Revert "deps: backport b5135bbc from c-ares repo"

This reverts commit 896e193.

Proper handling of TXT records requires API change, we can't afford it
in v0.10.

See nodejs#7371 for details.

deps/cares/src/ares_parse_txt_reply.c

@@ -54,7 +54,7 @@ int
 ares_parse_txt_reply (const unsigned char *abuf, int alen,
                       struct ares_txt_reply **txt_out)
 {
-  size_t substr_len;
+  size_t substr_len, str_len;
   unsigned int qdcount, ancount, i;
   const unsigned char *aptr;
   const unsigned char *strptr;
@@ -116,6 +116,23 @@ ares_parse_txt_reply (const unsigned char *abuf, int alen,
       /* Check if we are really looking at a TXT record */
       if (rr_class == C_IN && rr_type == T_TXT)
         {
+          /* Allocate storage for this TXT answer appending it to the list */
+          txt_curr = ares_malloc_data(ARES_DATATYPE_TXT_REPLY);
+          if (!txt_curr)
+            {
+              status = ARES_ENOMEM;
+              break;
+            }
+          if (txt_last)
+            {
+              txt_last->next = txt_curr;
+            }
+          else
+            {
+              txt_head = txt_curr;
+            }
+          txt_last = txt_curr;
+
           /*
            * There may be multiple substrings in a single TXT record. Each
            * substring may be up to 255 characters in length, with a
@@ -124,49 +141,36 @@ ares_parse_txt_reply (const unsigned char *abuf, int alen,
            * substrings contained therein.
            */
 
+          /* Compute total length to allow a single memory allocation */
           strptr = aptr;
           while (strptr < (aptr + rr_len))
             {
               substr_len = (unsigned char)*strptr;
-              if (strptr + substr_len + 1 > aptr + rr_len)
-                {
-                  status = ARES_EBADRESP;
-                  break;
-                }
-
-              ++strptr;
-
-              /* Allocate storage for this TXT answer appending it to the list */
-              txt_curr = ares_malloc_data(ARES_DATATYPE_TXT_REPLY);
-              if (!txt_curr)
-                {
-                  status = ARES_ENOMEM;
-                  break;
-                }
-              if (txt_last)
-                {
-                  txt_last->next = txt_curr;
-                }
-              else
-                {
-                  txt_head = txt_curr;
-                }
-              txt_last = txt_curr;
-
-              txt_curr->length = substr_len;
-              txt_curr->txt = malloc (substr_len + 1/* Including null byte */);
-              if (txt_curr->txt == NULL)
-                {
-                  status = ARES_ENOMEM;
-                  break;
-                }
-              memcpy ((char *) txt_curr->txt, strptr, substr_len);
-
-              /* Make sure we NULL-terminate */
-              txt_curr->txt[substr_len] = 0;
+              txt_curr->length += substr_len;
+              strptr += substr_len + 1;
+            }
 
+          /* Including null byte */
+          txt_curr->txt = malloc (txt_curr->length + 1);
+          if (txt_curr->txt == NULL)
+            {
+              status = ARES_ENOMEM;
+              break;
+            }
+
+          /* Step through the list of substrings, concatenating them */
+          str_len = 0;
+          strptr = aptr;
+          while (strptr < (aptr + rr_len))
+            {
+              substr_len = (unsigned char)*strptr;
+              strptr++;
+              memcpy ((char *) txt_curr->txt + str_len, strptr, substr_len);
+              str_len += substr_len;
               strptr += substr_len;
             }
+          /* Make sure we NULL-terminate */
+          *((char *) txt_curr->txt + txt_curr->length) = '\0';
         }
 
       /* Don't lose memory in the next iteration */