ethernet-padding

[daniel-noland]

Restores the transport-checksum fix that reached main on 2026-08-29 and was undone on
2026-09-01, and pins the behaviour with properties that cover the only way the fabric actually meets ethernet padding: inside a VXLAN tunnel.

[codecov]

Codecov Report

❌ Patch coverage is 96.62447% with 8 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
net/src/packet/mod.rs	96.44%	4 Missing and 4 partials ⚠️

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Essentials

Run ID: 84f5c113-022c-48c5-bdf2-9bd8bf26821a

📥 Commits

Reviewing files that changed from the base of the PR and between 9ab6f3b and bb5cd4c.

📒 Files selected for processing (2)

• net/src/headers/mod.rs
• net/src/packet/mod.rs

Included review availability: 4 reviews are currently available. Your included PR review attempts over the past 7 days set your current allowance at 5 reviews per hour.

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📝 Walkthrough

Walkthrough

Changes

Transport payload checksum bounds

Layer / File(s)	Summary
Transport payload length derivation net/src/headers/mod.rs	Headers::transport_payload_len derives the remaining transport payload length from IPv4 or IPv6 headers and returns None for unavailable or invalid lengths.
Checksum update and padding coverage net/src/packet/mod.rs	Packet::update_checksums limits checksum input to valid transport payload data and falls back to the full payload when needed. Tests cover padding, trailing octets, truncation, and inner VXLAN TCP packets.

Merge Risk: ⚪ Minimal · up to bb5cd

This change restores transport-checksum behavior for Ethernet padding inside VXLAN tunnels and adds properties for that behavior; no actionable merge-blocking risk remains based on the supplied evidence.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 56.52% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 23 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title identifies Ethernet padding, which is the primary scenario addressed by the checksum fix. It is concise and related to the changeset.
Description check	✅ Passed	The description accurately explains the restored transport-checksum fix and the added VXLAN padding properties.

• Fix all pre-merge checks with AI

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[mvachhar]

Please fix teh commit message to mention that this got undone by a rebased PR so we are just redoing it. Probably should refer to the original commits that got merged.

[Copilot]

🟢 Approval recommended

The checksum bounding change is localized and well-covered by new regression/property tests, with only a minor unused-import nit noted.

Pull request overview

This PR restores checksum calculation behavior by ensuring transport checksums are computed only over the IP-declared transport payload length (excluding trailing bytes such as Ethernet padding), and adds tests to lock in the expected behavior—especially for inner frames carried within VXLAN where padding is observed in practice.

Changes:

• Bound Packet::update_checksums() to the computed transport payload length before recalculating checksums.
• Added Headers::transport_payload_len() helper to derive the payload length from IP payload length minus extension + transport header sizes.
• Added targeted and property-based tests covering Ethernet padding/trailing octets, including VXLAN inner frames.

File summaries

File	Description
net/src/packet/mod.rs	Truncates checksum input to the transport payload length and adds padding/trailing-octet regression/property tests (including VXLAN inner frames).
net/src/headers/mod.rs	Introduces a helper to compute transport payload length from parsed header lengths to support bounded checksum updates.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite

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