Add grpc health check. (#304)

* Add grpc health check.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* fix missing package.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* fix readme..

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* fix vet

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

vendor/google.golang.org/grpc/status/status.go

@@ -28,9 +28,11 @@
 package status
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/golang/protobuf/proto"
+	"github.com/golang/protobuf/ptypes"
 	spb "google.golang.org/genproto/googleapis/rpc/status"
 	"google.golang.org/grpc/codes"
 )
@@ -128,3 +130,39 @@ func FromError(err error) (s *Status, ok bool) {
 	}
 	return nil, false
 }
+
+// WithDetails returns a new status with the provided details messages appended to the status.
+// If any errors are encountered, it returns nil and the first error encountered.
+func (s *Status) WithDetails(details ...proto.Message) (*Status, error) {
+	if s.Code() == codes.OK {
+		return nil, errors.New("no error details for status with code OK")
+	}
+	// s.Code() != OK implies that s.Proto() != nil.
+	p := s.Proto()
+	for _, detail := range details {
+		any, err := ptypes.MarshalAny(detail)
+		if err != nil {
+			return nil, err
+		}
+		p.Details = append(p.Details, any)
+	}
+	return &Status{s: p}, nil
+}
+
+// Details returns a slice of details messages attached to the status.
+// If a detail cannot be decoded, the error is returned in place of the detail.
+func (s *Status) Details() []interface{} {
+	if s == nil || s.s == nil {
+		return nil
+	}
+	details := make([]interface{}, 0, len(s.s.Details))
+	for _, any := range s.s.Details {
+		detail := &ptypes.DynamicAny{}
+		if err := ptypes.UnmarshalAny(any, detail); err != nil {
+			details = append(details, err)
+			continue
+		}
+		details = append(details, detail.Message)
+	}
+	return details
+}