partial cache

app.py

@@ -481,23 +481,76 @@ def serve_file(subpath):
             )
         return response
 
-    # 5) Non-image branch: ensure original is cached
+    # 5) Non-image branch: check if cached, otherwise create partial cache file
     try:
         with cache.read(subpath) as reader:
             file_path = reader.name
             cached_hit = True
     except KeyError:
         cached_hit = False
-        try:
-            cache.set(subpath, open(full_path, 'rb'), read=True)
-            with cache.read(subpath) as reader:
-                file_path = reader.name
-        except Exception as e:
-            app.logger.error(f"Failed to cache file {subpath}: {e}")
-            abort(500)
+        
+        # Create a temporary cache file that we'll write to and serve simultaneously
+        import hashlib
+        import tempfile
+        
+        # Generate cache key similar to diskcache
+        cache_key = hashlib.md5(subpath.encode('utf-8')).hexdigest()
+        cache_dir = os.path.join(cache.directory, cache_key[:2])
+        os.makedirs(cache_dir, exist_ok=True)
+        cache_file_path = os.path.join(cache_dir, f"{cache_key}.tmp")
+        
+        # Start copying to our cache file in chunks
+        def copy_to_cache_chunked():
+            try:
+                with open(full_path, 'rb') as source, open(cache_file_path, 'wb') as dest:
+                    while True:
+                        chunk = source.read(1024 * 1024)  # 1MB chunks
+                        if not chunk:
+                            break
+                        dest.write(chunk)
+                        dest.flush()  # Ensure data is written to disk immediately
+                
+                # Once complete, register with diskcache for proper management
+                try:
+                    with open(cache_file_path, 'rb') as f:
+                        cache.set(subpath, f, read=True)
+                    # Remove our temp file since diskcache now has it
+                    if os.path.exists(cache_file_path):
+                        os.remove(cache_file_path)
+                    app.logger.info(f"Finished caching {subpath}")
+                except Exception as e:
+                    app.logger.error(f"Failed to register with diskcache: {e}")
+                    
+            except Exception as e:
+                app.logger.error(f"Caching failed for {subpath}: {e}")
+                if os.path.exists(cache_file_path):
+                    try:
+                        os.remove(cache_file_path)
+                    except:
+                        pass
+        
+        # Start the background copy
+        cache_thread = threading.Thread(target=copy_to_cache_chunked, daemon=True)
+        cache_thread.start()
+        
+        # Wait for initial data to be written
+        max_wait = 5.0  # Maximum 5 seconds
+        wait_interval = 0.05  # Check every 50ms
+        elapsed = 0
+        
+        while elapsed < max_wait:
+            if os.path.exists(cache_file_path) and os.path.getsize(cache_file_path) > 0:
+                file_path = cache_file_path
+                break
+            time.sleep(wait_interval)
+            elapsed += wait_interval
+        else:
+            # Cache file not ready - abort
+            app.logger.error(f"Cache file not created in time for {subpath}")
+            abort(503, description="Service temporarily unavailable - cache initialization failed")
 
     # 6) Build response for non-image
-    filesize = os.path.getsize(file_path)
+    filesize = os.path.getsize(full_path)
     filename = os.path.basename(full_path)
     
     if as_attachment:
@@ -509,19 +562,46 @@ def serve_file(subpath):
         
 
     # Single send_file call with proper attachment handling
-    response = send_file(
-        file_path,
-        mimetype=mimetype,
-        conditional=True,
-        as_attachment=as_attachment,
-        download_name=filename if as_attachment else None
-    )
+    # For partial cache files, we need to handle this differently
+    if not cached_hit:
+        # Stream from the cache file as it's being written
+        def generate():
+            bytes_sent = 0
+            with open(file_path, 'rb') as f:
+                while bytes_sent < filesize:
+                    # Read what's available
+                    chunk = f.read(1024 * 1024)  # 1MB chunks
+                    if chunk:
+                        bytes_sent += len(chunk)
+                        yield chunk
+                    else:
+                        # No data available yet, wait a bit
+                        time.sleep(0.1)
         
-    if as_attachment:
-        response.headers['X-Content-Type-Options'] = 'nosniff'
-        response.headers['Content-Disposition'] = 'attachment'
+        response = make_response(generate())
+        response.headers['Content-Type'] = mimetype
+        response.headers['Content-Length'] = str(filesize)
+        response.headers['Accept-Ranges'] = 'bytes'
+        if as_attachment:
+            response.headers['Content-Disposition'] = f'attachment; filename="{filename}"'
+            response.headers['X-Content-Type-Options'] = 'nosniff'
+        else:
+            response.headers['Content-Disposition'] = 'inline'
     else:
-        response.headers['Content-Disposition'] = 'inline'
+        # Cached file - use normal send_file
+        response = send_file(
+            file_path,
+            mimetype=mimetype,
+            conditional=True,
+            as_attachment=as_attachment,
+            download_name=filename if as_attachment else None
+        )
+        
+        if as_attachment:
+            response.headers['X-Content-Type-Options'] = 'nosniff'
+            response.headers['Content-Disposition'] = 'attachment'
+        else:
+            response.headers['Content-Disposition'] = 'inline'
 
     response.headers['Cache-Control'] = 'public, max-age=86400'