Make server middleware standalone functions.

Removing direct dependencies from the server configuration.

Signed-off-by: David Calavera <david.calavera@gmail.com>

api/server/middleware/cors.go

@@ -0,0 +1,33 @@
+package middleware
+
+import (
+	"net/http"
+
+	"github.com/Sirupsen/logrus"
+	"github.com/docker/docker/api/server/httputils"
+	"golang.org/x/net/context"
+)
+
+// NewCORSMiddleware creates a new CORS middleware.
+func NewCORSMiddleware(defaultHeaders string) Middleware {
+	return func(handler httputils.APIFunc) httputils.APIFunc {
+		return func(ctx context.Context, w http.ResponseWriter, r *http.Request, vars map[string]string) error {
+			// If "api-cors-header" is not given, but "api-enable-cors" is true, we set cors to "*"
+			// otherwise, all head values will be passed to HTTP handler
+			corsHeaders := defaultHeaders
+			if corsHeaders == "" {
+				corsHeaders = "*"
+			}
+
+			writeCorsHeaders(w, r, corsHeaders)
+			return handler(ctx, w, r, vars)
+		}
+	}
+}
+
+func writeCorsHeaders(w http.ResponseWriter, r *http.Request, corsHeaders string) {
+	logrus.Debugf("CORS header is enabled and set to: %s", corsHeaders)
+	w.Header().Add("Access-Control-Allow-Origin", corsHeaders)
+	w.Header().Add("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept, X-Registry-Auth")
+	w.Header().Add("Access-Control-Allow-Methods", "HEAD, GET, POST, DELETE, PUT, OPTIONS")
+}