Refactor cache middleware and enhance health page error handling

- Updated the CacheMiddleware to remove placeholder files on non-200 responses and exceptions, allowing for retries instead of overwriting with error states.
- Introduced a new helper function `has_error` in the health page to check for errors in API results.
- Enhanced the health page to display error messages when fetching data for largest perp positions, most levered positions, largest spot borrows, and most levered spot borrows, improving user feedback during data retrieval.

Author: goldhaxx

backend/middleware/cache_middleware.py

@@ -392,9 +392,13 @@ async def _fetch_and_cache(
                 logger.warning(
                     f"Failed to fetch data for {request.url.path}. Status code: {response.status_code}"
                 )
-                # Overwrite placeholder with error state or remove? Let's overwrite.
-                with open(cache_file, "w") as f:
-                    json.dump({"content": ERROR_PLACEHOLDER, "status_code": response.status_code, "headers": {}}, f)
+                # On failure, remove the placeholder to allow retries
+                if os.path.exists(cache_file):
+                    try:
+                        os.remove(cache_file)
+                        logger.info(f"Removed placeholder file due to non-200 response: {cache_file}")
+                    except OSError as e:
+                        logger.error(f"Failed to remove placeholder file {cache_file} after non-200 response: {e}")
 
             # Run cleanup AFTER successfully writing new cache or error placeholder
             self.cleanup_old_cache_files()
@@ -403,12 +407,13 @@ async def _fetch_and_cache(
             logger.error(
                 f"Error in background task for {request.url.path} under key {cache_key}: {str(e)}"
             )
-            # Attempt to overwrite placeholder with error state
-            try:
-                with open(cache_file, "w") as f:
-                     json.dump({"content": ERROR_PLACEHOLDER, "status_code": 500, "headers": {}}, f)
-            except Exception as write_e:
-                 logger.error(f"Failed to write error placeholder for {cache_file}: {write_e}")
+            # On failure, remove the placeholder to allow retries
+            if os.path.exists(cache_file):
+                try:
+                    os.remove(cache_file)
+                    logger.info(f"Removed placeholder file due to exception: {cache_file}")
+                except OSError as remove_e:
+                    logger.error(f"Failed to remove placeholder file {cache_file} after exception: {remove_e}")
             import traceback
             traceback.print_exc()
         finally:

src/page/health.py

@@ -12,6 +12,9 @@ def is_processing(result):
     """Checks if the API result indicates backend processing."""
     return isinstance(result, dict) and result.get("result") == "processing"
 
+def has_error(result):
+    """Checks if the API result indicates an error."""
+    return isinstance(result, dict) and "error" in result
 
 def _get_perp_market_symbol_display(market_index):
     """Safely get the display string for a perp market index."""
@@ -190,6 +193,8 @@ def health_page():
 
         if is_processing(largest_perp_positions):
             is_still_processing = True
+        elif has_error(largest_perp_positions):
+            st.error(f"Error fetching largest perp positions: {largest_perp_positions.get('error', 'Unknown error')}")
         else:
             # Convert to DataFrame and add pagination
             df = pd.DataFrame(largest_perp_positions)
@@ -236,6 +241,8 @@ def health_page():
 
         if is_processing(most_levered_positions):
             is_still_processing = True
+        elif has_error(most_levered_positions):
+            st.error(f"Error fetching most levered perp positions: {most_levered_positions.get('error', 'Unknown error')}")
         else:
             # Format market index in most_levered_positions too
             most_levered_df = pd.DataFrame(most_levered_positions)
@@ -310,6 +317,8 @@ def health_page():
 
         if is_processing(largest_spot_borrows):
             is_still_processing = True
+        elif has_error(largest_spot_borrows):
+            st.error(f"Error fetching largest spot borrows: {largest_spot_borrows.get('error', 'Unknown error')}")
         else:
             # Convert to dataframe and add market symbols
             spot_df = pd.DataFrame(largest_spot_borrows)
@@ -356,6 +365,8 @@ def health_page():
         )
         if is_processing(most_levered_borrows):
             is_still_processing = True
+        elif has_error(most_levered_borrows):
+            st.error(f"Error fetching most levered spot borrows: {most_levered_borrows.get('error', 'Unknown error')}")
         else:
             # Convert to dataframe and add market symbols
             levered_spot_df = pd.DataFrame(most_levered_borrows)