add optional webui behind a build tag

internal/api/webui.go

@@ -0,0 +1,73 @@
+//go:build showbridge_webui
+
+package api
+
+import (
+	"embed"
+	"errors"
+	"io/fs"
+	"net/http"
+	"path"
+	"strings"
+
+	_ "embed"
+)
+
+//go:embed webui
+var webUIFS embed.FS
+
+var fsPrefix = "webui/browser"
+
+var index = path.Join(fsPrefix, "index.html")
+
+func handleWebUI(w http.ResponseWriter, req *http.Request) {
+	requestedPath := strings.TrimLeft(req.URL.Path, "/ui")
+	switch req.Method {
+	case http.MethodGet:
+		var pathToLoad string
+		stat, err := fs.Stat(webUIFS, path.Join(fsPrefix, requestedPath))
+		if err != nil {
+			if errors.Is(err, fs.ErrNotExist) {
+				pathToLoad = index
+			} else {
+				http.Error(w, "Internal server error", http.StatusInternalServerError)
+				return
+			}
+		}
+		if stat != nil {
+			if stat.IsDir() {
+				pathToLoad = index
+			} else {
+				pathToLoad = path.Join(fsPrefix, requestedPath)
+			}
+		}
+		file, err := webUIFS.ReadFile(pathToLoad)
+		if err != nil {
+			http.Error(w, "Internal server error", http.StatusInternalServerError)
+			return
+		}
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+
+		switch path.Ext(pathToLoad) {
+		case ".js":
+			w.Header().Set("Content-Type", "application/javascript")
+		case ".css":
+			w.Header().Set("Content-Type", "text/css")
+		case ".html":
+			w.Header().Set("Content-Type", "text/html")
+		case ".ico":
+			w.Header().Set("Content-Type", "image/x-icon")
+		}
+		w.Write(file)
+		return
+
+	case http.MethodOptions:
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		w.Header().Set("Access-Control-Allow-Methods", "GET, OPTIONS")
+		w.Header().Set("Access-Control-Allow-Headers", "Content-Type")
+		w.WriteHeader(http.StatusOK)
+	default:
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		w.WriteHeader(http.StatusMethodNotAllowed)
+	}
+}