Changeset 1356

Timestamp:

Jun 11, 2007 4:47:51 PM (17 years ago)

Author:

bennylp

Message:

Ticket #329: Added utility function to parse DNS A response in PJLIB-UTIL

Location:

pjproject/trunk/pjlib-util

Files:

• include/pjlib-util/errno.h (modified) (1 diff)
• include/pjlib-util/resolver.h (modified) (2 diffs)
• src/pjlib-util/errno.c (modified) (1 diff)
• src/pjlib-util/resolver.c (modified) (4 diffs)

pjproject/trunk/pjlib-util/include/pjlib-util/errno.h

@@ -175 +175 @@
  */
 #define PJLIB_UTIL_EDNSNOANSWERREC  (PJLIB_UTIL_ERRNO_START+47) /* 320047 */
+/**
+ * @hideinitializer
+ * Invalid DNS answer. This error is raised for example when the DNS
+ * answer does not have a query section, or the type of RR in the answer
+ * doesn't match the query.
+ */
+#define PJLIB_UTIL_EDNSINANSWER     (PJLIB_UTIL_ERRNO_START+48) /* 320048 */
 
 

pjproject/trunk/pjlib-util/include/pjlib-util/resolver.h

@@ -197 +197 @@
     unsigned    bad_ns_ttl;     /**< See #PJ_DNS_RESOLVER_BAD_NS_TTL        */
 } pj_dns_settings;
+
+
+/**
+ * This structure represents DNS A record, as the result of parsing
+ * DNS response packet using #pj_dns_parse_a_response().
+ */
+typedef struct pj_dns_a_record
+{
+    /** The target name being queried.   */
+    pj_str_t            name;
+
+    /** If target name corresponds to a CNAME entry, the alias contains
+     *  the value of the CNAME entry, otherwise it will be empty.
+     */
+    pj_str_t            alias;
+
+    /** Number of IP addresses. */
+    unsigned            addr_count;
+
+    /** IP addresses of the host found in the response */
+    pj_in_addr          addr[PJ_DNS_MAX_IP_IN_A_REC];
+
+    /** Internal buffer for hostname and alias. */
+    char                buf_[128];
+
+} pj_dns_a_record;
+
 
 /**
@@ -366 +393 @@
                                                   pj_bool_t notify);
 
+/**
+ * A utility function to parse a DNS response containing A records into 
+ * DNS A record.
+ *
+ * @param pkt       The DNS response packet.
+ * @param rec       The structure to be initialized with the parsed
+ *                  DNS A record from the packet.
+ *
+ * @return          PJ_SUCCESS if response can be parsed successfully.
+ */
+PJ_DECL(pj_status_t) pj_dns_parse_a_response(const pj_dns_parsed_packet *pkt,
+                                             pj_dns_a_record *rec);
+
 
 /**

pjproject/trunk/pjlib-util/src/pjlib-util/errno.c

@@ -59 +59 @@
     PJ_BUILD_ERR( PJLIB_UTIL_EDNSNOWORKINGNS,   "No working DNS nameserver"),
     PJ_BUILD_ERR( PJLIB_UTIL_EDNSNOANSWERREC,   "No answer record in the DNS response"),
+    PJ_BUILD_ERR( PJLIB_UTIL_EDNSINANSWER,      "Invalid DNS answer"),
 
     PJ_BUILD_ERR( PJLIB_UTIL_EDNS_FORMERR,      "DNS \"Format error\""),

pjproject/trunk/pjlib-util/src/pjlib-util/resolver.c

@@ -425 +425 @@
 
     PJ_ASSERT_RETURN(resolver && count && servers, PJ_EINVAL);
+    PJ_ASSERT_RETURN(count < PJ_DNS_RESOLVER_MAX_NS, PJ_EINVAL);
 
     pj_mutex_lock(resolver->mutex);
@@ -801 +802 @@
 }
 
+
+/* 
+ * DNS response containing A packet. 
+ */
+PJ_DEF(pj_status_t) pj_dns_parse_a_response(const pj_dns_parsed_packet *pkt,
+                                            pj_dns_a_record *rec)
+{
+    pj_str_t hostname, alias, *res_name;
+    unsigned bufstart = 0;
+    unsigned bufleft = sizeof(rec->buf_);
+    unsigned i, ansidx;
+
+    PJ_ASSERT_RETURN(pkt && rec, PJ_EINVAL);
+
+    /* Init the record */
+    pj_bzero(rec, sizeof(pj_dns_a_record));
+
+    /* Return error if there's error in the packet. */
+    if (PJ_DNS_GET_RCODE(pkt->hdr.flags))
+        return PJ_STATUS_FROM_DNS_RCODE(PJ_DNS_GET_RCODE(pkt->hdr.flags));
+
+    /* Return error if there's no query section */
+    if (pkt->hdr.qdcount == 0)
+        return PJLIB_UTIL_EDNSINANSWER;
+
+    /* Return error if there's no answer */
+    if (pkt->hdr.anscount == 0)
+        return PJLIB_UTIL_EDNSNOANSWERREC;
+
+    /* Get the hostname from the query. */
+    hostname = pkt->q[0].name;
+
+    /* Copy hostname to the record */
+    if (hostname.slen > (int)bufleft) {
+        return PJ_ENAMETOOLONG;
+    }
+
+    pj_memcpy(&rec->buf_[bufstart], hostname.ptr, hostname.slen);
+    rec->name.ptr = &rec->buf_[bufstart];
+    rec->name.slen = hostname.slen;
+
+    bufstart += hostname.slen;
+    bufleft -= hostname.slen;
+
+    /* Find the first RR which name matches the hostname */
+    for (ansidx=0; ansidx < pkt->hdr.anscount; ++ansidx) {
+        if (pj_stricmp(&pkt->ans[ansidx].name, &hostname)==0)
+            break;
+    }
+
+    if (ansidx == pkt->hdr.anscount)
+        return PJLIB_UTIL_EDNSNOANSWERREC;
+
+    /* If hostname is a CNAME, get the alias. */
+    if (pkt->ans[ansidx].type == PJ_DNS_TYPE_CNAME) {
+        alias = pkt->ans[ansidx].rdata.cname.name;
+        res_name = &alias;
+    } else if (pkt->ans[ansidx].type == PJ_DNS_TYPE_A) {
+        alias.ptr = NULL;
+        alias.slen = 0;
+        res_name = &hostname;
+    } else {
+        return PJLIB_UTIL_EDNSINANSWER;
+    }
+
+    /* Copy alias to the record, if present. */
+    if (alias.slen) {
+        if (alias.slen > (int)bufleft)
+            return PJ_ENAMETOOLONG;
+
+        pj_memcpy(&rec->buf_[bufstart], alias.ptr, alias.slen);
+        rec->alias.ptr = &rec->buf_[bufstart];
+        rec->alias.slen = alias.slen;
+
+        bufstart += alias.slen;
+        bufleft -= alias.slen;
+    }
+
+    /* Now scan the answer for all type A RRs where the name matches
+     * hostname or alias.
+     */
+    for (i=0; i<pkt->hdr.anscount; ++i) {
+        if (pkt->ans[i].type == PJ_DNS_TYPE_A &&
+            pj_stricmp(&pkt->ans[i].name, res_name)==0 &&
+            rec->addr_count < PJ_DNS_MAX_IP_IN_A_REC)
+        {
+            rec->addr[rec->addr_count].s_addr = 
+                pkt->ans[i].rdata.a.ip_addr.s_addr;
+            ++rec->addr_count;
+        }
+    }
+
+    if (rec->addr_count == 0)
+        return PJLIB_UTIL_EDNSNOANSWERREC;
+
+    return PJ_SUCCESS;
+}
 
 
@@ -1031 +1129 @@
 
     /* Duplicate the packet.
-     * We don't need to keep the query, NS, and AR sections from the packet,
-     * so exclude from duplication.
+     * We don't need to keep the NS and AR sections from the packet,
+     * so exclude from duplication. We do need to keep the Query
+     * section since DNS A parser needs the query section to know
+     * the name being requested.
      */
     res_pool = pj_pool_create_on_buf("respool", cache->buf, sizeof(cache->buf));
@@ -1038 +1138 @@
         cache->pkt = NULL;
         pj_dns_packet_dup(res_pool, pkt, 
-                          PJ_DNS_NO_QD | PJ_DNS_NO_NS | PJ_DNS_NO_AR,
+                          PJ_DNS_NO_NS | PJ_DNS_NO_AR,
                           &cache->pkt);
     }