Split out the local backend (#2052)

This splits the backend into two parts: the local backend for desktop cellxgene and the AWS backend for hosted cellxgene. The local backend is in local_server while the hosted remains in server. The general idea is to copy everything from server to local_server, pull unneeded stuff out of local_server, and keep server as-is for this PR. Not touching server means all the infra and deployment code will continue working just as it did before so we can make those changes incrementally.

local_server/common/errors.py

@@ -0,0 +1,57 @@
+from http import HTTPStatus
+
+
+class CellxgeneException(Exception):
+    """Base class for cellxgene exceptions"""
+
+    def __init__(self, message):
+        self.message = message
+        super().__init__(message)
+
+
+class RequestException(CellxgeneException):
+    """Baseclass for exceptions that can be raised from a request."""
+
+    # The default status code is 400 (Bad Request)
+    default_status_code = HTTPStatus.BAD_REQUEST
+
+    def __init__(self, message, status_code=None):
+        super().__init__(message)
+        self.status_code = status_code or self.default_status_code
+
+
+def define_exception(name, doc):
+    globals()[name] = type(name, (CellxgeneException,), dict(__doc__=doc))
+
+
+def define_request_exception(name, doc, default_status_code=HTTPStatus.BAD_REQUEST):
+    globals()[name] = type(name, (RequestException,), dict(__doc__=doc, default_status_code=default_status_code))
+
+
+define_request_exception("FilterError", "Raised when filter is malformed")
+define_request_exception("JSONEncodingValueError", "Raised when data cannot be encoded into json")
+define_request_exception("MimeTypeError", "Raised when incompatible MIME type selected")
+define_request_exception("DatasetAccessError", "Raised when file loaded into a DataAdaptor is misformatted")
+define_request_exception("DisabledFeatureError", "Raised when an attempt to use a disabled feature occurs")
+define_request_exception("AnnotationsError", "Raised when an attempt to use the annotations feature fails")
+define_request_exception(
+    "ComputeError",
+    "Raised when an error occurs during a compute algorithm (such as diffexp)",
+    HTTPStatus.INTERNAL_SERVER_ERROR,
+)
+define_request_exception("ExceedsLimitError", "Raised when an HTTP request exceeds a limit/quota")
+define_request_exception("ColorFormatException", "Raised when color helper functions encounter an unknown color format")
+define_request_exception(
+    "AuthenticationError", "Raised when there is an authentication error", default_status_code=HTTPStatus.UNAUTHORIZED
+)
+
+define_request_exception(
+    "AnnotationCategoryNameError",
+    "Raised when an annotation category name cant be saved",
+    default_status_code=HTTPStatus.UNPROCESSABLE_ENTITY,
+)
+
+define_exception("OntologyLoadFailure", "Raised when reading the ontology file fails")
+define_exception("ConfigurationError", "Raised when checking configuration errors")
+define_exception("PrepareError", "Raised when data is misprepared")
+define_exception("SecretKeyRetrievalError", "Raised when get_secret_key from AWS fails")