fall back to mirror if helioviewer.org is offline (fixes #5)

gcs/gui.py

@@ -18,16 +18,16 @@
 from matplotlib.gridspec import GridSpec
 from sunpy import log
 from sunpy.coordinates import get_horizons_coord
-from sunpy.io import read_file
 from sunpy.map import Map
-from sunpy.net import helioviewer
 
 from gcs.geometry import gcs_mesh_sunpy, apex_radius
+from gcs.utils.helioviewer import get_helioviewer_client
 from gcs.utils.widgets import SliderAndTextbox
 
 matplotlib.use('Qt5Agg')
 
-hv = helioviewer.HelioviewerClient()
+hv = get_helioviewer_client()
+
 straight_vertices, front_vertices, circle_vertices = 10, 10, 20
 filename = 'gcs_params.json'
 draw_modes = ['off', 'point cloud', 'grid']

gcs/utils/helioviewer.py

@@ -0,0 +1,18 @@
+from sunpy.net.helioviewer import HelioviewerClient
+
+
+def get_helioviewer_client():
+    hv = HelioviewerClient()
+    if not _is_online(hv):
+        # fall back to mirror server
+        print("https://www.helioviewer.org/ seems to be offline,"
+              "switching to mirror at https://helioviewer.ias.u-psud.fr/")
+        hv = HelioviewerClient("https://helioviewer-api.ias.u-psud.fr/")
+    return hv
+
+
+def _is_online(hv: HelioviewerClient):
+    try:
+        return hv.is_online()
+    except:
+        return False