[polari] urlPreview: Explicitly handle network failure

[Florian Müllner <fmuellner src gnome org>]

commit e9dd08c5a838ff329747bb7a5f0c3316df00e003
Author: Florian Müllner <fmuellner gnome org>
Date:   Tue Jul 28 02:26:13 2020 +0200

    urlPreview: Explicitly handle network failure
    
    We cannot generate a thumbnail without network access, so don't even
    try. This allows us to distinguish this failure from failed thumbnails,
    and retry when the network becomes available instead of waiting for the
    next application start.
    
    https://gitlab.gnome.org/GNOME/polari/-/issues/149

 src/urlPreview.js | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)
---
diff --git a/src/urlPreview.js b/src/urlPreview.js
index 5ff426f6..3e8e4de1 100644
--- a/src/urlPreview.js
+++ b/src/urlPreview.js
@@ -19,6 +19,11 @@ class Thumbnailer {
         GLib.mkdir_with_parents(this._thumbnailsDir, 0o755);
     }
 
+    get _hasNetwork() {
+        const monitor = Gio.NetworkMonitor.get_default();
+        return monitor.state_valid && monitor.network_available;
+    }
+
     getThumbnail(uri) {
         return new Promise((resolve, reject) => {
             const filename = this._generateFilename(uri);
@@ -31,6 +36,8 @@ class Thumbnailer {
     async _processData(data) {
         if (await this._thumbExists(data))
             this._generationDone(data);
+        else if (!this._hasNetwork)
+            this._generationUnavailable(data);
         else if (!this._subProc)
             this._generateThumbnail(data);
         else
@@ -48,6 +55,13 @@ class Thumbnailer {
             this._processData(nextData);
     }
 
+    _generationUnavailable(data) {
+        this._generationDone(data, new Gio.IOErrorEnum({
+            code: Gio.IOErrorEnum.NETWORK_UNREACHABLE,
+            message: 'Network unreachable',
+        }));
+    }
+
     async _generateThumbnail(data) {
         let { filename, uri } = data;
         this._subProc = Gio.Subprocess.new(
@@ -115,10 +129,22 @@ var URLPreview = GObject.registerClass({
         });
         this._label.get_style_context().add_class(Gtk.STYLE_CLASS_DIM_LABEL);
         this.add(this._label);
+
+        this._networkMonitor = Gio.NetworkMonitor.get_default();
+        this._networkChangedId = this._networkMonitor.connect('network-changed',
+            this._maybeLoadImage.bind(this));
+
+        this.connect('destroy', this._onDestroy.bind(this));
+    }
+
+    _onDestroy() {
+        if (this._networkChangedId)
+            this._networkMonitor.disconnect(this._networkChangedId);
+        this._networkChangedId = 0;
     }
 
     async _maybeLoadImage() {
-        if (this._imageLoaded)
+        if (this._imageLoaded || !this.get_mapped())
             return;
 
         this._imageLoaded = true;
@@ -132,7 +158,10 @@ var URLPreview = GObject.registerClass({
             const filename = await thumbnailer.getThumbnail(this.uri);
             this._image.set_from_file(filename);
         } catch (e) {
-            log(`Thumbnail generation for ${this.uri} failed: ${e}`);
+            if (e.matches(Gio.IOErrorEnum, Gio.IOErrorEnum.NETWORK_UNREACHABLE))
+                this._imageLoaded = false;
+            else
+                log(`Thumbnail generation for ${this.uri} failed: ${e}`);
             this._image.set({
                 icon_name: 'image-x-generic-symbolic',
                 pixel_size: 64,
@@ -150,7 +179,7 @@ var URLPreview = GObject.registerClass({
     }
 
     vfunc_map() {
-        this._maybeLoadImage();
         super.vfunc_map();
+        this._maybeLoadImage();
     }
 });