middleware.go

package circuitbreaker

import (
	"errors"
	"net/http"
)

// responseRecorder wraps http.ResponseWriter to capture the status code.
type responseRecorder struct {
	http.ResponseWriter
	statusCode int
}

// Middleware returns HTTP middleware that wraps requests with circuit breaker protection.
func Middleware(cb *CircuitBreaker) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			_, err := cb.Execute(func() (any, error) {
				rec := &responseRecorder{ResponseWriter: w, statusCode: http.StatusOK}
				next.ServeHTTP(rec, r)
				if rec.statusCode >= 500 {
					return nil, errors.New("internal server error")
				}
				return nil, nil
			})
			if errors.Is(err, ErrCircuitOpen) {
				http.Error(w, http.StatusText(http.StatusServiceUnavailable), http.StatusServiceUnavailable)
			}
		})
	}
}

func (r *responseRecorder) WriteHeader(statusCode int) {
	r.statusCode = statusCode
	r.ResponseWriter.WriteHeader(statusCode)
}