Fix some bugs

libc/stdio/tmpfile.c

@@ -17,59 +17,58 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
-#include "libc/errno.h"
-#include "libc/stdio/rand.h"
-#include "libc/runtime/runtime.h"
+#include "libc/stdio/stdio.h"
 #include "libc/stdio/temp.h"
-#include "libc/str/str.h"
-#include "libc/sysv/consts/o.h"
 
 /**
- * Opens stream backed by anonymous file.
+ * Opens stream backed by anonymous file, e.g.
  *
- * We use $TMPDIR or /tmp to create a temporary file securely, which
- * will be unlink()'d before this function returns. The file content
- * will be released from disk once fclose() is called.
+ *     FILE *f;
+ *     if (!(f = tmpfile())) {
+ *       perror("tmpfile");
+ *       exit(1);
+ *     }
+ *     // do stuff
+ *     fclose(f);
  *
- * @see mkostempsm(), kTmpPath
+ * This creates a secure temporary file inside $TMPDIR. If it isn't
+ * defined, then /tmp is used on UNIX and GetTempPath() is used on the
+ * New Technology. This resolution of $TMPDIR happens once in a ctor,
+ * which is copied to the `kTmpDir` global.
+ *
+ * Once fclose() is called, the returned file is guaranteed to be
+ * deleted automatically. On UNIX the file is unlink()'d before this
+ * function returns. On the New Technology it happens upon fclose().
+ *
+ * On newer Linux only (c. 2013) it's possible to turn the anonymous
+ * returned file back into a real file, by doing this:
+ *
+ *     linkat(AT_FDCWD, _gc(xasprintf("/proc/self/fd/%d", fileno(f))),
+ *            AT_FDCWD, "real.txt", AT_SYMLINK_FOLLOW)
+ *
+ * On the New Technology, temporary files created by this function
+ * should have better performance, because `kNtFileAttributeTemporary`
+ * asks the kernel to more aggressively cache and reduce i/o ops.
+ *
+ * Favor tmpfd() or tmpfile() over `open(O_TMPFILE)` because the latter
+ * is Linux-only and will cause open() failures on all other platforms.
+ *
+ * @see tmpfd() if you don't want to link stdio/malloc
  * @asyncsignalsafe
  * @threadsafe
  * @vforksafe
  */
 FILE *tmpfile(void) {
+  int fd;
   FILE *f;
-  unsigned x;
-  int fd, i, j, e;
-  char path[PATH_MAX], *p;
-  p = path;
-  p = stpcpy(p, kTmpPath);
-  p = stpcpy(p, "tmp.");
-  if (program_invocation_short_name &&
-      strlen(program_invocation_short_name) < 128) {
-    p = stpcpy(p, program_invocation_short_name);
-    *p++ = '.';
-  }
-  for (i = 0; i < 10; ++i) {
-    x = rand64();
-    for (j = 0; j < 6; ++j) {
-      p[j] = "0123456789abcdefghijklmnopqrstuvwxyz"[x % 36];
-      x /= 36;
-    }
-    p[j] = 0;
-    e = errno;
-    if ((fd = open(path, O_RDWR | O_CREAT | O_EXCL, 0600)) != -1) {
-      unlink(path);
-      if ((f = fdopen(fd, "w+"))) {
-        return f;
-      } else {
-        close(fd);
-        return 0;
-      }
-    } else if (errno == EEXIST) {
-      errno = e;
+  if ((fd = tmpfd()) != -1) {
+    if ((f = fdopen(fd, "w+"))) {
+      return f;
     } else {
-      break;
+      close(fd);
+      return 0;
     }
+  } else {
+    return 0;
   }
-  return 0;
 }