Behavioral

Chain of Responsibility

Passes requests along a chain of handlers.

Middleware chainsEvent handlingApproval workflows

Understanding Chain of Responsibility

The Chain of Responsibility pattern links a chain of handler objects, where each handler either processes a request or passes it to the next handler in the chain. This decouples the sender of a request from its receivers, allowing multiple objects a chance to handle it. In Go, each handler implements a common interface and holds a reference to the next handler. This pattern is the foundation of HTTP middleware pipelines in frameworks like Chi and Echo, where each middleware can process a request, modify it, or pass it along.

Key Concepts

  • •Handler interface — each handler implements the same interface with a method to process or delegate requests
  • •Next reference — each handler holds a pointer to the next handler, forming a linked chain
  • •Short-circuiting — a handler can choose to handle the request and stop the chain, or pass to the next handler
  • •Dynamic assembly — the chain can be configured at runtime by linking handlers in different orders

When to Use

✅ Use when
  • • Multiple objects may handle a request and the handler isn\'t known in advance
  • • You want to assemble processing pipelines dynamically
  • • You\'re building middleware chains (HTTP, logging, validation)
  • • Processing should continue until one handler can deal with the request
⚠️ Avoid when
  • • Every request must be handled — an unhandled request falling off the chain is a bug
  • • The chain is always the same and a simple function call sequence would be clearer
  • • Performance is critical and the chain traversal adds measurable overhead

Structure

Client
↓ sends request
Handler A → Handler B → Handler C
↓ each may handle or pass
Process or Forward

How It Works

Request
Handler1
handles < 10
Handler2
handles < 20
Handler3
handles all
Request enters chain
1

Request Arrives

A request enters the chain.

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Basic Implementation

Request handlers based on value size:

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Real-World Example: Logging System

Multi-level logging with console, file, and alerts:

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