fix cache fall through

Author: zshannon

server/server.go

@@ -165,6 +165,40 @@ func getFromCache(ctx context.Context, version, path string) *CacheEntry {
 		cacheMutex.RUnlock()
 	}
 
+	// Before hitting S3, check if parent directory is cached
+	// If so, we can determine if this file exists without S3
+	dirPath := filepath.Dir(strings.TrimPrefix(path, "/"))
+	if dirPath != "." && dirPath != "" {
+		dirCacheKey := fmt.Sprintf("%s%s", version, dirPath)
+		cacheMutex.RLock()
+		if dirEntry, ok := cache.Get(dirCacheKey); ok && time.Now().Before(dirEntry.ExpiresAt) {
+			cacheMutex.RUnlock()
+			if dirEntry.Exists && !dirEntry.IsFile {
+				// Parent directory is cached, check if file is in the list
+				filename := filepath.Base(path)
+				for _, f := range dirEntry.Files {
+					if f == filename {
+						// File exists in parent directory, fetch it
+						goto fetchFile
+					}
+				}
+				// File not in parent directory's file list, so it doesn't exist
+				s3CacheHits.Inc() // This is still a cache hit - we used cached dir info
+				entry := &CacheEntry{
+					Exists:    false,
+					ExpiresAt: time.Now().Add(cacheTTLNotFound),
+				}
+				cacheMutex.Lock()
+				cache.Add(cacheKey, entry)
+				cacheMutex.Unlock()
+				return entry
+			}
+		} else {
+			cacheMutex.RUnlock()
+		}
+	}
+	
+fetchFile:
 	s3CacheMisses.Inc()
 
 	// Try to fetch as a file first