path: root/e-util/e-client-selector.c

/*
 * e-client-selector.c
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 *
 */

/**
 * SECTION: e-client-selector
 * @include: e-util/e-util.h
 * @short_description: Tree view of #EClient instances
 *
 * #EClientSelector extends the functionality of #ESourceSelector by
 * utilizing an #EClientCache to display status information about the
 * backends associated with the displayed data sources.
 **/

#include "e-client-selector.h"

#define E_CLIENT_SELECTOR_GET_PRIVATE(obj) \
    (G_TYPE_INSTANCE_GET_PRIVATE \
    ((obj), E_TYPE_CLIENT_SELECTOR, EClientSelectorPrivate))

typedef struct _AsyncContext AsyncContext;

struct _EClientSelectorPrivate {
    EClientCache *client_cache;
    gulong backend_died_handler_id;
    gulong client_created_handler_id;
    gulong client_notify_online_handler_id;
};

struct _AsyncContext {
    EClientSelector *selector;
    ESource *source;
};

enum {
    PROP_0,
    PROP_CLIENT_CACHE
};

G_DEFINE_TYPE (
    EClientSelector,
    e_client_selector,
    E_TYPE_SOURCE_SELECTOR)

static void
async_context_free (AsyncContext *async_context)
{
    g_clear_object (&async_context->selector);
    g_clear_object (&async_context->source);

    g_slice_free (AsyncContext, async_context);
}

static void
client_selector_update_status_icon_cb (GtkTreeViewColumn *column,
                                       GtkCellRenderer *renderer,
                                       GtkTreeModel *model,
                                       GtkTreeIter *iter,
                                       gpointer user_data)
{
    GtkWidget *tree_view;
    EClient *client;
    const gchar *icon_name = NULL;

    tree_view = gtk_tree_view_column_get_tree_view (column);

    client = e_client_selector_ref_cached_client_by_iter (
        E_CLIENT_SELECTOR (tree_view), iter);

    if (client != NULL) {
        if (e_client_is_online (client))
            icon_name = "network-idle-symbolic";
        else
            icon_name = "network-offline-symbolic";

        g_object_unref (client);

    } else {
        ESource *source;

        /* No client... did the backend die? */
        source = e_source_selector_ref_source_by_iter (
            E_SOURCE_SELECTOR (tree_view), iter);

        if (source != NULL) {
            gboolean dead_backend;

            dead_backend = e_client_selector_is_backend_dead (
                E_CLIENT_SELECTOR (tree_view), source);
            if (dead_backend) {
                icon_name = "network-error-symbolic";
            } else {
                gpointer data;

                /* See client_selector_can_reach_cb() */
                data = g_object_get_data (
                    G_OBJECT (source),
                    "initial-icon-name");
                icon_name = (const gchar *) data;
            }

            g_object_unref (source);
        }
    }

    if (icon_name != NULL) {
        GIcon *icon;

        /* Use fallbacks if symbolic icons are not available. */
        icon = g_themed_icon_new_with_default_fallbacks (icon_name);
        g_object_set (renderer, "gicon", icon, NULL);
        g_object_unref (icon);
    } else {
        g_object_set (renderer, "gicon", NULL, NULL);
    }
}

static void
client_selector_update_row (EClientSelector *selector,
                            EClient *client)
{
    ESource *source;

    source = e_client_get_source (client);
    e_source_selector_update_row (E_SOURCE_SELECTOR (selector), source);
}

static void
client_selector_backend_died_cb (EClientCache *client_cache,
                                 EClient *client,
                                 EAlert *alert,
                                 EClientSelector *selector)
{
    client_selector_update_row (selector, client);
}

static void
client_selector_client_created_cb (EClientCache *client_cache,
                                   EClient *client,
                                   EClientSelector *selector)
{
    client_selector_update_row (selector, client);
}

static void
client_selector_client_notify_cb (EClientCache *client_cache,
                                  EClient *client,
                                  GParamSpec *pspec,
                                  EClientSelector *selector)
{
    client_selector_update_row (selector, client);
}

static void
client_selector_can_reach_cb (GObject *source_object,
                              GAsyncResult *result,
                              gpointer user_data)
{
    EClient *client;
    AsyncContext *async_context;
    gboolean reachable;

    async_context = (AsyncContext *) user_data;

    /* We don't care about errors here.  This is just to show some
     * initial icon next to the ESource before creating an EClient. */
    reachable = g_network_monitor_can_reach_finish (
        G_NETWORK_MONITOR (source_object), result, NULL);

    client = e_client_selector_ref_cached_client (
        async_context->selector, async_context->source);

    /* EClient's online state is authoritative.
     * Defer to it if an instance already exists. */
    if (client == NULL) {
        const gchar *icon_name;

        if (reachable)
            icon_name = "network-idle-symbolic";
        else
            icon_name = "network-offline-symbolic";

        /* XXX Hackish way to stash the initial icon name. */
        g_object_set_data (
            G_OBJECT (async_context->source),
            "initial-icon-name", (gpointer) icon_name);

        e_source_selector_update_row (
            E_SOURCE_SELECTOR (async_context->selector),
            async_context->source);
    }

    g_clear_object (&client);

    async_context_free (async_context);
}

static void
client_selector_set_client_cache (EClientSelector *selector,
                                  EClientCache *client_cache)
{
    g_return_if_fail (E_IS_CLIENT_CACHE (client_cache));
    g_return_if_fail (selector->priv->client_cache == NULL);

    selector->priv->client_cache = g_object_ref (client_cache);
}

static void
client_selector_set_property (GObject *object,
                              guint property_id,
                              const GValue *value,
                              GParamSpec *pspec)
{
    switch (property_id) {
        case PROP_CLIENT_CACHE:
            client_selector_set_client_cache (
                E_CLIENT_SELECTOR (object),
                g_value_get_object (value));
            return;
    }

    G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
}

static void
client_selector_get_property (GObject *object,
                              guint property_id,
                              GValue *value,
                              GParamSpec *pspec)
{
    switch (property_id) {
        case PROP_CLIENT_CACHE:
            g_value_take_object (
                value,
                e_client_selector_ref_client_cache (
                E_CLIENT_SELECTOR (object)));
            return;
    }

    G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
}

static void
client_selector_dispose (GObject *object)
{
    EClientSelectorPrivate *priv;

    priv = E_CLIENT_SELECTOR_GET_PRIVATE (object);

    if (priv->backend_died_handler_id > 0) {
        g_signal_handler_disconnect (
            priv->client_cache,
            priv->backend_died_handler_id);
        priv->backend_died_handler_id = 0;
    }

    if (priv->client_created_handler_id > 0) {
        g_signal_handler_disconnect (
            priv->client_cache,
            priv->client_created_handler_id);
        priv->client_created_handler_id = 0;
    }

    if (priv->client_notify_online_handler_id > 0) {
        g_signal_handler_disconnect (
            priv->client_cache,
            priv->client_notify_online_handler_id);
        priv->client_notify_online_handler_id = 0;
    }

    g_clear_object (&priv->client_cache);

    /* Chain up to parent's dispose() method. */
    G_OBJECT_CLASS (e_client_selector_parent_class)->dispose (object);
}

static void
client_selector_constructed (GObject *object)
{
    EClientSelector *selector;
    EClientCache *client_cache;
    ESourceRegistry *registry;
    GtkTreeView *tree_view;
    GtkTreeViewColumn *column;
    GtkCellRenderer *renderer;
    GNetworkMonitor *network_monitor;
    const gchar *extension_name;
    GList *list, *link;
    gulong handler_id;

    selector = E_CLIENT_SELECTOR (object);
    client_cache = e_client_selector_ref_client_cache (selector);

    /* Chain up to parent's constructed() method. */
    G_OBJECT_CLASS (e_client_selector_parent_class)->constructed (object);

    /* Append an icon to hint at backend status. */

    tree_view = GTK_TREE_VIEW (object);
    column = gtk_tree_view_column_new ();
    gtk_tree_view_append_column (tree_view, column);

    renderer = gtk_cell_renderer_pixbuf_new ();
    gtk_tree_view_column_pack_start (column, renderer, FALSE);

    gtk_tree_view_column_set_cell_data_func (
        column, renderer,
        client_selector_update_status_icon_cb,
        NULL, (GDestroyNotify) NULL);

    /* Listen for signals that may change the icon. */

    handler_id = g_signal_connect (
        client_cache, "backend-died",
        G_CALLBACK (client_selector_backend_died_cb),
        selector);
    selector->priv->backend_died_handler_id = handler_id;

    handler_id = g_signal_connect (
        client_cache, "client-created",
        G_CALLBACK (client_selector_client_created_cb),
        selector);
    selector->priv->client_created_handler_id = handler_id;

    handler_id = g_signal_connect (
        client_cache, "client-notify::online",
        G_CALLBACK (client_selector_client_notify_cb),
        selector);
    selector->priv->client_notify_online_handler_id = handler_id;

    g_object_unref (client_cache);

    /* Have GNetworkMonitor make an initial guess at the online
     * state of backends by evaluating the reachability of their
     * host name.  This will show an initial status icon for all
     * displayed ESources without actually opening a connection,
     * since some backends are expensive to start unnecessarily.
     *
     * XXX It occurred to me after writing this that it would be
     *     better for ESourceSelector to evaluate reachability of
     *     ESource host names, and keep it up-to-date in response
     *     to network changes.  It could automatically trigger a
     *     GtkTreeModel::row-changed signal when it has a new host
     *     reachability result, and provide that result via some
     *     e_source_selector_get_host_reachable() for us to fall
     *     back on if no EClient instance is available.
     *
     *     But the approach below is good enough for now.
     */

    network_monitor = g_network_monitor_get_default ();

    registry = e_source_selector_get_registry (
        E_SOURCE_SELECTOR (selector));
    extension_name = e_source_selector_get_extension_name (
        E_SOURCE_SELECTOR (selector));

    list = e_source_registry_list_sources (registry, extension_name);

    extension_name = E_SOURCE_EXTENSION_AUTHENTICATION;

    for (link = list; link != NULL; link = g_list_next (link)) {
        ESource *source = E_SOURCE (link->data);
        ESource *auth_source;
        ESourceAuthentication *auth_extension;
        GSocketConnectable *socket_connectable;
        const gchar *host;
        guint16 port;

        auth_source = e_source_registry_find_extension (
            registry, source, extension_name);

        if (auth_source == NULL)
            continue;

        auth_extension = e_source_get_extension (
            auth_source, extension_name);

        host = e_source_authentication_get_host (auth_extension);
        port = e_source_authentication_get_port (auth_extension);

        socket_connectable = g_network_address_new (host, port);

        /* XXX GNetworkAddress will happily take a NULL host
         *     but then crash while enumerating the address,
         *     so watch out for that. */
        if (host == NULL || !*host || g_ascii_strcasecmp (host, "localhost") == 0)
            g_clear_object (&socket_connectable);

        if (socket_connectable != NULL) {
            AsyncContext *async_context;

            async_context = g_slice_new0 (AsyncContext);
            async_context->selector = g_object_ref (selector);
            async_context->source = g_object_ref (source);

            g_network_monitor_can_reach_async (
                network_monitor, socket_connectable, NULL,
                client_selector_can_reach_cb, async_context);

            g_object_unref (socket_connectable);
        }

        g_object_unref (auth_source);
    }

    g_list_free_full (list, (GDestroyNotify) g_object_unref);
}

static void
e_client_selector_class_init (EClientSelectorClass *class)
{
    GObjectClass *object_class;

    g_type_class_add_private (class, sizeof (EClientSelectorPrivate));

    object_class = G_OBJECT_CLASS (class);
    object_class->set_property = client_selector_set_property;
    object_class->get_property = client_selector_get_property;
    object_class->dispose = client_selector_dispose;
    object_class->constructed = client_selector_constructed;

    /**
     * EClientSelector:client-cache:
     *
     * Cache of shared #EClient instances.
     **/
    g_object_class_install_property (
        object_class,
        PROP_CLIENT_CACHE,
        g_param_spec_object (
            "client-cache",
            "Client Cache",
            "Cache of shared EClient instances",
            E_TYPE_CLIENT_CACHE,
            G_PARAM_READWRITE |
            G_PARAM_CONSTRUCT_ONLY |
            G_PARAM_STATIC_STRINGS));
}

static void
e_client_selector_init (EClientSelector *selector)
{
    selector->priv = E_CLIENT_SELECTOR_GET_PRIVATE (selector);
}

/**
 * e_client_selector_new:
 * @client_cache: an #EClientCache
 * @extension_name: the name of an #ESource extension
 *
 * Displays a list of sources having an extension named @extension_name,
 * along with status information about the backends associated with them.
 * The sources are grouped by backend or groupware account, which are
 * described by the parent source.
 *
 * Returns: a new #EClientSelector
 **/
GtkWidget *
e_client_selector_new (EClientCache *client_cache,
                       const gchar *extension_name)
{
    ESourceRegistry *registry;
    GtkWidget *widget;

    g_return_val_if_fail (E_IS_CLIENT_CACHE (client_cache), NULL);
    g_return_val_if_fail (extension_name != NULL, NULL);

    registry = e_client_cache_ref_registry (client_cache);

    widget = g_object_new (
        E_TYPE_CLIENT_SELECTOR,
        "client-cache", client_cache,
        "extension-name", extension_name,
        "registry", registry, NULL);

    g_object_unref (registry);

    return widget;
}

/**
 * e_client_selector_ref_client_cache:
 * @selector: an #EClientSelector
 *
 * Returns the #EClientCache passed to e_client_selector_new().
 *
 * The returned #EClientCache is referenced for thread-safety and must be
 * unreferenced with g_object_unref() when finished with it.
 *
 * Returns: an #EClientCache
 **/
EClientCache *
e_client_selector_ref_client_cache (EClientSelector *selector)
{
    g_return_val_if_fail (E_IS_CLIENT_SELECTOR (selector), NULL);

    return g_object_ref (selector->priv->client_cache);
}

/**
 * e_client_selector_get_client_sync:
 * @selector: an #ESourceSelector
 * @source: an #ESource
 * @call_allow_auth_prompt: whether call allow-auth-prompt on the source first
 * @cancellable: optional #GCancellable object, or %NULL
 * @error: return location for a #GError, or %NULL
 *
 * Obtains a shared #EClient instance for @source, or else creates a new
 * #EClient instance to be shared.
 *
 * The #ESourceSelector:extension-name property determines the type of
 * #EClient to obtain.  See e_client_cache_get_client_sync() for a list
 * of valid extension names.
 *
 * If a request for the same @source and #ESourceSelector:extension-name
 * is already in progress when this function is called, this request will
 * "piggyback" on the in-progress request such that they will both succeed
 * or fail simultaneously.
 *
 * Unreference the returned #EClient with g_object_unref() when finished
 * with it.  If an error occurs, the function will set @error and return
 * %NULL.
 *
 * Returns: an #EClient, or %NULL
 **/
EClient *
e_client_selector_get_client_sync (EClientSelector *selector,
                                   ESource *source,
                   gboolean call_allow_auth_prompt,
                                   GCancellable *cancellable,
                                   GError **error)
{
    EAsyncClosure *closure;
    GAsyncResult *result;
    EClient *client;

    g_return_val_if_fail (E_IS_CLIENT_SELECTOR (selector), NULL);
    g_return_val_if_fail (E_IS_SOURCE (source), NULL);

    closure = e_async_closure_new ();

    e_client_selector_get_client (
        selector, source, call_allow_auth_prompt, cancellable,
        e_async_closure_callback, closure);

    result = e_async_closure_wait (closure);

    client = e_client_selector_get_client_finish (
        selector, result, error);

    e_async_closure_free (closure);

    return client;
}

/* Helper for e_client_selector_get_client() */
static void
client_selector_get_client_done_cb (GObject *source_object,
                                    GAsyncResult *result,
                                    gpointer user_data)
{
    EClient *client;
    GSimpleAsyncResult *simple;
    GError *error = NULL;

    simple = G_SIMPLE_ASYNC_RESULT (user_data);

    client = e_client_cache_get_client_finish (
        E_CLIENT_CACHE (source_object), result, &error);

    /* Sanity check. */
    g_return_if_fail (
        ((client != NULL) && (error == NULL)) ||
        ((client == NULL) && (error != NULL)));

    if (client != NULL) {
        g_simple_async_result_set_op_res_gpointer (
            simple, g_object_ref (client),
            (GDestroyNotify) g_object_unref);
        g_object_unref (client);
    }

    if (error != NULL)
        g_simple_async_result_take_error (simple, error);

    g_simple_async_result_complete (simple);

    g_object_unref (simple);
}

typedef struct _AllowAuthPromptData
{
    EClientSelector *selector;
    GSimpleAsyncResult *simple;
    GCancellable *cancellable;
} AllowAuthPromptData;

static void
client_selector_allow_auth_prompt_done_cb (GObject *source_object,
                       GAsyncResult *result,
                       gpointer user_data)
{
    AllowAuthPromptData *data;
    ESource *source;
    GError *local_error = NULL;

    g_return_if_fail (E_IS_SOURCE (source_object));
    g_return_if_fail (user_data != NULL);

    data = user_data;
    source = E_SOURCE (source_object);

    e_source_allow_auth_prompt_finish (source, result, &local_error);

    if (local_error) {
        g_simple_async_result_take_error (data->simple, local_error);
        g_simple_async_result_complete (data->simple);
        local_error = NULL;
    } else {
        EClientCache *client_cache;
        const gchar *extension_name;

        extension_name = e_source_selector_get_extension_name (
            E_SOURCE_SELECTOR (data->selector));

        client_cache = e_client_selector_ref_client_cache (data->selector);

        e_client_cache_get_client (
            client_cache, source,
            extension_name, data->cancellable,
            client_selector_get_client_done_cb,
            g_object_ref (data->simple));

        g_object_unref (client_cache);
    }

    g_clear_object (&data->selector);
    g_clear_object (&data->simple);
    g_clear_object (&data->cancellable);
    g_free (data);
}

/**
 * e_client_selector_get_client:
 * @selector: an #ESourceSelector
 * @source: an #ESource
 * @call_allow_auth_prompt: whether call allow-auth-prompt on the source first
 * @cancellable: optional #GCancellable object, or %NULL
 * @callback: a #GAsyncReadyCallback to call when the request is satisfied
 * @user_data: data to pass to the callback function
 *
 * Asynchronously obtains a shared #EClient instance for @source, or else
 * creates a new #EClient instance to be shared.
 *
 * The #ESourceSelector:extension-name property determines the type of
 * #EClient to obtain.  See e_client_cache_get_client_sync() for a list
 * of valid extension names.
 *
 * If a request for the same @source and #ESourceSelector:extension-name
 * is already in progress when this function is called, this request will
 * "piggyback" on the in-progress request such that they will both succeed
 * or fail simultaneously.
 *
 * When the operation is finished, @callback will be called.  You can
 * then call e_client_selector_get_client_finish() to get the result of
 * the operation.
 **/
void
e_client_selector_get_client (EClientSelector *selector,
                              ESource *source,
                  gboolean call_allow_auth_prompt,
                              GCancellable *cancellable,
                              GAsyncReadyCallback callback,
                              gpointer user_data)
{
    GSimpleAsyncResult *simple;

    g_return_if_fail (E_IS_CLIENT_SELECTOR (selector));
    g_return_if_fail (E_IS_SOURCE (source));

    simple = g_simple_async_result_new (
        G_OBJECT (selector), callback,
        user_data, e_client_selector_get_client);

    g_simple_async_result_set_check_cancellable (simple, cancellable);

    if (call_allow_auth_prompt) {
        AllowAuthPromptData *data;

        data = g_new0 (AllowAuthPromptData, 1);
        data->selector = g_object_ref (selector);
        data->simple = g_object_ref (simple);
        data->cancellable = cancellable ? g_object_ref (cancellable) : NULL;

        e_source_allow_auth_prompt (source, cancellable,
            client_selector_allow_auth_prompt_done_cb, data);
    } else {
        EClientCache *client_cache;
        const gchar *extension_name;

        extension_name = e_source_selector_get_extension_name (
            E_SOURCE_SELECTOR (selector));

        client_cache = e_client_selector_ref_client_cache (selector);

        e_client_cache_get_client (
            client_cache, source,
            extension_name, cancellable,
            client_selector_get_client_done_cb,
            g_object_ref (simple));

        g_object_unref (client_cache);
    }

    g_object_unref (simple);
}

/**
 * e_client_selector_get_client_finish:
 * @selector: an #EClientSelector
 * @result: a #GAsyncResult
 * @error: return location for a #GError, or %NULL
 *
 * Finishes the operation started with e_client_selector_get_client().
 *
 * Unreference the returned #EClient with g_object_unref() when finished
 * with it.  If an error occurred, the function will set @error and return
 * %NULL.
 *
 * Returns: an #EClient, or %NULL
 **/
EClient *
e_client_selector_get_client_finish (EClientSelector *selector,
                                     GAsyncResult *result,
                                     GError **error)
{
    GSimpleAsyncResult *simple;
    EClient *client;

    g_return_val_if_fail (
        g_simple_async_result_is_valid (
        result, G_OBJECT (selector),
        e_client_selector_get_client), NULL);

    simple = G_SIMPLE_ASYNC_RESULT (result);
    client = g_simple_async_result_get_op_res_gpointer (simple);

    if (g_simple_async_result_propagate_error (simple, error))
        return NULL;

    g_return_val_if_fail (client != NULL, NULL);

    return g_object_ref (client);
}

/**
 * e_client_selector_ref_cached_client:
 * @selector: an #EClientSelector
 * @source: an #ESource
 *
 * Returns a shared #EClient instance for @source and the value of
 * #ESourceSelector:extension-name if such an instance is already cached,
 * or else %NULL.  This function does not create a new #EClient instance,
 * and therefore does not block.
 *
 * The returned #EClient is referenced for thread-safety and must be
 * unreferenced with g_object_unref() when finished with it.
 *
 * Returns: an #EClient, or %NULL
 **/
EClient *
e_client_selector_ref_cached_client (EClientSelector *selector,
                                     ESource *source)
{
    EClient *client;
    EClientCache *client_cache;
    const gchar *extension_name;

    g_return_val_if_fail (E_IS_CLIENT_SELECTOR (selector), NULL);
    g_return_val_if_fail (E_IS_SOURCE (source), NULL);

    extension_name = e_source_selector_get_extension_name (
        E_SOURCE_SELECTOR (selector));

    client_cache = e_client_selector_ref_client_cache (selector);

    client = e_client_cache_ref_cached_client (
        client_cache, source, extension_name);

    g_object_unref (client_cache);

    return client;
}

/**
 * e_client_selector_ref_cached_client_by_iter:
 * @selector: an #EClientSelector
 * @iter: a #GtkTreeIter
 *
 * Returns a shared #EClient instance for the #ESource in the tree model
 * row pointed to by @iter and the value of #ESourceSelector:extension-name
 * if such an instance is already cached, or else %NULL.  This function does
 * not create a new #EClient instance, and therefore does not block.
 *
 * The returned #EClient is referenced for thread-safety and must be
 * unreferenced with g_object_unref() when finished with it.
 *
 * Returns: an #EClient, or %NULL
 **/
EClient *
e_client_selector_ref_cached_client_by_iter (EClientSelector *selector,
                                             GtkTreeIter *iter)
{
    EClient *client = NULL;
    ESource *source;

    g_return_val_if_fail (E_IS_CLIENT_SELECTOR (selector), NULL);
    g_return_val_if_fail (iter != NULL, NULL);

    source = e_source_selector_ref_source_by_iter (
        E_SOURCE_SELECTOR (selector), iter);

    if (source != NULL) {
        client = e_client_selector_ref_cached_client (
            selector, source);
        g_object_unref (source);
    }

    return client;
}

/**
 * e_client_selector_is_backend_dead:
 * @selector: an #EClientSelector
 * @source: an #ESource
 *
 * Returns %TRUE if an #EClient instance for @source and the value of
 * #ESourceSelector:extension-name was recently discarded after having
 * emitted a #EClient:backend-died signal, and a replacement #EClient
 * instance has not yet been created.
 *
 * Returns: whether the backend for @source died
 **/
gboolean
e_client_selector_is_backend_dead (EClientSelector *selector,
                                   ESource *source)
{
    EClientCache *client_cache;
    const gchar *extension_name;
    gboolean dead_backend;

    g_return_val_if_fail (E_IS_CLIENT_SELECTOR (selector), FALSE);
    g_return_val_if_fail (E_IS_SOURCE (source), FALSE);

    extension_name = e_source_selector_get_extension_name (
        E_SOURCE_SELECTOR (selector));

    client_cache = e_client_selector_ref_client_cache (selector);

    dead_backend = e_client_cache_is_backend_dead (
        client_cache, source, extension_name);

    g_object_unref (client_cache);

    return dead_backend;
}