[glib/wip/tingping/happy-eyeballs: 3/4] gsocketclient: Improve handling of slow initial connections

[Patrick Griffis <pgriffis src gnome org>]

commit 5167da9bf9f5acc89ed9477249fe2cbb99febbf9
Author: Patrick Griffis <pgriffis igalia com>
Date:   Mon Oct 29 09:53:07 2018 -0400

    gsocketclient: Improve handling of slow initial connections
    
    Currently a new connection will not be attempted until the previous
    one has timed out and as the current API only exposes a single
    timeout value in practice it often means that it will wait 30 seconds
    (or forever with 0 (the default)) on each connection.
    
    This is unacceptable so we are now trying to follow the behavior
    RFC 8305 recommends by making multiple connection attempts if
    the connection takes longer than 250ms. The first connection
    to make it to completion then wins.

 gio/gsocketclient.c | 163 ++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 138 insertions(+), 25 deletions(-)
---
diff --git a/gio/gsocketclient.c b/gio/gsocketclient.c
index ddd149734..990fc9449 100644
--- a/gio/gsocketclient.c
+++ b/gio/gsocketclient.c
@@ -2,6 +2,7 @@
  *
  * Copyright © 2008, 2009 codethink
  * Copyright © 2009 Red Hat, Inc
+ * Copyright © 2018 Igalia S.L.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -49,6 +50,10 @@
 #include <gio/ginetaddress.h>
 #include "glibintl.h"
 
+/* As recommended by RFC 8305 this is the time it waits
+ * on a connection before starting another concurrent attempt.
+ */
+#define HAPPY_EYEBALLS_CONNECTION_ATTEMPT_TIMEOUT_MS 250
 
 /**
  * SECTION:gsocketclient
@@ -1328,28 +1333,76 @@ typedef struct
   GSocketConnectable *connectable;
   GSocketAddressEnumerator *enumerator;
   GProxyAddress *proxy_addr;
-  GSocketAddress *current_addr;
-  GSocket *current_socket;
+  GSocket *socket;
   GIOStream *connection;
 
+  GSList *connection_attempts;
   GError *last_error;
 } GSocketClientAsyncConnectData;
 
+static void connection_attempt_unref (gpointer attempt);
+
 static void
 g_socket_client_async_connect_data_free (GSocketClientAsyncConnectData *data)
 {
   g_clear_object (&data->connectable);
   g_clear_object (&data->enumerator);
   g_clear_object (&data->proxy_addr);
-  g_clear_object (&data->current_addr);
-  g_clear_object (&data->current_socket);
+  g_clear_object (&data->socket);
   g_clear_object (&data->connection);
+  g_slist_free_full (data->connection_attempts, connection_attempt_unref);
 
   g_clear_error (&data->last_error);
 
   g_slice_free (GSocketClientAsyncConnectData, data);
 }
 
+typedef struct
+{
+  GSocketAddress *address;
+  GSocket *socket;
+  GIOStream *connection;
+  GSocketClientAsyncConnectData *data; /* unowned */
+  GSource *timeout_source;
+  GCancellable *cancellable;
+} ConnectionAttempt;
+
+static ConnectionAttempt *
+connection_attempt_new (void)
+{
+  return g_rc_box_new (ConnectionAttempt);
+}
+
+static ConnectionAttempt *
+connection_attempt_ref (ConnectionAttempt *attempt)
+{
+  return g_rc_box_acquire (attempt);
+}
+
+static void
+connection_attempt_clear (ConnectionAttempt *attempt)
+{
+  g_clear_object (&attempt->address);
+  g_clear_object (&attempt->socket);
+  g_clear_object (&attempt->connection);
+  g_clear_object (&attempt->cancellable);
+  g_clear_pointer (&attempt->timeout_source, g_source_destroy);
+}
+
+static void
+connection_attempt_unref (gpointer attempt)
+{
+  if (attempt)
+    g_rc_box_release_full (attempt, (GDestroyNotify)connection_attempt_clear);
+}
+
+static void
+connection_attempt_remove (ConnectionAttempt *attempt)
+{
+  attempt->data->connection_attempts = g_slist_remove (attempt->data->connection_attempts, attempt);
+  connection_attempt_unref (attempt);
+}
+
 static void
 g_socket_client_async_connect_complete (GSocketClientAsyncConnectData *data)
 {
@@ -1359,8 +1412,7 @@ g_socket_client_async_connect_complete (GSocketClientAsyncConnectData *data)
     {
       GSocketConnection *wrapper_connection;
 
-      wrapper_connection = g_tcp_wrapper_connection_new (data->connection,
-                                                        data->current_socket);
+      wrapper_connection = g_tcp_wrapper_connection_new (data->connection, data->socket);
       g_object_unref (data->connection);
       data->connection = (GIOStream *)wrapper_connection;
     }
@@ -1389,8 +1441,7 @@ static void
 enumerator_next_async (GSocketClientAsyncConnectData *data)
 {
   /* We need to cleanup the state */
-  g_clear_object (&data->current_socket);
-  g_clear_object (&data->current_addr);
+  g_clear_object (&data->socket);
   g_clear_object (&data->proxy_addr);
   g_clear_object (&data->connection);
 
@@ -1485,34 +1536,63 @@ g_socket_client_connected_callback (GObject      *source,
                                    GAsyncResult *result,
                                    gpointer      user_data)
 {
-  GSocketClientAsyncConnectData *data = user_data;
+  ConnectionAttempt *attempt = user_data;
+  GSocketClientAsyncConnectData *data = attempt->data;
+  GSList *l;
   GError *error = NULL;
   GProxy *proxy;
   const gchar *protocol;
 
-  if (g_task_return_error_if_cancelled (data->task))
+  if (data && g_task_return_error_if_cancelled (data->task))
     {
       g_object_unref (data->task);
+      connection_attempt_unref (attempt);
       return;
     }
 
+  g_clear_pointer (&attempt->timeout_source, g_source_destroy);
+
   if (!g_socket_connection_connect_finish (G_SOCKET_CONNECTION (source),
                                           result, &error))
     {
-      clarify_connect_error (error, data->connectable,
-                            data->current_addr);
-      set_last_error (data, error);
+      if (!g_cancellable_is_cancelled (attempt->cancellable))
+        {
+          clarify_connect_error (error, data->connectable, attempt->address);
+          set_last_error (data, error);
+        }
+      else
+        g_clear_error (&error);
+
+      if (data)
+        {
+          connection_attempt_remove (attempt);
+          enumerator_next_async (data);
+        }
+      else
+        connection_attempt_unref (attempt);
 
-      /* try next one */
-      enumerator_next_async (data);
       return;
     }
 
+  data->socket = g_steal_pointer (&attempt->socket);
+  data->connection = g_steal_pointer (&attempt->connection);
+
+  for (l = data->connection_attempts; l; l = g_slist_next (l))
+    {
+      ConnectionAttempt *attempt_entry = l->data;
+      g_cancellable_cancel (attempt_entry->cancellable);
+      attempt_entry->data = NULL;
+      connection_attempt_unref (attempt_entry);
+    }
+  g_slist_free (data->connection_attempts);
+  data->connection_attempts = NULL;
+  connection_attempt_unref (attempt);
+
   g_socket_connection_set_cached_remote_address ((GSocketConnection*)data->connection, NULL);
   g_socket_client_emit_event (data->client, G_SOCKET_CLIENT_CONNECTED, data->connectable, data->connection);
 
   /* wrong, but backward compatible */
-  g_socket_set_blocking (data->current_socket, TRUE);
+  g_socket_set_blocking (data->socket, TRUE);
 
   if (!data->proxy_addr)
     {
@@ -1565,6 +1645,23 @@ g_socket_client_connected_callback (GObject      *source,
     }
 }
 
+static gboolean
+on_connection_attempt_timeout (gpointer data)
+{
+  ConnectionAttempt *attempt = data;
+
+  enumerator_next_async (attempt->data);
+  return G_SOURCE_REMOVE;
+}
+
+static void
+on_connection_cancelled (GCancellable *cancellable, gpointer data)
+{
+  GCancellable *attempt_cancellable = data;
+
+  g_cancellable_cancel (attempt_cancellable);
+}
+
 static void
 g_socket_client_enumerator_callback (GObject      *object,
                                     GAsyncResult *result,
@@ -1573,6 +1670,7 @@ g_socket_client_enumerator_callback (GObject      *object,
   GSocketClientAsyncConnectData *data = user_data;
   GSocketAddress *address = NULL;
   GSocket *socket;
+  ConnectionAttempt *attempt;
   GError *error = NULL;
 
   if (g_task_return_error_if_cancelled (data->task))
@@ -1585,6 +1683,9 @@ g_socket_client_enumerator_callback (GObject      *object,
                                                     result, &error);
   if (address == NULL)
     {
+      if (data->connection_attempts)
+        return;
+
       g_socket_client_emit_event (data->client, G_SOCKET_CLIENT_COMPLETE, data->connectable, NULL);
       if (!error)
        {
@@ -1621,16 +1722,28 @@ g_socket_client_enumerator_callback (GObject      *object,
       return;
     }
 
-  data->current_socket = socket;
-  data->current_addr = address;
-  data->connection = (GIOStream *) g_socket_connection_factory_create_connection (socket);
-
-  g_socket_connection_set_cached_remote_address ((GSocketConnection*)data->connection, address);
-  g_socket_client_emit_event (data->client, G_SOCKET_CLIENT_CONNECTING, data->connectable, data->connection);
-  g_socket_connection_connect_async (G_SOCKET_CONNECTION (data->connection),
+  attempt = connection_attempt_new ();
+  attempt->data = data;
+  attempt->socket = socket;
+  attempt->address = address;
+  attempt->cancellable = g_cancellable_new ();
+  attempt->connection = (GIOStream *)g_socket_connection_factory_create_connection (socket);
+  attempt->timeout_source = g_timeout_source_new (HAPPY_EYEBALLS_CONNECTION_ATTEMPT_TIMEOUT_MS);
+  g_source_set_callback (attempt->timeout_source, on_connection_attempt_timeout,
+                         connection_attempt_ref (attempt), connection_attempt_unref);
+  g_source_attach (attempt->timeout_source, g_main_context_get_thread_default ());
+  data->connection_attempts = g_slist_append (data->connection_attempts, attempt);
+
+  if (g_task_get_cancellable (data->task))
+    g_cancellable_connect (g_task_get_cancellable (data->task), G_CALLBACK(on_connection_cancelled),
+                           g_object_ref (attempt->cancellable), g_object_unref);
+
+  g_socket_connection_set_cached_remote_address ((GSocketConnection *)attempt->connection, address);
+  g_socket_client_emit_event (data->client, G_SOCKET_CLIENT_CONNECTING, data->connectable, 
attempt->connection);
+  g_socket_connection_connect_async (G_SOCKET_CONNECTION (attempt->connection),
                                     address,
-                                    g_task_get_cancellable (data->task),
-                                    g_socket_client_connected_callback, data);
+                                    attempt->cancellable,
+                                    g_socket_client_connected_callback, connection_attempt_ref (attempt));
 }
 
 /**