Fix Dash loopback deadlock during spectrum rendering

metabolomics_spectrum_resolver/dashinterface.py

@@ -7,7 +7,6 @@
 import dash_core_components as dcc
 import dash_html_components as html
 import dash_table
-import requests
 from dash.dependencies import Input, Output, State
 from dash_table import DataTable, FormatTemplate
 from dash_table.Format import Format, Scheme
@@ -776,9 +775,6 @@ def _process_usi(
     _, source_link, splash_key = tasks.parse_usi(usi)
 
     usi_url = f"/svg/?{urlencode(drawing_controls, quote_via=quote)}"
-    # Pre-fetch the spectrum plot to warm the cache.
-    requests.get(f"http://localhost:5000{usi_url}")
-
     image_obj = html.Img(src=usi_url)
 
     json_button = html.A(
@@ -878,9 +874,6 @@ def _process_mirror_usi(
     _, source_link2, splash_key2 = tasks.parse_usi(usi2)
 
     mirror_url = f"/svg/mirror/?{urlencode(drawing_controls, quote_via=quote)}"
-    # Pre-fetch the mirror plot to warm the cache.
-    requests.get(f"http://localhost:5000{mirror_url}")
-
     image_obj = html.Img(src=mirror_url)
 
     json_button = html.A(

test/test_dashinterface.py

@@ -0,0 +1,55 @@
+from unittest import mock
+
+import requests
+
+
+USI_1 = "mzspec:GNPS:GNPS-LIBRARY:accession:CCMSLIB00005436077"
+USI_2 = "mzspec:MASSBANK::accession:EA266604"
+
+
+def test_process_usi_does_not_make_loopback_request():
+    from metabolomics_spectrum_resolver import dashinterface
+
+    drawing_controls = {"usi1": USI_1}
+    with mock.patch.object(
+        dashinterface.tasks,
+        "parse_usi",
+        return_value=(None, "https://example.org/source", "splash"),
+    ), mock.patch.object(
+        requests,
+        "get",
+        side_effect=AssertionError("Dash rendering must not make HTTP requests"),
+    ) as request_get:
+        _, image = dashinterface._process_usi(USI_1, drawing_controls)
+
+    request_get.assert_not_called()
+    assert image.src == (
+        "/svg/?usi1="
+        "mzspec%3AGNPS%3AGNPS-LIBRARY%3Aaccession%3ACCMSLIB00005436077"
+    )
+
+
+def test_process_mirror_usi_does_not_make_loopback_request():
+    from metabolomics_spectrum_resolver import dashinterface
+
+    drawing_controls = {"usi1": USI_1, "usi2": USI_2}
+    with mock.patch.object(
+        dashinterface.tasks,
+        "parse_usi",
+        return_value=(None, "https://example.org/source", "splash"),
+    ) as parse_usi, mock.patch.object(
+        requests,
+        "get",
+        side_effect=AssertionError("Dash rendering must not make HTTP requests"),
+    ) as request_get:
+        _, image, _ = dashinterface._process_mirror_usi(
+            USI_1, USI_2, drawing_controls
+        )
+
+    request_get.assert_not_called()
+    assert parse_usi.call_count == 2
+    assert image.src == (
+        "/svg/mirror/?usi1="
+        "mzspec%3AGNPS%3AGNPS-LIBRARY%3Aaccession%3ACCMSLIB00005436077"
+        "&usi2=mzspec%3AMASSBANK%3A%3Aaccession%3AEA266604"
+    )