util: introduce in_addr_random_prefix()

diff --git a/src/basic/in-addr-util.c b/src/basic/in-addr-util.c
index c715075c14f9f16446a36edbce0acfa6f9d7c43b..bc6b9ce44d552e1b4a996d0f707ac198ca88d413 100644 (file)
--- a/src/basic/in-addr-util.c
+++ b/src/basic/in-addr-util.c
@@ -11,6 +11,7 @@
 #include "in-addr-util.h"
 #include "macro.h"
 #include "parse-util.h"
+#include "random-util.h"
 #include "util.h"
 
 bool in4_addr_is_null(const struct in_addr *a) {
@@ -215,6 +216,83 @@ int in_addr_prefix_next(int family, union in_addr_union *u, unsigned prefixlen)
         return -EAFNOSUPPORT;
 }
 
+int in_addr_random_prefix(
+                int family,
+                union in_addr_union *u,
+                unsigned prefixlen_fixed_part,
+                unsigned prefixlen) {
+
+        assert(u);
+
+        /* Random network part of an address by one. */
+
+        if (prefixlen <= 0)
+                return 0;
+
+        if (family == AF_INET) {
+                uint32_t c, n;
+
+                if (prefixlen_fixed_part > 32)
+                        prefixlen_fixed_part = 32;
+                if (prefixlen > 32)
+                        prefixlen = 32;
+                if (prefixlen_fixed_part >= prefixlen)
+                        return -EINVAL;
+
+                c = be32toh(u->in.s_addr);
+                c &= ((UINT32_C(1) << prefixlen_fixed_part) - 1) << (32 - prefixlen_fixed_part);
+
+                random_bytes(&n, sizeof(n));
+                n &= ((UINT32_C(1) << (prefixlen - prefixlen_fixed_part)) - 1) << (32 - prefixlen);
+
+                u->in.s_addr = htobe32(n | c);
+                return 1;
+        }
+
+        if (family == AF_INET6) {
+                struct in6_addr n;
+                unsigned i, j;
+
+                if (prefixlen_fixed_part > 128)
+                        prefixlen_fixed_part = 128;
+                if (prefixlen > 128)
+                        prefixlen = 128;
+                if (prefixlen_fixed_part >= prefixlen)
+                        return -EINVAL;
+
+                random_bytes(&n, sizeof(n));
+
+                for (i = 0; i < 16; i++) {
+                        uint8_t mask_fixed_part = 0, mask = 0;
+
+                        if (i < (prefixlen_fixed_part + 7) / 8) {
+                                if (i < prefixlen_fixed_part / 8)
+                                        mask_fixed_part = 0xffu;
+                                else {
+                                        j = prefixlen_fixed_part % 8;
+                                        mask_fixed_part = ((UINT8_C(1) << (j + 1)) - 1) << (8 - j);
+                                }
+                        }
+
+                        if (i < (prefixlen + 7) / 8) {
+                                if (i < prefixlen / 8)
+                                        mask = 0xffu ^ mask_fixed_part;
+                                else {
+                                        j = prefixlen % 8;
+                                        mask = (((UINT8_C(1) << (j + 1)) - 1) << (8 - j)) ^ mask_fixed_part;
+                                }
+                        }
+
+                        u->in6.s6_addr[i] &= mask_fixed_part;
+                        u->in6.s6_addr[i] |= n.s6_addr[i] & mask;
+                }
+
+                return 1;
+        }
+
+        return -EAFNOSUPPORT;
+}
+
 int in_addr_to_string(int family, const union in_addr_union *u, char **ret) {
         char *x;
         size_t l;

diff --git a/src/basic/in-addr-util.h b/src/basic/in-addr-util.h
index c21567122caf254d39882f7e8ff620bb56f8332b..3517fe1ea355d2e2b7c88d7206d3a531667f6af6 100644 (file)
--- a/src/basic/in-addr-util.h
+++ b/src/basic/in-addr-util.h
@@ -35,6 +35,7 @@ bool in4_addr_is_non_local(const struct in_addr *a);
 int in_addr_equal(int family, const union in_addr_union *a, const union in_addr_union *b);
 int in_addr_prefix_intersect(int family, const union in_addr_union *a, unsigned aprefixlen, const union in_addr_union *b, unsigned bprefixlen);
 int in_addr_prefix_next(int family, union in_addr_union *u, unsigned prefixlen);
+int in_addr_random_prefix(int family, union in_addr_union *u, unsigned prefixlen_fixed_part, unsigned prefixlen);
 int in_addr_to_string(int family, const union in_addr_union *u, char **ret);
 int in_addr_ifindex_to_string(int family, const union in_addr_union *u, int ifindex, char **ret);
 int in_addr_from_string(int family, const char *s, union in_addr_union *ret);