dropped fiber for std http + gorilla websocket

Session serialization will use gob encoding instead of json.
Binary size will likely be reduced.
General backend code refactoring.

server/middleware/spa_handler.go

@@ -0,0 +1,93 @@
+package middlewares
+
+import (
+	"fmt"
+	"io"
+	"io/fs"
+	"mime"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+type SpaHandler struct {
+	Entrypoint string
+	Filesystem fs.FS
+	routes     []string
+}
+
+func NewSpaHandler(index string, fs fs.FS) *SpaHandler {
+	return &SpaHandler{
+		Entrypoint: index,
+		Filesystem: fs,
+	}
+}
+
+func (s *SpaHandler) AddClientRoute(route string) *SpaHandler {
+	s.routes = append(s.routes, route)
+	return s
+}
+
+// Handler for serving a compiled react frontend
+// each client-side routes must be provided
+func (s *SpaHandler) Handler() http.HandlerFunc {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet {
+			http.Error(
+				w,
+				http.StatusText(http.StatusMethodNotAllowed),
+				http.StatusMethodNotAllowed,
+			)
+			return
+		}
+
+		path := filepath.Clean(r.URL.Path)
+
+		// basically all frontend routes are needed :/
+		hasRoute := false
+		for _, route := range s.routes {
+			hasRoute = strings.HasPrefix(path, route)
+			if hasRoute {
+				break
+			}
+		}
+
+		if path == "/" || hasRoute {
+			path = s.Entrypoint
+		}
+
+		path = strings.TrimPrefix(path, "/")
+
+		file, err := s.Filesystem.Open(path)
+
+		if err != nil {
+			if os.IsNotExist(err) {
+				http.NotFound(w, r)
+				return
+			}
+			http.Error(
+				w,
+				http.StatusText(http.StatusInternalServerError),
+				http.StatusInternalServerError,
+			)
+			return
+		}
+
+		contentType := mime.TypeByExtension(filepath.Ext(path))
+		w.Header().Set("Content-Type", contentType)
+
+		if strings.HasPrefix(path, "assets/") {
+			w.Header().Set("Cache-Control", "public, max-age=2592000")
+		}
+
+		stat, err := file.Stat()
+		if err == nil && stat.Size() > 0 {
+			w.Header().Set("Content-Length", fmt.Sprintf("%d", stat.Size()))
+		}
+
+		w.WriteHeader(http.StatusOK)
+
+		io.Copy(w, file)
+	})
+}