CDRIVER-4234 Detect arc4random_buf using cmake

Detect the availability of arc4random_buf when running cmake rather than
using a hardcoded list of platforms on which it is available. Fixes
build failure on Mac OS X 10.6 where it is not available.

Also now make arc4random_buf the first choice to use if it is available.
Previously, if rand_r was not available, the older rand would be used
even if arc4random_buf was available.

Author: ryandesign

src/libbson/CMakeLists.txt

@@ -73,6 +73,13 @@ else ()
    set (BSON_HAVE_GMTIME_R 1)
 endif ()
 
+CHECK_SYMBOL_EXISTS (arc4random_buf stdlib.h BSON_HAVE_ARC4RANDOM_BUF)
+if (NOT BSON_HAVE_ARC4RANDOM_BUF)
+   set (BSON_HAVE_ARC4RANDOM_BUF 0)
+else ()
+   set (BSON_HAVE_ARC4RANDOM_BUF 1)
+endif ()
+
 CHECK_FUNCTION_EXISTS (rand_r BSON_HAVE_RAND_R)
 if (NOT BSON_HAVE_RAND_R)
    set (BSON_HAVE_RAND_R 0)

src/libbson/src/bson/bson-config.h.in

@@ -114,6 +114,15 @@
 #endif
 
 
+/*
+ * Define to 1 if you have arc4random_buf available on your platform.
+ */
+#define BSON_HAVE_ARC4RANDOM_BUF @BSON_HAVE_ARC4RANDOM_BUF@
+#if BSON_HAVE_ARC4RANDOM_BUF != 1
+# undef BSON_HAVE_ARC4RANDOM_BUF
+#endif
+
+
 /*
  * Define to 1 if you have rand_r available on your platform.
  */

src/libbson/src/bson/bson-context.c

@@ -225,15 +225,14 @@ static int32_t
 _get_rand (unsigned int *pseed)
 {
    int32_t result = 0;
-#ifndef BSON_HAVE_RAND_R
+#ifdef BSON_HAVE_ARC4RANDOM_BUF
+   arc4random_buf (&result, sizeof (result));
+#elif defined(BSON_HAVE_RAND_R)
+   result = rand_r (pseed);
+#else
    /* ms's runtime is multithreaded by default, so no rand_r */
    /* no rand_r on android either */
    result = rand ();
-#elif defined(__FreeBSD__) || defined(__NetBSD__) || defined(__DragonFly__) || \
-   defined(__OpenBSD__) || defined(__APPLE__)
-   arc4random_buf (&result, sizeof (result));
-#else
-   result = rand_r (pseed);
 #endif
    return result;
 }