fix segfault from readline; avoid unnecessary string copy

src/RcppExports.cpp

@@ -824,12 +824,12 @@ BEGIN_RCPP
 END_RCPP
 }
 // readline
-SEXP readline(const std::string& prompt);
+SEXP readline(const char* prompt);
 RcppExport SEXP _reticulate_readline(SEXP promptSEXP) {
 BEGIN_RCPP
  Rcpp::RObject rcpp_result_gen;
  Rcpp::RNGScope rcpp_rngScope_gen;
- Rcpp::traits::input_parameter< const std::string& >::type prompt(promptSEXP);
+ Rcpp::traits::input_parameter< const char* >::type prompt(promptSEXP);
  rcpp_result_gen = Rcpp::wrap(readline(prompt));
  return rcpp_result_gen;
 END_RCPP

src/readline.cpp

@@ -1,31 +1,30 @@
-
 #include <R.h>
 #include <Rinternals.h>
 
-#include <string>
+#include <cstring> // for strlen, strchr
 #define READLINE_BUFFER_SIZE (8192)
 extern "C" int R_ReadConsole(const char*, unsigned char*, int, int);
 
 // [[Rcpp::export]]
-SEXP readline(const std::string& prompt)
+SEXP readline(const char* prompt)
 {
  // read user input (ensure null termination)
  char buffer[READLINE_BUFFER_SIZE];
- R_ReadConsole(prompt.c_str(), (unsigned char*) buffer, READLINE_BUFFER_SIZE, 1);
- buffer[READLINE_BUFFER_SIZE - 1] = '\0';
+ if (R_ReadConsole(prompt, (unsigned char*) buffer, READLINE_BUFFER_SIZE, 1) == 0)
+  return R_NilValue;
 
- // construct resulting string
- std::string result(buffer, buffer + strlen(buffer));
+ buffer[READLINE_BUFFER_SIZE - 1] = '\0'; // Ensure null termination
 
- // truncate to location of inserted newline. if not found, assume
- // the user canceled input with e.g. R_EOF
- std::string::size_type index = result.find('\n');
- if (index == std::string::npos)
- return R_NilValue;
+ // Find the location of the newline character, if any
+ char* newline_pos = strchr(buffer, '\n');
+ if (newline_pos == nullptr)
+ return R_NilValue; // If no newline found, assume user canceled
+
+ // Determine length up to the newline (excluding the trailing newline)
+ size_t input_length = newline_pos - buffer;
 
- // return result (leaving out trailing newline)
  SEXP resultSEXP = PROTECT(Rf_allocVector(STRSXP, 1));
- SET_STRING_ELT(resultSEXP, 0, Rf_mkCharLen(buffer, index));
+ SET_STRING_ELT(resultSEXP, 0, Rf_mkCharLen(buffer, input_length));
  UNPROTECT(1);
  return resultSEXP;
 }