Task 1.10: The HTTP Handler Interface

Summary

Refactor buylater.email handlers to implement the http.Handler interface properly, improving code organization and preparing for advanced middleware and handler patterns.

Motivation

Following Let’s Go Chapter 2.10, we need to understand and implement the http.Handler interface correctly. This will improve our code’s idiomatic Go style and prepare us for advanced patterns like middleware, custom handler types, and better testing strategies.

Acceptance Criteria

Understand and document the http.Handler interface requirements
Refactor existing handler functions to implement proper interface patterns
Create custom handler types for buylater.email specific functionality
Implement handler methods that satisfy http.Handler interface
Use http.HandlerFunc for simple handler functions where appropriate
Demonstrate both function handlers and custom type handlers
Maintain all existing functionality while improving code structure
Prepare foundation for future middleware implementation

Technical Requirements

Handler Interface Implementation

type Handler interface {
    ServeHTTP(ResponseWriter, *Request)
}

Implementation Patterns

Convert simple handlers to http.HandlerFunc where appropriate
Create custom handler types for complex buylater.email logic
Implement ServeHTTP methods for custom types
Use method receivers for stateful handlers
Maintain clean separation of concerns

Dependencies

Task 1.9 completed (static file serving foundation)

Testing Strategy

Unit Tests

Test handler interface compliance
Verify ServeHTTP method implementations
Test custom handler type functionality

Integration Tests

All routes work with new handler implementations
Handler interface contracts are satisfied

Manual Testing

All existing routes (/, /buygone/view, /buygone/create) function correctly
POST requests still return proper status codes and headers
Static file serving continues to work
No regression in functionality after refactoring

Definition of Done

All acceptance criteria met
All specified tests pass
Code follows project conventions (go fmt, go vet)
Handler implementations are idiomatic Go
Interface contracts properly satisfied
Code is well-documented with examples
No functional regressions introduced
Human verification completed successfully
Git commit created with proper message format

Implementation Notes

Approach

Gradually refactor existing handlers to demonstrate different patterns for implementing the http.Handler interface. Focus on educational value while maintaining functionality.

Handler Patterns to Implement

Function Handlers: Use http.HandlerFunc for simple stateless handlers
Custom Types: Create custom handler types for buylater.email specific logic
Method Handlers: Implement ServeHTTP methods on custom types
Stateful Handlers: Demonstrate handlers with embedded state/configuration

Key Files to Modify

cmd/web/handlers.go - Refactor to use proper handler patterns
cmd/web/main.go - Update route registration for new handler types

Example Implementation Patterns

// Function handler
func homeHandler(w http.ResponseWriter, r *http.Request) { ... }

// Custom handler type
type SubmissionHandler struct {
    logger *log.Logger
}

func (sh *SubmissionHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) { ... }

Potential Risks

Handler signature changes could break existing functionality
Method receiver patterns might introduce complexity
Interface implementation errors could cause runtime panics

Success Metrics

Clean, idiomatic Go code that properly implements the http.Handler interface while maintaining all existing buylater.email functionality and preparing for future advanced patterns.

Blocks: Future middleware implementation and advanced handler patterns
Blocked by: Task 1.9 (needs complete foundation before refactoring)
Related: Clean code architecture and Go best practices

Implementation Log

Implementation details will be recorded here during development.

Final Verification

Human Tester: [Name]
Date Completed: [YYYY-MM-DD]
Verification Result: [Pass/Fail]
Notes: [Any issues found or additional observations]

task_id: “1.10” title: “The HTTP Handler Interface” status: “pending” priority: “high” estimated_effort: “medium” created: “2025-07-22” assigned_to: “pair” related_rfds: “RFD 004”