input stream from aws S3 into Rcpp - r

Question

I have .txt file named test_file.txt in my AWS S3 bucket stored in the location
s3://path/to/csv/test_file.txt which contains a sample statement like - this is for testing
I can read this file directly from the S3 bucket location using a combination of readLines and pipe statement in R as
df <- readLines(pipe("aws s3 cp s3://path/to/csv/test_file.txt -"))
df
#[1] "this is for testing"
When I try to replicate the same in Rcpp, I write a file rcoo_input_string.cpp as follows
#include <Rcpp.h>
#include <string.h>
// [[Rcpp::export]]
Rcpp::String rcpp_input_test() {
Rcpp::Environment base = Rcpp::Environment("package:base");
Rcpp::Function readline = base["readline"];
Rcpp::Function as_string = base["as.character"];
std::string input_string = Rcpp::as<std::string> (as_string(readline("> ")));
Rcpp::Rcout << input_string << std::endl;
return input_string;
}
/*** R
library(magrittr)
rcpp_input_test()
*/
Note:I got the idea that std::cin wont work in R or Rcpp, so I took inspiration from this post Getting user input from R console: Rcpp and std::cin
I write another file rcoo_input_string.R as follows
library(Rcpp)
sourceCpp("./rcoo_input_string.cpp")
and execute the rcoo_input_string.R file from the AWS CLI as
aws s3 cp s3://path/to/csv/test_file.txt - | Rscript rcoo_input_string.R
but I get the following output on the CLI
> library(magrittr)
> rcpp_input_test()
>
[1] ""
which means that the Rcpp function did not read the test_file.txt.
Please note that running
sourceCpp("./rcoo_input_string.cpp")
runs perfectly well and I can give the input and the Rcpp function returns the string value as well (like this)
> sourceCpp("./S3_to_R_data_import/rcoo_input_string.cpp")
> library(magrittr)
> rcpp_input_test()
> this is for testing
this is for testing
[1] "this is for testing"
Can someone guide me on how to create an input stream for this function in R ?
I say input stream, and please correct me if I am wrong, because I wrote a similar code for a C++ file and it executed perfectly.
Note: In trying to solve this problem, I tried cppFunction too, but that did not not solve the problem. Example of rcoo_input_string_2.R
library(Rcpp)
#sourceCpp("/mnt/legoland/S3_to_R_data_import/rcoo_input_string.cpp")
cppFunction(' String rcpp_input_test() {
Environment base = Environment("package:base");
Function readline = base["readline"];
Function as_string = base["as.character"];
std::string input_string = as<std::string> (as_string(readline("> ")));
Rcout << input_string << std::endl;
return input_string;
}
')
print(rcpp_input_test())