Reading the Rust Prover: Tracing the CuZK PoRep Deserialization Pipeline

The Message

The subject message is a single tool invocation by the AI assistant:

[read] /tmp/czk/extern/cuzk/cuzk-core/src/prover.rs

>

``rust 130: let total_start = Instant::now(); 131: let mut timings = ProofTimings::default(); 132: 133: // --- Phase: Deserialize --- 134: let deser_start = Instant::now(); 135: 136: // Parse the C1 wrapper JSON (outer Curio format) 137: debug!( 138: input_len = vanilla_proof_json.len(), 139: "parsing C1 outer wrapper JSON" 140: ); 141: let wrapper: C1OutputWrapper = se... ``

At first glance, this appears to be a routine code-reading action. But within the context of a multi-hour debugging session spanning Go, Rust, protobuf definitions, and JSON serialization semantics, this read call represents a pivotal moment in the investigation. The assistant is crossing the language boundary from Go into Rust, seeking to understand exactly how the CuZK proving engine consumes the data that the Go-side code paths produce differently.

Context: A Production Bug at the Go-Rust Boundary

To understand why this message was written, one must appreciate the debugging labyrinth that preceded it. The session had been investigating a production failure where PoRep (Proof of Replication) PSProve tasks failed with the error "porep failed to validate" when processed through the CuZK GPU proving engine. The failure was exquisitely specific: SnapDeals PSProve tasks worked fine, normal (non-PSProve) PoRep C2 through CuZK worked fine, but the combination of PSProve and PoRep and CuZK produced invalid SNARK proofs that failed verification.

The assistant had spent the preceding messages meticulously comparing two code paths in the Go source tree. The normal path (cuzk_funcs.go) passes the raw JSON bytes from ffi.SealCommitPhase1() directly into the CuZK wrapper — the data never touches Go's JSON marshaling machinery. The PSProve path (task_prove.go), by contrast, deserializes the C1 output from JSON into Go structs (specifically Commit1OutRaw), stores it in a database, transmits it across machines, and then re-serializes it back to JSON before handing it to CuZK. This "JSON round-trip" through Go's encoding/json package was the prime suspect.

The assistant had already discovered several concerning facts. The Go types PoseidonDomain and Sha256Domain (both [32]byte) had custom MarshalJSON methods but no corresponding UnmarshalJSON methods ([msg 1615]). The type alias type HasherDomain = any meant that generic struct fields would deserialize as []interface{} rather than the concrete domain types, bypassing the custom marshalers entirely ([msg 1617]). A dedicated round-trip test existed and passed ([msg 1623]), but the assistant remained unsatisfied — the test compared at the map[string]interface{} level, which might mask subtle differences in field ordering or whitespace that could affect the Rust serde_json deserializer.

Why This Message Was Written: The Need for a Rust-Side Perspective

The assistant had exhausted the Go-side analysis. The JSON round-trip appeared functionally correct at the Go level, yet the proofs still failed verification. This left two possibilities: either the verification parameters (sector ID, proof type, seed, ticket) were somehow wrong in the PSProve path, or the CuZK Rust engine was deserializing the re-marshaled JSON differently from the original Rust output.

The decision to read prover.rs was therefore a strategic pivot. The assistant needed to understand the consumer side of the data pipeline — the Rust code that parses the C1OutputWrapper JSON, base64-decodes the inner phase1_out field, and deserializes the SealCommitPhase1Output before calling seal::seal_commit_phase2. Only by tracing the full data flow from Go's json.Marshal through protobuf serialization, gRPC transport, and finally Rust's serde_json deserialization could the assistant determine whether the PSProve JSON round-trip introduced any structural differences that the Rust side would interpret differently.

This was not a casual read. The assistant was operating under a specific hypothesis: that the registered_proof field embedded inside the C1 JSON output (not the one in the gRPC request wrapper) was the authoritative source of the proof type for the Rust prover. Earlier investigation had revealed that the Rust CuZK prover ignores the registered_proof field from the gRPC request for PoRep and instead uses the value inside the C1 output itself ([msg 1625]). This meant that even if the Go wrapper sent the correct proof type in the outer envelope, a corrupted or subtly altered registered_proof value inside the re-marshaled C1 JSON could cause the Rust engine to select the wrong proving circuit — producing an invalid SNARK that would fail VerifySeal.

Assumptions and Their Validity

The assistant made several assumptions when reading this file. First, it assumed that the Rust deserialization code was the authoritative reference — that whatever serde_json produced from the JSON bytes would be the exact structure used for proof generation. This assumption was sound: the Rust CuZK engine is the sole consumer of this data, so its deserialization behavior is the ground truth.

Second, the assistant assumed that the C1OutputWrapper struct in Rust would have a phase1_out field of type Vec<u8> or similar, which would be base64-decoded from the JSON. This assumption was based on the Go-side wrapper definition where Phase1Out is []byte (which Go marshals as base64). The assistant was correct — the Rust side indeed base64-decodes the inner JSON before parsing it.

Third, the assistant implicitly assumed that the Rust serde_json deserializer would be sensitive to any differences between the original Rust-produced JSON and the Go-re-marshaled JSON. This assumption was reasonable but unproven: serde_json is generally flexible about field ordering, whitespace, and number formatting, but edge cases exist (e.g., u64 vs i64 type mismatches, or [u8; 32] arrays serialized as base64 strings vs integer arrays).

Input Knowledge Required

To understand this message, one needs considerable context spanning multiple programming languages and domains. The reader must understand:

  1. The Filecoin proof architecture: The distinction between PoRep (Proof of Replication) and SnapDeals, the role of SealCommitPhase1 and SealCommitPhase2, and the RegisteredProof enum that selects the proving circuit.
  2. The PSProve (ProofShare) system: A marketplace where clients generate Phase 1 commitments, upload them as JSON blobs, and providers download and compute Phase 2 SNARK proofs. This introduces a JSON serialization round-trip that the normal path avoids.
  3. The CuZK GPU proving engine: A custom Rust-based proving service that receives proof requests via gRPC, deserializes them from protobuf, and calls the standard filecoin-proofs Rust crate for actual proof generation.
  4. Go JSON marshaling semantics: How encoding/json handles [32]byte (base64), interface{} (type-dependent), and custom MarshalJSON/UnmarshalJSON methods. The subtlety of type HasherDomain = any erasing concrete type information is critical.
  5. Rust serde_json semantics: How serde_json handles [u8; 32] (integer array), Vec<u8> (base64 or array depending on serde attributes), and the flexibility of JSON deserialization with respect to field ordering and numeric types.
  6. The specific bug context: That Snap PSProve works, normal CuZK PoRep works, but PSProve + PoRep + CuZK fails — ruling out general infrastructure problems and narrowing the focus to the intersection of these three components.

Output Knowledge Created

This single read call produced several pieces of critical knowledge:

  1. Confirmation of the deserialization pipeline: The Rust code first parses the outer C1OutputWrapper JSON (the Curio-specific envelope), then base64-decodes the phase1_out field to get the inner SealCommitPhase1Output JSON, and finally deserializes that into the Rust struct that seal_commit_phase2 expects.
  2. Identification of the key data flow boundary: The critical transition point is the base64 decoding step. The Go side produces base64-encoded JSON (because []byte marshals as base64), and the Rust side decodes it. Any corruption or structural change in the inner JSON before it was base64-encoded would propagate through this boundary undetected.
  3. Confirmation that both paths converge: Both the normal path (raw Rust bytes wrapped directly) and the PSProve path (Go-re-marshaled JSON wrapped) go through the exact same Rust deserialization code. The Rust side has no special handling for either path — it simply parses whatever JSON it receives. This means the bug must be in the content of the inner JSON, not in the Rust parsing logic itself.
  4. A refined hypothesis space: With the Rust pipeline confirmed identical for both paths, the assistant could now focus on specific structural differences in the inner JSON. The registered_proof field, the SectorNum type (int64 in Go's wrapper vs u64 in Rust's), and the [u8; 32] array serialization format all became prime suspects.

The Thinking Process: A Detective's Method

The assistant's reasoning in the surrounding messages reveals a methodical, hypothesis-driven debugging approach. The thought process visible in [msg 1627] (the message immediately following the subject) shows the assistant synthesizing the new information:

"So the cuzk Rust side: 1. Parses the C1OutputWrapper JSON 2. Base64-decodes phase1_out to get the inner JSON 3. Deserializes SealCommitPhase1Output from JSON 4. Calls seal::seal_commit_phase2(c1_output, prover_id, sector_id)"

The assistant then reasons through the implications:

"Now here's the thing — both the normal path and PSProve path go through the exact same cuzk Rust code. The only difference is the source of the C1 data"

This is a classic debugging insight: when two paths converge on identical downstream code, the bug must be in the data itself, not in the processing logic. The assistant then enumerates the verification parameters used after proof generation (spt, sectorID, Ticket, Seed) and poses the two remaining possibilities:

"Either: 1. The cuzk SNARK output is somehow different for PSProve input (the C1 data difference causes cuzk to produce a bad proof) 2. The verification parameters are wrong (sectorID, spt, ticket, seed, commR, commD)"

This bifurcation of possibilities is characteristic of systematic debugging. The assistant does not jump to conclusions but instead structures the investigation around testable hypotheses.

The Broader Significance

This message, though outwardly trivial, represents a critical juncture in a complex cross-language debugging session. It marks the moment when the investigation shifted from analyzing how data is produced (the Go side) to analyzing how it is consumed (the Rust side). The assistant was building a complete mental model of the data pipeline from end to end — from the client's ffi.SealCommitPhase1() call, through JSON marshaling, database storage, network transmission, gRPC protobuf encoding, and finally Rust serde_json deserialization.

The debugging methodology on display here is worth noting. Rather than guessing at the root cause, the assistant systematically eliminated possibilities: it checked the JSON round-trip with a unit test, compared the wrapper struct definitions, traced the RegisteredProof field through both code paths, and finally read the Rust consumer code to confirm that both paths converge. Each step narrowed the hypothesis space, ruling out entire categories of potential bugs.

The next steps, visible in the following messages, would involve comparing the C1OutputWrapper struct definitions for type mismatches (particularly SectorNum as int64 vs u64), examining how the Rust engine parses the VanillaProof bytes, and potentially constructing a minimal reproduction of the JSON round-trip to compare byte-level output. The investigation was far from over, but the assistant had successfully traced the data flow to its terminus, laying the groundwork for a precise diagnosis.