https://github.com/openjdk/jdk/pull/2759

JDK-8262491-test.cpp

#include <iostream>
#include <cstring>

#ifndef O_RDONLY
#define O_RDONLY 0  // for debug
#endif

// Function pointer for stub functions
int (*open)(const char *pathname, int flags);
ssize_t(*read)(int fd, void *buf, size_t count);

// close(2) stub
int close(int fd){
  std::cout << "close() called" << std::endl;
}

/*********** test function **********************************/
void get_compatible_board(char *buf, int buflen) {
  *buf = '\0';
  int fd = open("/proc/device-tree/compatible", O_RDONLY);
  if (fd != -1) {
    ssize_t read_sz = read(fd, buf, buflen - 1);
    if (read_sz > 0) {
      buf[read_sz] = '\0';
      // Replace '\0' to ' '
      for (char *ch = buf; ch < buf + read_sz; ch++) {
        if (*ch == '\0') {
          *ch = ' ';
        }
      }
    } else {
      *buf = '\0';
    }
    close(fd);
  }
}
/************************************************************/


// open(2) stub which returns error
int open_failed(const char *pathname, int flags){
  return -1;
}

// open(2) stub which succeeds
int open_succeeded(const char *pathname, int flags){
  return 0;
}

// read(2) stub which returns error
ssize_t read_failed(int fd, void *buf, size_t count){
  return -1;
}

// read(2) stub which sets "t\0est" to buf
ssize_t read_succeeded(int fd, void *buf, size_t count){
  ((char *)buf)[0] = 't';
  ((char *)buf)[1] = '\0';
  ((char *)buf)[2] = 'e';
  ((char *)buf)[3] = 's';
  ((char *)buf)[4] = 't';
  return 5;
}

// read(2) stub which behaves to read nothing
ssize_t read_zero(int fd, void *buf, size_t count){
  return 0;
}

// read(2) stub which fills buf
ssize_t read_full(int fd, void *buf, size_t count){
  for(char *ch = (char *)buf; ch < (char *)buf + count; ch++){
    *ch = 'A';
  }
  return count;
}

// Set stub functions to read() and open(), and also clear buf with non-ascii value.
void init(int (*open_func)(const char *pathname, int flags),
          ssize_t (*read_func)(int fd, void *buf, size_t count),
          char *buf, int buflen){
  open = open_func;
  read = read_func;
  for(char *ch = buf; ch < buf + buflen; ch++){
    *ch = 0xff;
  }
}

// test driver
main(){
  const int BUFLEN = 7;
  char buf[BUFLEN];
  std::cout << "BUFLEN = " << BUFLEN << std::endl;

  std::cout << "test 1 (open failed): ";
  init(open_failed, NULL, buf, BUFLEN);
  get_compatible_board(buf, BUFLEN);
  std::cout << buf << " strlen: " << strlen(buf) << std::endl;

  std::cout << "test 2 (read failed): ";
  init(open_succeeded, read_failed, buf, BUFLEN);
  get_compatible_board(buf, BUFLEN);
  std::cout << buf << " strlen: " << strlen(buf) << std::endl;

  std::cout << "test 3 (read succeeded): ";
  init(open_succeeded, read_succeeded, buf, BUFLEN);
  get_compatible_board(buf, BUFLEN);
  std::cout << buf << " strlen: " << strlen(buf) << std::endl;

  std::cout << "test 4 (read zero): ";
  init(open_succeeded, read_zero, buf, BUFLEN);
  get_compatible_board(buf, BUFLEN);
  std::cout << buf << " strlen: " << strlen(buf) << std::endl;

  std::cout << "test 5 (read full): ";
  init(open_succeeded, read_full, buf, BUFLEN);
  get_compatible_board(buf, BUFLEN);
  std::cout << buf << " strlen: " << strlen(buf) << std::endl;
}