lib/util: add unique string generator helper function

lib/util/genrand.c

@@ -360,3 +360,62 @@ again:
 
 	return retstr;
 }
+
+/**
+ * Define our own pow() function to avoid linking in libm
+ */
+static double s_pow(double x, double y)
+{
+	int i;
+	double ret = x;
+
+	if (y == 0)
+		return 1;
+
+	for (i = 1; i < y; i++)
+		ret *= x;
+
+	return ret;
+}
+
+
+/**
+ * Generate an array of unique text strings all of the same length.
+ * The returned string will be allocated.
+ * Returns NULL if the number of unique combinations cannot be created.
+ *
+ * Characters used are: abcdefghijklmnopqrstuvwxyz0123456789+_-#.,
+ */
+_PUBLIC_ char** generate_unique_strs(TALLOC_CTX *mem_ctx, size_t len,
+				     uint32_t num)
+{
+	const char *c_list = "abcdefghijklmnopqrstuvwxyz0123456789+_-#.,";
+	const int c_size = 42;
+	int i, j, rem;
+	long long place;
+	char ** strs = NULL;
+
+	if (num == 0 || len == 0)
+		return NULL;
+
+	/* We'll never return more than UINT32_MAX strings. Since 42^6 is more
+	 * than UINT32_MAX, we only have to check if we've been asked to return
+	 * more than the total number of permutations for lengths less than 6.*/
+	if ((len < 6) && (num > s_pow(c_size, len)))
+		return NULL;
+
+	strs = talloc_array(mem_ctx, char *, num);
+
+	for (i = 0; i < num; i++) {
+		char *retstr = talloc_zero_size(mem_ctx, len + 1);
+		rem = i;
+		for (j = len - 1; j >= 0; j--) {
+			place = s_pow(c_size, j);
+			retstr[j] = c_list[rem / place];
+			rem = rem % place;
+		}
+		strs[i] = retstr;
+	}
+
+	return strs;
+}

lib/util/util.h

@@ -192,6 +192,16 @@ _PUBLIC_ char *generate_random_str_list(TALLOC_CTX *mem_ctx, size_t len, const c
  */
 _PUBLIC_ char *generate_random_str(TALLOC_CTX *mem_ctx, size_t len);
 
+/**
+ * Generate an array of unique text strings all of the same length.
+ * The returned strings will be allocated.
+ * Returns NULL if the number of unique combinations cannot be created.
+ *
+ * Characters used are: ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+_-#.,
+ */
+_PUBLIC_ char** generate_unique_strs(TALLOC_CTX *mem_ctx, size_t len,
+                                         uint32_t num);
+
 /* The following definitions come from lib/util/dprintf.c  */
 #if _SAMBA_BUILD_ == 4