swipl-mcp-server

# Code Review: SWI-Prolog MCP Server ## Executive Summary I've conducted a comprehensive review of your SWI-Prolog MCP Server codebase. Overall, this is a well-architected project with strong security considerations and good separation of concerns. However, I've identified several critical issues that should be addressed to improve performance, reliability, and maintainability. ## 🚨 Critical Issues (Priority 1) ### 1. **Memory Leak in Response Buffer** - `src/PrologInterface.ts:88` **Issue**: The `responseBuffer: string[]` array is declared but never used, and the `inputBuffer: string` can grow unbounded if incomplete lines accumulate. **Risk**: Potential memory exhaustion with large responses or network issues. **Fix**: ```typescript // Add buffer size limits private static readonly MAX_BUFFER_SIZE = 1024 * 1024; // 1MB private handleResponse(data: string): void { this.inputBuffer += data; // Prevent unbounded growth if (this.inputBuffer.length > PrologInterface.MAX_BUFFER_SIZE) { logger.error("Input buffer overflow, truncating"); this.inputBuffer = this.inputBuffer.slice(-PrologInterface.MAX_BUFFER_SIZE / 2); } // ... rest of method } ``` ### 2. **Race Condition in Command Queue** - `src/PrologInterface.ts:547-555` **Issue**: Command queue error handling can cause subsequent commands to fail even if they're valid, due to improper error propagation in the chain. **Risk**: System becomes unusable after first error. **Fix**: Isolate queue errors per command rather than propagating to subsequent commands. ### 3. **Inefficient String Processing** - `src/PrologInterface.ts:255-256` **Issue**: Using `split("\n")` and `pop()` repeatedly on potentially large strings is O(n) per line, creating O(n²) complexity for large responses. **Algorithmic Improvement**: ```typescript private processLines(): void { let startPos = 0; while (true) { const lineEnd = this.inputBuffer.indexOf('\n', startPos); if (lineEnd === -1) { // Keep remaining incomplete line this.inputBuffer = this.inputBuffer.slice(startPos); break; } const line = this.inputBuffer.slice(startPos, lineEnd).trim(); if (line) this.processResponseLine(line); startPos = lineEnd + 1; } } ``` ## ⚠️ High Priority Issues (Priority 2) ### 4. **Timeout Logic Inconsistency** - `src/PrologInterface.ts:535` **Issue**: Default timeout fallback uses `DEFAULT_READY_TIMEOUT_MS` instead of a query-specific default. ### 5. **Redundant Promise Wrapping** - `src/PrologInterface.ts:482-555` **Issue**: Complex nested promise structure with `outerResolve/outerReject` and `wrappedResolve/wrappedReject` makes error handling error-prone. ### 6. **Missing Input Validation** - `src/tools.ts:299` **Issue**: Query length validation is inconsistent across different tools (some check 1000 chars, others check 5000). ### 7. **Session State Management Complexity** - `src/PrologInterface.ts:97` **Issue**: 7 different session states with complex transitions could lead to edge cases. ## 🔧 Medium Priority Issues (Priority 3) ### 8. **Code Duplication in Tool Handlers** **Issue**: Similar error handling patterns repeated across `dbLoad`, `queryStart`, `queryStartEngine` (processing time calculation, error response formatting). **Fix**: Extract common error handling utility: ```typescript function createToolResponse( result: { success: boolean; data?: any; error?: string }, startTime: number ): ToolResponse { const processingTime = Date.now() - startTime; // ... common response formatting } ``` ### 9. **Magic String Constants** - Multiple files **Issue**: String literals like `"@@READY@@"`, `"solution("` scattered without centralization. ### 10. **Inconsistent Error Handling** **Issue**: Some errors throw, others return error responses, making client handling unpredictable. ## 👍 Positive Aspects ### Excellent Security Implementation - Comprehensive path validation with `ALLOWED_DIR` restriction - Pre-execution dangerous predicate detection - Good use of library(sandbox) for validation - Well-structured error types with `PrologErrorKind` enum ### Good Architecture Patterns - Proper separation of concerns (Interface, Tools, Schemas) - Command queue for serialization prevents race conditions - Comprehensive test coverage with edge case testing - Good logging with privacy-aware redaction ### Code Quality - Strong TypeScript typing - Good use of environment variables for configuration - Comprehensive documentation in README - Well-structured schemas with Zod validation ## 📊 Performance Analysis ### Bottlenecks Identified: 1. **String processing** in `handleResponse()` - O(n²) with large responses 2. **Synchronous file I/O** in `validateFilePath()` - could block event loop 3. **Command queuing overhead** - every command waits for previous completion ### Memory Usage: - **Good**: Limited process instances, proper cleanup on exit - **Concern**: Unbounded buffer growth potential - **Improvement**: Add memory monitoring and limits ## 🔄 Recommended Optimizations ### 1. Implement Buffer Management ```typescript private static readonly MAX_BUFFER_SIZE = 1024 * 1024; private static readonly MAX_QUERY_PROMISES = 100; // Add cleanup for old promises private cleanupExpiredPromises(): void { if (this.queryPromises.size > PrologInterface.MAX_QUERY_PROMISES) { // Remove oldest promises if map grows too large } } ``` ### 2. Batch Command Processing Allow grouping non-interfering commands to reduce queue overhead. ### 3. Add Performance Metrics ```typescript // Add timing metrics to identify slow operations private performanceMetrics = { queryStartTime: 0, responseParseTime: 0, commandQueueWait: 0 }; ``` ## 🧪 Testing Recommendations The test suite is comprehensive, but consider adding: 1. **Load testing** for memory leak detection 2. **Concurrent access testing** for race conditions 3. **Performance benchmarking** for timeout edge cases 4. **Security penetration testing** for path traversal attempts ## 📝 Code Quality Score: B+ (85/100) **Strengths**: Security, architecture, error handling, documentation **Improvement areas**: Performance optimization, code deduplication, buffer management This codebase demonstrates mature engineering practices with room for performance optimizations. The security implementation is particularly noteworthy and should be maintained as-is.