Design Pattern Review¶

This document explains how the MCP Server Fuzzer applies common design patterns, how well they fit the current implementation, and where future contributors can improve the architecture. Each section lists the primary patterns in play, a qualitative "fit score" (0-10), and concrete next steps.

Pattern Map¶

Module-by-Module Analysis¶

CLI Layer (Fit Score: 8/10)¶

• Patterns Used: Facade to shield users from subsystem complexity, Command objects for sub-commands/options, Builder for assembling runtime config.
• Strengths: The CLI is a clear entry point that composes transports, strategies, and reporters. Options map almost 1:1 to configuration objects.
• Gaps & Ideas: Reuse of parsing logic across sub-commands could improve if argument builders lived in a dedicated factory so the CLI does not own every instantiation detail.

Next steps: - Extract reusable CLI config builders so new commands inherit validation rules. - Create smoke tests that cover composite CLI scenarios (auth + transports + safety flags) to guard the Facade contract.

Transport Layer (Fit Score: 9/10)¶

• Patterns Used: Strategy for choosing HTTP/SSE/Stdio transports, Adapter to normalize differing protocol semantics, Abstract Factory for wiring the right transport + auth combo.
• Strengths: build_driver hides instantiation logic, and adapters expose uniform send/receive APIs. Test doubles are easy to swap in.
• Gaps & Ideas: Some transports share retry/backoff logic that could live in a Decorator for clarity.

Next steps: - Introduce a RetryingTransport decorator so timeouts/backoff are composable. - Document the adapter contract (open, close, send_message) to guide community transport additions.

Fuzzing Engine (Fit Score: 7/10)¶

• Patterns Used: Template Method drives fuzzing runs, Observer notifies reporters, Mediator coordinates strategies and safety modules.
• Strengths: The engine isolates orchestration from transport details and exposes hooks for reporting progress.
• Gaps & Ideas: Template steps are implicit in the engine's methods; naming them (prepare, execute, finalize) would make the template clearer.

Next steps: - Refactor engine workflows into explicit template methods to mitigate control flow duplication. - Introduce mediator interface tests to guarantee event ordering for reporters and safety filters.

Strategy System (Fit Score: 8/10)¶

• Patterns Used: Strategy for swapping data generators, Prototype for cloning request blueprints, Builder for constructing complex payloads.
• Strengths: Strategies encapsulate data semantics, which keeps fuzzing logic simple and testable.
• Gaps & Ideas: The builder/prototype separation is blurred; immutable strategy inputs would clarify responsibilities.

Next steps: - Add a registry (simple factory) so experimental strategies can be toggled at runtime. - Provide examples that show how to extend the Strategy interface for new domains (tools vs. resources).

Safety System (Fit Score: 7/10)¶

• Patterns Used: Chain of Responsibility for running filters in sequence, Decorator for layering mock responses and path blocking.
• Strengths: Safety features remain optional but composable—callers pass in the chain entry point.
• Gaps & Ideas: Chains are assembled imperatively; a configuration-driven builder would make the pattern more obvious.

Next steps: - Define a SafetyPolicy object that declares filter order and parameters. - Cover the chain with integration tests to ensure early exits and bypass clauses behave as expected.

Runtime & Process Management (Fit Score: 8/10)¶

• Patterns Used: State machine for process lifecycle, Watchdog pattern for supervising tasks, Object Pool/resource pool for concurrency limits.
• Strengths: Async primitives plus the watchdog isolate failure domains and keep resource usage predictable.
• Gaps & Ideas: Lifecycle transitions are implicit; documenting the state diagram would help contributors reason about edge cases.

Next steps: - Add a state transition table (docs or docstring) for the process manager. - Consider extracting the process pool into a reusable module for integration with future runners.

Reporting & Observability (Fit Score: 7/10)¶

• Patterns Used: Observer pattern for event sinks, Bridge to support JSON vs. Console outputs, Adapter for CI-friendly formats.
• Strengths: Reporters subscribe to the same event stream, enabling CLI, JSON, and text outputs without touching the engine.
• Gaps & Ideas: Event payloads are tightly coupled to engine internals; defining a stable DTO reduces accidental breakages.

Next steps: - Formalize event contracts (schema + version) to help external tooling. - Add regression tests to ensure reporters stay backward compatible.

Improvement Checklist¶

• Share code snippets in docs showing how to extend each layer.
• Automate linting/tests per module to validate pattern intent.
• Keep the pattern map updated whenever architecture changes.

Maintaining this review ensures new contributors can map their work to the existing architecture while spotting opportunities for better abstractions.