fix: S3 remote storage cold-cache read fails with 'size reported but no content available' (#7817)

fix: S3 remote storage cold-cache read fails with 'size reported but no content available' (#7815)

When a remote-only entry's initial caching attempt times out or fails,
streamFromVolumeServers() now detects this case and retries caching
synchronously before streaming, similar to how the filer server handles
remote-only entries.

Changes:
- Modified streamFromVolumeServers() to check entry.IsInRemoteOnly()
  before treating missing chunks as a data integrity error
- Added doCacheRemoteObject() as the core caching function (calls filer gRPC)
- Added buildRemoteObjectPath() helper to reduce code duplication
- Refactored cacheRemoteObjectWithDedup() and cacheRemoteObjectForStreaming()
  to reuse the shared functions
- Added integration tests for remote storage scenarios

Fixes https://github.com/seaweedfs/seaweedfs/issues/7815

weed/s3api/s3api_object_handlers.go

@@ -760,7 +760,7 @@ func (s3a *S3ApiServer) GetObjectHandler(w http.ResponseWriter, r *http.Request)
 
 	// Stream directly from volume servers with SSE support
 	tStream := time.Now()
-	err = s3a.streamFromVolumeServersWithSSE(w, r, objectEntryForSSE, primarySSEType)
+	err = s3a.streamFromVolumeServersWithSSE(w, r, objectEntryForSSE, primarySSEType, bucket, object, versionId)
 	streamTime = time.Since(tStream)
 	if err != nil {
 		glog.Errorf("GetObjectHandler: failed to stream from volume servers: %v", err)
@@ -784,7 +784,7 @@ func (s3a *S3ApiServer) GetObjectHandler(w http.ResponseWriter, r *http.Request)
 
 // streamFromVolumeServers streams object data directly from volume servers, bypassing filer proxy
 // This eliminates the ~19ms filer proxy overhead by reading chunks directly
-func (s3a *S3ApiServer) streamFromVolumeServers(w http.ResponseWriter, r *http.Request, entry *filer_pb.Entry, sseType string) error {
+func (s3a *S3ApiServer) streamFromVolumeServers(w http.ResponseWriter, r *http.Request, entry *filer_pb.Entry, sseType string, bucket, object, versionId string) error {
 	// Profiling: Track overall and stage timings
 	t0 := time.Now()
 	var (
@@ -937,17 +937,34 @@ func (s3a *S3ApiServer) streamFromVolumeServers(w http.ResponseWriter, r *http.R
 		len(chunks), totalSize, isRangeRequest, offset, size)
 
 	if len(chunks) == 0 {
-		// BUG FIX: If totalSize > 0 but no chunks and no content, this is a data integrity issue
-		if totalSize > 0 && len(entry.Content) == 0 {
+		// Check if this is a remote-only entry that needs caching
+		// This handles the case where initial caching attempt timed out or failed
+		if entry.IsInRemoteOnly() {
+			glog.V(1).Infof("streamFromVolumeServers: entry is remote-only, attempting to cache before streaming")
+			// Try to cache the remote object synchronously (like filer does)
+			cachedEntry := s3a.cacheRemoteObjectForStreaming(r, entry, bucket, object, versionId)
+			if cachedEntry != nil && len(cachedEntry.GetChunks()) > 0 {
+				chunks = cachedEntry.GetChunks()
+				entry = cachedEntry
+				glog.V(1).Infof("streamFromVolumeServers: successfully cached remote object, got %d chunks", len(chunks))
+			} else {
+				// Caching failed - return error to client
+				glog.Errorf("streamFromVolumeServers: failed to cache remote object for streaming")
+				s3err.WriteErrorResponse(w, r, s3err.ErrInternalError)
+				return newStreamErrorWithResponse(fmt.Errorf("failed to cache remote object for streaming"))
+			}
+		} else if totalSize > 0 && len(entry.Content) == 0 {
+			// Not a remote entry but has size without content - this is a data integrity issue
 			glog.Errorf("streamFromVolumeServers: Data integrity error - entry reports size %d but has no content or chunks", totalSize)
 			// Write S3-compliant XML error response
 			s3err.WriteErrorResponse(w, r, s3err.ErrInternalError)
 			return newStreamErrorWithResponse(fmt.Errorf("data integrity error: size %d reported but no content available", totalSize))
+		} else {
+			// Empty object - set headers and write status
+			s3a.setResponseHeaders(w, r, entry, totalSize)
+			w.WriteHeader(http.StatusOK)
+			return nil
 		}
-		// Empty object - set headers and write status
-		s3a.setResponseHeaders(w, r, entry, totalSize)
-		w.WriteHeader(http.StatusOK)
-		return nil
 	}
 
 	// Log chunk details (verbose only - high frequency)
@@ -1048,10 +1065,10 @@ func (s3a *S3ApiServer) createLookupFileIdFunction() func(context.Context, strin
 }
 
 // streamFromVolumeServersWithSSE handles streaming with inline SSE decryption
-func (s3a *S3ApiServer) streamFromVolumeServersWithSSE(w http.ResponseWriter, r *http.Request, entry *filer_pb.Entry, sseType string) error {
+func (s3a *S3ApiServer) streamFromVolumeServersWithSSE(w http.ResponseWriter, r *http.Request, entry *filer_pb.Entry, sseType string, bucket, object, versionId string) error {
 	// If not encrypted, use fast path without decryption
 	if sseType == "" || sseType == "None" {
-		return s3a.streamFromVolumeServers(w, r, entry, sseType)
+		return s3a.streamFromVolumeServers(w, r, entry, sseType, bucket, object, versionId)
 	}
 
 	// Profiling: Track SSE decryption stages
@@ -3338,35 +3355,26 @@ func (s3a *S3ApiServer) getMultipartInfo(entry *filer_pb.Entry, partNumber int)
 	return partsCount, nil
 }
 
-// cacheRemoteObjectWithDedup caches a remote-only object to the local cluster.
-// The filer server handles singleflight deduplication, so all clients (S3, HTTP, Hadoop) benefit.
-// On cache error, returns the original entry (streaming from remote will still work).
-// Uses a bounded timeout to avoid blocking requests indefinitely.
-func (s3a *S3ApiServer) cacheRemoteObjectWithDedup(ctx context.Context, bucket, object string, entry *filer_pb.Entry) *filer_pb.Entry {
-	// Use a bounded timeout for caching to avoid blocking requests indefinitely
-	// 30 seconds should be enough for most objects; large objects may timeout but will still stream
-	const cacheTimeout = 30 * time.Second
-	cacheCtx, cancel := context.WithTimeout(ctx, cacheTimeout)
-	defer cancel()
-
-	// Build the full path for the object
-	// Normalize object path: remove duplicate slashes and leading slash to avoid double slashes in path
-	dir := s3a.option.BucketsPath + "/" + bucket
-	normalizedObject := strings.TrimPrefix(removeDuplicateSlashes(object), "/")
-	if idx := strings.LastIndex(normalizedObject, "/"); idx > 0 {
-		dir = dir + "/" + normalizedObject[:idx]
-		normalizedObject = normalizedObject[idx+1:]
+// buildRemoteObjectPath builds the filer directory and object name from S3 bucket/object.
+// This is shared by all remote object caching functions.
+func (s3a *S3ApiServer) buildRemoteObjectPath(bucket, object string) (dir, name string) {
+	dir = s3a.option.BucketsPath + "/" + bucket
+	name = strings.TrimPrefix(removeDuplicateSlashes(object), "/")
+	if idx := strings.LastIndex(name, "/"); idx > 0 {
+		dir = dir + "/" + name[:idx]
+		name = name[idx+1:]
 	}
+	return dir, name
+}
 
-	glog.V(2).Infof("cacheRemoteObjectWithDedup: caching %s/%s (remote size: %d)", bucket, object, entry.RemoteEntry.RemoteSize)
-
-	// Call the filer's CacheRemoteObjectToLocalCluster via gRPC
-	// The filer handles singleflight deduplication internally
+// doCacheRemoteObject calls the filer's CacheRemoteObjectToLocalCluster gRPC endpoint.
+// This is the core caching function used by both cacheRemoteObjectWithDedup and cacheRemoteObjectForStreaming.
+func (s3a *S3ApiServer) doCacheRemoteObject(ctx context.Context, dir, name string) (*filer_pb.Entry, error) {
 	var cachedEntry *filer_pb.Entry
 	err := s3a.WithFilerClient(false, func(client filer_pb.SeaweedFilerClient) error {
-		resp, cacheErr := client.CacheRemoteObjectToLocalCluster(cacheCtx, &filer_pb.CacheRemoteObjectToLocalClusterRequest{
+		resp, cacheErr := client.CacheRemoteObjectToLocalCluster(ctx, &filer_pb.CacheRemoteObjectToLocalClusterRequest{
 			Directory: dir,
-			Name:      normalizedObject,
+			Name:      name,
 		})
 		if cacheErr != nil {
 			return cacheErr
@@ -3376,24 +3384,67 @@ func (s3a *S3ApiServer) cacheRemoteObjectWithDedup(ctx context.Context, bucket,
 		}
 		return nil
 	})
+	return cachedEntry, err
+}
 
+// cacheRemoteObjectWithDedup caches a remote-only object to the local cluster.
+// The filer server handles singleflight deduplication, so all clients (S3, HTTP, Hadoop) benefit.
+// On cache error, returns the original entry (will retry in streamFromVolumeServers).
+// Uses a bounded timeout to avoid blocking requests indefinitely.
+func (s3a *S3ApiServer) cacheRemoteObjectWithDedup(ctx context.Context, bucket, object string, entry *filer_pb.Entry) *filer_pb.Entry {
+	const cacheTimeout = 30 * time.Second
+	cacheCtx, cancel := context.WithTimeout(ctx, cacheTimeout)
+	defer cancel()
+
+	dir, name := s3a.buildRemoteObjectPath(bucket, object)
+	glog.V(2).Infof("cacheRemoteObjectWithDedup: caching %s/%s (remote size: %d)", bucket, object, entry.RemoteEntry.RemoteSize)
+
+	cachedEntry, err := s3a.doCacheRemoteObject(cacheCtx, dir, name)
 	if err != nil {
-		// Caching failed - log and return original entry
-		// Streaming from remote storage will still work via filer proxy
 		if errors.Is(err, context.DeadlineExceeded) {
-			glog.V(1).Infof("cacheRemoteObjectWithDedup: timeout caching %s/%s after %v (will stream from remote)", bucket, object, cacheTimeout)
+			glog.V(1).Infof("cacheRemoteObjectWithDedup: timeout caching %s/%s after %v (will retry in streaming)", bucket, object, cacheTimeout)
 		} else {
-			glog.Warningf("cacheRemoteObjectWithDedup: failed to cache %s/%s: %v (will stream from remote)", bucket, object, err)
+			glog.Warningf("cacheRemoteObjectWithDedup: failed to cache %s/%s: %v (will retry in streaming)", bucket, object, err)
 		}
 		return entry
 	}
 
-	// If caching succeeded and we got chunks, use the cached entry's chunks
 	if cachedEntry != nil && len(cachedEntry.GetChunks()) > 0 {
 		glog.V(1).Infof("cacheRemoteObjectWithDedup: successfully cached %s/%s (%d chunks)", bucket, object, len(cachedEntry.GetChunks()))
-		// Preserve original entry metadata but use new chunks
 		entry.Chunks = cachedEntry.Chunks
 	}
 
 	return entry
 }
+
+// cacheRemoteObjectForStreaming caches a remote-only object to the local cluster for streaming.
+// This is called from streamFromVolumeServers when the initial caching attempt timed out or failed.
+// Uses the request context (no artificial timeout) to allow the caching to complete.
+// For versioned objects, versionId determines the correct path in .versions/ directory.
+func (s3a *S3ApiServer) cacheRemoteObjectForStreaming(r *http.Request, entry *filer_pb.Entry, bucket, object, versionId string) *filer_pb.Entry {
+	var dir, name string
+	if versionId != "" && versionId != "null" {
+		// This is a specific version - entry is located at /buckets/<bucket>/<object>.versions/v_<versionId>
+		normalizedObject := strings.TrimPrefix(removeDuplicateSlashes(object), "/")
+		dir = s3a.option.BucketsPath + "/" + bucket + "/" + normalizedObject + s3_constants.VersionsFolder
+		name = s3a.getVersionFileName(versionId)
+	} else {
+		// Non-versioned object or "null" version - lives at the main path
+		dir, name = s3a.buildRemoteObjectPath(bucket, object)
+	}
+
+	glog.V(1).Infof("cacheRemoteObjectForStreaming: caching %s/%s (remote size: %d, versionId: %s)", dir, name, entry.RemoteEntry.RemoteSize, versionId)
+
+	cachedEntry, err := s3a.doCacheRemoteObject(r.Context(), dir, name)
+	if err != nil {
+		glog.Errorf("cacheRemoteObjectForStreaming: failed to cache %s/%s: %v", dir, name, err)
+		return nil
+	}
+
+	if cachedEntry != nil && len(cachedEntry.GetChunks()) > 0 {
+		glog.V(1).Infof("cacheRemoteObjectForStreaming: successfully cached %s/%s (%d chunks)", dir, name, len(cachedEntry.GetChunks()))
+		return cachedEntry
+	}
+
+	return nil
+}

weed/s3api/s3api_remote_storage_test.go

@@ -0,0 +1,273 @@
+package s3api
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/filer"
+	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
+	"github.com/seaweedfs/seaweedfs/weed/s3api/s3_constants"
+	"github.com/stretchr/testify/assert"
+)
+
+// TestIsInRemoteOnly tests the IsInRemoteOnly method on filer_pb.Entry
+func TestIsInRemoteOnly(t *testing.T) {
+	tests := []struct {
+		name     string
+		entry    *filer_pb.Entry
+		expected bool
+	}{
+		{
+			name: "remote-only entry with no chunks",
+			entry: &filer_pb.Entry{
+				Name:   "remote-file.txt",
+				Chunks: nil,
+				RemoteEntry: &filer_pb.RemoteEntry{
+					RemoteSize: 1024,
+				},
+			},
+			expected: true,
+		},
+		{
+			name: "remote entry with chunks (cached)",
+			entry: &filer_pb.Entry{
+				Name: "cached-file.txt",
+				Chunks: []*filer_pb.FileChunk{
+					{FileId: "1,abc123", Size: 1024, Offset: 0},
+				},
+				RemoteEntry: &filer_pb.RemoteEntry{
+					RemoteSize: 1024,
+				},
+			},
+			expected: false,
+		},
+		{
+			name: "local file with chunks (not remote)",
+			entry: &filer_pb.Entry{
+				Name: "local-file.txt",
+				Chunks: []*filer_pb.FileChunk{
+					{FileId: "1,abc123", Size: 1024, Offset: 0},
+				},
+				RemoteEntry: nil,
+			},
+			expected: false,
+		},
+		{
+			name: "empty remote entry (size 0)",
+			entry: &filer_pb.Entry{
+				Name:   "empty-remote.txt",
+				Chunks: nil,
+				RemoteEntry: &filer_pb.RemoteEntry{
+					RemoteSize: 0,
+				},
+			},
+			expected: false,
+		},
+		{
+			name: "no chunks but nil RemoteEntry",
+			entry: &filer_pb.Entry{
+				Name:        "empty-local.txt",
+				Chunks:      nil,
+				RemoteEntry: nil,
+			},
+			expected: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := tt.entry.IsInRemoteOnly()
+			assert.Equal(t, tt.expected, result,
+				"IsInRemoteOnly() for %s should return %v", tt.name, tt.expected)
+		})
+	}
+}
+
+// TestRemoteOnlyEntryDetection tests that the streamFromVolumeServers logic
+// correctly distinguishes between remote-only entries and data integrity errors
+func TestRemoteOnlyEntryDetection(t *testing.T) {
+	tests := []struct {
+		name              string
+		entry             *filer_pb.Entry
+		shouldBeRemote    bool
+		shouldBeDataError bool
+		shouldBeEmpty     bool
+	}{
+		{
+			name: "remote-only entry (no chunks, has remote entry)",
+			entry: &filer_pb.Entry{
+				Name:   "remote-file.txt",
+				Chunks: nil,
+				Attributes: &filer_pb.FuseAttributes{
+					FileSize: 1024,
+				},
+				RemoteEntry: &filer_pb.RemoteEntry{
+					RemoteSize: 1024,
+				},
+			},
+			shouldBeRemote:    true,
+			shouldBeDataError: false,
+			shouldBeEmpty:     false,
+		},
+		{
+			name: "data integrity error (no chunks, no remote, has size)",
+			entry: &filer_pb.Entry{
+				Name:   "corrupt-file.txt",
+				Chunks: nil,
+				Attributes: &filer_pb.FuseAttributes{
+					FileSize: 1024,
+				},
+				RemoteEntry: nil,
+			},
+			shouldBeRemote:    false,
+			shouldBeDataError: true,
+			shouldBeEmpty:     false,
+		},
+		{
+			name: "empty local file (no chunks, no remote, size 0)",
+			entry: &filer_pb.Entry{
+				Name:   "empty-file.txt",
+				Chunks: nil,
+				Attributes: &filer_pb.FuseAttributes{
+					FileSize: 0,
+				},
+				RemoteEntry: nil,
+			},
+			shouldBeRemote:    false,
+			shouldBeDataError: false,
+			shouldBeEmpty:     true,
+		},
+		{
+			name: "normal file with chunks",
+			entry: &filer_pb.Entry{
+				Name: "normal-file.txt",
+				Chunks: []*filer_pb.FileChunk{
+					{FileId: "1,abc123", Size: 1024, Offset: 0},
+				},
+				Attributes: &filer_pb.FuseAttributes{
+					FileSize: 1024,
+				},
+				RemoteEntry: nil,
+			},
+			shouldBeRemote:    false,
+			shouldBeDataError: false,
+			shouldBeEmpty:     false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			chunks := tt.entry.GetChunks()
+			totalSize := int64(filer.FileSize(tt.entry))
+
+			if len(chunks) == 0 {
+				// This mirrors the logic in streamFromVolumeServers
+				if tt.entry.IsInRemoteOnly() {
+					assert.True(t, tt.shouldBeRemote,
+						"Entry should be detected as remote-only")
+				} else if totalSize > 0 && len(tt.entry.Content) == 0 {
+					assert.True(t, tt.shouldBeDataError,
+						"Entry should be detected as data integrity error")
+				} else {
+					assert.True(t, tt.shouldBeEmpty,
+						"Entry should be detected as empty")
+				}
+			} else {
+				assert.False(t, tt.shouldBeRemote, "Entry with chunks should not be remote-only")
+				assert.False(t, tt.shouldBeDataError, "Entry with chunks should not be data error")
+				assert.False(t, tt.shouldBeEmpty, "Entry with chunks should not be empty")
+			}
+		})
+	}
+}
+
+// TestVersionedRemoteObjectPathBuilding tests that the path building logic
+// correctly handles versioned objects stored in .versions/ directory
+func TestVersionedRemoteObjectPathBuilding(t *testing.T) {
+	bucketsPath := "/buckets"
+
+	tests := []struct {
+		name         string
+		bucket       string
+		object       string
+		versionId    string
+		expectedDir  string
+		expectedName string
+	}{
+		{
+			name:         "non-versioned object (empty versionId)",
+			bucket:       "mybucket",
+			object:       "myobject.txt",
+			versionId:    "",
+			expectedDir:  "/buckets/mybucket",
+			expectedName: "myobject.txt",
+		},
+		{
+			name:         "null version",
+			bucket:       "mybucket",
+			object:       "myobject.txt",
+			versionId:    "null",
+			expectedDir:  "/buckets/mybucket",
+			expectedName: "myobject.txt",
+		},
+		{
+			name:         "specific version",
+			bucket:       "mybucket",
+			object:       "myobject.txt",
+			versionId:    "abc123",
+			expectedDir:  "/buckets/mybucket/myobject.txt" + s3_constants.VersionsFolder,
+			expectedName: "v_abc123",
+		},
+		{
+			name:         "nested object with version",
+			bucket:       "mybucket",
+			object:       "folder/subfolder/file.txt",
+			versionId:    "xyz789",
+			expectedDir:  "/buckets/mybucket/folder/subfolder/file.txt" + s3_constants.VersionsFolder,
+			expectedName: "v_xyz789",
+		},
+		{
+			name:         "object with leading slash and version",
+			bucket:       "mybucket",
+			object:       "/path/to/file.txt",
+			versionId:    "ver456",
+			expectedDir:  "/buckets/mybucket/path/to/file.txt" + s3_constants.VersionsFolder,
+			expectedName: "v_ver456",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var dir, name string
+
+			// This mirrors the logic in cacheRemoteObjectForStreaming
+			if tt.versionId != "" && tt.versionId != "null" {
+				// Versioned object path
+				normalizedObject := strings.TrimPrefix(removeDuplicateSlashesTest(tt.object), "/")
+				dir = bucketsPath + "/" + tt.bucket + "/" + normalizedObject + s3_constants.VersionsFolder
+				name = "v_" + tt.versionId
+			} else {
+				// Non-versioned path (simplified - just for testing)
+				dir = bucketsPath + "/" + tt.bucket
+				normalizedObject := strings.TrimPrefix(removeDuplicateSlashesTest(tt.object), "/")
+				if idx := strings.LastIndex(normalizedObject, "/"); idx > 0 {
+					dir = dir + "/" + normalizedObject[:idx]
+					name = normalizedObject[idx+1:]
+				} else {
+					name = normalizedObject
+				}
+			}
+
+			assert.Equal(t, tt.expectedDir, dir, "Directory path should match")
+			assert.Equal(t, tt.expectedName, name, "Name should match")
+		})
+	}
+}
+
+// removeDuplicateSlashesTest is a test helper that mirrors production code
+func removeDuplicateSlashesTest(s string) string {
+	for strings.Contains(s, "//") {
+		s = strings.ReplaceAll(s, "//", "/")
+	}
+	return s
+}