Tracing the JSON Round-Trip Bug: A Deep Dive into Cross-Language Serialization in the CuZK Proving Pipeline

Message 1604: "Now let me look at the Commit1OutRaw struct and how RegisteredProof is handled, since PSProve PoRep uses StackedDrg32GiBV1_1 (interactive) but the challenge from ProofShare might be using a different proof type: [read] /tmp/czk/lib/proof/porep_vproof_types.go"

This seemingly simple message — a developer reading a source file — marks a critical inflection point in a deep investigation into a production bug. The bug was a silent, cross-language serialization failure that caused PoRep (Proof of Replication) challenges to fail in the CuZK proving pipeline while Snap (SnapDeals) challenges worked perfectly. To understand why this message matters, we must unpack the full investigative context, the reasoning that led to this specific file read, and the cascade of discoveries it enabled.

The Production Bug: PSProve PoRep Validation Failures

The investigation began with a user report ([msg 1601]) describing a puzzling production failure: PSProve tasks — a mechanism where miners prove storage challenges through a ProofShare market — were failing for PoRep challenges with the error "failed to compute proof: porep failed to validate". Yet Snap PSProve tasks worked flawlessly, and normal (non-PSProve) PoRep C2 proofs also worked correctly through the CuZK accelerated proving engine. This created a Venn diagram of failure: the intersection of PSProve + PoRep + CuZK was the only combination that broke.

The user's report was unusually detailed, including the exact challenge derivation algorithm from the Rust storage-proofs-porep library, confirming that the challenge generation itself was not the issue. The challenges were derived identically to real miner PoRep challenges using SHA256 over (replica_id || seed || j). The code path was identical — ffi.SealCommitPhase1() → Rust seal_commit_phase1() → standard filecoin-proofs-api v18.1. The only variable input was a random seed. The user also noted a side finding: an unused Go re-implementation of DeriveInteractiveChallenges in porep_vproof_challenges.go had a latent endianness bug, but since it was never called, it couldn't be the cause.

The Investigation Begins: Subagent Analysis

The assistant launched a subagent task ([msg 1602]) to trace the PSProve PoRep code paths. The subagent returned a comprehensive analysis ([msg 1603]) revealing the critical structural difference between the two paths. In the normal PoRep C2 path (cuzk_funcs.go), the vanilla proof bytes came directly from ffi.SealCommitPhase1() — raw Rust-generated JSON. In the PSProve PoRep path (task_prove.go), the Commit1OutRaw struct was deserialized from JSON (received from the market), then re-marshaled back to JSON using Go's json.Marshal. This round-trip through Go structs was the prime suspect.

The subagent also discovered that the PSProve path defined a local c1OutputWrapper struct instead of using the shared wrapC1Output function from cuzk_funcs.go. This meant the PSProve path was constructing the CuZK gRPC request differently from the normal path — a potential source of structural divergence.

Message 1604: The Pivot to Data Structures

This brings us to the subject message. After absorbing the subagent's analysis, the assistant made a deliberate choice: instead of immediately diving into the wrapper struct differences or the CuZK Rust deserialization code, it first went to examine the data types themselves. The message reads:

"Now let me look at the Commit1OutRaw struct and how RegisteredProof is handled, since PSProve PoRep uses StackedDrg32GiBV1_1 (interactive) but the challenge from ProofShare might be using a different proof type"

This decision reveals a specific investigative strategy. The assistant was testing a hypothesis: perhaps the PSProve challenges used a different proof type than what the normal PoRep path expected. The user had mentioned that PoRep was "slightly different in cuzk vs snap," and the assistant knew that the RegisteredProof enum in Filecoin has many variants — interactive, synthetic, non-interactive — each with different challenge derivation algorithms. If the PSProve market was sending challenges tagged with StackedDrg32GiBV1_2_Feat_NonInteractivePoRep but the code expected StackedDrg32GiBV1_1 (interactive), the verification would fail because the challenge positions would be derived differently.

This was a reasonable hypothesis. The PSProve market is a separate service that generates challenge data and distributes it to workers. If the market used a different proof type variant when creating the challenge, the worker's verification would naturally fail. The assistant's reasoning was: before diving into the complex JSON serialization issue, rule out the simpler explanation of a proof type mismatch.

The File Being Read: porep_vproof_types.go

The file /tmp/czk/lib/proof/porep_vproof_types.go contains the Go type definitions for PoRep vanilla proof structures. These are hand-translated from the Rust storage-proofs-porep crate's types. The file defines:

The Thinking Process: What the Assistant Was Reasoning

The assistant's thinking at this point can be reconstructed from the sequence of actions. After receiving the subagent analysis, the assistant:

  1. Identified the error location: The error "porep failed to validate" came from task_prove.go:346, meaning ffi.VerifySeal() returned ok=false. The SNARK proof was generated successfully (no CuZK error) but didn't verify.
  2. Formulated two competing hypotheses: - Hypothesis A (Proof Type Mismatch): The PSProve challenge used a different RegisteredProof variant than what the verification code expected. Since the Rust CuZK prover might use the proof type from the gRPC request to select the verification algorithm, a mismatch would cause validation failure. - Hypothesis B (JSON Round-Trip Corruption): The Go json.Unmarshal → json.Marshal round-trip introduced subtle differences in the JSON representation that the Rust CuZK engine's serde_json deserialization couldn't handle correctly.
  3. Chose to test Hypothesis A first by reading the proof type definitions. This was the simpler, more easily falsifiable hypothesis. If the proof type was the same in both paths, Hypothesis A could be ruled out, and the investigation could focus on the more complex JSON serialization issue.
  4. Made an assumption about the PSProve challenge flow: The assistant assumed that the PSProve market might use a different proof type when generating challenges — perhaps StackedDrg32GiBV1_2_Feat_NonInteractivePoRep instead of the interactive StackedDrg32GiBV1_1 used by powsrv. This assumption was reasonable given the user's note that "porep is slightly different in cuzk vs snap" and the existence of multiple proof type variants in the codebase.

Input Knowledge Required

To understand this message, one needs:

  1. The Filecoin proof architecture: Knowledge of PoRep (Proof of Replication) vs SnapDeals proofs, the C1/C2 proof pipeline, and the RegisteredSealProof enum with its many variants (interactive, synthetic, non-interactive).
  2. The CuZK accelerated proving system: Understanding that CuZK is a GPU-accelerated proving engine that replaces the standard CPU-based SNARK generation, and that it communicates via gRPC with JSON serialization.
  3. The PSProve/ProofShare market model: Knowledge that PSProve is a distributed proof market where workers receive challenge data from a centralized service, compute proofs, and submit them for verification.
  4. Go/Rust cross-language serialization: Understanding that Go's encoding/json and Rust's serde_json have different default behaviors for byte arrays (Go uses base64, Rust uses number arrays), and that custom marshalers/unmarshalers are needed for compatibility.
  5. The specific codebase structure: Familiarity with the curio project's directory layout, particularly tasks/proofshare/task_prove.go (the PSProve task implementation), lib/ffi/cuzk_funcs.go (the normal CuZK path), and lib/proof/porep_vproof_types.go (the Go proof type definitions).

Output Knowledge Created

This message produced several important outputs:

  1. Confirmation of the proof type mapping: By reading the ToABI() method, the assistant could verify that the string-to-ABI conversion was comprehensive and correct for all proof type variants.
  2. Understanding of the JSON serialization structure: Seeing the Commit1OutRaw struct fields revealed how the proof type was embedded in the JSON payload — as a string field registered_proof inside the C1 output itself.
  3. A foundation for the deeper investigation: This read was the first step in what would become a detailed comparison of the two code paths. The assistant would go on to examine cuzk_funcs.go ([msg 1610]), discover the HasherDomain = any type alias ([msg 1613]), find the missing UnmarshalJSON methods ([msg 1615]), and ultimately trace the issue to a SectorNum type mismatch (int64 vs u64) in the wrapper struct.
  4. Ruling out the proof type hypothesis: Subsequent investigation ([msg 1611]) revealed that the Rust CuZK prover actually ignores the registered_proof field from the gRPC request for PoRep and instead uses the value embedded inside the C1 JSON output. This ruled out Hypothesis A and forced the investigation to focus on the JSON round-trip issue.

The Broader Significance

Message 1604 represents a classic debugging strategy: start with the simplest hypothesis and work toward the more complex. The assistant could have immediately jumped into the JSON serialization details — comparing Go's base64 encoding of [32]byte against Rust's array-of-numbers format, examining the custom MarshalJSON methods, and tracing through the CuZK Rust deserialization code. Instead, it first checked whether the proof type was even correct.

This approach was sound. The proof type mismatch hypothesis was easily testable and, if confirmed, would have been a trivial fix. By ruling it out first, the assistant avoided wasting time on the much more complex serialization analysis. The message also reveals a developer who thinks in terms of data boundaries — the places where data crosses between systems (Go ↔ Rust, market ↔ worker, JSON ↔ struct) are always the most likely sources of bugs in distributed systems.

The investigation that followed this message would eventually uncover a cascade of serialization issues: missing UnmarshalJSON methods on PoseidonDomain and Sha256Domain, the HasherDomain = any type alias that bypassed custom marshalers, and a SectorNum type mismatch between Go's int64 and Rust's u64. But all of that started with a simple question: "What proof type is being used here?" — asked in message 1604.