shared: add minimal firewall manipulation helpers for establishing NAT rules, using...

[elogind.git] / src / shared / in-addr-util.c

diff --git a/src/shared/in-addr-util.c b/src/shared/in-addr-util.c
index 457eedd6d81825f519984f06884cc0c91ab4c6c0..b02e7516ca4d69400dc7d5dd95d3776e7eba0614 100644 (file)
--- a/src/shared/in-addr-util.c
+++ b/src/shared/in-addr-util.c
@@ -243,8 +243,60 @@ int in_addr_from_string_auto(const char *s, int *family, union in_addr_union *re
         return -EINVAL;
 }
 
-unsigned in_addr_netmask_to_prefixlen(const struct in_addr *addr) {
+unsigned char in_addr_netmask_to_prefixlen(const struct in_addr *addr) {
         assert(addr);
 
         return 32 - u32ctz(be32toh(addr->s_addr));
 }
+
+struct in_addr* in_addr_prefixlen_to_netmask(struct in_addr *addr, unsigned char prefixlen) {
+        assert(addr);
+        assert(prefixlen <= 32);
+
+        /* Shifting beyond 32 is not defined, handle this specially. */
+        if (prefixlen == 0)
+                addr->s_addr = 0;
+        else
+                addr->s_addr = htobe32((0xffffffff << (32 - prefixlen)) & 0xffffffff);
+
+        return addr;
+}
+
+int in_addr_default_prefixlen(const struct in_addr *addr, unsigned char *prefixlen) {
+        uint8_t msb_octet = *(uint8_t*) addr;
+
+        /* addr may not be aligned, so make sure we only access it byte-wise */
+
+        assert(addr);
+        assert(prefixlen);
+
+        if (msb_octet < 128)
+                /* class A, leading bits: 0 */
+                *prefixlen = 8;
+        else if (msb_octet < 192)
+                /* class B, leading bits 10 */
+                *prefixlen = 16;
+        else if (msb_octet < 224)
+                /* class C, leading bits 110 */
+                *prefixlen = 24;
+        else
+                /* class D or E, no default prefixlen */
+                return -ERANGE;
+
+        return 0;
+}
+
+int in_addr_default_subnet_mask(const struct in_addr *addr, struct in_addr *mask) {
+        unsigned char prefixlen;
+        int r;
+
+        assert(addr);
+        assert(mask);
+
+        r = in_addr_default_prefixlen(addr, &prefixlen);
+        if (r < 0)
+                return r;
+
+        in_addr_prefixlen_to_netmask(mask, prefixlen);
+        return 0;
+}