in-addr-util: introduce in_addr_prefix_nth

diff --git a/src/basic/in-addr-util.c b/src/basic/in-addr-util.c
index bfe855fb4b9ca9ed0bd7d59508beb2c9eec7868d..d1e457b647246ad391de3f0ea01b0ff5667b2397 100644 (file)
--- a/src/basic/in-addr-util.c
+++ b/src/basic/in-addr-util.c
@@ -226,6 +226,92 @@ int in_addr_prefix_next(int family, union in_addr_union *u, unsigned prefixlen)
         return -EAFNOSUPPORT;
 }
 
+/*
+ * Calculates the nth prefix of size prefixlen starting from the address denoted by u.
+ *
+ * On success 1 will be returned and the calculated prefix will be available in
+ * u. In the case nth == 0 the input will be left unchanged and 1 will be returned.
+ * In case the calculation cannot be performed (invalid prefix length,
+ * overflows would occur) -ERANGE is returned. If the address family given isn't
+ * supported -EAFNOSUPPORT will be returned.
+ *
+ *
+ * Examples:
+ *   - in_addr_prefix_nth(AF_INET, 192.168.0.0, 24, 2), returns 1, writes 192.168.2.0 to u
+ *   - in_addr_prefix_nth(AF_INET, 192.168.0.0, 24, 0), returns 1, no data written
+ *   - in_addr_prefix_nth(AF_INET, 255.255.255.0, 24, 1), returns -ERANGE, no data written
+ *   - in_addr_prefix_nth(AF_INET, 255.255.255.0, 0, 1), returns -ERANGE, no data written
+ *   - in_addr_prefix_nth(AF_INET6, 2001:db8, 64, 0xff00) returns 1, writes 2001:0db8:0000:ff00:: to u
+ */
+int in_addr_prefix_nth(int family, union in_addr_union *u, unsigned prefixlen, uint64_t nth) {
+        assert(u);
+
+        if (prefixlen <= 0)
+                return -ERANGE;
+
+        if (nth == 0)
+                return 1;
+
+        if (family == AF_INET) {
+                uint32_t c, n, t;
+                if (prefixlen > 32)
+                        prefixlen = 32;
+
+                c = be32toh(u->in.s_addr);
+
+                t = nth << (32 - prefixlen);
+
+                /* Check for wrap */
+                if (c > UINT32_MAX - t)
+                        return -ERANGE;
+
+                n = c + t;
+
+                n &= UINT32_C(0xFFFFFFFF) << (32 - prefixlen);
+                u->in.s_addr = htobe32(n);
+                return 1;
+        }
+
+        if (family == AF_INET6) {
+                struct in6_addr result = {};
+                uint8_t overflow = 0;
+                uint64_t delta;  /* this assumes that we only ever have to up to 1<<64 subnets */
+                unsigned start_byte = (prefixlen - 1) / 8;
+
+                if (prefixlen > 128)
+                        prefixlen = 128;
+
+                /* First calculate what we have to add */
+                delta = nth << ((128 - prefixlen) % 8);
+
+                for (unsigned i = 16; i > 0; i--) {
+                        unsigned j = i - 1;
+                        unsigned d = 0;
+
+                        if (j <= start_byte) {
+                                int16_t t;
+
+                                d = delta & 0xFF;
+                                delta >>= 8;
+
+                                t = u->in6.s6_addr[j] + d + overflow;
+                                overflow = t > UINT8_MAX ? t - UINT8_MAX : 0;
+
+                                result.s6_addr[j] = (uint8_t)t;
+                        } else
+                                result.s6_addr[j] = u->in6.s6_addr[j];
+                }
+
+                if (overflow || delta != 0)
+                        return -ERANGE;
+
+                u->in6 = result;
+                return 1;
+        }
+
+        return -EAFNOSUPPORT;
+}
+
 int in_addr_random_prefix(
                 int family,
                 union in_addr_union *u,

diff --git a/src/basic/in-addr-util.h b/src/basic/in-addr-util.h
index ae2dad0bb1e92280cb6efe34b8e9e94dbd6e8949..90d79a5ef5089431a4c4892b0af077d26e04e163 100644 (file)
--- a/src/basic/in-addr-util.h
+++ b/src/basic/in-addr-util.h
@@ -36,6 +36,7 @@ bool in4_addr_equal(const struct in_addr *a, const struct in_addr *b);
 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_prefix_nth(int family, union in_addr_union *u, unsigned prefixlen, uint64_t nth);
 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_prefix_to_string(int family, const union in_addr_union *u, unsigned prefixlen, char **ret);

diff --git a/src/test/test-socket-util.c b/src/test/test-socket-util.c
index d36caaa71e73375637af4cbc61d09332625c3644..d63f212c196bae41aacbd0d3f75a82614f8839cd 100644 (file)
--- a/src/test/test-socket-util.c
+++ b/src/test/test-socket-util.c
@@ -173,6 +173,45 @@ static void test_in_addr_prefix_next(void) {
         test_in_addr_prefix_next_one(AF_INET6, "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ff00", 120, NULL);
 }
 
+static void test_in_addr_prefix_nth_one(unsigned f, const char *before, unsigned pl, uint64_t nth, const char *after) {
+        union in_addr_union ubefore, uafter, t;
+
+        assert_se(in_addr_from_string(f, before, &ubefore) >= 0);
+
+        t = ubefore;
+        assert_se((in_addr_prefix_nth(f, &t, pl, nth) > 0) == !!after);
+
+        if (after) {
+                assert_se(in_addr_from_string(f, after, &uafter) >= 0);
+                assert_se(in_addr_equal(f, &t, &uafter) > 0);
+        }
+}
+
+static void test_in_addr_prefix_nth(void) {
+        log_info("/* %s */", __func__);
+
+        test_in_addr_prefix_nth_one(AF_INET, "192.168.0.0", 24, 0, "192.168.0.0");
+        test_in_addr_prefix_nth_one(AF_INET, "192.168.0.0", 24, 1, "192.168.1.0");
+        test_in_addr_prefix_nth_one(AF_INET, "192.168.0.0", 24, 4, "192.168.4.0");
+        test_in_addr_prefix_nth_one(AF_INET, "192.168.0.0", 25, 1, "192.168.0.128");
+        test_in_addr_prefix_nth_one(AF_INET, "192.168.255.0", 25, 1, "192.168.255.128");
+        test_in_addr_prefix_nth_one(AF_INET, "192.168.255.0", 24, 0, "192.168.255.0");
+        test_in_addr_prefix_nth_one(AF_INET, "255.255.255.255", 32, 1, NULL);
+        test_in_addr_prefix_nth_one(AF_INET, "255.255.255.255", 0, 1, NULL);
+
+        test_in_addr_prefix_nth_one(AF_INET6, "4400::", 8, 1, "4500::");
+        test_in_addr_prefix_nth_one(AF_INET6, "4400::", 7, 1, "4600::");
+        test_in_addr_prefix_nth_one(AF_INET6, "4400::", 64, 1, "4400:0:0:1::");
+        test_in_addr_prefix_nth_one(AF_INET6, "4400::", 64, 2, "4400:0:0:2::");
+        test_in_addr_prefix_nth_one(AF_INET6, "4400::", 64, 0xbad, "4400:0:0:0bad::");
+        test_in_addr_prefix_nth_one(AF_INET6, "4400:0:0:ffff::", 64, 1, "4400:0:1::");
+        test_in_addr_prefix_nth_one(AF_INET6, "4400::", 56, ((uint64_t)1<<48) -1, "44ff:ffff:ffff:ff00::");
+        test_in_addr_prefix_nth_one(AF_INET6, "0000::", 8, 255, "ff00::");
+        test_in_addr_prefix_nth_one(AF_INET6, "0000::", 8, 256, NULL);
+        test_in_addr_prefix_nth_one(AF_INET6, "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff", 128, 1, NULL);
+        test_in_addr_prefix_nth_one(AF_INET6, "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff", 0, 1, NULL);
+}
+
 static void test_in_addr_to_string_one(int f, const char *addr) {
         union in_addr_union ua;
         _cleanup_free_ char *r = NULL;
@@ -673,6 +712,7 @@ int main(int argc, char *argv[]) {
         test_in_addr_is_null();
         test_in_addr_prefix_intersect();
         test_in_addr_prefix_next();
+        test_in_addr_prefix_nth();
         test_in_addr_to_string();
         test_in_addr_ifindex_to_string();
         test_in_addr_ifindex_from_string_auto();