multi: add CURLMOPT_NETWORK_CHANGED to signal network changed

New multi option CURLMOPT_NETWORK_CHANGED with a long bitmask value:

- CURLM_NWCOPT_CLEAR_CONNS: do not reuse existing connections, close all
  idle connections.

- CURLM_NWCOPT_CLEAR_DNS: clear the multi's DNS cache.

All other bits reserved for future extensions.

Fixes #17225
Reported-by: ウさん
Closes #17613

lib/conncache.c

@@ -709,7 +709,8 @@ static int cpool_reap_dead_cb(struct Curl_easy *data,
                               struct connectdata *conn, void *param)
 {
   struct cpool_reaper_ctx *rctx = param;
-  if(Curl_conn_seems_dead(conn, data, &rctx->now)) {
+  if((!CONN_INUSE(conn) && conn->bits.no_reuse) ||
+     Curl_conn_seems_dead(conn, data, &rctx->now)) {
     /* stop the iteration here, pass back the connection that was pruned */
     Curl_conn_terminate(data, conn, FALSE);
     return 1;
@@ -849,6 +850,40 @@ void Curl_cpool_do_locked(struct Curl_easy *data,
     cb(conn, data, cbdata);
 }
 
+static int cpool_mark_stale(struct Curl_easy *data,
+                            struct connectdata *conn, void *param)
+{
+  (void)data;
+  (void)param;
+  conn->bits.no_reuse = TRUE;
+  return 0;
+}
+
+static int cpool_reap_no_reuse(struct Curl_easy *data,
+                               struct connectdata *conn, void *param)
+{
+  (void)data;
+  (void)param;
+  if(!CONN_INUSE(conn) && conn->bits.no_reuse) {
+    Curl_conn_terminate(data, conn, FALSE);
+    return 1;
+  }
+  return 0; /* continue iteration */
+}
+
+void Curl_cpool_nw_changed(struct Curl_easy *data)
+{
+  struct cpool *cpool = cpool_get_instance(data);
+
+  if(cpool) {
+    CPOOL_LOCK(cpool, data);
+    cpool_foreach(data, cpool, NULL, cpool_mark_stale);
+    while(cpool_foreach(data, cpool, NULL, cpool_reap_no_reuse))
+      ;
+    CPOOL_UNLOCK(cpool, data);
+  }
+}
+
 #if 0
 /* Useful for debugging the connection pool */
 void Curl_cpool_print(struct cpool *cpool)

lib/conncache.h

@@ -163,4 +163,8 @@ void Curl_cpool_do_locked(struct Curl_easy *data,
                           struct connectdata *conn,
                           Curl_cpool_conn_do_cb *cb, void *cbdata);
 
+/* Close all unused connections, prevent reuse of existing ones. */
+void Curl_cpool_nw_changed(struct Curl_easy *data);
+
+
 #endif /* HEADER_CURL_CONNCACHE_H */

lib/easy.c

@@ -1102,6 +1102,7 @@ void curl_easy_reset(CURL *d)
   data->progress.hide = TRUE;
   data->state.current_speed = -1; /* init to negative == impossible */
   data->state.retrycount = 0;     /* reset the retry counter */
+  data->state.recent_conn_id = -1; /* clear remembered connection id */
 
   /* zero out authentication data: */
   memset(&data->state.authhost, 0, sizeof(struct auth));

lib/hostip.c

@@ -290,6 +290,16 @@ void Curl_dnscache_prune(struct Curl_easy *data)
   dnscache_unlock(data, dnscache);
 }
 
+void Curl_dnscache_clear(struct Curl_easy *data)
+{
+  struct Curl_dnscache *dnscache = dnscache_get(data);
+  if(dnscache) {
+    dnscache_lock(data, dnscache);
+    Curl_hash_clean(&dnscache->entries);
+    dnscache_unlock(data, dnscache);
+  }
+}
+
 #ifdef USE_ALARM_TIMEOUT
 /* Beware this is a global and unique instance. This is used to store the
    return address that we can jump back to from inside a signal handler. This

lib/hostip.h

@@ -130,6 +130,9 @@ void Curl_dnscache_destroy(struct Curl_dnscache *dns);
 /* prune old entries from the DNS cache */
 void Curl_dnscache_prune(struct Curl_easy *data);
 
+/* clear the DNS cache */
+void Curl_dnscache_clear(struct Curl_easy *data);
+
 /* IPv4 threadsafe resolve function used for synch and asynch builds */
 struct Curl_addrinfo *Curl_ipv4_resolve_r(const char *hostname, int port);
 

lib/multi.c

@@ -3235,6 +3235,16 @@ CURLMcode curl_multi_setopt(CURLM *m,
       multi->max_concurrent_streams = (unsigned int)streams;
     }
     break;
+  case CURLMOPT_NETWORK_CHANGED: {
+      long val = va_arg(param, long);
+      if(val & CURLM_NWCOPT_CLEAR_DNS) {
+        Curl_dnscache_clear(multi->admin);
+      }
+      if(val & CURLM_NWCOPT_CLEAR_CONNS) {
+        Curl_cpool_nw_changed(multi->admin);
+      }
+    break;
+  }
   default:
     res = CURLM_UNKNOWN_OPTION;
     break;

lib/url.c

@@ -843,7 +843,7 @@ static bool url_match_connect_config(struct connectdata *conn,
                                      struct url_conn_match *m)
 {
   /* connect-only or to-be-closed connections will not be reused */
-  if(conn->connect_only || conn->bits.close)
+  if(conn->connect_only || conn->bits.close || conn->bits.no_reuse)
     return FALSE;
 
   /* ip_version must match */

lib/urldata.h

@@ -423,6 +423,7 @@ struct ConnectBits {
   BIT(parallel_connect); /* set TRUE when a parallel connect attempt has
                             started (happy eyeballs) */
   BIT(aborted); /* connection was aborted, e.g. in unclean state */
+  BIT(no_reuse); /* connection should not be reused */
   BIT(shutdown_handler); /* connection shutdown: handler shut down */
   BIT(shutdown_filters); /* connection shutdown: filters shut down */
   BIT(in_cpool);     /* connection is kept in a connection pool */