storagenode/console/consoleserver: set content-type manually

http.FileServer relies on mime types defined in the operating system.
These values may be misconfigured, so a javascript file might
end up being served as "plain/text".

Change-Id: I3c13c8a9ac484bd765a4de0f8253bfe40dde7513

storagenode/console/consoleserver/mime.go

@@ -0,0 +1,35 @@
+// Copyright (C) 2020 Storj Labs, Inc.
+// See LICENSE for copying information.
+
+package consoleserver
+
+import "strings"
+
+// CommonContentType returns content-type for common extensions.
+func CommonContentType(ext string) (string, bool) {
+	ext = strings.ToLower(ext)
+	mime, ok := commonContentType[ext]
+	return mime, ok
+}
+
+var commonContentType = map[string]string{
+	".css":   "text/css; charset=utf-8",
+	".gif":   "image/gif",
+	".htm":   "text/html; charset=utf-8",
+	".html":  "text/html; charset=utf-8",
+	".jpeg":  "image/jpeg",
+	".jpg":   "image/jpeg",
+	".js":    "application/javascript",
+	".mjs":   "application/javascript",
+	".otf":   "font/otf",
+	".pdf":   "application/pdf",
+	".png":   "image/png",
+	".svg":   "image/svg+xml",
+	".ttf":   "font/ttf",
+	".wasm":  "application/wasm",
+	".webp":  "image/webp",
+	".xml":   "text/xml; charset=utf-8",
+	".sfnt":  "font/sfnt",
+	".woff":  "font/woff",
+	".woff2": "font/woff2",
+}

storagenode/console/consoleserver/server.go

@@ -8,6 +8,7 @@ import (
 	"encoding/json"
 	"net"
 	"net/http"
+	"path/filepath"
 
 	"github.com/gorilla/mux"
 	"github.com/zeebo/errs"
@@ -188,6 +189,16 @@ func (server *Server) satelliteHandler(w http.ResponseWriter, r *http.Request) {
 // cacheMiddleware is a middleware for caching static files.
 func (server *Server) cacheMiddleware(fn http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// "mime" package, which http.FileServer uses, depends on Operating System
+		// configuration for mime-types. When a system has hardcoded mime-types to
+		// something else, they might serve ".js" as a "plain/text".
+		//
+		// Override any of that default behavior to ensure we get the correct types for
+		// common files.
+		if contentType, ok := CommonContentType(filepath.Ext(r.URL.Path)); ok {
+			w.Header().Set("Content-Type", contentType)
+		}
+
 		w.Header().Set("Cache-Control", "public, max-age=31536000")
 		w.Header().Set("X-Content-Type-Options", "nosniff")