Add prover-client prototype

Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
-members = ["crates/*", "crates/frontend/ceck"]
+members = ["crates/*", "crates/frontend/ceck", "crates/prover-client"]
 resolver = "2"
 
 [workspace.package]

crates/prover-client/Cargo.toml

@@ -0,0 +1,34 @@
+[package]
+name = "binius-prover-client"
+version = "0.1.0"
+edition = "2021"
+authors = ["Irreducible Team <opensource@irreducible.com>"]
+description = "Simplified open-source interface to the Binius ZK prover using serialization"
+license = "MIT OR Apache-2.0"
+build = "build.rs"
+
+[lib]
+# This is a Rust crate (rlib). The cdylib is only built for internal testing purposes.
+crate-type = ["rlib", "cdylib"]
+
+[dependencies]
+# Core dependencies for serialization
+binius-core = { path = "../core" }
+binius-utils = { path = "../utils" }
+bytes = "1.7"
+
+# Error handling
+thiserror = "2.0"
+anyhow = "1.0"
+
+# Needed for the FFI implementation (only when building cdylib)
+binius-prover = { path = "../prover", optional = true }
+
+[features]
+default = []
+# Enable building the FFI implementation (for cdylib)
+ffi-impl = ["binius-prover"]
+
+[dev-dependencies]
+# For testing and benchmarking
+criterion = "0.6"

crates/prover-client/README.md

@@ -0,0 +1,180 @@
+# Binius Prover Client
+
+A Rust crate providing a clean API for Binius ZK proof generation.
+
+## Overview
+
+This is a standard Rust library that provides a type-safe interface for generating Binius proofs. It uses FFI to communicate with the prover via serialized data, enabling the prover to be distributed as a closed-source binary while keeping the interface open-source.
+
+## Architecture
+
+```
+┌─────────────────────┐    ┌─────────────────────┐    ┌──────────────────────┐
+│   Your Rust App     │────│  Prover Client      │────│   Binius Prover      │
+│                     │    │  (This Crate)       │    │  (C Library)         │
+│ - ConstraintSystem  │    │ - ProverClient      │    │ - binius_prove()     │
+│ - ValuesData        │    │ - Serialization     │    │ - Proof generation   │
+│ - Proof             │    │ - Error handling    │    │                      │
+└─────────────────────┘    └─────────────────────┘    └──────────────────────┘
+```
+
+## Installation
+
+Add this crate to your `Cargo.toml`:
+
+```toml
+[dependencies]
+binius-prover-client = { path = "../prover-client" }
+```
+
+## Requirements
+
+This crate requires the Binius prover to be available as a C library:
+
+```bash
+export BINIUS_PROVER_LIB_PATH=/path/to/prover/library
+```
+
+Without this, the crate will compile but return runtime errors when attempting to generate proofs.
+
+## Usage
+
+```rust
+use binius_prover_client::ProverClient;
+use binius_core::constraint_system::{ConstraintSystem, ValuesData};
+
+// Create a prover client instance
+let prover = ProverClient::new(1); // log_inv_rate = 1
+
+// Generate proof from constraint system and witness data
+let proof = prover.prove(&constraint_system, &public_witness, &private_witness)?;
+```
+
+The crate provides three API methods:
+- `prove()` - Takes Rust types, handles serialization internally
+- `prove_serialized()` - Takes pre-serialized bytes, returns deserialized `Proof`
+- `prove_serialized_raw()` - Takes and returns raw bytes for maximum efficiency
+
+## FFI Interface Details
+
+The FFI boundary uses a single C function with serialized inputs/outputs:
+
+```c
+// Returns proof size on success, negative error code on failure
+int32_t binius_prove(
+    const uint8_t* cs_bytes,          // Serialized ConstraintSystem
+    size_t cs_len,
+    const uint8_t* pub_witness_bytes, // Serialized public ValuesData  
+    size_t pub_witness_len,
+    const uint8_t* priv_witness_bytes,// Serialized private ValuesData
+    size_t priv_witness_len,
+    uint32_t log_inv_rate,            // Proof generation parameter
+    uint8_t* proof_out,               // Output buffer for serialized Proof
+    size_t proof_capacity             // Size of output buffer
+);
+```
+
+### Error Codes
+
+- **Positive number**: Size of the proof written to `proof_out` (success)
+- **-1**: Null pointer error
+- **-2**: Invalid input data  
+- **-3**: Proving error
+- **-4**: Serialization error
+- **-5**: Output buffer too small
+
+## Testing and Development
+
+### Running the Test Suite
+
+The crate includes a focused test suite with automatic FFI library management:
+
+```bash
+# Quick test - builds FFI library and runs all tests
+./test_prover_client.sh
+```
+
+This script will:
+1. Build the FFI library with the current implementation
+2. Set up library paths automatically  
+3. Run integration tests for all API variants
+4. Verify FFI boundary crossing works correctly
+
+### Manual Testing
+
+```bash
+# Build the FFI library
+cargo build --release --features ffi-impl
+
+# Set library path and run tests
+export BINIUS_PROVER_LIB_PATH=$(pwd)/target/release
+cargo test
+```
+
+### Test Coverage
+
+The test suite focuses on interface correctness:
+- **API methods**: All three variants (`prove`, `prove_serialized`, `prove_serialized_raw`)
+- **FFI boundary**: Verifies data crosses the FFI boundary correctly
+- **Serialization**: Ensures proper serialization/deserialization
+- **Trait implementation**: Tests Default trait and accessor methods
+
+## Implementation Notes
+
+### Library Detection
+
+The crate's build script automatically detects the external prover library:
+
+- Checks `BINIUS_PROVER_LIB_PATH` environment variable
+- Sets up linking when library is found
+- Provides graceful fallback when library is unavailable
+
+### FFI Implementation
+
+The file `src/ffi_impl.rs` contains the Binius prover wrapped in a C-compatible FFI interface. This is used to test the FFI boundary. In a closed-source deployment, this code would be compiled as a proprietary C library.
+
+## Advanced Usage
+
+### Error Handling
+
+The interface provides detailed error information:
+
+```rust
+use binius_prover_client::{ProverClient, ProverError};
+
+match prover.prove(&cs, &pub_witness, &priv_witness) {
+    Ok(proof) => println!("Proof generated: {} bytes", proof.data().len()),
+    Err(ProverError::LibraryNotAvailable(msg)) => {
+        eprintln!("FFI library not found: {}", msg);
+        // Handle library not available case
+    }
+    Err(ProverError::FfiError(code)) => {
+        eprintln!("FFI error code: {}", code);
+        // Handle specific FFI error codes
+    }
+    Err(e) => eprintln!("Other error: {}", e),
+}
+```
+
+### Performance Considerations
+
+- **Pre-serialized data**: Use `prove_serialized_raw()` when you already have serialized inputs
+- **Library linking**: Dynamic linking adds minimal overhead compared to proof generation time
+- **Memory management**: The FFI boundary uses copying; consider this for very large constraint systems
+
+### Integration with Existing Code
+
+The interface is designed to integrate easily with existing Binius workflows:
+
+```rust
+// Works with existing constraint system construction
+let cs = constraint_system_builder.build();
+let witness = witness_builder.build();
+
+// Drop-in replacement for direct prover usage  
+let prover = ProverClient::new(log_inv_rate);
+let proof = prover.prove(&cs.constraint_system, &witness.public, &witness.private)?;
+
+// Use proof with existing verification code
+verify_proof(&proof, &public_inputs)?;
+```

crates/prover-client/build.rs

@@ -0,0 +1,82 @@
+use std::env;
+use std::path::{Path, PathBuf};
+
+fn main() {
+    // Tell Cargo about our custom cfg flags
+    println!("cargo::rustc-check-cfg=cfg(has_binius_prover)");
+    println!("cargo::rustc-check-cfg=cfg(no_binius_prover)");
+
+    // Skip library detection when we're building the FFI implementation itself
+    // This avoids circular dependency when building as cdylib
+    if env::var("CARGO_FEATURE_FFI_IMPL").is_ok() {
+        println!("cargo:rustc-cfg=no_binius_prover");
+        return;
+    }
+
+    // Try to find the closed-source library via environment variable
+    if let Ok(path) = env::var("BINIUS_PROVER_LIB_PATH") {
+        let path = PathBuf::from(path);
+
+        if verify_library_exists(&path) {
+            // Set up linking
+            println!("cargo:rustc-link-search={}", path.display());
+            println!("cargo:rustc-link-lib=binius_prover");
+
+            // Store the library info for runtime access
+            println!("cargo:rustc-env=LINKED_BINIUS_LIB_PATH={}", path.display());
+            if let Some(file_name) = find_library_file(&path) {
+                println!("cargo:rustc-env=LINKED_BINIUS_LIB_NAME={}", file_name);
+            }
+
+            // Set a cfg flag to enable integration tests
+            println!("cargo:rustc-cfg=has_binius_prover");
+        } else {
+            println!("cargo:rustc-cfg=no_binius_prover");
+        }
+    } else {
+        // Library not found - this is OK for development
+        println!("cargo:rustc-cfg=no_binius_prover");
+    }
+
+    // Always rerun if these change
+    println!("cargo:rerun-if-env-changed=BINIUS_PROVER_LIB_PATH");
+    println!("cargo:rerun-if-changed=build.rs");
+}
+
+fn find_library_file(dir: &Path) -> Option<String> {
+    let lib_names = [
+        "libbinius_prover.so",      // Linux dynamic
+        "libbinius_prover.dylib",   // macOS dynamic
+        "binius_prover.dll",        // Windows dynamic
+        "libbinius_prover.a",       // Static library
+    ];
+
+    for name in &lib_names {
+        if dir.join(name).exists() {
+            return Some(name.to_string());
+        }
+    }
+    None
+}
+
+fn verify_library_exists(dir: &Path) -> bool {
+    if !dir.exists() {
+        return false;
+    }
+
+    // Check for different library naming conventions
+    let lib_names = [
+        "libbinius_prover.so",      // Linux
+        "libbinius_prover.dylib",   // macOS
+        "binius_prover.dll",        // Windows
+        "libbinius_prover.a",       // Static library
+    ];
+
+    for name in &lib_names {
+        if dir.join(name).exists() {
+            return true;
+        }
+    }
+
+    false
+}

crates/prover-client/src/error.rs

@@ -0,0 +1,45 @@
+use thiserror::Error;
+
+/// Error types for the prover interface
+#[derive(Debug, Error)]
+pub enum ProverError {
+    /// Invalid input data
+    #[error("Invalid input: {0}")]
+    InvalidInput(String),
+
+    /// Serialization error
+    #[error("Serialization error: {0}")]
+    Serialization(#[from] binius_utils::serialization::SerializationError),
+
+    /// FFI error from the closed-source prover
+    #[error("FFI error (code {0})")]
+    FFIError(i32),
+
+    /// Library not available
+    #[error("Library not available: {0}")]
+    LibraryNotAvailable(String),
+
+    /// Prover operation failed
+    #[error("Prover failed: {0}")]
+    ProverFailed(String),
+
+    /// IO error
+    #[error("IO error: {0}")]
+    Io(#[from] std::io::Error),
+}
+
+impl ProverError {
+    /// Create an error from an FFI error code
+    pub fn from_ffi_code(code: i32) -> Self {
+        match code {
+            -1 => ProverError::ProverFailed("General prover failure".to_string()),
+            -2 => ProverError::InvalidInput("Invalid constraint system".to_string()),
+            -3 => ProverError::InvalidInput("Invalid witness data".to_string()),
+            -4 => ProverError::ProverFailed("Out of memory".to_string()),
+            _ => ProverError::FFIError(code),
+        }
+    }
+}
+
+/// Result type for prover operations
+pub type Result<T> = std::result::Result<T, ProverError>;