Keep support for ICO formats by defaulting to PNG if necessary

e2e/scripts/st_set_page_config_icon.py

@@ -0,0 +1,5 @@
+import streamlit as st
+
+st.set_page_config(
+    page_icon="e2e/scripts/assets/favicon.ico",
+)

e2e/specs/st_set_page_config_icon.spec.js

@@ -0,0 +1,31 @@
+/**
+ * @license
+ * Copyright 2018-2022 Streamlit Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+describe("st.set_page_config with ICO", () => {
+  before(() => {
+    cy.loadApp("http://localhost:3000/");
+  });
+
+  it("sets the page favicon with ico file", () => {
+    cy.get("link[rel='shortcut icon']")
+      .invoke("attr", "href")
+      .should(
+        "eq",
+        "http://localhost:8501/media/92018b2805266c4cb9a98e90c849ce5b5e7ba6d1af423bd7b7c345da.png"
+      );
+  });
+});

lib/streamlit/elements/image.py

@@ -207,6 +207,8 @@ def _normalize_to_bytes(data, width, output_format):
     if output_format.lower() == "auto":
         ext = imghdr.what(None, data)
         mimetype = mimetypes.guess_type("image.%s" % ext)[0]
+        if mimetype is None:
+            mimetype = "image/" + format.lower()
     else:
         mimetype = "image/" + format.lower()