fix: Handle WSClient write failure when server closes WebSocket

[pratikmankawde]

High Level Overview of Change

Fix intermittent xrpl.rpc.RPCOverload test failure caused by an unhandled exception in WSClientImpl::invoke() when the server closes the WebSocket connection after booting an overloaded client.

Context of Change

Failing CI job: https://github.com/XRPLF/rippled/actions/runs/23560752956/job/68599747791

The bug was introduced when the test infrastructure was originally written. WSClientImpl::invoke() uses the throwing overload of ws_.write_some(). When the server boots a client for exceeding resource thresholds (session->close({policy_error, "threshold exceeded"}) in ServerHandler::processSession), a WebSocket close frame is sent. There is a race between:

1. The server sending the close frame
2. The test's main thread calling invoke() → write_some() on the next loop iteration

If write_some() executes before the async read handler (on_read_msg) processes the close frame, Beast's internal check_stop_now() throws Operation canceled [system:125]. Since invoke() has no exception handling around the write, this propagates as an unhandled exception.

The fix replaces the throwing write_some overload with the error_code overload. On write failure, invoke() returns {} (empty Json::Value) — the same return value it already produces when findMsg() times out. The RPCOverload test already handles this correctly: if (jv.isNull()) { booted = true; }.

Observed in CI job rhel-10-clang-any-amd64-release (PR #6619 merge queue run, 2026-03-25):

#19 failed: unhandled exception: Operation canceled [system:125 at
boost/beast/websocket/impl/stream_impl.hpp:355:68 in function
'bool boost::beast::websocket::stream::impl_type::check_stop_now(error_code &)']
failed: xrpl.rpc.RPCOverload had 1 failures.

API Impact

None — this change is limited to test infrastructure (src/test/jtx/impl/WSClient.cpp).

[xrplf-ai-reviewer]

No issues.

Review by Claude Opus 4.6 · Prompt: V12

[xrplf-ai-reviewer]

No issues.

Review by Claude Opus 4.6 · Prompt: V12

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.4%. Comparing base (2c765f6) to head (6884543).
⚠️ Report is 37 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #6671     +/-   ##
=========================================
- Coverage     81.4%   81.4%   -0.0%     
=========================================
  Files          998     998             
  Lines        74443   74443             
  Branches      7563    7562      -1     
=========================================
- Hits         60632   60624      -8     
- Misses       13811   13819      +8     

see 4 files with indirect coverage changes

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[kuznetsss]

👍

[Copilot]

Pull request overview

Fixes an intermittent unit test failure in the WebSocket-based test client (WSClientImpl) by preventing an exception from escaping when the server has already initiated WebSocket close (e.g., booting an overloaded client).

Changes:

• Switch WSClientImpl::invoke() from the throwing ws_.write_some() overload to the error_code overload.
• On write failure, return an empty Json::Value (null) to match existing “no response” behavior (e.g., findMsg() timeout), allowing the RPCOverload test to treat it as “booted”.

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