doh: use dedicated probe slots

... to easier allow additional DNS transactions.

Closes #4629

1 files changed, 19 insertions, 1 deletions

diff --git a/lib/urldata.h b/lib/urldata.h
index da7e58f45..a70b2b09a 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -528,6 +528,24 @@ enum upgrade101 {
   UPGR101_WORKING             /* talking upgraded protocol */
 };
 
+enum doh_slots {
+  /* Explicit values for first two symbols so as to match hard-coded
+   * constants in existing code
+   */
+  DOH_PROBE_SLOT_IPADDR_V4 = 0, /* make 'V4' stand out for readability */
+  DOH_PROBE_SLOT_IPADDR_V6 = 1, /* 'V6' likewise */
+
+  /* Space here for (possibly build-specific) additional slot definitions */
+
+  /* for example */
+  /* #ifdef WANT_DOH_FOOBAR_TXT */
+  /*   DOH_PROBE_SLOT_FOOBAR_TXT, */
+  /* #endif */
+
+  /* AFTER all slot definitions, establish how many we have */
+  DOH_PROBE_SLOTS
+};
+
 struct dohresponse {
   unsigned char *memory;
   size_t size;
@@ -544,7 +562,7 @@ struct dnsprobe {
 
 struct dohdata {
   struct curl_slist *headers;
-  struct dnsprobe probe[2];
+  struct dnsprobe probe[DOH_PROBE_SLOTS];
   unsigned int pending; /* still outstanding requests */
   const char *host;
   int port;