1 files changed, 49 insertions, 0 deletions
diff --git a/dns_mx.c b/dns_mx.c
new file mode 100644
index 0000000..8d38a7f
--- /dev/null
+++ b/dns_mx.c
@@ -0,0 +1,49 @@
+#include "stralloc.h"
+#include "byte.h"
+#include "uint16.h"
+#include "dns.h"
+
+static char *q = 0;
+
+int dns_mx_packet(stralloc *out,const char *buf,unsigned int len)
+{
+  unsigned int pos;
+  char header[12];
+  char pref[2];
+  uint16 numanswers;
+  uint16 datalen;
+
+  if (!stralloc_copys(out,"")) return -1;
+
+  pos = dns_packet_copy(buf,len,0,header,12); if (!pos) return -1;
+  uint16_unpack_big(header + 6,&numanswers);
+  pos = dns_packet_skipname(buf,len,pos); if (!pos) return -1;
+  pos += 4;
+
+  while (numanswers--) {
+    pos = dns_packet_skipname(buf,len,pos); if (!pos) return -1;
+    pos = dns_packet_copy(buf,len,pos,header,10); if (!pos) return -1;
+    uint16_unpack_big(header + 8,&datalen);
+    if (byte_equal(header,2,DNS_T_MX))
+      if (byte_equal(header + 2,2,DNS_C_IN)) {
+	if (!dns_packet_copy(buf,len,pos,pref,2)) return -1;
+	if (!dns_packet_getname(buf,len,pos + 2,&q)) return -1;
+	if (!stralloc_catb(out,pref,2)) return -1;
+	if (!dns_domain_todot_cat(out,q)) return -1;
+	if (!stralloc_0(out)) return -1;
+      }
+    pos += datalen;
+  }
+
+  return 0;
+}
+
+int dns_mx(stralloc *out,const stralloc *fqdn)
+{
+  if (!dns_domain_fromdot(&q,fqdn->s,fqdn->len)) return -1;
+  if (dns_resolve(q,DNS_T_MX) == -1) return -1;
+  if (dns_mx_packet(out,dns_resolve_tx.packet,dns_resolve_tx.packetlen) == -1) return -1;
+  dns_transmit_free(&dns_resolve_tx);
+  dns_domain_free(&q);
+  return 0;
+}