F fix timeout error messages

Summary

For #215 (closed) (https://gitlab.com/linkahead/linkahead-pylib/-/issues/87). Fixes an issue whereby the HTTPServerError class would have too strong assumptions regarding the validity and the contents of the XML response. This would cause problems especially when encountering proxy or other network timeouts.

Focus

This doesn't extend any error handling, it simply ensures that the error can be created correctly.

Test Environment

New unit tests should be sufficient. You can also provoke the original bug by starting LinkAhead with envoy_enabled: true and envoy_rout_timeout set to something very low, e.g., 5 s. Then, I could provoke the original bug by inserting a container with 5000 entities.

Check List for the Author

Please, prepare your MR for a review. Be sure to write a summary and a focus and create gitlab comments for the reviewer. They should guide the reviewer through the changes, explain your changes and also point out open questions. For further good practices have a look at our review guidelines

• All automated tests pass
• Reference related issues
• Up-to-date CHANGELOG.md (or not necessary)
• Up-to-date JSON schema (or not necessary)
• Appropriate user and developer documentation (or not necessary)
  • How do I use the software? Assume "stupid" users.
  • How do I develop or debug the software? Assume novice developers.
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

For further good practices have a look at our review guidelines.

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)