[PeerDAS] Expose compute_cells (cells without proofs) through the C ABI and constantine-go

[syjn99]

On the PeerDAS/Fulu block proposal hot path, consensus clients receive cell proofs from the execution layer for free (BlobsBundleV2 / engine_getBlobsV2) and only need the erasure-extended cells.

I'm assessing Constantine for Prysm's KZG operations (OffchainLabs/prysm#16850); in our benchmarks of constantine-go against c-kzg-4844 Constantine wins every measured operation, but this API gap is currently the main blocker to adoption: Prysm calls a cells-only ComputeCells at

• beacon-chain/blockchain/kzg/validation.go (proof verification path), and
• beacon-chain/core/peerdas/reconstruction.go (data-column reconstruction)

c-kzg-4844, go-eth-kzg and rust-eth-kzg all expose the equivalent entry point, matching the consensus-spec function compute_cells. With this change, migrating to constantine from other kzg libraries would be much easier.

Summary by CodeRabbit

• New Features

  • Added support for computing all 128 EIP-7594 cells from an extended blob without generating KZG proofs.
  • Exposed cell computation through the C and Go APIs, including error handling for invalid inputs.

• Tests

  • Added Go test-vector coverage for cells-only computation.
  • Updated PeerDAS benchmarks and tests for the new cell-computation interface.

[coderabbitai]

📝 Walkthrough

Walkthrough

The EIP-7594 cells-only computation API now supports FFI-compatible output buffers, exposes a C declaration, and adds a Go binding with test-vector validation. Nim benchmarks and tests pass unchecked cell buffers while preserving existing assertions and recovery logic.

Changes

EIP-7594 compute-cells API

Layer / File(s)	Summary
FFI and public API contract include/constantine/protocols/..., constantine/eth_eip7594_peerdas.nim	The public C API and Nim implementation now accept caller-provided unchecked cell buffers, validate nil inputs, and bridge the buffer to internal computation.
Go binding and vector validation constantine-go/constantine.go, constantine-go/eth_kzg7594_peerdas_test.go	EthKzgContext.ComputeCells calls the C API, converts failures to Go errors, and is validated against cells-only EIP-7594 vectors.
Nim callers and benchmark validation benchmarks/..., tests/...	Benchmarks and PeerDAS tests pass buffers through asUnchecked() while retaining existing status, recovery, and output checks.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant TestComputeCells
  participant EthKzgContext
  participant CApi
  participant NimComputeCells
  TestComputeCells->>EthKzgContext: ComputeCells(blob)
  EthKzgContext->>CApi: ctt_eth_kzg_compute_cells(ctx, cells, blob)
  CApi->>NimComputeCells: forward output buffer and blob
  NimComputeCells-->>CApi: return status and populated cells
  CApi-->>EthKzgContext: return status
  EthKzgContext-->>TestComputeCells: cells or error

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Possibly related PRs

• mratsim/constantine#613: Introduces the connected EIP-7594 compute_cells implementation and related plumbing.

Suggested reviewers: mratsim

Poem

A rabbit hops through cells so bright,
Unchecked buffers fit just right.
Go gathers one-twenty-eight,
Tests compare each cell’s fate.
Nim benchmarks cheer: “Compute straight!”

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.
Title check	✅ Passed	The title clearly and concisely describes exposing PeerDAS compute_cells through the C ABI and constantine-go, matching the main changes.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[greptile-apps]

Public Nim API signature breaks

When an existing Nim consumer calls compute_cells(ctx, cells, blob) with a fixed array[CELLS_PER_EXT_BLOB, Cell], the new pointer-only signature rejects the argument, causing downstream compilation to fail. Retain a typed compatibility overload or separate the C export wrapper from the existing Nim API.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[greptile-apps]

Greptile Summary

Adds cells-only PeerDAS computation across the existing implementation and language bindings.

• Exports compute_cells through the C ABI with null-pointer validation.
• Adds a Go ComputeCells wrapper returning 128 cells.
• Adds consensus-vector tests and updates Nim tests and benchmarks for the pointer-based interface.

Confidence Score: 4/5

The PR is not yet safe to merge because the previously reported public Nim API compatibility break remains unfixed.

The current public compute_cells declaration still accepts only ptr UncheckedArray[Cell]; no exported fixed-array overload preserves the former call form, so existing Nim consumers passing array[CELLS_PER_EXT_BLOB, Cell] fail to compile.

Files Needing Attention: constantine/eth_eip7594_peerdas.nim

Important Files Changed

Filename	Overview
constantine/eth_eip7594_peerdas.nim	Exports cells-only computation through the C ABI and adds pointer validation, but the pointer-only public signature leaves the previously reported Nim source-compatibility break outstanding.
include/constantine/protocols/ethereum_eip7594_peerdas.h	Declares the new C ABI function and its caller-allocated 128-cell output contract.
constantine-go/constantine.go	Adds a nil-safe Go wrapper whose cell and blob layouts match the C ABI types.
constantine-go/eth_kzg7594_peerdas_test.go	Adds consensus-vector coverage for successful and invalid cells-only inputs.

Sequence Diagram

sequenceDiagram
    participant Client as Go/C client
    participant ABI as ctt_eth_kzg_compute_cells
    participant KZG as Constantine PeerDAS
    Client->>ABI: context, 128-cell output buffer, blob
    ABI->>KZG: compute_cells
    KZG->>KZG: deserialize and extend blob
    KZG-->>ABI: 128 cells and status
    ABI-->>Client: cells or error

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_{Reviews (2): Last reviewed commit: "[PeerDAS] constantine-go: add EthKzgCont..." | Re-trigger Greptile}

[mratsim]

SGTM, will create a separate issue to expose the same in Rust as well as this is go only.

Seems like there are unrelated CI stuff to fix though. Will have a look

[mratsim]

Hopefully CI is unblocked by #627

[syjn99]

@mratsim thanks, will wait until #627 got merged.

[mratsim]

The go tests are done first and are passing. The issue left seems to be a regression in an unreleased Nim v2.2.x that affects unit tests but not integration tests or building the static library so merging. Regression tracked in #628.