Implement priority/weight for DNS SRV records

From RFC 2782:

  A client MUST attempt to contact the target host with the

  lowest-numbered priority it can reach.

This patch sorts the DNS SRV records by their priority, and

additionally gives records with a larger weight a higher probability

of appearing earlier. This way, the DNS SRV records are tried in the

order of their priority.

Author: James M Leddy <james.leddy@redhat.com>

Upstream ITS: #7027

Resolves: #733078

---

 libraries/libldap/dnssrv.c |  106 ++++++++++++++++++++++++++++++++++----------

 1 files changed, 83 insertions(+), 23 deletions(-)

diff --git a/libraries/libldap/dnssrv.c b/libraries/libldap/dnssrv.c

index 16b1544..40f93b4 100644

--- a/libraries/libldap/dnssrv.c

+++ b/libraries/libldap/dnssrv.c

@@ -174,6 +174,46 @@ int ldap_domain2dn(

 	return LDAP_SUCCESS;

 }

+#ifdef HAVE_RES_QUERY

+#define DNSBUFSIZ (64*1024)

+typedef struct srv_record {

+    u_short priority;

+    u_short weight;

+    u_short port;

+    char hostname[DNSBUFSIZ];

+} srv_record;

+

+

+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;

+    

+    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;

+	    }

+	}

+	total = a->weight + b->weight;

+	if (rand() % total < a->weight) {

+	    return -1;

+	} else {

+	    return 1;

+	}

+    }

+}

+#endif /* HAVE_RES_QUERY */

+

 /*

  * Lookup and return LDAP servers for domain (using the DNS

  * SRV record _ldap._tcp.domain).

@@ -183,15 +223,16 @@ int ldap_domain2hostlist(

 	char **list )

 {

 #ifdef HAVE_RES_QUERY

-#define DNSBUFSIZ (64*1024)

-    char *request;

-    char *hostlist = NULL;

+    char *request; 

+   char *hostlist = NULL;

+    srv_record *hostent_head=NULL;

+    int i;

     int rc, len, cur = 0;

     unsigned char reply[DNSBUFSIZ];

+    int hostent_count=0;

 	assert( domain != NULL );

 	assert( list != NULL );

-

 	if( *domain == '\0' ) {

 		return LDAP_PARAM_ERROR;

 	}

@@ -223,8 +264,7 @@ int ldap_domain2hostlist(

 	unsigned char *p;

 	char host[DNSBUFSIZ];

 	int status;

-	u_short port;

-	/* int priority, weight; */

+	u_short port, priority, weight; 

 	/* Parse out query */

 	p = reply;

@@ -263,40 +303,56 @@ int ldap_domain2hostlist(

 	    size = (p[0] << 8) | p[1];

 	    p += 2;

 	    if (type == T_SRV) {

-		int buflen;

 		status = dn_expand(reply, reply + len, p + 6, host, sizeof(host));

 		if (status < 0) {

 		    goto out;

 		}

-		/* ignore priority and weight for now */

-		/* priority = (p[0] << 8) | p[1]; */

-		/* weight = (p[2] << 8) | p[3]; */

+		

+		/* Get priority weight and port */

+		priority = (p[0] << 8) | p[1];

+		weight = (p[2] << 8) | p[3]; 

 		port = (p[4] << 8) | p[5];

 		if ( port == 0 || host[ 0 ] == '\0' ) {

 		    goto add_size;

 		}

-		buflen = strlen(host) + STRLENOF(":65355 ");

-		hostlist = (char *) LDAP_REALLOC(hostlist, cur + buflen + 1);

-		if (hostlist == NULL) {

-		    rc = LDAP_NO_MEMORY;

-		    goto out;

+		hostent_head = (srv_record *) LDAP_REALLOC(hostent_head, (hostent_count+1)*(sizeof(srv_record)));

+		if(hostent_head==NULL){

+		  rc=LDAP_NO_MEMORY;

+		  goto out;

+		  

 		}

-		if (cur > 0) {

-		    /* not first time around */

-		    hostlist[cur++] = ' ';

-		}

-		cur += sprintf(&hostlist[cur], "%s:%hu", host, port);

+		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;

 	    }

 add_size:;

 	    p += size;

 	}

     }

+    qsort(hostent_head, hostent_count, sizeof(srv_record), srv_cmp);

+

+    for(i=0; i

+	int buflen;

+        buflen = strlen(hostent_head[i].hostname) + STRLENOF(":65355" );

+        hostlist = (char *) LDAP_REALLOC(hostlist, cur+buflen+1);

+        if (hostlist == NULL) {

+            rc = LDAP_NO_MEMORY;

+            goto out;

+        }

+        if(cur>0){

+            hostlist[cur++]=' ';

+        }

+        cur += sprintf(&hostlist[cur], "%s:%hd", hostent_head[i].hostname, hostent_head[i].port);

+    }

+

     if (hostlist == NULL) {

-	/* No LDAP servers found in DNS. */

-	rc = LDAP_UNAVAILABLE;

-	goto out;

+         /* No LDAP servers found in DNS. */

+         rc = LDAP_UNAVAILABLE;

+         goto out;

     }

     rc = LDAP_SUCCESS;

@@ -308,8 +364,12 @@ add_size:;

     if (request != NULL) {

 	LDAP_FREE(request);

     }

+    if (hostent_head != NULL) {

+	LDAP_FREE(hostent_head);

+    }

     if (rc != LDAP_SUCCESS && hostlist != NULL) {

 	LDAP_FREE(hostlist);

+	

     }

     return rc;

 #else

-- 

1.7.6