PluginFrontend

Platform-specific plumbing that lets protoc talk to a generator inside this JVM.

protoc only knows how to launch executables that read a CodeGeneratorRequest from stdin and write a CodeGeneratorResponse to stdout. A frontend therefore fabricates a tiny executable whose only job is to forward those two streams into this process:

1. protoc writes the request to the plugin's stdin
2. the plugin forwards it over a pipe or socket
3. this JVM reads it, runs the generator
4. this JVM writes the response back over the channel and closes it
5. the plugin copies that to its stdout, where protoc picks it up