issue-11: add back util function is_failed_response

onc/+util/is_failed_response.m

@@ -0,0 +1,23 @@
+function isFailed = is_failed_response(response, status)
+    %% Checks if a server response describes a failure
+    %
+    % * response: (struct) Response as returned by do_request()
+    % - status:   (double) http status code
+    %
+    % Returns: (Logical) true when the response is a failure
+    isFailed = false;
+
+    % Fail if HTTP status code is not a 2xx
+    if exist('status', 'var')
+        if status < 200 || status > 226
+            isFailed = true;
+            return
+        end
+    end
+
+    % Fail if the response is an error description
+    if isfield(response, "errors")
+        names = fieldnames(response.errors(1));
+        isFailed = ismember("errorCode", names) && ismember("errorMessage", names);
+    end
+end