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/// @file
/// @brief C implementation of `gv_fopen`
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <util/gv_fopen.h>
#include <util/streq.h>
/// platform abstraction over `fopen`
static FILE *fopen_(const char *filename, const char *mode) {
assert(filename != NULL);
assert(mode != NULL);
#ifdef _MSC_VER
{
FILE *result = NULL;
if (fopen_s(&result, filename, mode) != 0) {
return NULL;
}
return result;
}
#else
return fopen(filename, mode);
#endif
}
FILE *gv_fopen(const char *filename, const char *mode) {
assert(filename != NULL);
assert(mode != NULL);
assert(streq(mode, "r") || streq(mode, "rb") || streq(mode, "w") ||
streq(mode, "wb"));
// does `fopen` support 'e' for setting close-on-exec?
bool have_e = false;
// does `fopen` support 'N' for setting close-on-exec?
bool have_n = false;
#if defined(__DragonFly__) || defined(__FreeBSD__) || defined(__linux__) || \
defined(__NetBSD__) || defined(__OpenBSD__)
have_e = true;
#endif
#ifdef _MSC_VER
have_n = true;
#endif
// Attempt 1: `fopen`+'e'
if (have_e) {
char mode_with_cloexec[4] = {0};
snprintf(mode_with_cloexec, sizeof(mode_with_cloexec), "%se", mode);
return fopen_(filename, mode_with_cloexec);
}
// Attempt 2: `fopen`+'N'
if (have_n) {
char mode_with_cloexec[4] = {0};
snprintf(mode_with_cloexec, sizeof(mode_with_cloexec), "%sN", mode);
return fopen_(filename, mode_with_cloexec);
}
// Attempt 3: `open`+`O_CLOEXEC`; `fdopen` (e.g. for macOS)
#ifdef O_CLOEXEC
{
int flags = mode[0] == 'w' ? (O_WRONLY | O_CREAT | O_TRUNC) : O_RDONLY;
#ifdef O_BINARY
if (strchr(mode, 'b') != NULL) {
flags |= O_BINARY;
}
#endif
#ifdef _O_BINARY
if (strchr(mode, 'b') != NULL) {
flags |= _O_BINARY;
}
#endif
const int fd = open(filename, flags | O_CLOEXEC, 0666);
if (fd < 0) {
return NULL;
}
FILE *f = fdopen(fd, mode);
if (f == NULL) {
const int err = errno;
(void)close(fd);
errno = err;
}
return f;
}
#endif
// Attempt 4: `fopen`; `fcntl`+`FD_CLOEXEC`
// We are on a platform that supported none of the above, so we need to
// fallback on an unmodified `fopen`. The platform either does not have a
// concept of close-on-exec or does not support a race-free way of achieving
// it.
FILE *f = fopen_(filename, mode);
if (f == NULL) {
return NULL;
}
#ifdef FD_CLOEXEC
{
const int fd = fileno(f);
const int flags = fcntl(fd, F_GETFD);
if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) < 0) {
const int err = errno;
(void)fclose(f);
errno = err;
return NULL;
}
}
#endif
return f;
}
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