Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/ui/static_app_icon.go

@@ -0,0 +1,43 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package ui // import "miniflux.app/v2/internal/ui"
+
+import (
+	"net/http"
+	"path/filepath"
+	"time"
+
+	"miniflux.app/v2/internal/http/request"
+	"miniflux.app/v2/internal/http/response"
+	"miniflux.app/v2/internal/http/response/html"
+	"miniflux.app/v2/internal/ui/static"
+)
+
+func (h *handler) showAppIcon(w http.ResponseWriter, r *http.Request) {
+	filename := request.RouteStringParam(r, "filename")
+	etag, err := static.GetBinaryFileChecksum(filename)
+	if err != nil {
+		html.NotFound(w, r)
+		return
+	}
+
+	response.New(w, r).WithCaching(etag, 72*time.Hour, func(b *response.Builder) {
+		blob, err := static.LoadBinaryFile(filename)
+		if err != nil {
+			html.ServerError(w, r, err)
+			return
+		}
+
+		switch filepath.Ext(filename) {
+		case ".png":
+			b.WithHeader("Content-Type", "image/png")
+		case ".svg":
+			b.WithHeader("Content-Type", "image/svg+xml")
+		}
+
+		b.WithoutCompression()
+		b.WithBody(blob)
+		b.Write()
+	})
+}