Handle large DNS responses.

Source: poorly-named qmail-103.patch

dns.c

@@ -19,10 +19,12 @@ extern int res_search();
 static unsigned short getshort(c) unsigned char *c;
 { unsigned short u; u = c[0]; return (u << 8) + c[1]; }
 
-static union { HEADER hdr; unsigned char buf[PACKETSZ]; } response;
+static struct { unsigned char *buf; } response;
+static int responsebuflen = 0;
 static int responselen;
 static unsigned char *responseend;
 static unsigned char *responsepos;
+static u_long saveresoptions;
 
 static int numanswers;
 static char name[MAXDNAME];
@@ -43,18 +45,33 @@ int type;
  errno = 0;
  if (!stralloc_copy(&glue,domain)) return DNS_MEM;
  if (!stralloc_0(&glue)) return DNS_MEM;
- responselen = lookup(glue.s,C_IN,type,response.buf,sizeof(response));
+ if (!responsebuflen)
+  if (response.buf = (unsigned char *)alloc(PACKETSZ+1))
+   responsebuflen = PACKETSZ+1;
+  else return DNS_MEM;
+
+ responselen = lookup(glue.s,C_IN,type,response.buf,responsebuflen);
+ if ((responselen >= responsebuflen) ||
+     (responselen > 0 && (((HEADER *)response.buf)->tc)))
+  {
+   if (responsebuflen < 65536)
+    if (alloc_re(&response.buf, responsebuflen, 65536))
+     responsebuflen = 65536;
+    else return DNS_MEM;
+    saveresoptions = _res.options;
+    _res.options |= RES_USEVC;
+    responselen = lookup(glue.s,C_IN,type,response.buf,responsebuflen);
+    _res.options = saveresoptions;
+  }
  if (responselen <= 0)
   {
    if (errno == ECONNREFUSED) return DNS_SOFT;
    if (h_errno == TRY_AGAIN) return DNS_SOFT;
    return DNS_HARD;
   }
- if (responselen >= sizeof(response))
-   responselen = sizeof(response);
  responseend = response.buf + responselen;
  responsepos = response.buf + sizeof(HEADER);
- n = ntohs(response.hdr.qdcount);
+ n = ntohs(((HEADER *)response.buf)->qdcount);
  while (n-- > 0)
   {
    i = dn_expand(response.buf,responseend,responsepos,name,MAXDNAME);
@@ -64,7 +81,7 @@ int type;
    if (i < QFIXEDSZ) return DNS_SOFT;
    responsepos += QFIXEDSZ;
   }
- numanswers = ntohs(response.hdr.ancount);
+ numanswers = ntohs(((HEADER *)response.buf)->ancount);
  return 0;
 }