[feat] add native iOS client support

src/tools/file_transfer_protocol.h

@@ -0,0 +1,67 @@
+#ifndef _FILE_TRANSFER_PROTOCOL_H_
+#define _FILE_TRANSFER_PROTOCOL_H_
+
+#include <array>
+#include <cstddef>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+namespace crossdesk {
+
+inline constexpr uint32_t kFileChunkMagic = 0x4A4E544D;  // 'JNTM'
+inline constexpr uint32_t kFileAckMagic = 0x4A4E5443;    // 'JNTC'
+
+#pragma pack(push, 1)
+struct FileChunkHeader {
+  uint32_t magic;
+  uint32_t file_id;
+  uint64_t offset;
+  uint64_t total_size;
+  uint32_t chunk_size;
+  uint16_t name_len;
+  uint8_t flags;
+};
+
+struct FileTransferAck {
+  uint32_t magic;
+  uint32_t file_id;
+  uint64_t acked_offset;
+  uint64_t total_size;
+  uint32_t flags;
+};
+#pragma pack(pop)
+
+static_assert(sizeof(FileChunkHeader) == 31,
+              "FileChunkHeader wire layout must remain stable");
+static_assert(sizeof(FileTransferAck) == 28,
+              "FileTransferAck wire layout must remain stable");
+
+namespace protocol {
+
+struct FileChunkView {
+  FileChunkHeader header{};
+  std::string file_name;
+  const char* payload = nullptr;
+  std::size_t payload_size = 0;
+};
+
+std::vector<char> EncodeFileChunk(uint32_t file_id, uint64_t offset,
+                                  uint64_t total_size, const char* data,
+                                  uint32_t data_size,
+                                  const std::string* file_name, bool is_first,
+                                  bool is_last);
+
+bool DecodeFileChunk(const char* data, std::size_t size,
+                     FileChunkView* output);
+
+std::array<char, sizeof(FileTransferAck)> EncodeFileTransferAck(
+    const FileTransferAck& ack);
+
+bool DecodeFileTransferAck(const char* data, std::size_t size,
+                           FileTransferAck* output);
+
+}  // namespace protocol
+}  // namespace crossdesk
+
+#endif