prosgarz35 commented on PR #3198:
URL: https://github.com/apache/james-project/pull/3198#issuecomment-5806832789
### [IMAP] IDLE robustness: transport liveness checks and graceful
teardown on mid-IDLE LOGOUT
#### Context & Motivation
1. **Heartbeat ghost writes on dropped TCP connections**:
When a client terminates abruptly (TCP RST, connection drop, or
network disruption), the Netty channel becomes inactive immediately, but the
internal IMAP session state (`session.getState()`) may temporarily remain
`SELECTED`
until channel teardown finishes. During this window, the periodic
`IdleProcessor` heartbeat runnable continued waking up and attempting writes
into a closed channel, generating futile I/O work and relying on downstream
write failures
to stop.
2. **Resource retention on mid-IDLE LOGOUT**:
Certain scripts and non-conformant clients attempt to disconnect
mid-IDLE by directly sending `tag LOGOUT` instead of the RFC 2177 mandated
`DONE`. While `IdleProcessor` rejected this input with `BAD
INVALID_CONTINUATION`, the
underlying mailbox listener and session remained active and selected.
#### Changes
- **Added `ImapSession#isConnected()`**:
- Introduced a default method in `ImapSession` returning `true` for
100% backward compatibility with test fakes.
- Implemented in `NettyImapSession` via `channel.isActive()`.
- **Liveness guards in `IdleProcessor`**:
- Heartbeat scheduling loop checks `session.isConnected()` both before
sending the untagged heartbeat and before rescheduling itself. If disconnected,
it proactively unregisters the mailbox listener, pops the line handler, and
terminates immediately.
- Continuation handler checks `!session.isConnected()` to avoid futile
`BAD` responses when the remote peer is already disconnected.
- **Graceful session teardown on `LOGOUT`**:
- In `IdleProcessor`, if the continuation line indicates an intended
`LOGOUT`, `session.logout().subscribe()` is triggered to ensure immediate
mailbox deselection and resource release.
#### Impact & Safety
- **Zero API breakage**: Default interface method preserves binary and
source compatibility for external implementations and test harnesses.
- **Resource efficiency**: Eliminates useless background scheduling
cycles and prevents leaked mailbox listeners on abnormal disconnections.
- **Verification**: Passes `mvn test-compile -pl
:protocols-imap,:james-server-protocols-imap4` and Checkstyle with 0 violations.
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