private boolean checkChannel(final Endpoint endpoint, final boolean createIfAbsent) {
        final ManagedChannel ch = getChannel(endpoint, createIfAbsent);

        if (ch == null) {
            return false;
        }

        return checkConnectivity(endpoint, ch);
    }
GRPC RPC client implement.

@author nicholas.jxf
@author jiachun.fjc
jraft-extension/rpc-grpc-impl/src/main/java/com/alipay/sofa/jraft/rpc/impl/GrpcClient.java