Added better validation of link to the model

Because if link is without host (e.g. only "http://"), the JS of the
svelte will crash with unexpected exception.

app.py

@@ -15,7 +15,7 @@ from content import (
     MORE_DETAILS_MARKDOWN,
     ABOUT_MARKDOWN,
 )
-from server import LeaderboardServer, xmlAndMarkdownEscape, xmlQuoteAttr, api
+from server import LeaderboardServer, xmlAndMarkdownEscape, xmlQuoteAttr, api, requests
 
 HF_SPACE_TOKEN = os.environ["HF_SPACE_TOKEN"]
 HF_SPACE_ID = os.environ["HF_SPACE_ID"]
@@ -44,15 +44,33 @@ SUBMISSION_INPUTS = dict.fromkeys((
 def on_submit_pressed():
     return gr.update(value='Processing submission…', interactive=False)
 
+def validate_url(url):
+    try:
+        response = requests.get(url, timeout=5)
+    except requests.exceptions.ConnectTimeout:
+        pass
+    except requests.exceptions.ConnectionError as e:
+        return str(e).rsplit(":", 1)[-1].strip()
+    except Exception as e:
+        return str(e)
+    else:
+        if response.status_code != 200:
+            return f'Failed to get <{url}>. Status code: {response.status_code}'
+
 def validate_submission_inputs(**inputs):
     if any(key for key, value in inputs.items() if key != "description" and value in (None, "")):
         raise ValueError('Please fill in all fields (only the description field is optional)')
+    
     if not os.path.exists(inputs["submission_file"]):
         raise ValueError('File does not exist')
-    if not (inputs["link_to_model"].startswith("http://") or inputs["link_to_model"].startswith("https://")):
-        raise ValueError('Link does not starts with "http://" or "https://"')
+    
+    error_msg = validate_url(inputs["link_to_model"])
+    if error_msg:
+        raise ValueError(f'Link to the model is not valid: {error_msg}')
+    
     if not inputs["parameters"] > 0:
         raise ValueError('Attribute `Parameters (B)` should be greater than zero')
+    
     if not (inputs["input_length"] > 0 and inputs["input_length"] == int(inputs["input_length"])):
         raise ValueError('Attribute `Input length (# tokens)` should be greater than zero and integer type')