refactor datasource caching

pkg/middleware/headers.go

@@ -0,0 +1,14 @@
+package middleware
+
+import (
+	m "github.com/grafana/grafana/pkg/models"
+	macaron "gopkg.in/macaron.v1"
+)
+
+const HeaderNameNoBackendCache = "X-Grafana-NoCache"
+
+func HandleNoCacheHeader() macaron.Handler {
+	return func(ctx *m.ReqContext) {
+		ctx.SkipCache = ctx.Req.Header.Get(HeaderNameNoBackendCache) == "true"
+	}
+}

pkg/middleware/middleware.go

@@ -29,6 +29,7 @@ func GetContextHandler() macaron.Handler {
 			Session:        session.GetSession(),
 			IsSignedIn:     false,
 			AllowAnonymous: false,
+			SkipCache:      false,
 			Logger:         log.New("context"),
 		}