feat(middleware/breaker): add circuit breaker middleware (#1299)

* add breaker middleware

middleware/circuitbreaker/circuitbreaker.go

@@ -0,0 +1,53 @@
+package circuitbreaker
+
+import (
+	"context"
+
+	"github.com/go-kratos/kratos/v2/errors"
+	"github.com/go-kratos/kratos/v2/middleware"
+	"github.com/go-kratos/sra/circuitbreaker"
+	"github.com/go-kratos/sra/circuitbreaker/sre"
+)
+
+type Option func(*options)
+
+// WithBreaker set circuit breaker implentation
+func WithBreaker(breaker circuitbreaker.CircuitBreaker) Option {
+	return func(o *options) {
+		o.breaker = breaker
+	}
+}
+
+type options struct {
+	breaker circuitbreaker.CircuitBreaker
+}
+
+// Client circuitbreaker middleware will return errBreakerTriggered when the circuit
+// breaker is triggered and the request is rejected directly.
+func Client(opts ...Option) middleware.Middleware {
+	options := &options{
+		breaker: sre.NewBreaker(),
+	}
+	for _, o := range opts {
+		o(options)
+	}
+	return func(handler middleware.Handler) middleware.Handler {
+		return func(ctx context.Context, req interface{}) (interface{}, error) {
+			if err := options.breaker.Allow(); err != nil {
+				// rejected
+				// NOTE: when client reject requets locally,
+				// continue add counter let the drop ratio higher.
+				options.breaker.MarkFailed()
+				return nil, errors.New(503, "CIRCUITBREAKER", "request failed due to circuit breaker triggered")
+			}
+			// allowed
+			reply, err := handler(ctx, req)
+			if err != nil {
+				options.breaker.MarkFailed()
+			} else {
+				options.breaker.MarkSuccess()
+			}
+			return reply, err
+		}
+	}
+}