fix: middleware uses sentinel error (#1463)

middleware/circuitbreaker/circuitbreaker.go

@@ -11,6 +11,9 @@ import (
 	"github.com/go-kratos/kratos/v2/transport"
 )
 
+// ErrNotAllowed is request failed due to circuit breaker triggered.
+var ErrNotAllowed = errors.New(503, "CIRCUITBREAKER", "request failed due to circuit breaker triggered")
+
 // Option is circuit breaker option.
 type Option func(*options)
 
@@ -46,7 +49,7 @@ func Client(opts ...Option) middleware.Middleware {
 				// NOTE: when client reject requets locally,
 				// continue add counter let the drop ratio higher.
 				breaker.MarkFailed()
-				return nil, errors.New(503, "CIRCUITBREAKER", "request failed due to circuit breaker triggered")
+				return nil, ErrNotAllowed
 			}
 			// allowed
 			reply, err := handler(ctx, req)

middleware/ratelimit/ratelimit.go

@@ -9,6 +9,9 @@ import (
 	"github.com/go-kratos/kratos/v2/middleware"
 )
 
+// ErrLimitExceed is service unavailable due to rate limit exceeded.
+var ErrLimitExceed = errors.New(429, "RATELIMIT", "service unavailable due to rate limit exceeded")
+
 // Option is ratelimit option.
 type Option func(*options)
 
@@ -37,7 +40,7 @@ func Server(opts ...Option) middleware.Middleware {
 			done, e := options.limiter.Allow()
 			if e != nil {
 				// rejected
-				return nil, errors.New(429, "RATELIMIT", "service unavailable due to rate limit exceeded")
+				return nil, ErrLimitExceed
 			}
 			// allowed
 			reply, err = handler(ctx, req)

middleware/recovery/recovery.go

@@ -2,7 +2,6 @@ package recovery
 
 import (
 	"context"
-	"fmt"
 	"runtime"
 
 	"github.com/go-kratos/kratos/v2/errors"
@@ -10,6 +9,9 @@ import (
 	"github.com/go-kratos/kratos/v2/middleware"
 )
 
+// ErrUnknownRequest is unknown request error.
+var ErrUnknownRequest = errors.InternalServer("UNKNOWN", "unknown request error")
+
 // HandlerFunc is recovery handler func.
 type HandlerFunc func(ctx context.Context, req, err interface{}) error
 
@@ -40,7 +42,7 @@ func Recovery(opts ...Option) middleware.Middleware {
 	op := options{
 		logger: log.DefaultLogger,
 		handler: func(ctx context.Context, req, err interface{}) error {
-			return errors.InternalServer("RECOVERY", fmt.Sprintf("panic triggered: %v", err))
+			return ErrUnknownRequest
 		},
 	}
 	for _, o := range opts {