.remove(rpc_state)
                    if _stop_serving(state):
                        return


def _stop(state, grace):
    with state.lock:
        if state.stage is _ServerStage.STOPPED:
            shutdown_event = threading.Event()
            shutdown_event.set()
            return shutdown_event
        else:
            if state.stage is _ServerStage.STARTED:
                state.server.shutdown(state.completion_queue, _SHUTDOWN_TAG)
                state.stage = _ServerStage.GRACE
                state.shutdown_events = []
                state.due.add(_SHUTDOWN_TAG)
            shutdown_event = threading.Event()
            state.shutdown_events.append(shutdown_event)
            if grace is None:
                state.server.cancel_all_calls()
                # TODO(https://github.com/grpc/grpc/issues/6597): delete this loop.
                for rpc_state in state.rpc_states:
                    with rpc_state.condition:
                        rpc_state.client = _CANCELLED
                        rpc_state.condition.notify_all()
            else:

                def cancel_all_calls_after_grace():
                    shutdown_event.wait(timeout=grace)
                    with state.lock:
                        state.server.cancel_all_calls()
                        # TODO(https://github.com/grpc/grpc/issues/6597): delete this loop.
                        for rpc_state in state.rpc_states:
                            with rpc_state.condition:
                                rpc_state.client = _CANCELLED
                                rpc_state.condition.notify_all()

                thread = threading.Thread(target=cancel_all_calls_after_grace)
                thread.start()
                return shutdown_event
    shutdown_event.wait()
    return shutdown_event


def _start(state):
    with state.lock:
        if state.stage is not _ServerStage.STOPPED:
            raise ValueError('Cannot start already-started server!')
        state.server.start()
        state.stage = _ServerStage.STARTED
        _request_call(state)

        def cleanup_server(timeout):
            if timeout is None:
                _stop(state, _UNEXPECTED_EXIT_SERVER_GRACE).wait()
            else:
                _stop(state, timeout).wait()

        thread = _common.CleanupThread(
            cleanup_server, target=_serve, args=(state,))
        thread.start()


class Server(grpc.Server):

    def __init__(self, thread_pool, generic_handlers, options):
        completion_queue = cygrpc.CompletionQueue()
        server = cygrpc.Server(_common.channel_args(options))
        server.register_completion_queue(completion_queue)
        self._state = _ServerState(completion_queue, server, generic_handlers,
                                   thread_pool)

    def add_generic_rpc_handlers(self, generic_rpc_handlers):
        _add_generic_handlers(self._state, generic_rpc_handlers)

    def add_insecure_port(self, address):
        return _add_insecure_port(self._state, _common.encode(address))

    def add_secure_port(self, address, server_credentials):
        return _add_secure_port(self._state,
                                _common.encode(address), server_credentials)

    def start(self):
        _start(self._state)

    def stop(self, grace):
        return _stop(self._state, grace)

    def __del__(self):
        _stop(self._state, None)
