Add UTF-16 BOM support for Vaadin file uploads

[Copilot]

Some data providers encode files in UTF-16 with BOM rather than UTF-8, causing upload failures when parsing JSON data.

Changes

• New EncodingUtils utility: Detects and handles UTF-8, UTF-16LE, UTF-16BE with or without BOM

  • BOM detection at byte level (FF FE, FE FF, EF BB BF)
  • Heuristic fallback for UTF-16 without BOM (null byte pattern analysis)
  • Automatic BOM removal and control character cleanup

• Updated upload handlers: Replace new String(data) with EncodingUtils.bytesToString(data)

  • BopEditorView, BopManagementView, EntrylistEditorView
  • 5 upload handlers total (entrylist, BoP files, session results, custom cars)

Example

// Before
AccBop accBop = JsonClient.fromJson(new String(data), AccBop.class);

// After
String content = EncodingUtils.bytesToString(data);
AccBop accBop = JsonClient.fromJson(content, AccBop.class);

The utility defaults to UTF-8 when no BOM is present, maintaining backward compatibility. Test coverage includes all encoding combinations with and without BOMs.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Support UTF-16 BOM for file uploads since some providers do not use common UTF-8 encoding</issue_title>
<issue_description>Add support for UTF16 with BOM to all Vaadin File Uploads. Keep the business logic identical, just parse the input data differently.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Support UTF-16 BOM for file uploads since some providers do not use common UTF-8 encoding #260

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.