filter internal handles

- add easy struct member 'internal' to signal an easy handle is for
  internal use and the user does not have ownership.

- set easy 'internal' true for DoH easy handle and connection cache
  easy handle.

- add a CURLHND parameter to curl_multi_get_handles so that the user can
  request only their (user) easy handles, or internal handles, or both,
  in the multi.

include/curl/multi.h

@@ -426,6 +426,12 @@ CURL_EXTERN CURLMcode curl_multi_setopt(CURLM *multi_handle,
 CURL_EXTERN CURLMcode curl_multi_assign(CURLM *multi_handle,
                                         curl_socket_t sockfd, void *sockp);
 
+typedef enum {
+  CURLHND_USER,       /* easy handle owned by the user */
+  CURLHND_INTERNAL,   /* easy handle owned internally */
+  CURLHND_ALL         /* both */
+} CURLHND;
+
 /*
  * Name:    curl_multi_get_handles()
  *
@@ -436,7 +442,7 @@ CURL_EXTERN CURLMcode curl_multi_assign(CURLM *multi_handle,
  *
  * Returns: NULL on failure, otherwise a CURL **array pointer
  */
-CURL_EXTERN CURL **curl_multi_get_handles(CURLM *multi_handle);
+CURL_EXTERN CURL **curl_multi_get_handles(CURLM *multi_handle, CURLHND filter);
 
 /*
  * Name: curl_push_callback

lib/conncache.c

@@ -107,6 +107,7 @@ int Curl_conncache_init(struct conncache *connc, int size)
   connc->closure_handle = curl_easy_init();
   if(!connc->closure_handle)
     return 1; /* bad */
+  connc->closure_handle->internal = true;
 
   Curl_hash_init(&connc->hash, size, Curl_hash_str,
                  Curl_str_key_compare, free_bundle_hash_entry);

lib/doh.c

@@ -242,6 +242,7 @@ static CURLcode dohprobe(struct Curl_easy *data,
     /* pass in the struct pointer via a local variable to please coverity and
        the gcc typecheck helpers */
     struct dynbuf *resp = &p->serverdoh;
+    doh->internal = true;
     ERROR_CHECK_SETOPT(CURLOPT_URL, url);
     ERROR_CHECK_SETOPT(CURLOPT_DEFAULT_PROTOCOL, "https");
     ERROR_CHECK_SETOPT(CURLOPT_WRITEFUNCTION, doh_write_cb);

lib/multi.c

@@ -3846,7 +3846,8 @@ unsigned int Curl_multi_max_concurrent_streams(struct Curl_multi *multi)
   return multi->max_concurrent_streams;
 }
 
-struct Curl_easy **curl_multi_get_handles(struct Curl_multi *multi)
+struct Curl_easy **curl_multi_get_handles(struct Curl_multi *multi,
+                                          CURLHND filter)
 {
   struct Curl_easy **a = malloc(sizeof(struct Curl_easy *) *
                                 (multi->num_easy + 1));
@@ -3855,7 +3856,10 @@ struct Curl_easy **curl_multi_get_handles(struct Curl_multi *multi)
     struct Curl_easy *e = multi->easyp;
     while(e) {
       DEBUGASSERT(i < multi->num_easy);
-      a[i++] = e;
+      if(filter == CURLHND_ALL ||
+         (filter == CURLHND_INTERNAL && e->internal) ||
+         (filter == CURLHND_USER && !e->internal))
+        a[i++] = e;
       e = e->next;
     }
     a[i] = NULL; /* last entry is a NULL */

lib/urldata.h

@@ -1945,7 +1945,7 @@ struct Curl_easy {
      other using the same cache. For easier tracking
      in log output.
      This may wrap around after LONG_MAX to 0 again, so it
-     has no uniqueness guarantuee for very large processings. */
+     has no uniqueness guarantee for very large processings. */
   curl_off_t id;
 
   /* first, two fields for the linked list of these */
@@ -2008,6 +2008,10 @@ struct Curl_easy {
 #ifdef USE_HYPER
   struct hyptransfer hyp;
 #endif
+
+  /* internal: true if this easy handle was created for internal use and the
+     user does not have ownership of the handle. */
+  bool internal;
 };
 
 #define LIBCURL_NAME "libcurl"