GRPC not passing value when one service calls another service? - c++

Question

My grpc client code has 2 services, and it calls the Stat service from within the Delete service (and others not listed here), to populate the message properties before querying the server to delete it. The issue is, when I pass my path value from Stat to get_stat, it no longer exists. Just curious if there is a better way to structure my code to prevent this from happening? Very new to grpc and c++.
Client:
StatusCode DFSClientNodeP1::Stat(const std::string &filename, void *file_status)
{
Status return_status;
grpc::ClientContext context;
dfs_service::Empty request;
dfs_service::File_Metadata response;
if (file_status != NULL)
response = *(static_cast<dfs_service::File_Metadata *>(file_status));
response.set_filename(filename.c_str());
std::cout << "CLIENT: " << response.filename() << std::endl;
return_status = this->service_stub->get_status(&context, request, &response);
return return_status.error_code();
}
StatusCode DFSClientNodeP1::Delete(const std::string &filename)
{
StatusCode return_status;
grpc::ClientContext context;
dfs_service::File_Metadata request;
dfs_service::Empty response;
return_status = Stat(filename, &request);
if (return_status == 0)
{
return this->service_stub->delete_file(&context, request, &response).error_code();
}
else if (return_status == 5)
{
return return_status;
}
else
{
return StatusCode::CANCELLED;
}
}
Server:
Status get_status(ServerContext *context, const dfs_service::Empty *request, dfs_service::File_Metadata *response) override
{
std::cout << "SERVER: " << response->filename() << std::endl;
struct stat result;
if (stat(this->WrapPath(response->filename()).c_str(), &result) == 0)
{
response->set_filesize(result.st_size);
response->set_blocksize(result.st_blksize);
// metadata.set_creation_time(result.st_ctim);
response->set_modified_time(result.st_mtime);
return Status::OK;
}
else
{
return Status(StatusCode::NOT_FOUND, "File Not Found");
}
}
Output:
Client: TEST.jpg
Server:

Answer 1

In gRPC, the request message is sent from the client to the server, and the response message is sent from the server to the client. What you're doing here is sending an empty message from the client to the server. Your client code is setting the filename field in the response message before it gets the response from the server, but that entire message is getting overwritten by the actual server response.
What you need to do here is pass the filename as a field in the request message rather than making it a field in the response message.