add a function to parse a srv reply with ttl

This adds a new private srv record struct with a ttl field. It also adds public accessor functions to set all of the fields. Finally, it replicates the ares_parse_srv_reply function to use the new struct and accessors.
c-ares · kylebevans · Jan 25, 2021 · Jan 25, 2021 · Jan 30, 2021 · Jan 30, 2021
commit 7a26cb65c1c2136fe1a2a41636ee95587b91633f
diff --git a/.gitignore b/.gitignore
@@ -54,3 +54,4 @@ CHANGES.dist
 c-ares-*.tar.gz.asc
 ares_parse_mx_reply.pdf
 /[0-9]*.patch
+.dirstamp
diff --git a/include/ares.h b/include/ares.h
@@ -545,6 +545,10 @@ struct ares_srv_reply {
   unsigned short          port;
 };
 
+struct ares_srv_ext;
+
+typedef struct ares_srv_ext ares_srv_ext;
+
 struct ares_mx_reply {
   struct ares_mx_reply   *next;
   char                   *host;
@@ -665,6 +669,39 @@ CARES_EXTERN int ares_parse_srv_reply(const unsigned char* abuf,
                                       int alen,
                                       struct ares_srv_reply** srv_out);
 
+CARES_EXTERN int ares_parse_srv_reply_ext(const unsigned char* abuf,
+                                          int alen,
+                                          struct ares_srv_ext** srv_out);
+
+CARES_EXTERN struct ares_srv_ext* ares_srv_ext_get_next(const ares_srv_ext* srv_reply);
+
+CARES_EXTERN char* ares_srv_ext_get_host(const ares_srv_ext* srv_reply);
+
+CARES_EXTERN unsigned short ares_srv_ext_get_priority(const ares_srv_ext* srv_reply);
+
+CARES_EXTERN unsigned short ares_srv_ext_get_weight(const ares_srv_ext* srv_reply);
+
+CARES_EXTERN unsigned short ares_srv_ext_get_port(const ares_srv_ext* srv_reply);
+
+CARES_EXTERN int ares_srv_ext_get_ttl(const ares_srv_ext* srv_reply);
+
+CARES_EXTERN void ares_srv_ext_set_next(ares_srv_ext* srv_reply,
+                                        struct ares_srv_ext* next);
+
+CARES_EXTERN void ares_srv_ext_set_host(ares_srv_ext* srv_reply, char* host);
+
+CARES_EXTERN void ares_srv_ext_set_priority(ares_srv_ext* srv_reply,
+                                            const unsigned short priority);
+
+CARES_EXTERN void ares_srv_ext_set_weight(ares_srv_ext* srv_reply,
+                                          const unsigned short weight);
+
+CARES_EXTERN void ares_srv_ext_set_port(ares_srv_ext* srv_reply,
+                                        const unsigned short port);
+
+CARES_EXTERN void ares_srv_ext_set_ttl(ares_srv_ext* srv_reply,
+                                       const int ttl);
+
 CARES_EXTERN int ares_parse_mx_reply(const unsigned char* abuf,
                                       int alen,
                                       struct ares_mx_reply** mx_out);

diff --git a/src/lib/Makefile.inc b/src/lib/Makefile.inc
@@ -38,10 +38,12 @@ CSOURCES = ares__close_sockets.c	\
   ares_parse_ptr_reply.c		\
   ares_parse_soa_reply.c		\
   ares_parse_srv_reply.c		\
+  ares_parse_srv_reply_ext.c		\
   ares_parse_txt_reply.c		\
   ares_platform.c			\
   ares_process.c			\
   ares_query.c				\
+  ares_reply_ext.c    \
   ares_search.c				\
   ares_send.c				\
   ares_strcasecmp.c			\

diff --git a/src/lib/ares_data.c b/src/lib/ares_data.c
@@ -70,6 +70,7 @@ void ares_free_data(void *dataptr)
           break;
 
         case ARES_DATATYPE_SRV_REPLY:
+        case ARES_DATATYPE_SRV_EXT:
 
           if (ptr->data.srv_reply.next)
             next_data = ptr->data.srv_reply.next;
@@ -120,7 +121,7 @@ void ares_free_data(void *dataptr)
           break;
 
         case ARES_DATATYPE_CAA_REPLY:
- 
+
           if (ptr->data.caa_reply.next)
             next_data = ptr->data.caa_reply.next;
           if (ptr->data.caa_reply.property)
@@ -166,6 +167,10 @@ void *ares_malloc_data(ares_datatype type)
         ptr->data.mx_reply.priority = 0;
         break;
 
+      case ARES_DATATYPE_SRV_EXT:
+        ptr->data.srv_ext.ttl = 0;
+        /* FALLTHROUGH */
+
       case ARES_DATATYPE_SRV_REPLY:
         ptr->data.srv_reply.next = NULL;
         ptr->data.srv_reply.host = NULL;

diff --git a/src/lib/ares_data.h b/src/lib/ares_data.h
@@ -14,9 +14,11 @@
  * without express or implied warranty.
  */
 
+#include "ares_private.h"
 typedef enum {
   ARES_DATATYPE_UNKNOWN = 1,  /* unknown data type     - introduced in 1.7.0 */
   ARES_DATATYPE_SRV_REPLY,    /* struct ares_srv_reply - introduced in 1.7.0 */
+  ARES_DATATYPE_SRV_EXT,      /* struct ares_srv_ext */
   ARES_DATATYPE_TXT_REPLY,    /* struct ares_txt_reply - introduced in 1.7.0 */
   ARES_DATATYPE_TXT_EXT,      /* struct ares_txt_ext   - introduced in 1.11.0 */
   ARES_DATATYPE_ADDR_NODE,    /* struct ares_addr_node - introduced in 1.7.1 */
@@ -61,6 +63,7 @@ struct ares_data {
     struct ares_txt_reply    txt_reply;
     struct ares_txt_ext      txt_ext;
     struct ares_srv_reply    srv_reply;
+    struct ares_srv_ext      srv_ext;
     struct ares_addr_node    addr_node;
     struct ares_addr_port_node  addr_port_node;
     struct ares_mx_reply     mx_reply;

diff --git a/src/lib/ares_parse_srv_reply_ext.c b/src/lib/ares_parse_srv_reply_ext.c
@@ -0,0 +1,173 @@
+
+/* Copyright 1998 by the Massachusetts Institute of Technology.
+ * Copyright (C) 2009 by Jakub Hrozek <jhrozek@redhat.com>
+ *
+ * Permission to use, copy, modify, and distribute this
+ * software and its documentation for any purpose and without
+ * fee is hereby granted, provided that the above copyright
+ * notice appear in all copies and that both that copyright
+ * notice and this permission notice appear in supporting
+ * documentation, and that the name of M.I.T. not be used in
+ * advertising or publicity pertaining to distribution of the
+ * software without specific, written prior permission.
+ * M.I.T. makes no representations about the suitability of
+ * this software for any purpose.  It is provided "as is"
+ * without express or implied warranty.
+ */
+
+#include "ares_setup.h"
+
+#ifdef HAVE_NETINET_IN_H
+#  include <netinet/in.h>
+#endif
+#ifdef HAVE_NETDB_H
+#  include <netdb.h>
+#endif
+#ifdef HAVE_ARPA_INET_H
+#  include <arpa/inet.h>
+#endif
+
+#include "ares_nameser.h"
+
+#include "ares.h"
+#include "ares_dns.h"
+#include "ares_data.h"
+#include "ares_private.h"
+
+int
+ares_parse_srv_reply_ext (const unsigned char *abuf, int alen,
+                          struct ares_srv_ext **srv_out)
+{
+  unsigned int qdcount, ancount, i;
+  const unsigned char *aptr, *vptr;
+  int status, rr_type, rr_class, rr_ttl, rr_len;
+  long len;
+  char *hostname = NULL, *rr_name = NULL;
+  struct ares_srv_ext *srv_head = NULL;
+  struct ares_srv_ext *srv_last = NULL;
+  struct ares_srv_ext *srv_curr;
+
+  /* Set *srv_out to NULL for all failure cases. */
+  *srv_out = NULL;
+
+  /* Give up if abuf doesn't have room for a header. */
+  if (alen < HFIXEDSZ)
+    return ARES_EBADRESP;
+
+  /* Fetch the question and answer count from the header. */
+  qdcount = DNS_HEADER_QDCOUNT (abuf);
+  ancount = DNS_HEADER_ANCOUNT (abuf);
+  if (qdcount != 1)
+    return ARES_EBADRESP;
+  if (ancount == 0)
+    return ARES_ENODATA;
+
+  /* Expand the name from the question, and skip past the question. */
+  aptr = abuf + HFIXEDSZ;
+  status = ares_expand_name (aptr, abuf, alen, &hostname, &len);
+  if (status != ARES_SUCCESS)
+    return status;
+
+  if (aptr + len + QFIXEDSZ > abuf + alen)
+    {
+      ares_free (hostname);
+      return ARES_EBADRESP;
+    }
+  aptr += len + QFIXEDSZ;
+
+  /* Examine each answer resource record (RR) in turn. */
+  for (i = 0; i < ancount; i++)
+    {
+      /* Decode the RR up to the data field. */
+      status = ares_expand_name (aptr, abuf, alen, &rr_name, &len);
+      if (status != ARES_SUCCESS)
+        {
+          break;
+        }
+      aptr += len;
+      if (aptr + RRFIXEDSZ > abuf + alen)
+        {
+          status = ARES_EBADRESP;
+          break;
+        }
+      rr_type = DNS_RR_TYPE (aptr);
+      rr_class = DNS_RR_CLASS (aptr);
+      rr_ttl = DNS_RR_TTL (aptr);
+      rr_len = DNS_RR_LEN (aptr);
+      aptr += RRFIXEDSZ;
+      if (aptr + rr_len > abuf + alen)
+        {
+          status = ARES_EBADRESP;
+          break;
+        }
+
+      /* Check if we are really looking at a SRV record */
+      if (rr_class == C_IN && rr_type == T_SRV)
+        {
+          /* parse the SRV record itself */
+          if (rr_len < 6)
+            {
+              status = ARES_EBADRESP;
+              break;
+            }
+
+          /* Allocate storage for this SRV answer appending it to the list */
+          srv_curr = ares_malloc_data(ARES_DATATYPE_SRV_EXT);
+          if (!srv_curr)
+            {
+              status = ARES_ENOMEM;
+              break;
+            }
+          if (srv_last)
+            {
+              srv_last->next = srv_curr;
+            }
+          else
+            {
+              srv_head = srv_curr;
+            }
+          srv_last = srv_curr;
+
+          vptr = aptr;
+          ares_srv_ext_set_priority(srv_curr, DNS__16BIT(vptr));
+          vptr += sizeof(unsigned short);
+          ares_srv_ext_set_weight(srv_curr, DNS__16BIT(vptr));
+          vptr += sizeof(unsigned short);
+          ares_srv_ext_set_port(srv_curr, DNS__16BIT(vptr));
+          vptr += sizeof(unsigned short);
+          ares_srv_ext_set_ttl(srv_curr, rr_ttl);
+
+          char* srv_host = NULL;
+
+          status = ares_expand_name (vptr, abuf, alen, &srv_host, &len);
+          printf("srv host: %s\n", srv_host);
+          ares_srv_ext_set_host(srv_curr, srv_host);
+          printf("srv curr host: %s\n", ares_srv_ext_get_host(srv_curr));
+          if (status != ARES_SUCCESS)
+            break;
+        }
+
+      /* Don't lose memory in the next iteration */
+      ares_free (rr_name);
+      rr_name = NULL;
+
+      /* Move on to the next record */
+      aptr += rr_len;
+    }
+  if (hostname)
+    ares_free (hostname);
+  if (rr_name)
+    ares_free (rr_name);
+
+  /* clean up on error */
+  if (status != ARES_SUCCESS)
+    {
+      if (srv_head)
+        ares_free_data (srv_head);
+      return status;
+    }
+
+  /* everything looks fine, return the data */
+  *srv_out = srv_head;
+  return ARES_SUCCESS;
+}
diff --git a/src/lib/ares_private.h b/src/lib/ares_private.h
@@ -416,4 +416,18 @@ int ares__connect_socket(ares_channel channel,
       (c)->sock_state_cb((c)->sock_state_cb_data, (s), (r), (w));       \
   } WHILE_FALSE
 
+/* Private definition of extended ares srv reply so that c-ares users
+ * only have access to the type definition in ares.h and must use
+ * accessor functions to interact with the struct.  This way,
+ * ares_srv_reply_ext can be modified without breaking ABI.
+ */
+ struct ares_srv_ext {
+  struct ares_srv_ext  *next;
+  char                 *host;
+  unsigned short        priority;
+  unsigned short        weight;
+  unsigned short        port;
+  int                   ttl;
+};
+
 #endif /* __ARES_PRIVATE_H */
diff --git a/src/lib/ares_reply_ext.c b/src/lib/ares_reply_ext.c
@@ -0,0 +1,80 @@
+/* Copyright (C) 2021 by Kyle Evans
+ *
+ * Permission to use, copy, modify, and distribute this software and its
+ * documentation for any purpose and without fee is hereby granted, provided
+ * that the above copyright notice appear in all copies and that both that
+ * copyright notice and this permission notice appear in supporting
+ * documentation, and that the name of M.I.T. not be used in advertising or
+ * publicity pertaining to distribution of the software without specific,
+ * written prior permission.  M.I.T. makes no representations about the
+ * suitability of this software for any purpose.  It is provided "as is"
+ * without express or implied warranty.
+ */
+
+#include "ares_setup.h"
+#include "ares.h"
+#include "ares_private.h"
+
+struct ares_srv_ext* ares_srv_ext_get_next(const struct ares_srv_ext* srv_reply)
+{
+  return srv_reply->next;
+}
+
+char* ares_srv_ext_get_host(const struct ares_srv_ext* srv_reply)
+{
+  return srv_reply->host;
+}
+
+unsigned short ares_srv_ext_get_priority(const struct ares_srv_ext* srv_reply)
+{
+  return srv_reply->priority;
+}
+
+unsigned short ares_srv_ext_get_weight(const struct ares_srv_ext* srv_reply)
+{
+  return srv_reply->weight;
+}
+
+unsigned short ares_srv_ext_get_port(const struct ares_srv_ext* srv_reply)
+{
+  return srv_reply->port;
+}
+
+int ares_srv_ext_get_ttl(const struct ares_srv_ext* srv_reply)
+{
+  return srv_reply->ttl;
+}
+
+void ares_srv_ext_set_next(struct ares_srv_ext* srv_reply,
+                           struct ares_srv_ext* next)
+{
+  srv_reply->next = next;
+}
+
+void ares_srv_ext_set_host(struct ares_srv_ext* srv_reply, char* host)
+{
+  srv_reply->host = host;
+}
+
+void ares_srv_ext_set_priority(struct ares_srv_ext* srv_reply,
+                               const unsigned short priority)
+{
+  srv_reply->priority = priority;
+}
+
+void ares_srv_ext_set_weight(struct ares_srv_ext* srv_reply,
+                             const unsigned short weight)
+{
+  srv_reply->weight = weight;
+}
+
+void ares_srv_ext_set_port(struct ares_srv_ext* srv_reply,
+                           const unsigned short port)
+{
+  srv_reply->port = port;
+}
+
+void ares_srv_ext_set_ttl(struct ares_srv_ext* srv_reply, const int ttl)
+{
+  srv_reply->ttl = ttl;
+}