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fix(interfaces): only queue one disconnect marker per connection - #4011
HttpClientInterface#disconnect (Ruby and Python) empties response_queue and then queues a nil marker so a blocked read_interface returns. connect never cleared that queue, so a marker nobody read carried over into the next connection.
That happens on every write error with auto-reconnect enabled:
The request raises, so Interface write error handling calls disconnect, which queues marker GitHub actions #1.
After the reconnect, the first read_interface returns marker Removing a target should remove it from Limits Monitor #2, which triggers another connection loss and another marker. The interface never stops cycling between disconnect and reconnect.
The fix empties response_queue at the start of connect. This is safe because connect and read run on the same microservice thread, so nothing is waiting on the queue at that point.
Test plan
New Ruby spec and Python test (disconnect, consume marker, disconnect again, reconnect, queue is empty). Both fail without the fix.
HttpClientInterface.disconnect queues a nil marker to unblock read_interface,
and a write error disconnects twice (Interface write handler, then the
microservice), leaving an unconsumed marker. On auto-reconnect the first read
returned it, so the interface looped through disconnect/reconnect forever.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.56%. Comparing base (d2ed704) to head (6a2a46d). ⚠️ Report is 95 commits behind head on main.
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Yes, that's the root cause. Fixed in bff50c9 along the lines you suggested. disconnect now records was_connected = !@http.nil? and only clears the queue and pushes the nil marker when it was connected. The microservice calls disconnect again after read_interface returns nil, and that second call is now a no-op. It no longer leaves a marker nothing consumes. It also can't clear away a marker the reader hasn't consumed yet.
I kept the @response_queue.clear in connect as a backstop and updated its comment. It also discards a response to a request that completed after the disconnect, so that response isn't read as part of the new connection.
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Same fix in Python (bff50c9). disconnect only drains the queue and puts (None, None) when self.http was set. The drain in connect stays as a backstop for late responses. The tests now follow the real sequence: disconnect, read_interface consumes the marker, then disconnect again. They check that the queue stays empty and that a repeated disconnect doesn't drop an unconsumed marker. These tests fail on the old code.
disconnect is called again once read_interface returns nil, and each call
queued another marker that nothing consumed, so the next connection was
immediately disconnected. HTTP client, File and Python MQTT now queue the
marker only when actually connected and clear stale entries on connect.
Ruby MQTT is unaffected since each connect creates a new client queue.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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Walkthrough
The Ruby and Python file and HTTP client interfaces clear queued entries on connect and add disconnect markers only when connected. The Python MQTT interface also clears its queue on connect and adds a marker only when a client exists. Tests cover repeated disconnects and reconnect queue cleanup.
Changes: Interface queue lifecycle
Layer / File(s)
Summary
Connection and disconnection queue handling openc3/lib/openc3/interfaces/file_interface.rb, openc3/lib/openc3/interfaces/http_client_interface.rb, openc3/python/openc3/interfaces/file_interface.py, openc3/python/openc3/interfaces/http_client_interface.py, openc3/python/openc3/interfaces/mqtt_interface.py
File and HTTP client interfaces clear queued entries on connect and add disconnect markers only when connected. The MQTT interface drains its queue on connect, adds a marker only when a client exists, and stops the network loop on disconnect.
Tests verify that repeated disconnects do not add extra markers and that reconnecting clears queued entries. MQTT tests also check that disconnect stops the client network loop.
Reconnect can still misassociate an HTTP response with a later command, and the MQTT callback cleanup ordering remains insufficiently verified; resolve both lifecycle risks before merging.
Security architecture risk: Moderate · up to bff50
Normal disconnect and reconnect recovery is improved. A timing-dependent MQTT concern remains: reconnect cleanup may separate topic identity from its payload, potentially attributing telemetry to the wrong configured packet. No new network endpoint or authentication bypass was identified, and this conditional failure has not been reproduced.
Retained concerns
Medium · security · inferred: MQTT reconnect cleanup does not atomically preserve topic/payload ownership. If an old callback appends a topic after read_topics is reset and its payload is then drained, that topic remains available to identify a later payload as the wrong configured telemetry packet. The new drain introduces this additional interleaving atop pre-existing stale-queue problems. This is conditional on callback overlap across disconnect; dependency-level quiescence was not established.
Security review details
Security Blast Radius
inferred — The conditional MQTT integrity impact is bounded to packet mappings subscribed by the affected interface instance. Misidentified non-stored packets can reach the current-value update path under their assigned identity. Stream publication still checks whether that target is enabled. Cross-tenant or cross-environment exposure was not established.
Security Findings and Attack Paths
inferred — A publisher able to supply messages on a subscribed topic could influence telemetry under another configured topic identity if reconnect overlaps an old callback and the drain removes its payload but retains its topic. This requires the callback timing condition and compatible packet processing; no exploit or authentication bypass was verified. The additional payload-removal window is PR-specific, while broader stale-generation exposure predates this change.
Trust Boundaries and Controls
observed — The MQTT lifecycle diff leaves configured TLS, credentials, and topic subscriptions unchanged. These existing controls do not establish callback quiescence or preserve the positional association between topic identity and payload during cleanup. External broker authorization policy was not supplied.
Resilience and Maintainability Implications
observed — The normal Python owner runs connect and read on its run thread, serializes lifecycle operations, invokes disconnect after partial-connect failure, and prevents reconnect during shutdown. This is strong counterevidence against an ordinary reader-versus-connect race, but its mutex does not encompass MQTT on_message callbacks.
Hardening Proposals
proposed — Keep topic and payload together in a session-scoped queue entry, and either fence callbacks by connection generation or establish callback quiescence before resetting state. Validate the chosen invariant with a deterministic callback-versus-reconnect interleaving.
Pre-merge checks: 5
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Title check
The title clearly and concisely describes the main change: limiting disconnect markers to one per connection across the affected interfaces.
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Docstring coverage is inconclusive: files from earlier reviews still need to be rechecked within the check's analysis limits. Not blocking.
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Check skipped because no linked issues were found for this pull request.
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Check skipped because no linked issues were found for this pull request.
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ryanmelt
changed the title
fix(interfaces): clear stale disconnect markers on http client connect
fix(interfaces): only queue one disconnect marker per connection
Oct 26, 2026
On the review question about MQTT and FileInterface having the same bug: they did, mostly. Fixed in bff50c9:
FileInterface (Ruby and Python):disconnect always queued a nil marker on a queue that outlives the connection. It now queues one only when connected, and connect clears stale entries. Clearing is safe because queue entries only wake read_interface, which finds files by listing the folder.
MqttInterface (Python): same bug, and worse. connect called self.pkt_queue.empty(), which only checks whether the queue is empty, so nothing was ever cleared. connect now really drains the queue, and disconnect only queues the marker when there is a client.
MqttInterface (Ruby): not affected. Each connect creates a new MQTT::Client with its own read queue, so a stale marker stays in the old client's queue.
Added tests for File in both languages and for Python MQTT. They fail without the fix. I retitled the PR since it now covers more than the HTTP client.
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Actionable comments posted: 2
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Inline comments:
Review comments at @openc3/lib/openc3/interfaces/http_client_interface.rb:
- Line 56: Track a connection generation in both the Ruby and Python HTTP client
implementations: capture it when each request starts, and enqueue its response
only if the generation still matches after the request completes. Advance the
generation when the connection changes so responses from an earlier connection
cannot enter the queue cleared during reconnect or be returned by
read_interface.
Review comments at @openc3/python/openc3/interfaces/mqtt_interface.py:
- Around line 69-70: Update the disconnect cleanup in the method containing the
shown packet-queue drain to stop the previous Paho network loop and wait for its
callback thread to finish before connect resets read_topics or drains pkt_queue;
keep the existing disconnect and cleanup behavior.
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Wait for the paho loop thread in disconnect so a late on_message can't
race the next connect's reset of read_topics and pkt_queue, which would
misalign topics and payloads. Clarify that the http client connect only
discards responses already queued; in-flight responses are still read.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Summary
HttpClientInterface#disconnect(Ruby and Python) emptiesresponse_queueand then queues anilmarker so a blockedread_interfacereturns.connectnever cleared that queue, so a marker nobody read carried over into the next connection.That happens on every write error with auto-reconnect enabled:
Interfacewrite error handling callsdisconnect, which queues marker GitHub actions #1.readreturns nil, andInterfaceMicroservice#handle_connection_lostcallsinterface.disconnectagain (the state is stillCONNECTED). That queues marker Removing a target should remove it from Limits Monitor #2, and nothing reads it.read_interfacereturns marker Removing a target should remove it from Limits Monitor #2, which triggers another connection loss and another marker. The interface never stops cycling between disconnect and reconnect.The fix empties
response_queueat the start ofconnect. This is safe becauseconnectandreadrun on the same microservice thread, so nothing is waiting on the queue at that point.Test plan
bundle exec rspec spec/interfaces/http_client_interface_spec.rb: 23 examples, 0 failuresuv run pytest test/interfaces/test_http_client_interface.py: 11 passedruff check/ruff format --checkclean🤖 Generated with Claude Code
Summary by CodeRabbit