Stop client process and clean up if client disconnects#4737
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Previously, when processing long running streaming requests, such as _find with a highly selective selector, when no rows are emitted for a while, the client could disconnect but the request process, and all the associated workers on remote nodes would continue running, consuming server resources. We already handle remote (RPC) process cleanup if the coordinator crashes, we just need a way to kill that coordinator if the connection is closed in the case when no data may be emitted for a long time. This is what the current commit accomplishes. It turns out there is no simple way to detect passive mode socket disconnects in current versions of Erlang/OTP. The socket at the kernel level may be closed (in close_wait state), however `inet:info/1` will continue reporting it as `connected`. The only ways to obtain an accurate connection state is to try to write, read, or query the TCP info state. Here we attempt to query the state with tcp_info. Unfortunately, not all versions of supported OTP platforms have this option, so it probably never became an officially supported inet socket option, so we use `raw` socket option for it. However, it turns out most of CouchDB supported platforms do have that option. The only platform this is not working currently is Windows. In that case, or future platform cases we default to the previous behavior, assuming the socket is still open. Co-Authored-By: Robert Newson <rnewson@apache.org>
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Draft version of the PR #4736 to test running the full CI.