[DNM] feat(da): support fiber (not via c-node)

[julienrbrt]

Overview

Support Fiber client (based on https://github.com/celestiaorg/celestia-app/blob/63fbf31cca216fc4e067a9e1b3a3431115c7009b/fibre), but not via celestia node or apex for this PoC
celestiaorg/celestia-node#4892

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The latest Buf updates on your PR. Results from workflow CI / buf-check (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	⏩ skipped	✅ passed	✅ passed	May 12, 2026, 1:40 PM

[claude]

Claude finished @julienrbrt's task in 4m 58s —— View job

---

Code Review: [DNM] feat(da): support fiber (not via c-node)

• Read AGENTS.md and repo guidelines
• Review core Fiber DA client (block/internal/da/fiber_client.go)
• Review Fiber mock (block/internal/da/fibremock/mock.go)
• Review Fiber types (block/internal/da/fiber/types.go)
• Review submitting subsystem changes
• Review syncing subsystem changes
• Review config changes (pkg/config/config.go)
• Review block/public.go changes
• Review tools/celestia-node-fiber/ new package
• Review test coverage and quality
• Compile overall review findings

---

This is a substantial PoC introducing a Fiber (Fibre) DA backend alongside significant architectural changes (removing P2P sync, combining header+data blobs, new custom binary encoding). The DIVERGENCE.md does a good job documenting intentional deviations from main. Below are issues found, ordered by severity.

---

🔴 Critical Issues

1. Submit drops its ctx — passes context.Background() to Upload (Fix this →)

fiber_client.go:102:

result, err := c.fiber.Upload(context.Background(), nsID, flat)  // BUG

The method signature accepts ctx context.Context but ignores it for the upload, so cancellations and deadlines from callers are never propagated. Consequently the error-handling branches on lines 115–118 (errors.Is(err, context.Canceled) / context.DeadlineExceeded) can never trigger — they are dead code. Fix: pass ctx directly.

2. FiberDAConfig.Validate() is never called from Config.Validate()

pkg/config/config.go:536-618 — Config.Validate() calls c.Raft.Validate() and c.Pruning.Validate(...) but not c.DA.Fiber.Validate(). A misconfigured Fiber setup (empty ConsensusAddress, wrong BridgeAddress scheme, etc.) will pass ParseConfig silently and only fail at runtime, with a cryptic dial error instead of a clear message. Fix: add c.DA.Fiber.Validate() to Config.Validate(). Fix this →

3. fibremock.MockDA: subscriber removal can close wrong channel, panicking on next Upload

block/internal/da/fibremock/mock.go:224-237 — The swap-with-last cleanup pattern is unsafe when multiple subscriber cleanup goroutines run concurrently:

• Subscriber A (idx=0) is cancelled first; its goroutine swaps subscribers[0] with subscribers[2] (C), shrinking to [C, B]. C's entry is now at index 0.
• C's cleanup goroutine then runs with its captured idx=2. Since 2 > last(1), no swap occurs, and the slice is truncated to [C]. C's goroutine then closes C's channel.
• But C's entry is still at index 0 in the subscribers slice. A future Upload call sends to C's now-closed channel — panics (send on closed channel).

The default: branch in the upload loop handles a full buffer, not a closed channel. Fix: use a different approach for subscriber tracking (e.g., keyed map with a unique ID, or mark-and-sweep) rather than index-based swap removal.

---

🟠 Moderate Issues

4. NewFiberDAClient panics instead of returning an error (block/public.go:103)

base, err := da.NewFiberClient(da.FiberConfig{...})
if err != nil {
    panic(err)  // ← library-facing function should not panic
}

The upstream check in run_node.go:157-159 guards the nil-client case, but NewFiberDAClient is a public API and panicking in a library breaks any caller that doesn't pre-validate. Return the error instead and let callers decide.

5. SetMaxBlobSize races against concurrent readers

block/public.go:26-28:

func SetMaxBlobSize(n uint64) {
    common.DefaultMaxBlobSize = n  // unguarded write to global
}

DefaultMaxBlobSize is read on hot paths by the DA submitter and executor. Even "one-shot startup wiring" (before goroutines are launched) isn't guaranteed to be safe without a memory barrier. Use sync/atomic or, better, thread the value through BlockOptions.

6. Submit height is always 0 — DA inclusion tracking is broken for Fiber

fiber_client.go:142, 149: The submission result always returns Height: 0 /* TODO */. The cache manager uses SetHeaderDAIncluded(hash, daHeight, ...) where daHeight comes from res.Height. All Fiber-submitted blocks will be recorded with DA height 0, which will confuse the syncer when trying to replay or verify inclusion. This is likely the most impactful correctness gap short of being a PoC.

7. KeyringPath not exposed as a CLI flag

FiberDAConfig.KeyringPath is in the struct and documented, but there is no FlagDAFiberKeyringPath constant and it is never registered in AddFlags. It can only be set via the YAML config file, not on the command line — an operational footgun.

8. defaultMaxBlobSizeStr overrides the default for all backends

block/internal/common/consts.go:29: The default is now 128 MiB - 5 bytes (Fibre's limit). The HACK comment is clear that this will silently break non-Fiber nodes. This global cap should not ship to main in this form; the per-backend cap needs to be resolved before merging.

---

🟡 Minor / Polish Issues

9. Typo: heigth variable (fiber_client.go:370)

heigth, err := c.fiber.Head(headCtx)  // "heigth" → "height"

Non-breaking but should be fixed. Fix this →

10. DIVERGENCE.md names the wrong branch (block/DIVERGENCE.md:1)

The header says perf/block-optimization but the branch is julien/fiber. Fix this →

11. GetProofs always errors; Validate always succeeds

fiber_client.go:378-397 — GetProofs returns fmt.Errorf("not implemented") rather than nil, nil. Some callers may not handle the non-nil error defensively. The Validate stub also silently returns all-true, which could mask a real integrity gap if the interface is ever called in a real verification flow. Both should have a clear // PoC: not implemented comment or, preferably, return an error that callers can test with errors.Is.

12. Listen adapter does a Download per blob event to populate DataSize

tools/celestia-node-fiber/listen.go:108-143 — DataSize is only set by the download; the comment acknowledges the per-blob FSP round-trip. In the current fiber_client.go, BlobEvent.DataSize is never actually consumed (it's only used in mock assertions). Consider setting it to 0 and removing the extra download until DataSize has a real consumer, or track it as a known latency concern with a TODO.

13. Subscribe goroutine fails silently on Listen error

fiber_client.go:320-321: If c.fiber.Listen fails after Subscribe has already returned the channel, the goroutine logs and exits, closing the channel. Callers that don't tolerate an immediately-closed channel could silently miss all DA events without a clear error path. Consider returning the error through a side channel or adopting a retry policy.

14. splitBlobs does not bound the allocation from count (fiber_client.go:434-436)

count := int(binary.BigEndian.Uint32(data))
blobs := make([][]byte, 0, count)  // count can be up to 4 billion

While this data is produced by the node itself, any external blob (e.g. from a buggy encoder, or in a future scenario where untrusted blobs are retrieved) can trigger a massive allocation. Cap count against len(data)/4 as a sanity check.

15. fiberSubscribeChanSize = 42 — magic number

fiber_client.go:309 — The comment-free constant 42 is the channel buffer size for subscription events. Should be named and commented to explain why 42 is appropriate here.

---

✅ Positive Notes

• DIVERGENCE.md is excellent — clearly documents all breaking protocol changes with rationale.
• fiber/types.go package doc is thorough: design assumptions, confirmation semantics, and interface contract are all explained.
• flattenBlobs/splitBlobs encoding is clean and well-tested; the magic byte check in UnmarshalBlockBlob helps identify corrupt blobs early.
• fibremock.MockDA is thoughtfully designed with replay support, configurable retention, and LRU eviction. The concurrency issue above is the only structural concern.
• chunkBlobsForFibre correctly accounts for flattenBlobs overhead in its budget math.
• da_follower.go inline fast-path (processing blobs from the subscription event instead of re-fetching) is a nice optimization.
• The adapter's fromModules constructor pattern makes testing clean.

[codecov]

Codecov Report

❌ Patch coverage is 90.65657% with 37 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.16%. Comparing base (2865d6d) to head (4485d91).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
block/public.go	0.00%	12 Missing ⚠️
block/internal/da/fibremock/mock.go	90.90%	5 Missing and 5 partials ⚠️
block/internal/da/fiber_client.go	96.74%	5 Missing and 3 partials ⚠️
pkg/sequencers/solo/sequencer.go	61.53%	5 Missing ⚠️
pkg/config/config.go	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3244      +/-   ##
==========================================
+ Coverage   62.33%   63.16%   +0.82%     
==========================================
  Files         122      124       +2     
  Lines       12873    13258     +385     
==========================================
+ Hits         8024     8374     +350     
- Misses       3968     3995      +27     
- Partials      881      889       +8     

Flag	Coverage Δ
combined	63.16% <90.65%> (+0.82%)	⬆️

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