grpc empty object when updating the library index

[Bikappa]

Describe the problem

When using an grpclient to update the library index, command UpdateLibrariesIndex, the download process is ended by and empty object following the "end" message

To reproduce

Start the CLI in deamon mode

arduino-cli daemon

Create an instance (here using the grpcurl tool)

grpcurl \
  -plaintext \
  -import-path ./rpc \
  -proto cc/arduino/cli/commands/v1/commands.proto \
  127.0.0.1:50051 \
  cc.arduino.cli.commands.v1.ArduinoCoreService.Create

Issue an UpdateLibrariesIndex command

grpcurl \
  -plaintext \
  -import-path ./rpc \
  -proto cc/arduino/cli/commands/v1/commands.proto \
  -d '{"instance": {"id": 1}}' \
  127.0.0.1:50051 \
  cc.arduino.cli.commands.v1.ArduinoCoreService.UpdateLibrariesIndex

You should observe an output similar to the following

{
 "downloadProgress": {
   "start": {
     "url": "https://downloads.arduino.cc/libraries/library_index.tar.bz2",
     "label": "Downloading index: library_index.tar.bz2"
   }
 }
}
{
 "downloadProgress": {
   "update": {
     "downloaded": "2358123",
     "totalSize": "2358123"
   }
 }
}
{
 "downloadProgress": {
   "end": {
     "success": true
   }
 }
}
{

}

Notice how there's an empty {} object at the bottom

Expected behavior

The message

{
  "downloadProgress": {
    "end": {
      "success": true
    }
  }
}

Closes the stream with no additional objects

Arduino CLI version

commit a58d5ad

Operating system

macOS

Operating system version

13.1 (22C65)

Additional context

No response

Issue checklist

• I searched for previous reports in the issue tracker
• I verified the problem still occurs when using the nightly build
• My report contains all necessary details

[cmaglie]

I think it's due to this line:

arduino-cli/commands/daemon/daemon.go

Line 165 in 4b70e02

return stream.Send(&rpc.UpdateLibrariesIndexResponse{})

just returning nil instead of an empty response should be fine.
I guess there are other "streaming" calls that have the same problem.