workspaces: add validation function for the workflows

Goes on top of reanahub/reana-client#545 PR set, and reanahub/reana#532 PR set

Closes reanahub/reana-client#546

reana_commons/config.py

@@ -339,6 +339,8 @@ def kubernetes_node_label_to_dict(node_label):
 DEFAULT_WORKSPACE_PATH = os.getenv("DEFAULT_WORKSPACE_PATH", "/var/reana")
 """Default workspace path defined by the admin."""
 
+ADMIN_ALLOWED_WORKSPACES = os.getenv("ADMIN_ALLOWED_WORKSPACES", None)
+
 K8S_CERN_EOS_MOUNT_CONFIGURATION = {
     "volume": {"name": "eos", "hostPath": {"path": "/var/eos"}},
     "volumeMounts": {

reana_commons/workspaces.py

@@ -0,0 +1,31 @@
+# -*- coding: utf-8 -*-
+#
+# This file is part of REANA.
+# Copyright (C) 2020 CERN.
+#
+# REANA is free software; you can redistribute it and/or modify it
+# under the terms of the MIT License; see LICENSE file for more details.
+"""REANA-Commons workspaces util."""
+
+from reana_commons.errors import REANAValidationError
+from reana_commons.config import ADMIN_ALLOWED_WORKSPACES, SHARED_VOLUME_PATH
+
+
+def validate_workspace(workspace_option):
+    """Validate and return workspace.
+
+    :param workspace_option: A string of the workspace.
+    :returns: A string of the validated workspace.
+    """
+    if ADMIN_ALLOWED_WORKSPACES:
+        allowed_workspaces = ADMIN_ALLOWED_WORKSPACES.split(",")
+        allowed_workspaces.append(SHARED_VOLUME_PATH)
+    else:
+        allowed_workspaces = [SHARED_VOLUME_PATH]
+
+    if workspace_option:
+        if workspace_option not in allowed_workspaces:
+            raise REANAValidationError(
+                '==> ERROR: Workspace "{0}" not valid.'.format(workspace_option)
+            )
+    return workspace_option