1 files changed, 74 insertions, 0 deletions
diff --git a/vere/pkg/ent/ent.c b/vere/pkg/ent/ent.c
new file mode 100644
index 0000000..0375774
--- /dev/null
+++ b/vere/pkg/ent/ent.c
@@ -0,0 +1,74 @@
+// Use `getentropy` from unistd.h //////////////////////////////////////////////
+
+#if defined(ENT_GETENTROPY_UNISTD)
+#include <stddef.h>
+#include <unistd.h>
+int ent_getentropy(void* buf, size_t len) {
+  return getentropy(buf, len);
+}
+
+
+// Use `getentropy` from sys/random.h //////////////////////////////////////////
+
+#elif defined(ENT_GETENTROPY_SYSRANDOM)
+#include <stddef.h>
+// See https://www.mail-archive.com/bug-gnulib@gnu.org/msg38583.html.
+#include <stdlib.h>
+#include <sys/random.h>
+int ent_getentropy(void* buf, size_t len) {
+  return getentropy(buf, len);
+}
+
+
+// Use the `getrandom` syscall /////////////////////////////////////////////////
+
+#elif defined(ENT_GETRANDOM_SYSCALL)
+#include <stddef.h>
+#include <errno.h>
+#define _GNU_SOURCE
+#include <unistd.h>
+#include <sys/syscall.h>
+
+#define ENTFAIL { errno=EIO; return -1; }
+
+int ent_getentropy(void* buf, size_t len) {
+  if (len > 256) ENTFAIL
+  int r = syscall(SYS_getrandom, buf, len, 0);
+  if (r < 0) return r;
+  if (r != len) ENTFAIL
+  return 0;
+}
+
+
+// Use `/dev/urandom` //////////////////////////////////////////////////////////
+
+#elif defined(ENT_DEV_URANDOM)
+#include <stddef.h>
+#include <errno.h>
+#include <stdio.h>
+
+#define ENTFAIL { errno=EIO; return -1; }
+
+int ent_getentropy(void* buf, size_t len) {
+    if (len > 256) ENTFAIL;
+    FILE *f = fopen("/dev/urandom", "re");
+    if (!f) return -1;
+    int r = fread(buf, 1, len, f);
+    (void) fclose(f);
+    if (r != len) ENTFAIL
+    return 0;
+}
+
+
+// Use `BCryptGenRandom` on Windows ////////////////////////////////////////////
+
+#elif defined(ENT_GETENTROPY_BCRYPTGENRANDOM)
+#include <windows.h>
+#include <bcrypt.h>
+int ent_getentropy(void* buf, size_t len) {
+  return BCryptGenRandom(NULL, (PUCHAR)buf, len, BCRYPT_USE_SYSTEM_PREFERRED_RNG);
+}
+
+#else
+#error "One of these must be set: ENT_GETENTROPY_BCRYPTGENRANDOM, ENT_DEV_URANDOM, ENT_GETENTROPY_UNISTD, ENT_GETENTROPY_SYSRANDOM, ENT_GETRANDOM_SYSCALL"
+#endif