rand: accept seed for rand()/srandom() from the outside

So we can use reproducible seeds in tests to make reproducing test
crashes easier.

src/dfuzzer.c

@@ -231,7 +231,7 @@ static int df_fuzz(GDBusConnection *dcon, const char *name, const char *object,
         int rv = DF_BUS_OK;
 
         // initialization of random module
-        df_rand_init();
+        df_rand_init(time(NULL));
 
         // Sanity check fuzzing target
         if (isempty(name) || isempty(object) || isempty(interface)) {

src/rand.c

@@ -39,10 +39,10 @@ static struct external_dictionary df_external_dictionary;
  * numbers generators.
  * @param buf_size Maximum buffer size for generated strings (in Bytes)
  */
-void df_rand_init()
+void df_rand_init(unsigned int seed)
 {
-        srand(time(NULL));  // for int rand()
-        srandom(time(NULL));    // for long int random()
+        srand(seed);
+        srandom(seed);
 }
 
 int df_rand_load_external_dictionary(const char *filename)

src/rand.h

@@ -30,11 +30,7 @@ struct external_dictionary {
         char **strings;
 };
 
-/**
- * @function Initializes global flag variables and seeds pseudo-random
- * numbers generators.
- */
-void df_rand_init();
+void df_rand_init(unsigned int seed);
 int df_rand_load_external_dictionary(const char *filename);
 
 GVariant *df_generate_random_basic(const GVariantType *type, guint64 iteration);

test/test-rand.c

@@ -109,8 +109,16 @@ static void test_df_rand_GVariant(void)
 int main(int argc, char *argv[])
 {
         g_test_init(&argc, &argv, NULL);
-        /* Init our internal pseudo-random number generators */
-        df_rand_init();
+        /* Init our internal pseudo-random number generators
+         *
+         * Since we can't access the g_test_*() seed directly, let's use one
+         * of the g_test_rand*() functions that generate reproducible numbers
+         * (using the internal seed), so a possible test crash can be later
+         * reproduced using the `--seed xxx` option
+         *
+         * See: https://docs.gtk.org/glib/func.test_rand_int.html
+         * */
+        df_rand_init(g_test_rand_int());
 
         g_test_add_func("/df_rand/df_rand_unichar", test_df_rand_unichar);
         g_test_add_func("/df_rand/df_rand_string", test_df_rand_string);