Fix CoAP ping response over unreliable transport

[svenschwermer]

As per RFC 7252, the CoAP ping (empty, confirmable message) must be responded to with a reset message.

Resolves #603

Summary by CodeRabbit

• Refactor
  • Simplified the messaging response process to ensure a more consistent and reliable experience. Responses are now handled uniformly, enhancing overall communication efficiency while maintaining robust error reporting.

[coderabbitai[bot]]

Walkthrough

The pull request simplifies the logic in the sendPong method of the Conn struct by removing conditional checks based on the incoming message type. The method now unconditionally sets the response message type to Reset and directly assigns the incoming message's ID to the response. Error handling for response setup remains unchanged.

Changes

File(s)	Summary of Changes
udp/client/conn.go	Removed conditional logic from the sendPong method. Now, the response message type is always set to Reset, and the message ID is copied directly from the incoming message.

Sequence Diagram(s)

sequenceDiagram
    participant Client
    participant Conn
    Client->>Conn: Send empty confirmable message (CoAP ping)
    Conn-->>Client: Respond with Reset (using incoming message ID)

Assessment against linked issues

Objective	Addressed	Explanation
Respond with Reset for empty confirmable messages [#603]	✅

Poem

I'm a hopper coding with glee,
Simplifying logic, oh so breezy!
No more twists in my ping reply,
Just a Reset wave as time drifts by.
Hop along with this streamlined code fly!
🐇✨

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📜 Recent review details

Configuration used: CodeRabbit UI Review profile: CHILL Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 71407dadc3b4066060ee1e32095311160b6d058c and e09631edf158b2013e944468992f282cf445b382.

📒 Files selected for processing (1)

• udp/client/conn.go (1 hunks)

🧰 Additional context used

🪛 golangci-lint (1.64.8)

udp/client/conn.go

651-651: File is not properly formatted

(gofumpt)

🔇 Additional comments (1)

udp/client/conn.go (1)

646-652: Improved RFC compliance for CoAP ping responses.

The changed code correctly implements RFC 7252 section 4.2 which states that a CoAP Ping (empty confirmable message) should be responded to with a Reset message. This change simplifies the previous conditional logic and ensures proper protocol compliance.

The response message type is now unconditionally set to Reset and the message ID is correctly preserved from the request, which is the appropriate behavior for ping responses in CoAP.

🧰 Tools

🪛 golangci-lint (1.64.8)

651-651: File is not properly formatted

(gofumpt)

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652-652: unnecessary trailing newline

(whitespace)

✨ Finishing Touches

• [ ] 📝 Generate Docstrings

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