[coverage] Conformance findings: CONNPOOL-009

[peco-engineer-bot]

Summary

Surfaced by the multi-language coverage fan-out while conformance-testing these SPEC-IDs against databricks/databricks-sql-python. Each finding is committed as an expected-failure (xfail) test in the coverage PR — the test asserts the CORRECT (post-fix) behavior and stays red until THIS driver (databricks/databricks-sql-python) is fixed, then flips green as a tripwire.

Findings

• CONNPOOL-009 [thrift, sea]: ClientContext.__init__ uses pool_maxsize or 20, so a zero per-host connection-pool cap (_pool_maxsize=0) is silently coerced to the default 20 and a session is opened, instead of being rejected with an invalid-argument error naming the option; positive values and the omitted-default path are forwarded correctly
  • failing test: test_max_connections_option_validated_and_forwarded (see the coverage PR diff under tests/)

Reproduce & Expected

CONNPOOL-009 — Verify the per-host idle-connection cap option is accepted and forwarded to HTTP config leaving other HTTP defaults intact, that the default is preserved when the option is omitted, and that zero is…

Reproduce:

SELECT 1
SELECT 1

Expected (per the shared spec):

• A positive cap is accepted: the session opens and no error is raised.
• SELECT 1 returns 1 row with the cap configured.
• {'other_http_defaults_unchanged': {'knobs': ['request_timeout', 'retry_min_wait', 'retry_max_wait', 'retry_max_attempts'], 'description': 'Setting ONLY this option must leave every other HTTP knob at its\ndriver default. Where the driver exposes no config introspection,\nassert this behaviorally: request-timeout and retry behavior are\nindistinguishable from a session opened without the option.\n'}}
• Omitting the option keeps the driver's own default cap (kernel: 100). The driver must not substitute a different value, and must not skip applying its default HTTP configuration.
• {'error_on_invalid_value': {'value': 0, 'error_class': 'invalid_argument', 'description': 'Zero is rejected with an invalid-argument-class failure: PyO3 raises\nValueError; the C ABI setter returns InvalidArgument; other surfaces\nraise their own invalid-argument/illegal-argument equivalent. The\nmessage names the option and states it must be greater than zero.\n'}}
• The zero case fails before any session is established — no session-open request reaches the server with a zero cap.
• The rejected zero leaves an earlier valid value intact (C ABI: the config still holds the previously set value after the InvalidArgument).

Context

• The behavior was first fixed in a DIFFERENT driver — reference PR: https://github.com/databricks/databricks-sql-kernel/pull/311 — which seeded the shared language-neutral spec. This issue tracks the same conformance gap in databricks/databricks-sql-python; the reference PR is for cross-referencing the intended behavior, NOT a change to this repo.
• Coverage PR carrying the reproducing xfail test(s): https://github.com/databricks/databricks-driver-test/pull/1537