Defining variables twice leads to undefined/undesired behavior

[hillu]

The following program is a C reimplementation of what was reported as hillu/go-yara#25. Removing the second call of yr_compiler_define_string_variable() restores expected behavior.

#include <yara.h>
#include <stdio.h>
void errcheck(int code) {
  if (code == 0) {
    puts("ok");
  } else {
    printf("error %d\n", code);
  }
}

int scan_callback(int message, void* message_data, void* user_data) {
  switch(message) {
  case CALLBACK_MSG_RULE_MATCHING:
    printf("match %s\n", ((YR_RULE*)message_data)->identifier);
    break;
  case CALLBACK_MSG_RULE_NOT_MATCHING:
    printf("not matching %s\n", ((YR_RULE*)message_data)->identifier);
    break;
  }
}

int main(int argc, char **argv) {
  YR_COMPILER *c;
  yr_initialize();
  errcheck(yr_compiler_create(&c));
  errcheck(yr_compiler_define_string_variable(c, "category", ""));
  errcheck(yr_compiler_define_string_variable(c, "category", ""));
  errcheck(yr_compiler_add_string(c, "rule category_is_empty { condition: category == \"\" }", "default"));
  errcheck(yr_compiler_add_string(c, "rule category_is_not_empty { condition: category != \"\" }", "default"));
  YR_RULES *r;
  errcheck(yr_compiler_get_rules(c, &r));
  errcheck(yr_rules_define_string_variable(r, "category", "http"));
  errcheck(yr_rules_scan_mem(r, "", 0, 0, scan_callback, NULL, 0));
}