feat: handle migration errors from the template

fix #2769

renku/core/template/usecase.py

@@ -132,7 +132,12 @@ def update_template(
             "break your project"
         )
 
-    templates_source = fetch_templates_source(source=template_metadata.source, reference=template_metadata.reference)
+    try:
+        templates_source = fetch_templates_source(
+            source=template_metadata.source, reference=template_metadata.reference
+        )
+    except errors.InvalidTemplateError:
+        raise errors.TemplateUpdateError("Template cannot be fetched.")
 
     update_available, latest_reference = templates_source.is_update_available(
         id=template_metadata.id, reference=template_metadata.reference, version=template_metadata.version

renku/ui/service/errors.py

@@ -668,6 +668,26 @@ def __init__(self, exception=None):
         super().__init__(exception=exception)
 
 
+class IntermittentProjectTemplateUnavailable(ServiceError):
+    """The reference template for the project is currently unavailable.
+
+    It may be a temporary issue in accessing the remote template, or it may have been deleted,
+    moved, or otherwise not-accessible.
+    """
+
+    code = SVC_ERROR_INTERMITTENT + 140
+    userMessage = (
+        "The reference template for the project is currently unavailable."
+        " It may be a temporary problem, or the template may not be accessible anymore."
+    )
+    devMessage = (
+        "Error accessing the project template. This may be temporary, or the project may not be accessible anymore."
+    )
+
+    def __init__(self, exception=None):
+        super().__init__(exception=exception)
+
+
 class IntermittentTimeoutError(ServiceError):
     """An operation timed out."""
 

renku/ui/service/views/cache.py

@@ -28,7 +28,11 @@
 from renku.ui.service.gateways.gitlab_api_provider import GitlabAPIProvider
 from renku.ui.service.views.api_versions import V0_9, V1_0, V1_1, VersionedBlueprint
 from renku.ui.service.views.decorators import accepts_json, optional_identity, requires_cache, requires_identity
-from renku.ui.service.views.error_handlers import handle_common_except, handle_migration_errors
+from renku.ui.service.views.error_handlers import (
+    handle_common_except,
+    handle_migration_read_errors,
+    handle_migration_write_errors,
+)
 from renku.ui.service.views.v0_9.cache import add_v0_9_specific_endpoints
 from renku.ui.service.views.v1_0.cache import add_v1_0_specific_endpoints
 
@@ -156,7 +160,7 @@ def list_projects_view(user_data, cache):
 
 @cache_blueprint.route("/cache.migrate", methods=["POST"], provide_automatic_options=False, versions=[V1_1])
 @handle_common_except
-@handle_migration_errors
+@handle_migration_write_errors
 @accepts_json
 @requires_cache
 @requires_identity
@@ -187,6 +191,7 @@ def migrate_project_view(user_data, cache):
     "/cache.migrations_check", methods=["GET"], provide_automatic_options=False, versions=[V1_0, V1_1]
 )
 @handle_common_except
+@handle_migration_read_errors
 @requires_cache
 @optional_identity
 def migration_check_project_view(user_data, cache):

renku/ui/service/views/error_handlers.py

@@ -44,6 +44,7 @@
     IntermittentDatasetExistsError,
     IntermittentFileNotExistsError,
     IntermittentProjectIdError,
+    IntermittentProjectTemplateUnavailable,
     IntermittentRedisError,
     IntermittentSettingExistsError,
     IntermittentTimeoutError,
@@ -375,8 +376,24 @@ def decorated_function(*args, **kwargs):
     return decorated_function
 
 
-def handle_migration_errors(f):
-    """Wrapper which handles migrations exceptions."""
+def handle_migration_read_errors(f):
+    """Wrapper which handles migrations read exceptions."""
+    # noqa
+    @wraps(f)
+    def decorated_function(*args, **kwargs):
+        """Represents decorated function."""
+        # NOTE: verify if this may better go in MigrationsCheckCtrl as try/except in to_response()
+        try:
+            return f(*args, **kwargs)
+        except (InvalidTemplateError, TemplateUpdateError, UninitializedProject) as e:
+            raise IntermittentProjectTemplateUnavailable(e)
+
+    return decorated_function
+
+
+@handle_migration_read_errors
+def handle_migration_write_errors(f):
+    """Wrapper which handles migrations write exceptions."""
     # noqa
     @wraps(f)
     def decorated_function(*args, **kwargs):

renku/ui/service/views/v1_0/cache.py

@@ -22,11 +22,11 @@
 from renku.ui.service.serializers.v1_0.cache import ProjectMigrateResponseRPC_1_0
 from renku.ui.service.views.api_versions import V0_9, V1_0
 from renku.ui.service.views.decorators import accepts_json, requires_cache, requires_identity
-from renku.ui.service.views.error_handlers import handle_common_except, handle_migration_errors
+from renku.ui.service.views.error_handlers import handle_common_except, handle_migration_write_errors
 
 
 @handle_common_except
-@handle_migration_errors
+@handle_migration_write_errors
 @accepts_json
 @requires_cache
 @requires_identity