extend cache-not-ready handling to filer HTTP path

Mirror the s3api change for the native filer HTTP handlers. When the
filer GET hits a remote-only object whose cache fill hasn't completed,
return 503 Service Unavailable with Retry-After: 5 instead of 500
Internal Error, and treat client disconnects as silent cancellations
rather than logging them as errors.

Adds an ErrCacheNotReady sentinel and a small helper used at the
prepareWriteFn-error sites in ProcessRangeRequest, so the same
classification (cancel / not-ready / other) applies to plain GETs,
single-range, and multi-range requests.

weed/server/common.go

@@ -3,6 +3,7 @@ package weed_server
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -39,6 +40,28 @@ var writePool = sync.Pool{New: func() interface{} {
 },
 }
 
+// ErrCacheNotReady signals that a remote-only object's local cache is still
+// filling. Callers should map it to 503 + Retry-After so SDKs back off and retry.
+var ErrCacheNotReady = errors.New("remote object not cached yet")
+
+// writePrepareWriteFnErr writes an HTTP response for an error from
+// prepareWriteFn, before any 2xx headers have been written. Client cancels are
+// silent; ErrCacheNotReady becomes 503 + Retry-After; everything else is 500.
+func writePrepareWriteFnErr(w http.ResponseWriter, err error) {
+	w.Header().Del("Content-Length")
+	switch {
+	case errors.Is(err, context.Canceled):
+		glog.V(3).Infof("ProcessRangeRequest: client disconnected: %v", err)
+	case errors.Is(err, ErrCacheNotReady):
+		glog.V(1).Infof("ProcessRangeRequest: cache not ready, returning 503: %v", err)
+		w.Header().Set("Retry-After", "5")
+		http.Error(w, err.Error(), http.StatusServiceUnavailable)
+	default:
+		glog.Errorf("ProcessRangeRequest: %v", err)
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+	}
+}
+
 func init() {
 	serverStats = stats.NewServerStats()
 	go serverStats.Start()
@@ -290,9 +313,7 @@ func ProcessRangeRequest(r *http.Request, w http.ResponseWriter, totalSize int64
 		w.Header().Set("Content-Length", strconv.FormatInt(totalSize, 10))
 		writeFn, err := prepareWriteFn(0, totalSize)
 		if err != nil {
-			glog.Errorf("ProcessRangeRequest: %v", err)
-			w.Header().Del("Content-Length")
-			http.Error(w, err.Error(), http.StatusInternalServerError)
+			writePrepareWriteFnErr(w, err)
 			return fmt.Errorf("ProcessRangeRequest: %w", err)
 		}
 		if err = writeFn(bufferedWriter); err != nil {
@@ -340,9 +361,7 @@ func ProcessRangeRequest(r *http.Request, w http.ResponseWriter, totalSize int64
 
 		writeFn, err := prepareWriteFn(ra.start, ra.length)
 		if err != nil {
-			glog.Errorf("ProcessRangeRequest range[0]: %+v err: %v", w.Header(), err)
-			w.Header().Del("Content-Length")
-			http.Error(w, err.Error(), http.StatusInternalServerError)
+			writePrepareWriteFnErr(w, err)
 			return fmt.Errorf("ProcessRangeRequest: %w", err)
 		}
 		w.WriteHeader(http.StatusPartialContent)
@@ -365,9 +384,8 @@ func ProcessRangeRequest(r *http.Request, w http.ResponseWriter, totalSize int64
 		}
 		writeFn, err := prepareWriteFn(ra.start, ra.length)
 		if err != nil {
-			glog.Errorf("ProcessRangeRequest range[%d] err: %v", i, err)
-			http.Error(w, "Internal Error", http.StatusInternalServerError)
-			return fmt.Errorf("ProcessRangeRequest range[%d] err: %v", i, err)
+			writePrepareWriteFnErr(w, err)
+			return fmt.Errorf("ProcessRangeRequest range[%d]: %w", i, err)
 		}
 		writeFnByRange[i] = writeFn
 	}

weed/server/filer_server_handlers_read.go

@@ -211,8 +211,13 @@ func (fs *FilerServer) GetOrHeadHandler(w http.ResponseWriter, r *http.Request)
 				Name:      name,
 			}); err != nil {
 				stats.FilerHandlerCounter.WithLabelValues(stats.ErrorReadCache).Inc()
-				glog.ErrorfCtx(ctx, "CacheRemoteObjectToLocalCluster %s: %v", entry.FullPath, err)
-				return nil, fmt.Errorf("cache %s: %v", entry.FullPath, err)
+				// Client disconnected: surface ctx error so caller stays silent.
+				if ctxErr := ctx.Err(); ctxErr != nil {
+					return nil, ctxErr
+				}
+				// Cache still filling: tag with sentinel so caller maps to 503 + Retry-After.
+				glog.WarningfCtx(ctx, "CacheRemoteObjectToLocalCluster %s: %v", entry.FullPath, err)
+				return nil, fmt.Errorf("cache %s: %w", entry.FullPath, ErrCacheNotReady)
 			} else {
 				chunks = resp.Entry.GetChunks()
 			}