[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 3, 2026, 8:53 AM

[claude]

Claude finished @julienrbrt's task in 3m 40s —— View job

---

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

• Gather context (AGENTS.md, repo structure)
• Review fiber client implementation (block/internal/da/fiber_client.go)
• Review DA submitter changes (block/internal/submitting/da_submitter.go)
• Review config changes (pkg/config/config.go)
• Review cache/pending_base changes
• Review public API changes (block/public.go)
• Review tools/celestia-node-fiber package
• Review concurrency, error handling, and security
• Post comprehensive review

---

Summary

This is a substantial PoC introducing Fiber (Fibre) as a direct DA backend, bypassing celestia-node/apex. The architecture is sound — a clean fiber.DA interface, an in-memory mock for tests, and a tools/celestia-node-fiber adapter that wraps the actual celestia-node API. The overall structure is well-thought-out, testing coverage is reasonable, and the in-flight claim/gap system in pendingBase is impressively robust. The comments are thorough.

Several issues need attention before promotion beyond PoC, from a potential production panic down to typos.

---

🔴 Critical Issues

1. context.Background() discards the caller's context in Submit
block/internal/da/fiber_client.go:102

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

The ctx parameter passed to Submit is completely ignored for the upload call. If the caller passes a deadline-bearing or cancel-bearing context, the upload will continue running after the caller has given up, wasting resources and potentially causing ghost uploads. The parameter should be used directly (or wrapped with c.defaultTimeout if that protection is needed):

result, err := c.fiber.Upload(ctx, nsID, flat)

Fix this →

---

2. DefaultMaxBlobSize globally changed to Fiber's cap — breaks non-Fiber users
block/internal/common/consts.go:29
The default is now 134217723 (128 MiB − 5), which is Fibre's cap. The HACK comment is honest, but the consequence is that any non-Fiber node using this binary would submit blobs up to 128 MiB against a Celestia bridge that enforces a ~2 MiB per-blob cap, causing immediate and confusing failures. This needs to either:

• Restore the old default and require callers to block.SetMaxBlobSize() when enabling Fiber, or
• Gate DefaultMaxBlobSize on config.DA.IsFiberEnabled() at startup (in ApplyFiberDefaults).

The comment itself says "non-fiber callers should override via ldflag or local config" — that's not a safe assumption for a library.

---

3. Config.Validate() never calls FiberDAConfig.Validate()
pkg/config/config.go:562
FiberDAConfig.Validate() is a well-written validator, but it is never invoked from Config.Validate(). A user who sets fiber.enabled=true but omits consensus_address or bridge_address will get a confusing nil-pointer or connection error at runtime, not a clean validation error. Add to Config.Validate():

if err := c.DA.Fiber.Validate(); err != nil {
    return fmt.Errorf("fiber DA config: %w", err)
}

Fix this →

---

4. Subscriber removal index bug in MockDA.Listen
block/internal/da/fibremock/mock.go:224
The cleanup goroutine uses a swap-with-last pattern but captures a stale idx. When a subscriber is removed, the subscriber previously at last is moved to idx. The goroutine for that moved subscriber still holds its original (now wrong) index. Subsequent cleanup will swap or truncate the wrong slot, leaving live subscribers silently dropped or zombie subscribers retained.

Example: 3 subscribers [A(0), B(1), C(2)]. A cancels → C moves to 0, but C's goroutine still has idx=2. C cancels: last=1, 2<=1 is false, so slice is truncated to [:1] — B is lost and C is retained.

A safe implementation stores the subscriber in a map keyed by a unique ID, or uses sync.Map.

Also: m.subscribers = m.subscribers[:last] panics when len(m.subscribers) == 0 since last = -1. Fix this →

---

🟠 High Priority Issues

5. Namespace slice panics on short namespaces
block/internal/da/fiber_client.go:95, also lines 202, 321

nsID := namespace[len(namespace)-10:]

This panics if namespace is fewer than 10 bytes. While the Celestia namespace specification guarantees a 29-byte namespace, no bounds check protects against misconfiguration. Add a guard:

if len(namespace) < 10 {
    return datypes.ResultSubmit{BaseResult: datypes.BaseResult{Code: datypes.StatusError, Message: "namespace too short"}}
}

Fix this →

---

6. NewFiberDAClient panics instead of returning an error
block/public.go:101

base, err := da.NewFiberClient(da.FiberConfig{...})
if err != nil {
    panic(err)
}

NewFiberClient only errors when cfg.Client == nil, which callers already guard against, but panicking in a library constructor is unacceptable. The function signature should propagate the error:

func NewFiberDAClient(...) (FullDAClient, error)

Fix this →

---

7. Dangling comment for non-existent field in FiberDAConfig
pkg/config/config.go:306

// UploadConcurrency limits the number of concurrent upload connections

This comment appears after KeyName but there is no UploadConcurrency field. The struct closes after this comment. Either add the field or remove the comment.

---

🟡 Medium Priority Issues

8. height is always 0 in Submit result — breaks DA tracking
block/internal/da/fiber_client.go:143-152

Height: 0, /* TODO */

The daSubmitter uses res.Height to call postSubmit(..., daHeight), which feeds cache.SetHeaderDAIncluded(hash, daHeight, ...). With daHeight = 0, the DA inclusion height is always wrong. The IsHeightDAIncluded checks in submitter.go will produce incorrect results. This isn't just cosmetic — it affects correctness of finality tracking for Fiber-backed nodes.

---

9. Subscribe has no retry on Listen failure
block/internal/da/fiber_client.go:311
When c.fiber.Listen returns an error, the goroutine closes out immediately with no backoff or retry. Any transient Fiber network hiccup will permanently kill the subscription, requiring the node to restart. Consider wrapping in an exponential-backoff retry loop, or at minimum log the error prominently and add a comment that the caller must detect channel closure and re-subscribe.

---

10. FiberDAConfig.KeyringPath not validated
pkg/config/config.go:311
KeyringPath is listed in the struct comment as required "for signing payment promises," but FiberDAConfig.Validate() does not check that it is non-empty. If left unset, the adapter will likely fail with an opaque keyring-not-found error. Add:

if c.KeyringPath == "" {
    return fmt.Errorf("%s is required when fiber DA is enabled", FlagDAFiberKeyName)
}

---

11. DefaultMaxBlobSize global mutated without synchronization
block/internal/common/consts.go:47 / block/public.go:26
SetMaxBlobSize(n) writes to DefaultMaxBlobSize with no mutex and is called from startup code. If any goroutine reads DefaultMaxBlobSize concurrently with a SetMaxBlobSize call (e.g., a batch-size check in the submitter goroutines), this is an unsynchronized write to a non-atomic. Use sync/atomic or call SetMaxBlobSize strictly before starting any goroutines.

---

12. Extra store instantiation in run_node.go
pkg/cmd/run_node.go:161

mainKV := store.NewEvNodeKVStore(datastore)
baseStore := store.New(mainKV)
// ... read latestState ...
// baseStore is then discarded

A throwaway store is created just to read latestState.DAHeight, then discarded. The node.NewNode call creates its own store from the same datastore. This is wasteful and potentially confusing. Consider passing latestDAHeight as a parameter, or using a leaner metadata read.

---

🔵 Low / Style Issues

13. Typo heigth in GetLatestDAHeight
block/internal/da/fiber_client.go:370

heigth, err := c.fiber.Head(headCtx)

Fix this →

14. GetProofs and Validate return stub errors / always-true results
block/internal/da/fiber_client.go:378-398
GetProofs returns fmt.Errorf("not implemented") and Validate returns all true. These are acceptable for a PoC, but should be marked with //nolint:errcheck or documented prominently so they don't silently satisfy interfaces in production wiring.

15. Dropped events in MockDA subscribers are silent
block/internal/da/fibremock/mock.go:132

default:
    // Channel full, drop event. Subscriber is too slow.

In tests, dropped events lead to flaky failures that are hard to debug. Consider incrementing a counter (DroppedEvents int64) on MockDA so tests can assert no events were dropped.

16. ApplyFiberDefaults docs suggest it should be called from Validate
pkg/config/config.go:355
The function comment says "Intended to be invoked once at runner startup, after parsing the usual config." The run_node.go never calls it — there is no code path that actually triggers it. Verify this is wired up somewhere or add a call in StartNode before constructing the DA client.

Actually checking run_node.go more carefully — ApplyFiberDefaults is indeed not called. The BatchingStrategy and BlockTime defaults won't be applied for Fiber users.

17. Security: unpinned Action in CI workflow
The GitHub Advanced Security scan flagged dorny/paths-filter@v3 — pin to a commit SHA to prevent supply chain attacks.

---

Positive Aspects

• The pendingBase in-flight claim/gap system is an elegant solution for concurrent DA submission with gap-recovery.
• The fiber.DA interface design is minimal and clean — Head/Upload/Download/Listen is the right surface.
• The chunkBlobsForFibre function correctly accounts for flattenBlobs framing overhead.
• The FiberDAConfig.Validate() with WebSocket scheme check is a nice touch.
• Parallel signing in signEnvelopesParallel is well-structured with proper goroutine lifecycle.
• Test coverage for fiberDAClient is thorough; the fault-injector pattern in the test file is reusable.

[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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