BUG: Fix https://gitlab.com/linkahead/linkahead-pylib/-/issues/87

src/linkahead/exceptions.py

@@ -94,12 +94,26 @@ class HTTPServerError(LinkAheadException):
     """HTTPServerError represents 5xx HTTP server errors."""
 
     def __init__(self, body):
-        xml = etree.fromstring(body)
-        error = xml.xpath('/Response/Error')[0]
-        msg = error.get("description")
-
-        if error.text is not None:
-            msg = msg + "\n\n" + error.text
+        try:
+            # This only works if the server sends a valid XML
+            # response. Then it can be parsed for more information.
+            xml = etree.fromstring(body)
+            if xml.xpath('/Response/Error'):
+                error = xml.xpath('/Response/Error')[0]
+                msg = error.get("description") if error.get("description") is not None else ""
+
+                if error.text is not None:
+                    if msg:
+                        msg = msg + "\n\n" + error.text
+                    else:
+                        msg = error.text
+            else:
+                # Valid XML, but no error information
+                msg = body
+        except etree.XMLSyntaxError:
+            # Handling of incomplete responses, e.g., due to timeouts,
+            # c.f. https://gitlab.com/linkahead/linkahead-pylib/-/issues/87.
+            msg = body
         LinkAheadException.__init__(self, msg)