add domain whois/dns support, refactor codebase

internal/server/response.go

@@ -0,0 +1,23 @@
+package server
+
+import (
+	"encoding/json"
+	"log/slog"
+	"net/http"
+)
+
+// sendJSONResponse sends a JSON response with the given data and status code.
+func sendJSONResponse(w http.ResponseWriter, data any, statusCode int) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	w.WriteHeader(statusCode)
+	encoder := json.NewEncoder(w)
+	encoder.SetIndent("", "  ")
+	if err := encoder.Encode(data); err != nil {
+		slog.Error("failed to encode json response", "error", err)
+	}
+}
+
+// sendJSONError sends a JSON error response with the given message and status code.
+func sendJSONError(w http.ResponseWriter, errMsg string, statusCode int) {
+	sendJSONResponse(w, map[string]string{"error": errMsg}, statusCode)
+}