use the http3.CapsuleProtocolHeader instead of redefining it (#33)

client.go

@@ -45,7 +45,7 @@ func Dial(ctx context.Context, conn *http3.ClientConn, template *uritemplate.Tem
 		Method: http.MethodConnect,
 		Proto:  requestProtocol,
 		Host:   u.Host,
-		Header: http.Header{capsuleHeader: []string{capsuleProtocolHeaderValue}},
+		Header: http.Header{http3.CapsuleProtocolHeader: []string{capsuleProtocolHeaderValue}},
 		URL:    u,
 	}); err != nil {
 		return nil, nil, fmt.Errorf("connect-ip: failed to send request: %w", err)

proxy.go

@@ -12,7 +12,7 @@ var contextIDZero = quicvarint.Append([]byte{}, 0)
 type Proxy struct{}
 
 func (s *Proxy) Proxy(w http.ResponseWriter, _ *Request) (*Conn, error) {
-	w.Header().Set(capsuleHeader, capsuleProtocolHeaderValue)
+	w.Header().Set(http3.CapsuleProtocolHeader, capsuleProtocolHeaderValue)
 	w.WriteHeader(http.StatusOK)
 
 	str := w.(http3.HTTPStreamer).HTTPStream()

request.go

@@ -8,13 +8,11 @@ import (
 	"reflect"
 
 	"github.com/dunglas/httpsfv"
+	"github.com/quic-go/quic-go/http3"
 	"github.com/yosida95/uritemplate/v3"
 )
 
-const (
-	requestProtocol = "connect-ip"
-	capsuleHeader   = "Capsule-Protocol"
-)
+const requestProtocol = "connect-ip"
 
 var capsuleProtocolHeaderValue string
 
@@ -70,7 +68,7 @@ func ParseRequest(r *http.Request, template *uritemplate.Template) (*Request, er
 			Err:        fmt.Errorf("host in :authority (%s) does not match template host (%s)", r.Host, u.Host),
 		}
 	}
-	capsuleHeaderValues, ok := r.Header[capsuleHeader]
+	capsuleHeaderValues, ok := r.Header[http3.CapsuleProtocolHeader]
 	if !ok {
 		return nil, &RequestParseError{
 			HTTPStatus: http.StatusBadRequest,