[feat] use receiver ack to calculate file transfer progress

src/tools/file_transfer.h

@@ -17,6 +17,10 @@
 
 namespace crossdesk {
 
+// Magic constants for file transfer protocol
+constexpr uint32_t kFileChunkMagic = 0x4A4E544D;  // 'JNTM'
+constexpr uint32_t kFileAckMagic = 0x4A4E5443;    // 'JNTC'
+
 #pragma pack(push, 1)
 struct FileChunkHeader {
   uint32_t magic;       // magic to identify file-transfer chunks
@@ -27,6 +31,14 @@ struct FileChunkHeader {
   uint16_t name_len;    // filename length (bytes), only set on first chunk
   uint8_t flags;        // bit0: is_first, bit1: is_last, others reserved
 };
+
+struct FileTransferAck {
+  uint32_t magic;         // magic to identify file-transfer ack
+  uint32_t file_id;       // must match FileChunkHeader.file_id
+  uint64_t acked_offset;  // received offset
+  uint64_t total_size;    // total file size
+  uint32_t flags;         // bit0: completed, bit1: error
+};
 #pragma pack(pop)
 
 class FileSender {
@@ -43,9 +55,11 @@ class FileSender {
   // `path`  : full path to the local file.
   // `label` : logical filename to send (usually path.filename()).
   // `send`  : callback that pushes one encoded chunk into the data channel.
+  // `file_id` : file id to use (0 means auto-generate).
   // Return 0 on success, <0 on error.
   int SendFile(const std::filesystem::path& path, const std::string& label,
-               const SendFunc& send, std::size_t chunk_size = 64 * 1024);
+               const SendFunc& send, std::size_t chunk_size = 64 * 1024,
+               uint32_t file_id = 0);
 
   // build a single encoded chunk buffer according to FileChunkHeader protocol.
   static std::vector<char> BuildChunk(uint32_t file_id, uint64_t offset,
@@ -66,6 +80,7 @@ class FileReceiver {
 
   using OnFileComplete =
       std::function<void(const std::filesystem::path& saved_path)>;
+  using OnSendAck = std::function<int(const FileTransferAck& ack)>;
 
  public:
   // save to default desktop directory.
@@ -80,6 +95,8 @@ class FileReceiver {
 
   void SetOnFileComplete(OnFileComplete cb) { on_file_complete_ = cb; }
 
+  void SetOnSendAck(OnSendAck cb) { on_send_ack_ = cb; }
+
   const std::filesystem::path& OutputDir() const { return output_dir_; }
 
  private:
@@ -92,6 +109,7 @@ class FileReceiver {
   std::filesystem::path output_dir_;
   std::unordered_map<uint32_t, FileContext> contexts_;
   OnFileComplete on_file_complete_ = nullptr;
+  OnSendAck on_send_ack_ = nullptr;
 };
 
 }  // namespace crossdesk