code: func (cmd *command) Execute(ch io.ReadWriter) (err error) {
  	if cmd.Flags.Source {
  		err = cmd.serveSource(ch)
  	} else {
  		err = cmd.serveSink(ch)
  	}
  	if err != nil {
  		if cmd.Config.RunOnServer == false {
  			return trace.Wrap(err)
  		} else {
  			// when 'teleport scp' encounters an error, it SHOULD NOT be logged
  			// to stderr (i.e. we should not return an error here) and instead
  			// it should be sent back to scp client using scp protocol
  			cmd.sendError(ch, err)
  		}
  	}
  	return nil
  }
docs: // Execute() implements SSH file copy (SCP). It is called on both tsh (client)
  // and teleport (server) side.