[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	Apr 27, 2026, 12:15 PM

[claude]

Claude finished @sysrex's task in 2m 55s —— View job

---

PR Review: feat(da): support fiber (not via c-node)

Tasks:

• Gather context (AGENTS.md, PR overview)
• Review block/internal/da/fiber_client.go
• Review block/internal/da/fiber/types.go
• Review block/internal/da/fibremock/mock.go
• Review block/public.go
• Review pkg/config/config.go and pkg/config/defaults.go
• Review pkg/cmd/run_node.go
• Review pkg/sequencers/solo/sequencer.go
• Review tools/celestia-node-fiber/ package
• Compile and post full review

---

Overview

This is a [DNM] PoC adding a Fiber DA backend directly (without going through celestia-node or apex). The architecture is clean — a thin fiber.DA interface, an in-memory mock, and a celestia-node adapter in tools/. The following covers the most important issues to address before this becomes production-ready.

---

Bugs

1. Submit ignores the caller's context — uses context.Background() instead

block/internal/da/fiber_client.go:92

result, err := c.fiber.Upload(context.Background(), namespace[len(namespace)-10:], flat)

If the caller cancels their context (e.g. on shutdown), the upload continues indefinitely. Should be ctx here.

Fix this →

---

2. Namespace slicing panics on short namespaces

block/internal/da/fiber_client.go:92 and :141

namespace[len(namespace)-10:]

If namespace has fewer than 10 bytes, this panics at runtime. There is no bounds check. Either validate namespace length in NewFiberClient or add a guard at the slice site.

Fix this →

---

3. GetLatestDAHeight panics instead of returning an error

block/internal/da/fiber_client.go:303-305

func (c *fiberDAClient) GetLatestDAHeight(context.Context) (uint64, error) {
    panic(fmt.Errorf("p2p should not be enabled"))
}

Panics in interface implementations are always wrong — they kill the whole process and bypass recover() in most callers. Return 0, fmt.Errorf("GetLatestDAHeight not supported for fiber backend") instead.

Fix this →

---

4. NewFiberDAClient in block/public.go panics on error

block/public.go:94

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

da.NewFiberClient only errors when cfg.Client == nil, and StartNode guards that path (line 157-159 in run_node.go), so in practice this won't fire. But a public constructor that panics is still a footgun. Change the signature to (FullDAClient, error) and let the caller handle the error.

Fix this →

---

5. MockDA subscriber index race on concurrent context cancellation

block/internal/da/fibremock/mock.go:196-233

The idx captured in the cleanup goroutine is the position at insertion time:

idx := len(m.subscribers)
m.subscribers = append(m.subscribers, subscriber{...})
// ...
go func() {
    <-ctx.Done()
    m.mu.Lock()
    last := len(m.subscribers) - 1
    if idx <= last {
        m.subscribers[idx] = m.subscribers[last]  // could remove wrong subscriber
    }
    m.subscribers = m.subscribers[:last]
    ...
}()

If a subscriber with a lower index is removed first (via the same swap-with-last pattern), the current subscriber's entry is now at a different index, but idx still holds the old one. The swap removes the wrong subscriber and leaks the channel or corrupts the list. This is benign for sequential tests but will break under concurrent subscribe/cancel patterns. Consider using a map keyed by an ID, or the sync/atomic pointer-to-list approach.

---

Design Issues

6. Height is always 0 after Submit — Retrieve is essentially broken

block/internal/da/fiber_client.go:115-124

Height: 0, /* TODO */

Because Submit returns Height: 0, any Retrieve(ctx, height, ns) call with a real height will never find blobs from Submit. This is why TestFiberClient_Retrieve_Success, TestFiberClient_Subscribe, and several others are t.Skip-ped. This is a known gap but it's worth tracking as a top-priority item — the Retrieve path is central to full-node sync.

---

7. P2P broadcast is silently disabled when Fiber is enabled — undocumented constraint

block/internal/executing/executor.go:631

if !e.config.DA.IsFiberEnabled() {
    // Broadcast header and data to P2P network

This is a significant architectural decision: Fiber mode and P2P sync are mutually exclusive. Full nodes in Fiber mode cannot receive blocks via P2P gossip; they must rely entirely on DA retrieval. This constraint deserves a comment (and ideally a section in the docs) because operators won't expect P2P to be disabled by a DA flag.

---

8. forwardFibreBlobs silently swallows errors without logging

tools/celestia-node-fiber/listen.go:72-76

event, err := a.fibreBlobToEvent(ctx, b.Blob, height)
if err != nil {
    continue  // no log
}

A blob is silently dropped. If this happens in production due to, say, a transient FSP failure, operators have no signal. Add a log.Warn() at minimum.

Fix this →

---

9. Listen does a Download per blob just to resolve DataSize

tools/celestia-node-fiber/listen.go (fibreBlobToEvent)

The doc comment acknowledges this tradeoff. For a PoC it's fine, but DataSize is only used for metrics/logging in BlobEvent — it's not load-bearing for correctness. Emitting DataSize: 0 (or deriving it from the v2 share) and skipping the extra round-trip would be significantly cheaper at scale.

---

Code Quality

10. retrieve bool parameter is unused — Retrieve and RetrieveBlobs are identical

block/internal/da/fiber_client.go:137

func (c *fiberDAClient) retrieve(ctx context.Context, height uint64, namespace []byte, _ bool) datypes.ResultRetrieve {

The bool is ignored; both callers behave identically. Either remove the parameter, or implement the distinction (include full data vs. IDs only) before shipping.

---

11. failOnNthUpload is defined but never used in any test

block/internal/da/fiber_client_test.go:468-481

Dead test helper. Remove or wire it up.

---

12. Magic constant fiberSubscribeChanSize = 42

block/internal/da/fiber_client.go:248

The value 42 is unusual. Use a named constant with a comment explaining the rationale (e.g. matches upstream blob.Subscribe buffer, or chosen to hold N seconds of expected traffic). Right now it looks like a placeholder.

---

13. Incorrect flag comment in config.go

pkg/config/config.go:102-103

// FlagConsensusChainID is the Chain ID of the celestia app node
FlagDAFiberConsensusChainID = FlagPrefixEvnode + "da.fiber.consensus_chain_id"

The comment says FlagConsensusChainID but the constant is FlagDAFiberConsensusChainID. Also the comment is a copy-paste of the description rather than describing the flag constant.

---

14. FiberDAConfig.Validate doesn't check KeyName or KeyringPath

pkg/config/config.go:311-338

When Enabled is true, signing payment promises requires a key. The validator checks ConsensusAddress, BridgeAddress, and ConsensusChainID, but not KeyName. If KeyName is empty, the adapter will fail at runtime rather than at startup validation.

---

Summary

Severity	Count	Notes
Bug	5	Context ignored, panic, namespace bounds, subscriber race, public panic
Design	4	Height unimplemented, P2P silent disable, error swallowing, per-blob Download
Code quality	5	Unused helper, magic const, dead param, wrong comment, incomplete validation

Given this is [DNM] PoC, the design gaps (height=0, Retrieve broken) are expected. The bugs and code quality issues are still worth fixing before the branch is ready for review since they'll otherwise generate noise later. Happy to help with any of these.

[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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