snmp: fix async handling by bennyz · Pull Request #349 · jumpstarter-dev/jumpstarter-python

bennyz · 2025-03-15T15:06:57Z

Have the callback fire an event to avoid waiting too long

Summary by CodeRabbit

New Features
- Improved asynchronous processing of SNMP operations with streamlined callback handling for more responsive communications.
Refactor
- Reorganized SNMP command flow to provide clearer error notifications and a more efficient event management system.

coderabbitai · 2025-03-15T15:07:05Z

Walkthrough

The changes refactor the SNMPServer class in driver.py by modifying the _snmp_set method to leverage asynchronous operations. A new callback generator (_create_snmp_callback) is introduced to handle SNMP responses, and additional methods (_setup_event_loop and _run_snmp_dispatcher) are added to manage the asyncio event loop and the SNMP dispatcher. Enhanced error handling and modular design improve the overall SNMP command execution flow.

Changes

File	Change Summary
packages/jumpstarter-driver-snmp/…/driver.py	- Modified `_snmp_set` to incorporate asynchronous handling using `asyncio.Event` and enhanced error messages. - Added `_create_snmp_callback` to generate callbacks for processing SNMP responses. - Added `_setup_event_loop` and `_run_snmp_dispatcher` for better event loop and dispatcher management.

Sequence Diagram(s)

sequenceDiagram
    participant Client
    participant SNMPServer
    participant SNMPEngine
    Client->>SNMPServer: _snmp_set(state)
    SNMPServer->>SNMPServer: _setup_event_loop()
    SNMPServer->>SNMPServer: _create_snmp_callback(result, event)
    SNMPServer->>SNMPEngine: _run_snmp_dispatcher(event)
    SNMPEngine-->>SNMPServer: SNMP response arrives
    SNMPServer->>SNMPServer: Callback updates result and sets event
    SNMPServer-->>Client: Return SNMP operation result

Poem

I'm a rabbit with a bright code nose,
Hopping through loops where async magic flows.
SNMP calls now dance in a neat display,
With callbacks and dispatchers leading the way.
Carrots and cheers for a hop-tastic day!
🥕🐇

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Reviewing files that changed from the base of the PR and between 1c93766 and 9ac28bc.

📒 Files selected for processing (1)

packages/jumpstarter-driver-snmp/jumpstarter_driver_snmp/driver.py (5 hunks)

⏰ Context from checks skipped due to timeout of 90000ms (4)

GitHub Check: pytest-matrix (3.13)
GitHub Check: pytest-matrix (3.12)
GitHub Check: pytest-matrix (3.11)
GitHub Check: e2e

🔇 Additional comments (6)

packages/jumpstarter-driver-snmp/jumpstarter_driver_snmp/driver.py (6)

5-5: Import additions for new type annotations

Good addition of the necessary typing imports to support the new method signatures.

120-139: Well-structured callback generation with event signaling

The new _create_snmp_callback method is a good refactoring that encapsulates callback creation logic. It properly handles error conditions and, most importantly, signals the completion of the SNMP operation by setting the event, which is crucial for the async improvement.

The error handling is comprehensive, covering both indication errors and status errors with detailed logging.

141-149: Robust event loop setup with proper error handling

The _setup_event_loop method elegantly handles both scenarios - whether running within an existing event loop context or needing to create a new one. The returned boolean flag for tracking loop creation is important for proper cleanup later.

This addresses the situation mentioned in the past review comments about needing a new loop when not in an event loop context.

150-153: Improved dispatcher handling with async/await pattern

This new async method properly manages the SNMP dispatcher lifecycle, waiting for the response event rather than using a fixed timeout. This is more efficient and responsive, preventing the excessive waiting that was mentioned in the PR objective.

The implementation aligns with the library's recommended approach as discussed in the past review comments.

155-184: Comprehensive refactoring of SNMP command execution flow

The refactored _snmp_set method now properly integrates the asynchronous execution model with:

Structured initialization of result tracking and event signaling

Proper event loop management

Asynchronous dispatcher execution with timeout handling

Improved error reporting

The implementation properly waits for the SNMP response or times out after the configured duration, providing better responsiveness as intended by the PR.

192-193: Clean loop cleanup in finally block

Good practice to only close the loop if it was created by this method. This prevents issues that could occur if the method was called within an existing event loop context.

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netlify · 2025-03-15T15:07:14Z

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NickCao · 2025-03-15T15:13:00Z

+        except RuntimeError:
+            loop = asyncio.new_event_loop()


When would this happen?

each time as we are not in the context of an event loop

mangelajo · 2025-03-15T15:37:00Z


-            snmp_engine.open_dispatcher(self.timeout)
-            snmp_engine.close_dispatcher()
+            dispatcher_task = loop.create_task(self._run_snmp_dispatcher(snmp_engine, response_received))


I wonder if this dispatcher should be started before we send?

Is it used to receive the response?

I know it was like this before, but I wonder if it works just because it sets up very quickly before the response arrives?

Haven't checked the library docs though ...

def open_dispatcher(self, timeout: float = 0): """ Open the dispatcher used by SNMP engine. This method is called when SNMP engine is ready to process SNMP messages. It opens the dispatcher and starts processing incoming messages. """ if self.transport_dispatcher: self.transport_dispatcher.run_dispatcher(timeout)

In lib's docs they always call it last
https://github.com/lextudio/pysnmp/blob/8ddc451816c85d7ef238eb9cfdd5a74c114fae28/examples/v3arch/asyncio/manager/cmdgen/v2c-set.py#L12

ahh, the dispatcher sends the messages and collects answers, ok :)

mangelajo · 2025-03-15T15:37:22Z

Thanks for handling this!!! :-)

Have the callback fire an event to avoid waiting too long Signed-off-by: Benny Zlotnik <bzlotnik@redhat.com>

bennyz requested review from NickCao and mangelajo March 15, 2025 15:07

NickCao reviewed Mar 15, 2025

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mangelajo reviewed Mar 15, 2025

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snmp: fix async handling

9ac28bc

Have the callback fire an event to avoid waiting too long Signed-off-by: Benny Zlotnik <bzlotnik@redhat.com>

bennyz force-pushed the snmp-fix branch from 1c93766 to 9ac28bc Compare March 16, 2025 10:22

mangelajo approved these changes Mar 16, 2025

View reviewed changes

mangelajo enabled auto-merge March 16, 2025 17:38

Merge branch 'main' into snmp-fix

0edf18c

mangelajo merged commit 860deda into jumpstarter-dev:main Mar 16, 2025

bennyz deleted the snmp-fix branch March 16, 2025 18:32

mangelajo added this to the 0.6.0 milestone May 8, 2025

coderabbitai Bot mentioned this pull request Jan 16, 2026

Simplify SNMP driver #803

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