ITS#7027 actually implement RFC 2782 shuffle

diff --git a/libraries/libldap/dnssrv.c b/libraries/libldap/dnssrv.c
index de849e30d5b01ae855853c79e88fb06d7aea1137..51a711ac67322d8f234792d0f3ccd15229d889c2 100644 (file)
--- a/libraries/libldap/dnssrv.c
+++ b/libraries/libldap/dnssrv.c
@@ -176,41 +176,77 @@ int ldap_domain2dn(
 
 #ifdef HAVE_RES_QUERY
 #define DNSBUFSIZ (64*1024)
+#define MAXHOST        254     /* RFC 1034, max length is 253 chars */
 typedef struct srv_record {
     u_short priority;
     u_short weight;
     u_short port;
-    char hostname[DNSBUFSIZ];
+    char hostname[MAXHOST];
 } srv_record;
 
+/* Linear Congruential Generator - we don't need
+ * high quality randomness, and we don't want to
+ * interfere with anyone else's use of srand().
+ *
+ * The PRNG here cycles thru 941,955 numbers.
+ */
+static float srv_seed;
+
+static void srv_srand(int seed) {
+       srv_seed = (float)seed / (float)RAND_MAX;
+}
+
+static float srv_rand() {
+       float val = 9821.0 * srv_seed + .211327;
+       srv_seed = val - (int)val;
+       return srv_seed;
+}
 
 static int srv_cmp(const void *aa, const void *bb){
-    srv_record *a=(srv_record *)aa;
-    srv_record *b=(srv_record *)bb;
-    u_long total;
+       srv_record *a=(srv_record *)aa;
+       srv_record *b=(srv_record *)bb;
+       int i = a->priority - b->priority;
+       if (i) return i;
+       return b->weight - a->weight;
+}
 
-    if(a->priority < b->priority) {
-       return -1;
-    }
-    if(a->priority > b->priority) {
-       return 1;
-    }
-    if(a->priority == b->priority){
-       /* targets with same priority are in psudeo random order */
-       if (a->weight == 0 && b->weight == 0) {
-           if (rand() % 2) {
-               return -1;
-           } else {
-               return 1;
-           }
+static void srv_shuffle(srv_record *a, int n) {
+       int i, j, total = 0, r, p;
+
+       for (i=0; i<n; i++)
+               total += a[i].weight;
+
+       /* all weights are zero, do a straight Fisher-Yates shuffle */
+       if (!total) {
+               while (n) {
+                       srv_record t;
+                       i = srv_rand() * n--;
+                       t = a[n];
+                       a[n] = a[i];
+                       a[i] = t;
+               }
+               return;
        }
-       total = a->weight + b->weight;
-       if (rand() % total < a->weight) {
-           return -1;
-       } else {
-           return 1;
+
+       /* Do a shuffle per RFC2782 Page 4 */
+       p = n;
+       for (i=0; i<n-1; i++) {
+               r = srv_rand() * total;
+               for (j=0; j<p; j++) {
+                       r -= a[j].weight;
+                       if (r <= 0) {
+                               if (j) {
+                                       srv_record t = a[0];
+                                       a[0] = a[j];
+                                       a[j] = t;
+                               }
+                               total -= a[0].weight;
+                               a++;
+                               p--;
+                               break;
+                       }
+               }
        }
-    }
 }
 #endif /* HAVE_RES_QUERY */
 
@@ -226,7 +262,7 @@ int ldap_domain2hostlist(
     char *request;
     char *hostlist = NULL;
     srv_record *hostent_head=NULL;
-    int i;
+    int i, j;
     int rc, len, cur = 0;
     unsigned char reply[DNSBUFSIZ];
     int hostent_count=0;
@@ -325,15 +361,31 @@ int ldap_domain2hostlist(
                hostent_head[hostent_count].priority=priority;
                hostent_head[hostent_count].weight=weight;
                hostent_head[hostent_count].port=port;
-               strncpy(hostent_head[hostent_count].hostname, host,255);
-               hostent_count=hostent_count+1;
+               strncpy(hostent_head[hostent_count].hostname, host, MAXHOST);
+               hostent_count++;
            }
 add_size:;
            p += size;
        }
-    }
     qsort(hostent_head, hostent_count, sizeof(srv_record), srv_cmp);
 
+       if (!srv_seed)
+               srv_srand(time(0L));
+
+       /* shuffle records of same priority */
+       j = 0;
+       priority = hostent_head[0].priority;
+       for (i=1; i<hostent_count; i++) {
+               if (hostent_head[i].priority != priority) {
+                       priority = hostent_head[i].priority;
+                       if (i-j > 1)
+                               srv_shuffle(hostent_head+j, i-j);
+                       j = i;
+               }
+       }
+       if (i-j > 1)
+               srv_shuffle(hostent_head+j, i-j);
+
     for(i=0; i<hostent_count; i++){
        int buflen;
         buflen = strlen(hostent_head[i].hostname) + STRLENOF(":65535 ");
@@ -347,6 +399,7 @@ add_size:;
         }
         cur += sprintf(&hostlist[cur], "%s:%hd", hostent_head[i].hostname, hostent_head[i].port);
     }
+    }
 
     if (hostlist == NULL) {
        /* No LDAP servers found in DNS. */