使用 C++ 中的协议缓冲区将文件上传到服务器

Question

My objective is to chunk a file and then use a streaming connection to send the file to a server using gRPC++. Can somebody confirm whether the below code works for the client?

My proto file has a single object "bytes"

message FileContent {
  bytes content = 1;
}

Client Code

char *buffer = new char[2048];
// Open a stream-based connection with the gRPC server
std::unique_ptr<ClientWriter<FileContent> > writer(this->service_stub->Store(&context, &fileack));

// send the file name to the server
filecontent.set_content(filename);
std::cout << "Client: RPC call with File Name:" << filecontent.content() << endl;
writer->Write(filecontent);

// Get a file handle for the file we want to upload and the file length 

fileStream.open(filename, ios::binary);


while (!fileStream.eof())
{
     std::this_thread::sleep_for(std::chrono::milliseconds(100));
     filecontent.clear_content();
     fileStream.read(buffer,2048);
     filecontent.set_content(std::string(buffer, 2048));
     writer->Write(filecontent);
}

Server Code

    Status Store(ServerContext* context, ServerReader<FileContent>* reader, FileAck* fileack) override {

 FileContent filecontent;
 ofstream fileStream;
 std::string serverfilepath;

 if (fileStream.is_open())
 {
     std::cout << "Reading Data";
     while (reader->Read(&filecontent))
     {
         std::cout << "Reading Data";
         fileStream << filecontent.mutable_content();
     }

     fileStream.close();
 }

 else
 {
    reader->Read(&filecontent);
    fileStream.open(serverfilepath, ios::binary);
 }

 return Status::OK;

}

Answer 1

The protobuf bytes type generates a field of type std::string on the C++ side. Your char *buffer is thus implicitly converted to an std::string .

The problem is that the constructor used for this expects a null-terminated string, but your buffer does not have a terminator byte (nor can it, because it may contain \\0 bytes in the middle). This may cause the std::string constructor to run over the end of the buffer looking for the terminator byte.

To fix this, construct the std::string with a length explicitly:

filecontent.set_content(std::string(buffer, 2048));