Return 404 when the dataset does not exist (#1581)

Also in this PR, restructure the exception handling.

fixes #1566

server/app/app.py

@@ -9,7 +9,7 @@ from server_timing import Timing as ServerTiming
 from http import HTTPStatus
 
 import server.common.rest as common_rest
-from server.common.errors import DatasetAccessError
+from server.common.errors import DatasetAccessError, RequestException
 from server.common.utils import path_join, Float32JSONEncoder
 from server.common.data_locator import DataLocator
 from server.common.health import health_check
@@ -81,9 +81,9 @@ def dataset_index(url_dataroot=None, dataset=None):
             return render_template(
                 "index.html", datasetTitle=dataset_title, SCRIPTS=scripts, INLINE_SCRIPTS=inline_scripts
             )
-    except DatasetAccessError:
+    except DatasetAccessError as e:
         return common_rest.abort_and_log(
-            HTTPStatus.BAD_REQUEST, f"Invalid dataset {dataset}", loglevel=logging.INFO, include_exc_info=True
+            e.status_code, f"Invalid dataset {dataset}: {e.message}", loglevel=logging.INFO, include_exc_info=True
         )
 
 
@@ -94,6 +94,11 @@ def health():
     return health_check(config)
 
 
+@webbp.errorhandler(RequestException)
+def handle_request_exception(error):
+    return common_rest.abort_and_log(error.status_code, error.message, loglevel=logging.INFO, include_exc_info=True)
+
+
 def get_data_adaptor(url_dataroot=None, dataset=None):
     config = current_app.app_config
 
@@ -123,9 +128,9 @@ def rest_get_data_adaptor(func):
         try:
             with get_data_adaptor(self.url_dataroot, dataset) as data_adaptor:
                 return func(self, data_adaptor)
-        except DatasetAccessError:
+        except DatasetAccessError as e:
             return common_rest.abort_and_log(
-                HTTPStatus.BAD_REQUEST, f"Invalid dataset {dataset}", loglevel=logging.INFO, include_exc_info=True
+                e.status_code, f"Invalid dataset {dataset}: {e.message}", loglevel=logging.INFO, include_exc_info=True
             )
 
     return wrapped_function

server/common/errors.py

@@ -1,92 +1,85 @@
-class FilterError(Exception):
-    """
-    Raised when filter is malformed
-    """
+from http import HTTPStatus
+
+
+class RequestException(Exception):
+    """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):
+        Exception.__init__(self)
+        self.message = message
+        self.status_code = status_code or self.default_status_code
+
+
+class FilterError(RequestException):
+    """Raised when filter is malformed"""
 
     pass
 
 
-class JSONEncodingValueError(Exception):
-    """
-    Raised when data cannot be encoded into json
-    """
+class JSONEncodingValueError(RequestException):
+    """Raised when data cannot be encoded into json"""
 
     pass
 
 
-class MimeTypeError(Exception):
-    """
-    Raised when incompatible MIME type selected
-    """
+class MimeTypeError(RequestException):
+    """Raised when incompatible MIME type selected"""
 
     pass
 
 
-class PrepareError(Exception):
-    """
-    Raised when data is misprepared
-    """
+class DatasetAccessError(RequestException):
+    """Raised when file loaded into a DataAdaptor is misformatted"""
 
     pass
 
 
-class DatasetAccessError(Exception):
-    """
-    Raised when file loaded into a DataAdaptor is misformatted
-    """
+class DisabledFeatureError(RequestException):
+    """Raised when an attempt to use a disabled feature occurs"""
 
     pass
 
 
-class DisabledFeatureError(Exception):
-    """
-    Raised when an attempt to use a disabled feature occurs
-    """
+class AnnotationsError(RequestException):
+    """Raised when an attempt to use the annotations feature fails"""
 
     pass
 
 
-class AnnotationsError(Exception):
-    """
-    Raised when an attempt to use the annotations feature fails
-    """
+class ComputeError(RequestException):
+    """Raised when an error occurs during a compute algorithm (such as diffexp)"""
+
+    default_status_code = HTTPStatus.INTERNAL_SERVER_ERROR
+
+
+class ExceedsLimitError(RequestException):
+    """Raised when an HTTP request exceeds a limit/quota"""
+
+    pass
+
+
+class ColorFormatException(RequestException):
+    """Raised when color helper functions encounter an unknown color format"""
 
     pass
 
 
 class OntologyLoadFailure(Exception):
-    """
-    Raised when reading the ontology file fails
-    """
+    """Raised when reading the ontology file fails"""
 
     pass
 
 
 class ConfigurationError(Exception):
-    """
-    Raised when checking configuration errors
-    """
+    """Raised when checking configuration errors"""
 
     pass
 
 
-class ExceedsLimitError(Exception):
-    """
-    Raised when an HTTP request exceeds a limit/quota
-    """
-
-    pass
-
-
-class ComputeError(Exception):
-    """
-    Raised when an error occurs during a compute algorithm (such as diffexp)
-    """
-
-    pass
-
-
-class ColorFormatException(Exception):
-    """Raised when color helper functions encounter an unknown color format"""
+class PrepareError(Exception):
+    """Raised when data is misprepared"""
 
     pass

server/data_common/matrix_loader.py

@@ -5,6 +5,7 @@ from server.data_common.rwlock import RWLock
 from server.common.errors import DatasetAccessError
 from server.common.data_locator import DataLocator
 from contextlib import contextmanager
+from http import HTTPStatus
 
 
 class MatrixDataCacheItem(object):
@@ -217,7 +218,7 @@ class MatrixDataLoader(object):
         region_name = None if app_config is None else app_config.data_locator__s3__region_name
         self.location = DataLocator(location, region_name=region_name)
         if not self.location.exists():
-            raise DatasetAccessError("Dataset does not exist.")
+            raise DatasetAccessError("Dataset does not exist.", HTTPStatus.NOT_FOUND)
 
         # matrix_data_type is an enum value of type MatrixDataType
         self.matrix_data_type = matrix_data_type