prosgarz35 commented on PR #3198:
URL: https://github.com/apache/james-project/pull/3198#issuecomment-5806292515
### Additional Hardening: Heartbeat Listener Teardown & Graceful Empty
Continuation
This update addresses two edge cases during client disconnection:
#### 1. Mailbox Listener Teardown on Heartbeat Failure
* **Problem**:
When a periodic heartbeat write fails due to an abnormal network drop
(`Broken pipe` / socket disconnect), the exception handler stopped further
scheduling via `idleActive.set(false)`. However, because the client was already
disconnected, it would never send `DONE`. Consequently, `pushLineHandler`
would never fire, and `sm.unregisterIdle()` was never invoked. This left the
mailbox listener actively registered in `SelectedMailbox`, continuing to listen
for and process incoming mailbox events in vain for a dead client until
garbage collection.
* **Fix**:
Added defensive `if (sm != null) sm.unregisterIdle();` directly inside
the heartbeat exception catch block.
* **Benefit**:
Provides immediate self-healing: if keepalive delivery fails, the
mailbox listener is released on the spot, halting unnecessary event processing
for disconnected sessions.
#### 2. Graceful EOF / Disconnect Handling on Continuation Input
* **Problem**:
When a client or intermediate reverse proxy abruptly resets/terminates
the TCP connection, Netty flushes an empty line (`""`) to the line handler.
Previously, James treated this empty line as an unrecognized command, logged an
`INFO` warning, and attempted to write a tagged `BAD` response to an
already half-closed/dead socket, generating unnecessary I/O warnings.
* **Fix**:
- Added an explicit check for `line.isEmpty()`, treating it as a
client disconnect rather than a protocol syntax error.
- Lowered invalid continuation log messages from `INFO` to `DEBUG` to
keep production logs clean from spurious warnings caused by unstable mobile
clients.
* **Benefit**:
Eliminates futile socket write attempts to dead connections and
prevents log pollution in high-concurrency production environments.
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