1 files changed, 81 insertions, 0 deletions
diff --git a/stdio/mkostempsm.c b/stdio/mkostempsm.c
new file mode 100644
index 0000000..f42e46f
--- /dev/null
+++ b/stdio/mkostempsm.c
@@ -0,0 +1,81 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
+#include "libc/calls/calls.h"
+#include "libc/errno.h"
+#include "libc/rand/lcg.internal.h"
+#include "libc/rand/rand.h"
+#include "libc/stdio/temp.h"
+#include "libc/str/str.h"
+#include "libc/sysv/consts/o.h"
+#include "libc/sysv/errfuns.h"
+
+#define RESEED   1024
+#define ATTEMPTS 10
+#define WILDCARD "XXXXXX"
+
+int mkostempsmi(char *tpl, int slen, unsigned flags, uint64_t *rando, int mode,
+                int openit(const char *file, int flags, ...)) {
+  size_t len = strlen(tpl);
+  size_t wildlen = strlen(WILDCARD);
+  if (len < wildlen || slen > len - wildlen) {
+    return einval();
+  }
+  char *ss = tpl + len - wildlen - slen;
+  assert(memcmp(ss, WILDCARD, wildlen) == 0);
+  flags = (flags & ~(flags & O_ACCMODE)) | O_RDWR | O_CREAT | O_EXCL;
+  unsigned attempts = ATTEMPTS;
+  do {
+    char *p = ss;
+    uint32_t num = KnuthLinearCongruentialGenerator(rando) >> 32;
+    for (unsigned i = 0; i < wildlen; ++i) {
+      p[i] = "0123456789abcdefghijklmnopqrstuvwxyz"[num & 31];
+      num >>= 5;
+    }
+    int fd;
+    if ((fd = openit(tpl, flags, 0600)) != -1) return fd;
+  } while (--attempts && errno == EEXIST);
+  memcpy(ss, WILDCARD, wildlen);
+  return -1;
+}
+
+static uint64_t g_mkostemps_rand;
+static uint64_t g_mkostemps_reseed;
+
+/**
+ * Opens unique temporary file.
+ *
+ * The substring XXXXXX is replaced with a pseudorandom number that's
+ * seeded automatically and grants 30 bits of randomness to each value.
+ * Retries are made in the unlikely event of collisions.
+ *
+ * @param template is a pathname relative to current directory by default,
+ *     that needs to have "XXXXXX" at the end of the string
+ * @param suffixlen may be nonzero to permit characters after the XXXXXX
+ * @param flags can have O_APPEND, O_CLOEXEC, etc.
+ * @param mode is conventionally 0600, for owner-only non-exec access
+ * @return exclusive open file descriptor for generated pathname,
+ *     or -1 w/ errno
+ * @see kTmpPath
+ */
+nodiscard int mkostempsm(char *template, int suffixlen, unsigned flags,
+                         int mode) {
+  if (g_mkostemps_reseed++ % RESEED == 0) g_mkostemps_rand = rand64();
+  return mkostempsmi(template, suffixlen, flags, &g_mkostemps_rand, mode, open);
+}