Max/lwd stream patch by mfahampshire · Pull Request #7098 · nymtech/nym

mfahampshire · 2026-08-26T11:22:23Z

Implementing a few tweaks in line with conversation in https://forum.zcashcommunity.com/t/lwd-mixnet-proxy-light-wallet-grpc-over-the-nym-mixnet-and-what-three-days-of-measuring-it-found/57000/32

This change is

Summary by CodeRabbit

Bug Fixes
- Improved stream reliability by distinguishing temporary lost frames from closed connections, allowing recoverable connection attempts to continue.
- Stream data-loss events are now reported clearly, while subsequent messages can continue flowing where possible.
- Added clearer errors when a recipient cannot be reached through the current network topology.
- Improved bridge handling so transient failures are retried and fatal disconnections are reported consistently.
Documentation
- Clarified stream failure behavior, buffering limits, and connection-opening errors.

…utable

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vercel · 2026-08-26T11:22:30Z

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coderabbitai · 2026-08-26T11:23:46Z

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📝 Walkthrough

Walkthrough

The SDK now reports unroutable recipients and reorder-buffer data loss. Stream receivers carry failures, while MixnetStream exposes and persists them through I/O methods. IPR handling ignores lost frames, and the bridge returns fatal disconnect errors.

Changes

Stream reliability and routing

Layer / File(s)	Summary
Failure contracts and routing `sdk/rust/nym-sdk/src/error.rs`, `sdk/rust/nym-sdk/src/mixnet/stream/mod.rs`, `sdk/rust/nym-sdk/src/mixnet/native_client.rs`, `sdk/rust/nym-sdk/src/mixnet/stream/ARCHITECTURE.md`	The SDK adds `Error::UnroutableRecipient`. Stream channels now carry `Result<Vec<u8>, StreamFailure>`. `open_stream` validates recipient topology. Documentation describes the 8 MiB reorder-buffer behavior.
Reorder-buffer loss signaling `sdk/rust/nym-sdk/src/mixnet/stream/mod.rs`	The reorder buffer tracks payload bytes and emits `StreamFailure::DataLoss` when it skips a missing range. Tests cover overflow and late gap filling.
Stream I/O failure persistence `sdk/rust/nym-sdk/src/mixnet/stream/mixnet_stream.rs`	`MixnetStream` returns I/O results from `recv`, persists read failures, and rejects later reads and writes after persistent failure.
Bridge disconnect handling `sdk/rust/nym-sdk/src/ipr_wrapper/ip_mix_stream.rs`, `smolmix/core/src/bridge.rs`	IPR connection handling ignores lost frames but reports stream closure. The bridge records fatal channel and SDK disconnect errors before returning them.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: ⚪ Minimal · up to ee075

The change is merge-ready after normal checks and review; no actionable merge-blocking risk remains. A minor documentation follow-up is recommended to keep the reorder-buffer limits consistent.

Sequence Diagram(s)

sequenceDiagram
  participant ReorderBuffer
  participant MixnetStream
  participant StreamConsumer
  ReorderBuffer->>MixnetStream: send Result<Vec<u8>, StreamFailure>
  MixnetStream->>StreamConsumer: recv returns I/O result
  MixnetStream->>MixnetStream: persist poll_read failure
  MixnetStream->>StreamConsumer: reject later reads and writes

Suggested reviewers: simonwicky

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Title check	❓ Inconclusive	The title indicates a stream-related patch, but it is vague. It does not identify the main changes, such as stream data-loss reporting, reorder-buffer updates, or unroutable-recipient handling.	Replace the title with a concise description of the primary change, such as "Report mixnet stream data loss and unroutable recipients".

✅ Passed checks (4 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 87.50% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 24 functions across 6 files. (1 skipped: 1 …
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.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

Full details: Docstring Coverage

Explanation

Docstring coverage is 87.50% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 24 functions across 6 files. (1 skipped: 1 unsupported.)

✨ Finishing Touches 💡 1

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Actionable comments posted: 1

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Inline comments:
In `@sdk/rust/nym-sdk/src/mixnet/stream/ARCHITECTURE.md`:
- Around line 116-122: Update the earlier wire-protocol section describing
MAX_REORDER_BUFFER so it instead references MAX_REORDER_BUFFER_BYTES and
accurately states the 8 MiB per-stream byte limit, keeping the surrounding
reorder-buffer behavior unchanged.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: db91ebea-88dc-4778-8810-d8d87470e76c

📥 Commits

Reviewing files that changed from the base of the PR and between d8951ac and ee07554.

📒 Files selected for processing (7)

sdk/rust/nym-sdk/src/error.rs
sdk/rust/nym-sdk/src/ipr_wrapper/ip_mix_stream.rs
sdk/rust/nym-sdk/src/mixnet/native_client.rs
sdk/rust/nym-sdk/src/mixnet/stream/ARCHITECTURE.md
sdk/rust/nym-sdk/src/mixnet/stream/mixnet_stream.rs
sdk/rust/nym-sdk/src/mixnet/stream/mod.rs
smolmix/core/src/bridge.rs

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mfahampshire added 3 commits August 26, 2026 09:09

fix: fail open_stream at dial time when the recipient gateway is unro…

87857e0

…utable

fix: report stream reorder-buffer data loss in-band and cap the buffe…

6e353c8

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fix: stop smolmix bridge on terminal mixnet receive errors

ee07554

mfahampshire marked this pull request as draft August 26, 2026 11:22

mfahampshire added this to the Essaouria - (mainnet release 15th sept) milestone Aug 26, 2026

coderabbitai Bot reviewed Aug 26, 2026

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Comment thread sdk/rust/nym-sdk/src/mixnet/stream/ARCHITECTURE.md Outdated

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feat(sdk): add stream establishment acknowledgement

ca1ce53

mfahampshire force-pushed the max/lwd-stream-patch branch from f5e46b7 to ca1ce53 Compare September 2, 2026 08:21

vercel Bot deployed to Preview – nym-explorer-v2 September 2, 2026 08:24 View deployment

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refactor(smolmix): unblock bridge loop during receive-error backoff

b31cd94

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vercel Bot deployed to Preview – docs-nextra September 2, 2026 08:47 View deployment

refactor: address establishment-ack review nits

362e736

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Max/lwd stream patch - #7098

Max/lwd stream patch#7098
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