Make experimental a runtime flag

Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com>
Upstream-commit: 7781a1bf0fef748877326632b88e92fbf3c90daa
Component: engine

components/engine/api/server/middleware/experimental.go

@@ -0,0 +1,29 @@
+package middleware
+
+import (
+	"net/http"
+
+	"golang.org/x/net/context"
+)
+
+// ExperimentalMiddleware is a the middleware in charge of adding the
+// 'Docker-Experimental' header to every outgoing request
+type ExperimentalMiddleware struct {
+	experimental string
+}
+
+// NewExperimentalMiddleware creates a new ExperimentalMiddleware
+func NewExperimentalMiddleware(experimentalEnabled bool) ExperimentalMiddleware {
+	if experimentalEnabled {
+		return ExperimentalMiddleware{"true"}
+	}
+	return ExperimentalMiddleware{"false"}
+}
+
+// WrapHandler returns a new handler function wrapping the previous one in the request chain.
+func (e ExperimentalMiddleware) WrapHandler(handler func(ctx context.Context, w http.ResponseWriter, r *http.Request, vars map[string]string) error) func(ctx context.Context, w http.ResponseWriter, r *http.Request, vars map[string]string) error {
+	return func(ctx context.Context, w http.ResponseWriter, r *http.Request, vars map[string]string) error {
+		w.Header().Set("Docker-Experimental", e.experimental)
+		return handler(ctx, w, r, vars)
+	}
+}