https://github.com/grpc-ecosystem/go-grpc-middleware/blob/master/logging/zap/client_interceptors.go

go-grpc-middleware example.go

// UnaryClientInterceptor returns a new unary client interceptor that optionally logs the execution of external gRPC calls.
func UnaryClientInterceptor(logger *zap.Logger, opts ...Option) grpc.UnaryClientInterceptor {
	o := evaluateClientOpt(opts)
	return func(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
		fields := newClientLoggerFields(ctx, method)
		startTime := time.Now()
		err := invoker(ctx, method, req, reply, cc, opts...)
		newCtx := ctxzap.ToContext(ctx, logger.With(fields...))
		logFinalClientLine(newCtx, o, startTime, err, "finished client unary call")
		return err
	}
}