The Cross-Language Detective: Tracing a PoRep PSProve Failure Through Go and Rust Code

Introduction

In the complex world of distributed proof generation for the Filecoin network, a production bug had emerged that was both specific and baffling: PoRep (Proof of Replication) tasks processed through the PSProve (Proof Share) pipeline were failing with the error "porep failed to validate" when routed through the CuZK GPU proving engine. Yet SnapDeals PSProve tasks worked perfectly, and normal CuZK PoRep C2 (Commit Phase 2) proofs also worked fine. The failure was exquisitely specific: the combination of PSProve + CuZK + PoRep was the only failing configuration.

In message 1636 of this coding session, the assistant undertakes a meticulous side-by-side comparison of the two code paths that feed data into the CuZK proving engine. This message represents a critical turning point in the investigation—moving from broad hypothesis generation to precise structural comparison. The assistant lays out both paths verbatim, annotates the differences, and begins tracing how the RegisteredProof enum flows through the system. This article examines that message in depth, exploring the reasoning, assumptions, and knowledge required to understand this cross-language debugging effort.

The Context: A Production Bug in a Distributed Proving System

To understand message 1636, one must first understand the architecture it operates within. The system under development is a distributed GPU proving network for Filecoin, where "provers" (machines with GPUs) register to compute SNARK proofs for storage providers. The CuZK (CUDA Zero-Knowledge) engine accelerates the most computationally intensive part of Filecoin proving: the Commit Phase 2 (C2) SNARK generation.

The system has two main paths for producing PoRep C2 proofs:

  1. The normal CuZK path (cuzk_funcs.go): A storage provider's own machine runs ffi.SealCommitPhase1() locally, producing raw Rust JSON bytes. These bytes are wrapped in a C1OutputWrapper struct and sent directly to the CuZK daemon for GPU-accelerated C2 proving.
  2. The PSProve path (task_prove.go): A "client" storage provider generates the C1 output on their own machine, serializes it to JSON, and submits it through a market mechanism. A "provider" (a vast.ai GPU instance running CuZK) picks up this task, deserializes the JSON into a Go struct, re-marshals it, wraps it in the same C1OutputWrapper, and sends it to the local CuZK daemon for proving. The PSProve path involves an extra JSON round-trip through Go structs that the normal path avoids. The bug manifested only when these two conditions coincided: PSProve task routing AND CuZK GPU proving. The assistant's task in message 1636 is to find the exact plumbing difference that causes this specific failure.

The Side-by-Side Analysis: A Methodical Comparison

Message 1636 opens with the assistant declaring its intent: "Let me do a careful side-by-side of the two code paths." This is not casual browsing—it is a structured forensic comparison. The assistant reproduces both code paths in full, annotated with comments explaining what each line does.

The normal path (PoRepSnarkCuzk in cuzk_funcs.go) is shown first:

wrapped, err := wrapC1Output(vproof, uint64(sn.ID.Number), uint64(ssize))
resp, err := cuzkClient.Prove(ctx, &cuzk.SubmitProofRequest{
    RequestId:       fmt.Sprintf("porep-%d-%d", sn.ID.Miner, sn.ID.Number),
    ProofKind:       cuzk.ProofKind_POREP_SEAL_COMMIT,
    SectorSize:      uint64(ssize),
    RegisteredProof: uint64(sn.ProofType),
    Priority:        cuzk.Priority_NORMAL,
    VanillaProof:    wrapped,
    SectorNumber:    uint64(sn.ID.Number),
    MinerId:         uint64(sn.ID.Miner),
})

The PSProve path (computePoRep in task_prove.go) is shown second:

vproof, err := json.Marshal(request)
spt, err := request.RegisteredProof.ToABI()
wrapped, err := json.Marshal(c1OutputWrapper{
    SectorNum:  int64(sectorID.Number),
    Phase1Out:  vproof,
    SectorSize: uint64(ssize),
})
resp, err := cuzkClient.Prove(ctx, &cuzk.SubmitProofRequest{
    RequestId:       fmt.Sprintf("ps-porep-%d-%d", sectorID.Miner, sectorID.Number),
    ProofKind:       cuzk.ProofKind_POREP_SEAL_COMMIT,
    SectorSize:      uint64(ssize),
    RegisteredProof: uint64(spt),
    Priority:        cuzk.Priority_NORMAL,
    VanillaProof:    wrapped,
    SectorNumber:    uint64(sectorID.Number),
    MinerId:         uint64(sectorID.Miner),
})

The assistant then enumerates the differences it can see:

  1. VanillaProof content: The normal path wraps raw Rust JSON bytes from ffi.SealCommitPhase1(). The PSProve path re-marshals a Go struct that was itself deserialized from JSON. This round-trip through Go serialization is the most suspicious difference.
  2. RequestId prefix: Different prefixes (porep- vs ps-porep-), but the assistant correctly dismisses this as irrelevant—the request ID is just a label for tracking.
  3. RegisteredProof value: Both paths compute uint64(spt) or uint64(sn.ProofType). At first glance, these should produce the same enum value. The assistant then immediately pivots to tracing how RegisteredProof is used on the Rust side, reading prover.rs from the CuZK core library. This shows a key insight: the assistant understands that the Go-side enum value must match what the Rust side expects, and any mismatch in the enum mapping could cause the Rust prover to use the wrong circuit parameters, producing an invalid SNARK.

The Reasoning Process: What the Assistant is Thinking

Message 1636 reveals a sophisticated debugging methodology. The assistant is not just reading code—it is constructing a mental model of the data flow across a language boundary (Go → JSON → Rust) and reasoning about where corruption could occur.

The key insight the assistant demonstrates is understanding that the RegisteredProof field in the gRPC request is not the only source of truth for the Rust prover. Earlier in the conversation (messages 1624-1627), the assistant had discovered that the Rust CuZK prover ignores the registered_proof field from the gRPC request for PoRep and instead uses the value embedded inside the C1 JSON output itself. This is a critical architectural detail: the Rust code parses the C1OutputWrapper, base64-decodes the inner Phase1Out field, deserializes SealCommitPhase1Output from JSON, and uses that struct's registered_proof field to select the circuit.

This discovery reframes the entire investigation. If the Rust code ignores the outer RegisteredProof field, then the only way a proof-type mismatch could occur is if the inner C1 JSON has a different registered_proof value after the Go round-trip. The assistant's side-by-side comparison is therefore aimed at answering: does the Go re-marshaling preserve the registered_proof field correctly?

Assumptions and Knowledge Required

To fully understand message 1636, several pieces of domain knowledge are necessary:

Filecoin Proof Architecture: The reader must understand that Filecoin proving has two phases. Phase 1 (Commit1) produces a "vanilla proof" that contains the challenge-response data. Phase 2 (Commit2) produces the actual SNARK proof that is verified on-chain. The CuZK engine accelerates Phase 2. The C1 output is the bridge between these phases.

The PSProve Market Model: In the proof-sharing system, a client generates the C1 output on their own hardware (which requires only CPU and memory, not GPU) and submits it as a task. A provider with a GPU picks up the task, runs C2 via CuZK, and returns the final proof. This separation allows storage providers without GPUs to still participate in the network.

Go JSON Marshaling vs Rust serde_json: The Go json.Marshal and Rust serde_json libraries have subtle differences in how they handle certain types. Field ordering, null handling, enum representation, and type width (int64 vs u64) can all produce JSON that is semantically equivalent but structurally different. The Rust deserializer may be strict about field order or absent fields.

The RegisteredProof Enum Mapping: Filecoin defines multiple proof types (StackedDrgV1, StackedDrgV1_1, SyntheticPoRep, NonInteractivePoRep, etc.) with different numeric values in different contexts (ABI, FFI, protobuf). The assistant has previously discovered that there are multiple enum mappings and that the Rust CuZK code may use a different mapping than the Go FFI code.

The assistant also makes several assumptions that are worth examining. It assumes that the wrapC1Output function in cuzk_funcs.go and the locally-defined c1OutputWrapper struct in task_prove.go are functionally identical. While the struct fields appear the same, the assistant does not verify that wrapC1Output uses the same field types (e.g., int64 vs uint64 for SectorNum). This assumption is reasonable but not proven—and as we'll see, the SectorNum type mismatch (int64 in the local struct vs what Rust expects) later becomes a key suspect.

The Output Knowledge Created

Message 1636 produces several concrete outputs that advance the investigation:

  1. A documented side-by-side comparison of the two code paths, annotated with the assistant's analysis. This serves as a reference for future debugging.
  2. Identification of the JSON round-trip as the primary suspect. By showing that the PSProve path re-marshals Go structs while the normal path passes raw Rust bytes, the assistant narrows the search space significantly.
  3. Confirmation that the RegisteredProof field is structurally equivalent in both paths (both use uint64(spt/ProofType)), ruling out a simple enum mapping bug at the gRPC layer.
  4. A pivot to the Rust side: By reading prover.rs, the assistant begins tracing how the Rust CuZK engine actually uses the data it receives. This cross-language tracing is essential because the bug could manifest in either the Go marshaling or the Rust deserialization.
  5. A foundation for deeper investigation: The message sets up the next steps—comparing the C1OutputWrapper struct definitions for type mismatches (particularly SectorNum), examining how the Rust pipeline deserializes VanillaProof bytes, and checking if field ordering or whitespace differences in the re-marshaled JSON affect serde_json deserialization.

The Thinking Process Visible in the Message

The assistant's reasoning in message 1636 is notable for its structure and discipline. Rather than jumping to conclusions or pursuing speculative hypotheses, the assistant:

  1. Reproduces both code paths verbatim from the source files, ensuring accuracy.
  2. Annotates each path with comments that explain what each line does and where the data comes from.
  3. Enumerates differences explicitly with numbered points, separating confirmed differences from irrelevant ones.
  4. Immediately follows up on the most promising lead by reading the Rust prover code to understand how RegisteredProof is consumed.
  5. Maintains awareness of prior discoveries (the Rust code ignoring the outer registered_proof field) and integrates them into the current analysis. This disciplined approach is characteristic of debugging across language boundaries, where assumptions about data fidelity can hide subtle bugs. The assistant is essentially building a chain of custody for the data: tracing every transformation from the original Rust JSON output of ffi.SealCommitPhase1(), through Go deserialization, through Go re-marshaling, through base64 encoding in the wrapper, through Rust deserialization, and finally into the seal_commit_phase2 function.

Conclusion

Message 1636 represents the investigative pivot in a complex production debugging session. By laying out both code paths side by side and methodically comparing them, the assistant transforms a vague "PoRep PSProve fails with CuZK" bug report into a focused investigation of the JSON serialization boundary between Go and Rust. The message demonstrates the kind of cross-language forensic thinking required when a distributed system spans multiple programming languages, serialization formats, and runtime environments.

The side-by-side comparison reveals that the two paths are nearly identical in structure—the same fields, the same gRPC call, the same wrapper format. The only significant difference is the provenance of the inner C1 JSON data: raw from Rust in the normal path, round-tripped through Go in the PSProve path. This narrows the investigation to a single question: does the Go JSON round-trip preserve the C1 output faithfully enough for the Rust CuZK engine to produce a valid SNARK? The answer to that question would determine whether the fix lies in the Go serialization code, the Rust deserialization code, or somewhere else entirely in the pipeline.