limiter: move to internal/backend

internal/backend/limiter/limiter.go

@@ -0,0 +1,29 @@
+package limiter
+
+import (
+	"io"
+	"net/http"
+)
+
+// Limiter defines an interface that implementors can use to rate limit I/O
+// according to some policy defined and configured by the implementor.
+type Limiter interface {
+	// Upstream returns a rate limited reader that is intended to be used in
+	// uploads.
+	Upstream(r io.Reader) io.Reader
+
+	// UpstreamWriter returns a rate limited writer that is intended to be used
+	// in uploads.
+	UpstreamWriter(w io.Writer) io.Writer
+
+	// Downstream returns a rate limited reader that is intended to be used
+	// for downloads.
+	Downstream(r io.Reader) io.Reader
+
+	// Downstream returns a rate limited reader that is intended to be used
+	// for downloads.
+	DownstreamWriter(r io.Writer) io.Writer
+
+	// Transport returns an http.RoundTripper limited with the limiter.
+	Transport(http.RoundTripper) http.RoundTripper
+}