http/2, http/3: decouple stream state from easy handle

- add `Curl_hash_offt` as hashmap between a `curl_off_t` and
  an object. Use this in h2+h3 connection filters to associate
  `data->id` with the internal stream state.
- changed implementations of all affected connection filters
- removed `h2_ctx*` and `h3_ctx*` from `struct HTTP` and thus
  the easy handle
- solves the problem of attaching "foreign protocol" easy handles
  during connection shutdown

Test 1616 verifies the new hash functions.

Closes #13204

lib/cfilters.c

@@ -670,6 +670,19 @@ size_t Curl_conn_get_max_concurrent(struct Curl_easy *data,
   return (result || n <= 0)? 1 : (size_t)n;
 }
 
+int Curl_conn_get_stream_error(struct Curl_easy *data,
+                               struct connectdata *conn,
+                               int sockindex)
+{
+  CURLcode result;
+  int n = 0;
+
+  struct Curl_cfilter *cf = conn->cfilter[sockindex];
+  result = cf? cf->cft->query(cf, data, CF_QUERY_STREAM_ERROR,
+                              &n, NULL) : CURLE_UNKNOWN_OPTION;
+  return (result || n < 0)? 0 : n;
+}
+
 int Curl_conn_sockindex(struct Curl_easy *data, curl_socket_t sockfd)
 {
   if(data && data->conn &&

lib/cfilters.h

@@ -160,6 +160,7 @@ typedef CURLcode Curl_cft_cntrl(struct Curl_cfilter *cf,
 #define CF_QUERY_SOCKET             3  /* -          curl_socket_t */
 #define CF_QUERY_TIMER_CONNECT      4  /* -          struct curltime */
 #define CF_QUERY_TIMER_APPCONNECT   5  /* -          struct curltime */
+#define CF_QUERY_STREAM_ERROR       6  /* error code - */
 
 /**
  * Query the cfilter for properties. Filters ignorant of a query will
@@ -498,6 +499,12 @@ size_t Curl_conn_get_max_concurrent(struct Curl_easy *data,
                                     struct connectdata *conn,
                                     int sockindex);
 
+/**
+ * Get the underlying error code for a transfer stream or 0 if not known.
+ */
+int Curl_conn_get_stream_error(struct Curl_easy *data,
+                               struct connectdata *conn,
+                               int sockindex);
 
 /**
  * Get the index of the given socket in the connection's sockets.

lib/hash.c

@@ -368,3 +368,25 @@ void Curl_hash_print(struct Curl_hash *h,
   fprintf(stderr, "\n");
 }
 #endif
+
+void Curl_hash_offt_init(struct Curl_hash *h,
+                         unsigned int slots,
+                         Curl_hash_dtor dtor)
+{
+  Curl_hash_init(h, slots, Curl_hash_str, Curl_str_key_compare, dtor);
+}
+
+void *Curl_hash_offt_set(struct Curl_hash *h, curl_off_t id, void *elem)
+{
+  return Curl_hash_add(h, &id, sizeof(id), elem);
+}
+
+int Curl_hash_offt_remove(struct Curl_hash *h, curl_off_t id)
+{
+  return Curl_hash_delete(h, &id, sizeof(id));
+}
+
+void *Curl_hash_offt_get(struct Curl_hash *h, curl_off_t id)
+{
+  return Curl_hash_pick(h, &id, sizeof(id));
+}

lib/hash.h

@@ -98,5 +98,14 @@ Curl_hash_next_element(struct Curl_hash_iterator *iter);
 void Curl_hash_print(struct Curl_hash *h,
                      void (*func)(void *));
 
+/* Hash for `curl_off_t` as key */
+void Curl_hash_offt_init(struct Curl_hash *h,
+                         unsigned int slots,
+                         Curl_hash_dtor dtor);
+
+void *Curl_hash_offt_set(struct Curl_hash *h, curl_off_t id, void *elem);
+int Curl_hash_offt_remove(struct Curl_hash *h, curl_off_t id);
+void *Curl_hash_offt_get(struct Curl_hash *h, curl_off_t id);
+
 
 #endif /* HEADER_CURL_HASH_H */

lib/http.h

@@ -188,12 +188,8 @@ void Curl_http_exp100_got100(struct Curl_easy *data);
  * HTTP unique setup
  ***************************************************************************/
 struct HTTP {
-#ifndef CURL_DISABLE_HTTP
-  void *h2_ctx;              /* HTTP/2 implementation context */
-  void *h3_ctx;              /* HTTP/3 implementation context */
-#else
+  /* TODO: no longer used, we should remove it from SingleRequest */
   char unused;
-#endif
 };
 
 CURLcode Curl_http_size(struct Curl_easy *data);