RFC: [Go] Middleware V2

[apascal07]

View doc: https://github.com/firebase/genkit/blob/ap/go-middleware-design/docs/go-middleware-design.md

[gemini-code-assist]

Summary of Changes

Hello @apascal07, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This RFC outlines a significant redesign of the middleware system for Genkit Go, moving from a limited model-only wrapper to a comprehensive framework. The new design introduces a flexible Middleware interface with hooks for various stages of AI generation, including tool execution and overall generation flow, allowing for per-invocation state and robust plugin integration. This change aims to enhance extensibility and control over AI generation processes, with a clear path for deprecating older middleware implementations.

Highlights

• New Middleware Interface: Introduced a new Middleware interface with Generate, Model, and Tool hooks, providing comprehensive control over the AI generation lifecycle, including tool execution and overall generation flow.
• Per-Invocation State: The Middleware interface now includes a New() method, enabling the creation of fresh middleware instances for each ai.Generate() call, allowing for per-invocation state management.
• Base Implementation for Convenience: A BaseMiddleware struct is provided to offer default pass-through behavior for hooks, simplifying the implementation of custom middleware.
• Enhanced Registration and Configuration: New mechanisms like DefineMiddlewareFor and NewMiddlewareFor facilitate middleware registration, expose configuration schemas to the Dev UI, and enable dynamic configuration from JSON.
• Plugin Integration: A MiddlewarePlugin interface has been added, allowing plugins to automatically register middleware and provide factory methods for injecting dependencies into middleware instances.
• API and Schema Updates: The API and associated Zod and Go schemas have been updated to support middleware references and their configurations within GenerateActionOptions, ensuring seamless integration with the Dev UI.
• Reflection API Endpoint: A new reflection API endpoint, GET /api/middlewares, has been introduced to list all registered middleware, aiding in discovery and dynamic UI generation.
• Deprecation Plan: Existing core.Middleware and ai.ModelMiddleware types are slated for deprecation, with internal middleware being refactored to use the new design and a plan for complete removal in a future major version.

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Changelog

• docs/go-middleware-design.md
  • This new document details the proposed Middleware V2 design for Genkit Go, covering its core interface, usage, registration, plugin integration, API schema, and deprecation strategy for existing middleware.

Activity

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Code Review

This pull request introduces a comprehensive design for a new middleware system in Genkit Go, addressing the limitations of the existing ModelMiddleware. The document clearly outlines the core interface, base implementation, usage patterns, and integration points for plugins and the API. The examples, especially the RetryMiddleware and TracingMiddleware, effectively demonstrate how to implement and use the new system, including handling per-invocation state and injected dependencies. The deprecation plan for older middleware types is also well-defined. Overall, this is a well-thought-out and clearly documented design that significantly enhances the flexibility and power of middleware in Genkit Go.