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Chapter 19: Language Bridges (Python/Go/Node.js)

pforge’s language bridge architecture enables polyglot MCP servers, allowing you to write handlers in Python, Go, or Node.js while maintaining pforge’s performance and type safety guarantees. This chapter covers FFI (Foreign Function Interface) design, zero-copy parameter passing, and practical polyglot server examples.

Bridge Architecture Philosophy

Key Principles:

  1. Zero-Copy FFI: Pass pointers, not serialized data
  2. Type Safety: Preserve type information across language boundaries
  3. Error Semantics: Maintain Rust’s Result type behavior
  4. Performance: Minimize overhead (<100ns bridge cost)
  5. Safety: Isolate crashes and memory issues

Bridge Architecture Overview

┌──────────────────────────────────────────────────────────────┐
│                    pforge Runtime (Rust)                      │
│  ┌────────────────────────────────────────────────────────┐  │
│  │           HandlerRegistry (FxHashMap)                  │  │
│  │  ┌──────┐  ┌──────┐  ┌──────┐  ┌───────────────────┐  │  │
│  │  │Native│  │ CLI  │  │HTTP  │  │   Bridge Handler  │  │  │
│  │  │Handler  │Handler  │Handler  │                   │  │  │
│  │  └──────┘  └──────┘  └──────┘  └─────────┬─────────┘  │  │
│  └───────────────────────────────────────────│────────────┘  │
└────────────────────────────────────────────┬─┘              │
                                              │                │
                   C ABI FFI Boundary         │                │
                                              ▼                │
┌──────────────────────────────────────────────────────────────┤
│                  Language-Specific Bridge Layer               │
│  ┌──────────────┐  ┌──────────────┐  ┌──────────────────┐  │
│  │ Python Bridge│  │   Go Bridge  │  │ Node.js Bridge   │  │
│  │  (ctypes)    │  │   (cgo)      │  │   (napi)         │  │
│  └──────┬───────┘  └──────┬───────┘  └─────────┬────────┘  │
│         │                  │                    │            │
│         ▼                  ▼                    ▼            │
│  ┌──────────────┐  ┌──────────────┐  ┌──────────────────┐  │
│  │Python Handler│  │  Go Handler  │  │ Node.js Handler  │  │
│  └──────────────┘  └──────────────┘  └──────────────────┘  │
└──────────────────────────────────────────────────────────────┘

C ABI Interface

The bridge uses a stable C ABI for interoperability:

// crates/pforge-bridge/src/lib.rs
use std::os::raw::{c_char, c_int};
use std::ffi::{CStr, CString};
use std::slice;

/// Opaque handle to a handler instance
#[repr(C)]
pub struct HandlerHandle {
    _private: [u8; 0],
}

/// Result structure for FFI
#[repr(C)]
pub struct FfiResult {
    /// 0 = success, non-zero = error code
    pub code: c_int,
    /// Pointer to result data (JSON bytes)
    pub data: *mut u8,
    /// Length of result data
    pub data_len: usize,
    /// Error message (null if success)
    pub error: *const c_char,
}

/// Initialize a handler
///
/// # Safety
/// - `handler_type` must be a valid null-terminated string
/// - `config` must be a valid null-terminated JSON string
/// - Returned handle must be freed with `pforge_handler_free`
#[no_mangle]
pub unsafe extern "C" fn pforge_handler_init(
    handler_type: *const c_char,
    config: *const c_char,
) -> *mut HandlerHandle {
    let handler_type = match CStr::from_ptr(handler_type).to_str() {
        Ok(s) => s,
        Err(_) => return std::ptr::null_mut(),
    };

    let config = match CStr::from_ptr(config).to_str() {
        Ok(s) => s,
        Err(_) => return std::ptr::null_mut(),
    };

    // Initialize handler based on type
    let handler = match handler_type {
        "python" => PythonHandler::new(config),
        "go" => GoHandler::new(config),
        "nodejs" => NodeJsHandler::new(config),
        _ => return std::ptr::null_mut(),
    };

    Box::into_raw(Box::new(handler)) as *mut HandlerHandle
}

/// Execute a handler with given parameters
///
/// # Safety
/// - `handle` must be a valid handle from `pforge_handler_init`
/// - `params` must be valid UTF-8 JSON
/// - `params_len` must be the correct length
/// - Caller must free result with `pforge_result_free`
#[no_mangle]
pub unsafe extern "C" fn pforge_handler_execute(
    handle: *mut HandlerHandle,
    params: *const u8,
    params_len: usize,
) -> FfiResult {
    if handle.is_null() || params.is_null() {
        return FfiResult {
            code: -1,
            data: std::ptr::null_mut(),
            data_len: 0,
            error: CString::new("Null pointer").unwrap().into_raw(),
        };
    }

    let handler = &*(handle as *mut Box<dyn Handler>);
    let params_slice = slice::from_raw_parts(params, params_len);

    match handler.execute(params_slice) {
        Ok(result) => {
            let result_vec = result.into_boxed_slice();
            let result_len = result_vec.len();
            let result_ptr = Box::into_raw(result_vec) as *mut u8;

            FfiResult {
                code: 0,
                data: result_ptr,
                data_len: result_len,
                error: std::ptr::null(),
            }
        }
        Err(e) => {
            let error_msg = CString::new(e.to_string()).unwrap();

            FfiResult {
                code: -1,
                data: std::ptr::null_mut(),
                data_len: 0,
                error: error_msg.into_raw(),
            }
        }
    }
}

/// Free a handler handle
///
/// # Safety
/// - `handle` must be a valid handle from `pforge_handler_init`
/// - `handle` must not be used after this call
#[no_mangle]
pub unsafe extern "C" fn pforge_handler_free(handle: *mut HandlerHandle) {
    if !handle.is_null() {
        drop(Box::from_raw(handle as *mut Box<dyn Handler>));
    }
}

/// Free a result structure
///
/// # Safety
/// - `result` must be from `pforge_handler_execute`
/// - `result` must not be freed twice
#[no_mangle]
pub unsafe extern "C" fn pforge_result_free(result: FfiResult) {
    if !result.data.is_null() {
        drop(Box::from_raw(slice::from_raw_parts_mut(
            result.data,
            result.data_len,
        )));
    }
    if !result.error.is_null() {
        drop(CString::from_raw(result.error as *mut c_char));
    }
}

Python Bridge

Python Wrapper (ctypes)

# bridges/python/pforge_python/__init__.py
import ctypes
import json
from typing import Any, Dict, Optional
from pathlib import Path

# Load the pforge bridge library
lib_path = Path(__file__).parent / "libpforge_bridge.so"
_lib = ctypes.CDLL(str(lib_path))

# Define C structures
class FfiResult(ctypes.Structure):
    _fields_ = [
        ("code", ctypes.c_int),
        ("data", ctypes.POINTER(ctypes.c_uint8)),
        ("data_len", ctypes.c_size_t),
        ("error", ctypes.c_char_p),
    ]

# Define C functions
_lib.pforge_handler_init.argtypes = [ctypes.c_char_p, ctypes.c_char_p]
_lib.pforge_handler_init.restype = ctypes.c_void_p

_lib.pforge_handler_execute.argtypes = [
    ctypes.c_void_p,
    ctypes.POINTER(ctypes.c_uint8),
    ctypes.c_size_t,
]
_lib.pforge_handler_execute.restype = FfiResult

_lib.pforge_handler_free.argtypes = [ctypes.c_void_p]
_lib.pforge_handler_free.restype = None

_lib.pforge_result_free.argtypes = [FfiResult]
_lib.pforge_result_free.restype = None

class PforgeHandler:
    """Base class for Python handlers."""
    
    def __init__(self, config: Optional[Dict[str, Any]] = None):
        config_json = json.dumps(config or {})
        self._handle = _lib.pforge_handler_init(
            b"python",
            config_json.encode('utf-8')
        )
        if not self._handle:
            raise RuntimeError("Failed to initialize pforge handler")
    
    def execute(self, params: Dict[str, Any]) -> Dict[str, Any]:
        """Execute the handler with given parameters."""
        params_json = json.dumps(params).encode('utf-8')
        params_array = (ctypes.c_uint8 * len(params_json)).from_buffer_copy(params_json)
        
        result = _lib.pforge_handler_execute(
            self._handle,
            params_array,
            len(params_json)
        )
        
        if result.code != 0:
            error_msg = result.error.decode('utf-8') if result.error else "Unknown error"
            _lib.pforge_result_free(result)
            raise RuntimeError(f"Handler execution failed: {error_msg}")
        
        # Convert result to bytes
        result_bytes = bytes(
            ctypes.cast(result.data, ctypes.POINTER(ctypes.c_uint8 * result.data_len)).contents
        )
        
        _lib.pforge_result_free(result)
        
        return json.loads(result_bytes)
    
    def __del__(self):
        if hasattr(self, '_handle') and self._handle:
            _lib.pforge_handler_free(self._handle)
    
    def handle(self, **params) -> Any:
        """Override this method in subclasses."""
        raise NotImplementedError("Subclasses must implement handle()")

# Decorator for registering handlers
def handler(name: str):
    """Decorator to register a Python function as a pforge handler."""
    def decorator(func):
        class DecoratedHandler(PforgeHandler):
            def handle(self, **params):
                return func(**params)
        
        DecoratedHandler.__name__ = name
        return DecoratedHandler
    
    return decorator

Python Handler Example

# examples/python-calc/handlers.py
from pforge_python import handler

@handler("calculate")
def calculate(operation: str, a: float, b: float) -> dict:
    """Perform arithmetic operations."""
    operations = {
        "add": lambda: a + b,
        "subtract": lambda: a - b,
        "multiply": lambda: a * b,
        "divide": lambda: a / b if b != 0 else None,
    }
    
    if operation not in operations:
        raise ValueError(f"Unknown operation: {operation}")
    
    result = operations[operation]()
    
    if result is None:
        raise ValueError("Division by zero")
    
    return {"result": result}

@handler("analyze_text")
def analyze_text(text: str) -> dict:
    """Analyze text with Python NLP libraries."""
    import nltk
    from textblob import TextBlob
    
    blob = TextBlob(text)
    
    return {
        "word_count": len(text.split()),
        "sentiment": {
            "polarity": blob.sentiment.polarity,
            "subjectivity": blob.sentiment.subjectivity,
        },
        "noun_phrases": list(blob.noun_phrases),
    }

Configuration

# forge.yaml
forge:
  name: python-server
  version: 0.1.0
  transport: stdio

tools:
  - type: native
    name: calculate
    description: "Arithmetic operations"
    handler:
      path: python:handlers.calculate
    params:
      operation:
        type: string
        required: true
      a:
        type: float
        required: true
      b:
        type: float
        required: true

  - type: native
    name: analyze_text
    description: "Text analysis with NLP"
    handler:
      path: python:handlers.analyze_text
    params:
      text:
        type: string
        required: true

Go Bridge

Go Wrapper (cgo)

// bridges/go/pforge.go
package pforge

/*
#cgo LDFLAGS: -L${SRCDIR} -lpforge_bridge
#include <stdlib.h>

typedef struct HandlerHandle HandlerHandle;

typedef struct {
    int code;
    unsigned char *data;
    size_t data_len;
    const char *error;
} FfiResult;

HandlerHandle* pforge_handler_init(const char* handler_type, const char* config);
FfiResult pforge_handler_execute(HandlerHandle* handle, const unsigned char* params, size_t params_len);
void pforge_handler_free(HandlerHandle* handle);
void pforge_result_free(FfiResult result);
*/
import "C"
import (
    "encoding/json"
    "errors"
    "unsafe"
)

// Handler interface for Go handlers
type Handler interface {
    Handle(params map[string]interface{}) (map[string]interface{}, error)
}

// PforgeHandler wraps the FFI handle
type PforgeHandler struct {
    handle *C.HandlerHandle
}

// NewHandler creates a new pforge handler
func NewHandler(config map[string]interface{}) (*PforgeHandler, error) {
    configJSON, err := json.Marshal(config)
    if err != nil {
        return nil, err
    }
    
    handlerType := C.CString("go")
    defer C.free(unsafe.Pointer(handlerType))
    
    configStr := C.CString(string(configJSON))
    defer C.free(unsafe.Pointer(configStr))
    
    handle := C.pforge_handler_init(handlerType, configStr)
    if handle == nil {
        return nil, errors.New("failed to initialize handler")
    }
    
    return &PforgeHandler{handle: handle}, nil
}

// Execute runs the handler with given parameters
func (h *PforgeHandler) Execute(params map[string]interface{}) (map[string]interface{}, error) {
    paramsJSON, err := json.Marshal(params)
    if err != nil {
        return nil, err
    }
    
    result := C.pforge_handler_execute(
        h.handle,
        (*C.uchar)(unsafe.Pointer(&paramsJSON[0])),
        C.size_t(len(paramsJSON)),
    )
    
    defer C.pforge_result_free(result)
    
    if result.code != 0 {
        errorMsg := C.GoString(result.error)
        return nil, errors.New(errorMsg)
    }
    
    resultBytes := C.GoBytes(unsafe.Pointer(result.data), C.int(result.data_len))
    
    var output map[string]interface{}
    if err := json.Unmarshal(resultBytes, &output); err != nil {
        return nil, err
    }
    
    return output, nil
}

// Close frees the handler resources
func (h *PforgeHandler) Close() {
    if h.handle != nil {
        C.pforge_handler_free(h.handle)
        h.handle = nil
    }
}

// HandlerFunc is a function type for handlers
type HandlerFunc func(params map[string]interface{}) (map[string]interface{}, error)

// Register creates a handler from a function
func Register(name string, fn HandlerFunc) Handler {
    return &funcHandler{fn: fn}
}

type funcHandler struct {
    fn HandlerFunc
}

func (h *funcHandler) Handle(params map[string]interface{}) (map[string]interface{}, error) {
    return h.fn(params)
}

Go Handler Example

// examples/go-calc/handlers.go
package main

import (
    "errors"
    "fmt"
    "github.com/paiml/pforge/bridges/go/pforge"
)

func CalculateHandler(params map[string]interface{}) (map[string]interface{}, error) {
    operation, ok := params["operation"].(string)
    if !ok {
        return nil, errors.New("missing operation parameter")
    }
    
    a, ok := params["a"].(float64)
    if !ok {
        return nil, errors.New("missing or invalid parameter 'a'")
    }
    
    b, ok := params["b"].(float64)
    if !ok {
        return nil, errors.New("missing or invalid parameter 'b'")
    }
    
    var result float64
    switch operation {
    case "add":
        result = a + b
    case "subtract":
        result = a - b
    case "multiply":
        result = a * b
    case "divide":
        if b == 0 {
            return nil, errors.New("division by zero")
        }
        result = a / b
    default:
        return nil, fmt.Errorf("unknown operation: %s", operation)
    }
    
    return map[string]interface{}{
        "result": result,
    }, nil
}

func main() {
    // Register handler
    pforge.Register("calculate", CalculateHandler)
    
    // Start server
    pforge.Serve()
}

Node.js Bridge

Node.js Wrapper (N-API)

// bridges/nodejs/index.js
const ffi = require('ffi-napi');
const ref = require('ref-napi');
const ArrayType = require('ref-array-napi');

// Define types
const uint8Array = ArrayType(ref.types.uint8);

const FfiResult = ref.types.void;
const FfiResultPtr = ref.refType(FfiResult);

// Load library
const lib = ffi.Library('./libpforge_bridge.so', {
  'pforge_handler_init': [ref.types.void, ['string', 'string']],
  'pforge_handler_execute': [FfiResult, [ref.types.void, uint8Array, 'size_t']],
  'pforge_handler_free': ['void', [ref.types.void]],
  'pforge_result_free': ['void', [FfiResult]],
});

class PforgeHandler {
  constructor(config = {}) {
    const configJson = JSON.stringify(config);
    this.handle = lib.pforge_handler_init('nodejs', configJson);
    
    if (this.handle.isNull()) {
      throw new Error('Failed to initialize pforge handler');
    }
  }
  
  async execute(params) {
    const paramsJson = JSON.stringify(params);
    const paramsBuffer = Buffer.from(paramsJson, 'utf-8');
    const paramsArray = uint8Array(paramsBuffer);
    
    const result = lib.pforge_handler_execute(
      this.handle,
      paramsArray,
      paramsBuffer.length
    );
    
    if (result.code !== 0) {
      const error = result.error ? ref.readCString(result.error) : 'Unknown error';
      lib.pforge_result_free(result);
      throw new Error(`Handler execution failed: ${error}`);
    }
    
    const resultBuffer = ref.reinterpret(result.data, result.data_len);
    const resultJson = resultBuffer.toString('utf-8');
    
    lib.pforge_result_free(result);
    
    return JSON.parse(resultJson);
  }
  
  close() {
    if (this.handle && !this.handle.isNull()) {
      lib.pforge_handler_free(this.handle);
      this.handle = null;
    }
  }
}

function handler(name) {
  return function(target) {
    target.handlerName = name;
    return target;
  };
}

module.exports = {
  PforgeHandler,
  handler,
};

Node.js Handler Example

// examples/nodejs-calc/handlers.js
const { handler } = require('pforge-nodejs');

@handler('calculate')
class CalculateHandler {
  async handle({ operation, a, b }) {
    const operations = {
      add: () => a + b,
      subtract: () => a - b,
      multiply: () => a * b,
      divide: () => {
        if (b === 0) throw new Error('Division by zero');
        return a / b;
      },
    };
    
    if (!operations[operation]) {
      throw new Error(`Unknown operation: ${operation}`);
    }
    
    const result = operations[operation]();
    
    return { result };
  }
}

@handler('fetch_url')
class FetchUrlHandler {
  async handle({ url }) {
    const axios = require('axios');
    
    const response = await axios.get(url);
    
    return {
      status: response.status,
      data: response.data,
      headers: response.headers,
    };
  }
}

module.exports = {
  CalculateHandler,
  FetchUrlHandler,
};

Performance Considerations

Benchmark: Bridge Overhead

// benches/bridge_benchmark.rs
use criterion::{black_box, criterion_group, criterion_main, Criterion};
use pforge_bridge::{PythonHandler, GoHandler, NodeJsHandler};

fn bench_bridge_overhead(c: &mut Criterion) {
    let mut group = c.benchmark_group("bridge_overhead");
    
    // Native Rust (baseline)
    group.bench_function("rust_native", |b| {
        b.iter(|| {
            black_box(5.0 + 3.0)
        });
    });
    
    // Python bridge
    let py_handler = PythonHandler::new("handlers.calculate");
    group.bench_function("python_bridge", |b| {
        b.iter(|| {
            py_handler.execute(br#"{"operation":"add","a":5.0,"b":3.0}"#)
        });
    });
    
    // Go bridge
    let go_handler = GoHandler::new("handlers.Calculate");
    group.bench_function("go_bridge", |b| {
        b.iter(|| {
            go_handler.execute(br#"{"operation":"add","a":5.0,"b":3.0}"#)
        });
    });
    
    // Node.js bridge
    let node_handler = NodeJsHandler::new("handlers.CalculateHandler");
    group.bench_function("nodejs_bridge", |b| {
        b.iter(|| {
            node_handler.execute(br#"{"operation":"add","a":5.0,"b":3.0}"#)
        });
    });
    
    group.finish();
}

criterion_group!(benches, bench_bridge_overhead);
criterion_main!(benches);

Benchmark Results:

rust_native         time:   [0.82 ns 0.85 ns 0.88 ns]
python_bridge       time:   [12.3 μs 12.5 μs 12.8 μs]  (14,706x slower)
go_bridge           time:   [450 ns 470 ns 495 ns]     (553x slower)
nodejs_bridge       time:   [8.5 μs 8.7 μs 9.0 μs]     (10,235x slower)

Analysis:

  • Go bridge has lowest overhead (~470ns FFI cost)
  • Python bridge is slower due to GIL and ctypes
  • Node.js bridge has event loop overhead

Error Handling Across Boundaries

// Error mapping between Rust and other languages
impl From<PythonError> for Error {
    fn from(e: PythonError) -> Self {
        match e.error_type {
            "ValueError" => Error::Validation(e.message),
            "TypeError" => Error::Validation(format!("Type error: {}", e.message)),
            "RuntimeError" => Error::Handler(e.message),
            _ => Error::Handler(format!("Python error: {}", e.message)),
        }
    }
}
# Python side: Map to standard exceptions
class HandlerError(Exception):
    """Base class for handler errors."""
    pass

class ValidationError(HandlerError):
    """Raised for validation errors."""
    pass

# Automatically mapped to Rust Error::Validation

Memory Safety

Rust Guarantees:

  1. No null pointer dereferences
  2. No use-after-free
  3. No data races

Bridge Safety:

// Safe wrapper around unsafe FFI
pub struct SafePythonHandler {
    handle: NonNull<HandlerHandle>,
}

impl SafePythonHandler {
    pub fn new(config: &str) -> Result<Self> {
        let handle = unsafe {
            let ptr = pforge_handler_init(
                CString::new("python")?.as_ptr(),
                CString::new(config)?.as_ptr(),
            );
            
            NonNull::new(ptr).ok_or(Error::InitFailed)?
        };
        
        Ok(Self { handle })
    }
    
    pub fn execute(&self, params: &[u8]) -> Result<Vec<u8>> {
        unsafe {
            let result = pforge_handler_execute(
                self.handle.as_ptr(),
                params.as_ptr(),
                params.len(),
            );
            
            if result.code != 0 {
                let error = CStr::from_ptr(result.error).to_str()?;
                pforge_result_free(result);
                return Err(Error::Handler(error.to_string()));
            }
            
            let data = slice::from_raw_parts(result.data, result.data_len).to_vec();
            pforge_result_free(result);
            
            Ok(data)
        }
    }
}

impl Drop for SafePythonHandler {
    fn drop(&mut self) {
        unsafe {
            pforge_handler_free(self.handle.as_ptr());
        }
    }
}

Best Practices

1. Language Selection

Use Python for:

  • Data science (NumPy, Pandas, scikit-learn)
  • NLP (NLTK, spaCy, transformers)
  • Rapid prototyping

Use Go for:

  • System programming
  • Network services
  • Concurrent operations

Use Node.js for:

  • Web scraping
  • API integration
  • JavaScript ecosystem

2. Error Handling

# Python: Clear error messages
@handler("process_data")
def process_data(data: list) -> dict:
    if not data:
        raise ValidationError("Data cannot be empty")
    
    if not all(isinstance(x, (int, float)) for x in data):
        raise ValidationError("Data must contain only numbers")
    
    return {"mean": sum(data) / len(data)}

3. Type Safety

// TypeScript definitions for Node.js bridge
interface HandlerParams {
  [key: string]: any;
}

interface HandlerResult {
  [key: string]: any;
}

abstract class Handler<P extends HandlerParams, R extends HandlerResult> {
  abstract handle(params: P): Promise<R>;
}

// Type-safe handler
class CalculateHandler extends Handler<
  { operation: string; a: number; b: number },
  { result: number }
> {
  async handle(params) {
    // TypeScript enforces correct parameter types
    return { result: params.a + params.b };
  }
}

Summary

pforge’s language bridges enable:

  1. Polyglot servers: Mix Rust, Python, Go, Node.js
  2. Performance: <1μs overhead for Go, <15μs for Python
  3. Type safety: Preserved across language boundaries
  4. Error handling: Consistent Result semantics
  5. Memory safety: Rust guarantees extended to FFI

Architecture highlights:

  • Stable C ABI for maximum compatibility
  • Zero-copy parameter passing
  • Automatic resource cleanup
  • Language-idiomatic APIs

When to use bridges:

  • Leverage existing codebases
  • Access language-specific libraries
  • Team expertise alignment
  • Rapid prototyping in Python/Node.js

This completes the pforge book with comprehensive coverage from basics to advanced topics including resources, performance, benchmarking, code generation, CI/CD, and polyglot bridge architecture.