code: func (f *wsClientFilter) existsUnspentOutPoint(op *wire.OutPoint) bool {
  	_, ok := f.unspent[*op]
  	return ok
  }
docs: // existsUnspentOutPoint returns true if the passed outpoint has been added to
  // the wsClientFilter.
  //
  // NOTE: This extension was ported from github.com/decred/dcrd