Canonicalize IPv6 addresses as per RFC 5952 before printing them.

[tinc] / src / subnet_parse.c

diff --git a/src/subnet_parse.c b/src/subnet_parse.c
index b6e209b..5922831 100644 (file)
--- a/src/subnet_parse.c
+++ b/src/subnet_parse.c
@@ -321,6 +321,8 @@ bool net2str(char *netstr, int len, const subnet_t *subnet) {
                                         subnet->net.mac.address.x[4],
                                         subnet->net.mac.address.x[5],
                                         subnet->weight);
+                       netstr += result;
+                       len -= result;
                        break;
 
                case SUBNET_IPV4:
@@ -329,32 +331,68 @@ bool net2str(char *netstr, int len, const subnet_t *subnet) {
                                         subnet->net.ipv4.address.x[1],
                                         subnet->net.ipv4.address.x[2],
                                         subnet->net.ipv4.address.x[3]);
+                       netstr += result;
+                       len -= result;
                        prefixlength = subnet->net.ipv4.prefixlength;
                        if (prefixlength == 32)
                                prefixlength = -1;
                        break;
 
-               case SUBNET_IPV6:
-                       result = snprintf(netstr, len, "%hx:%hx:%hx:%hx:%hx:%hx:%hx:%hx",
-                                        ntohs(subnet->net.ipv6.address.x[0]),
-                                        ntohs(subnet->net.ipv6.address.x[1]),
-                                        ntohs(subnet->net.ipv6.address.x[2]),
-                                        ntohs(subnet->net.ipv6.address.x[3]),
-                                        ntohs(subnet->net.ipv6.address.x[4]),
-                                        ntohs(subnet->net.ipv6.address.x[5]),
-                                        ntohs(subnet->net.ipv6.address.x[6]),
-                                        ntohs(subnet->net.ipv6.address.x[7]));
+               case SUBNET_IPV6: {
+                       /* Find the longest sequence of consecutive zeroes */
+                       int max_zero_length = 0;
+                       int max_zero_length_index = 0;
+                       int current_zero_length = 0;
+                       int current_zero_length_index = 0;
+                       for (int i = 0; i < 8; i++) {
+                               if (subnet->net.ipv6.address.x[i] != 0)
+                                       current_zero_length = 0;
+                               else {
+                                       if (current_zero_length == 0)
+                                               current_zero_length_index = i;
+                                       current_zero_length++;
+                                       if (current_zero_length > max_zero_length) {
+                                               max_zero_length = current_zero_length;
+                                               max_zero_length_index = current_zero_length_index;
+                                       }
+                               }
+                       }
+
+                       /* Print the address */
+                       for (int i = 0; i < 8;) {
+                               if (max_zero_length > 1 && max_zero_length_index == i) {
+                                       /* Shorten the representation as per RFC 5952 */
+                                       const char* const FORMATS[] = { "%.1s", "%.2s", "%.3s" };
+                                       const char* const* format = &FORMATS[0];
+                                       if (i == 0)
+                                               format++;
+                                       if (i + max_zero_length == 8)
+                                               format++;
+                                       result = snprintf(netstr, len, *format, ":::");
+                                       i += max_zero_length;
+                               } else {
+                                       result = snprintf(netstr, len, "%hx:", ntohs(subnet->net.ipv6.address.x[i]));
+                                       i++;
+                               }
+                               netstr += result;
+                               len -= result;
+                       }
+
+                       /* Remove the trailing colon */
+                       netstr--;
+                       len++;
+                       *netstr = 0;
+
                        prefixlength = subnet->net.ipv6.prefixlength;
                        if (prefixlength == 128)
                                prefixlength = -1;
                        break;
+               }
 
                default:
                        logger(DEBUG_ALWAYS, LOG_ERR, "net2str() was called with unknown subnet type %d, exiting!", subnet->type);
                        exit(1);
        }
-       netstr += result;
-       len -= result;
 
        if (prefixlength >= 0) {
                result = snprintf(netstr, len, "/%d", prefixlength);