changes to make app.current_request thread safe when running chalice locally

- fixes race conditions that can occur when chalice is being run locally
  and it handling multiple concurrent requests

Author: Joel Tetrault

chalice/local.py

@@ -16,7 +16,16 @@
 from six.moves.BaseHTTPServer import HTTPServer
 from six.moves.BaseHTTPServer import BaseHTTPRequestHandler
 from six.moves.socketserver import ThreadingMixIn
-from typing import List, Any, Dict, Tuple, Callable, Optional, Union  # noqa
+from typing import (
+    List,
+    Any,
+    Dict,
+    Tuple,
+    Callable,
+    Optional,
+    Union,
+    cast,
+)  # noqa
 
 from chalice.app import Chalice  # noqa
 from chalice.app import CORSConfig  # noqa
@@ -47,7 +56,9 @@ def time(self):
 
 def create_local_server(app_obj, config, host, port):
     # type: (Chalice, Config, str, int) -> LocalDevServer
-    return LocalDevServer(app_obj, config, host, port)
+    local_app_obj = LocalChalice(app_obj)
+    casted_local_app_obj = cast(Chalice, local_app_obj)
+    return LocalDevServer(casted_local_app_obj, config, host, port)
 
 
 class LocalARNBuilder(object):
@@ -661,3 +672,32 @@ def shutdown(self):
         # type: () -> None
         if self._server is not None:
             self._server.shutdown()
+
+
+class LocalChalice(object):
+    def __init__(self, chalice):
+        # type: (Chalice) -> None
+        self._current_request_lookup = {}  # type: Dict[int, Optional[Request]]
+        self._chalice = chalice
+
+    @property
+    def current_request(self):  # noqa
+        # type: () -> Optional[Request]
+        thread_id = threading.current_thread().ident
+        assert thread_id is not None
+        return self._current_request_lookup.get(thread_id, None)
+
+    @current_request.setter
+    def current_request(self, value):  # noqa
+        # type: (Optional[Request]) -> None
+        thread_id = threading.current_thread().ident
+        assert thread_id is not None
+        self._current_request_lookup[thread_id] = value
+
+    def __getattr__(self, name):
+        # type: (str) -> Any
+        return getattr(self._chalice, name)
+
+    def __call__(self, *args, **kwargs):
+        # type: (Any, Any) -> Any
+        return self._chalice(*args, **kwargs)

tests/unit/test_local.py

@@ -20,6 +20,7 @@
 from chalice.local import ForbiddenError
 from chalice.local import InvalidAuthorizerError
 from chalice.local import LocalDevServer
+from chalice.local import LocalChalice
 
 
 AWS_REQUEST_ID_PATTERN = re.compile(
@@ -667,6 +668,21 @@ def test_can_provide_host_to_local_server(sample_app):
     assert dev_server.host == '0.0.0.0'
 
 
+def test_wraps_sample_app_with_local_chalice(sample_app):
+    dev_server = local.create_local_server(
+        sample_app, None, "127.0.0.1", 23456
+    )
+    assert isinstance(dev_server.app_object, LocalChalice)
+    assert dev_server.app_object._chalice is sample_app
+    assert dev_server.app_object.app_name is sample_app.app_name
+    dev_server.app_object.current_request = "foo"
+    assert dev_server.app_object.current_request == "foo"
+    assert (
+        dev_server.app_object.current_request
+        is not sample_app.current_request
+    )
+
+
 class TestLambdaContext(object):
     def test_can_get_remaining_time_once(self, lambda_context_args):
         time_source = FakeTimeSource([0, 5])