chunker: improve detection of incompatible metadata #4917

Before this patch chunker required that there is at least one
data chunk to start checking for a composite object.

Now if chunker finds at least one potential temporary or control
chunk, it marks found files as a suspected composite object.
When later rclone tries a concrete operation on the object,
it performs postponed metadata read and decides: is this a native
composite object, incompatible metadata or just garbage.

backend/chunker/chunker.go

@@ -121,6 +121,8 @@ const maxTransactionProbes = 100
 // standard chunker errors
 var (
 	ErrChunkOverflow = errors.New("chunk number overflow")
+	ErrMetaTooBig    = errors.New("metadata is too big")
+	ErrMetaUnknown   = errors.New("unknown metadata, please upgrade rclone")
 )
 
 // variants of baseMove's parameter delMode
@@ -693,43 +695,47 @@ func (f *Fs) processEntries(ctx context.Context, origEntries fs.DirEntries, dirP
 		switch entry := dirOrObject.(type) {
 		case fs.Object:
 			remote := entry.Remote()
-			if mainRemote, chunkNo, ctrlType, xactID := f.parseChunkName(remote); mainRemote != "" {
-				if xactID != "" {
-					if revealHidden {
-						fs.Infof(f, "ignore temporary chunk %q", remote)
-					}
-					break
+			mainRemote, chunkNo, ctrlType, xactID := f.parseChunkName(remote)
+			if mainRemote == "" {
+				// this is meta object or standalone file
+				object := f.newObject("", entry, nil)
+				byRemote[remote] = object
+				tempEntries = append(tempEntries, object)
+				break
+			}
+			// this is some kind of chunk
+			// metobject should have been created above if present
+			isSpecial := xactID != "" || ctrlType != ""
+			mainObject := byRemote[mainRemote]
+			if mainObject == nil && f.useMeta && !isSpecial {
+				fs.Debugf(f, "skip orphan data chunk %q", remote)
+				break
+			}
+			if mainObject == nil && !f.useMeta {
+				// this is the "nometa" case
+				// create dummy chunked object without metadata
+				mainObject = f.newObject(mainRemote, nil, nil)
+				byRemote[mainRemote] = mainObject
+				if !badEntry[mainRemote] {
+					tempEntries = append(tempEntries, mainObject)
 				}
-				if ctrlType != "" {
-					if revealHidden {
-						fs.Infof(f, "ignore control chunk %q", remote)
-					}
-					break
+			}
+			if isSpecial {
+				if revealHidden {
+					fs.Infof(f, "ignore non-data chunk %q", remote)
 				}
-				mainObject := byRemote[mainRemote]
-				if mainObject == nil && f.useMeta {
-					fs.Debugf(f, "skip chunk %q without meta object", remote)
-					break
-				}
-				if mainObject == nil {
-					// useMeta is false - create chunked object without metadata
-					mainObject = f.newObject(mainRemote, nil, nil)
-					byRemote[mainRemote] = mainObject
-					if !badEntry[mainRemote] {
-						tempEntries = append(tempEntries, mainObject)
-					}
-				}
-				if err := mainObject.addChunk(entry, chunkNo); err != nil {
-					if f.opt.FailHard {
-						return nil, err
-					}
-					badEntry[mainRemote] = true
+				// need to read metadata to ensure actual object type
+				if f.useMeta && mainObject != nil && mainObject.size <= maxMetadataSize {
+					mainObject.unsure = true
 				}
 				break
 			}
-			object := f.newObject("", entry, nil)
-			byRemote[remote] = object
-			tempEntries = append(tempEntries, object)
+			if err := mainObject.addChunk(entry, chunkNo); err != nil {
+				if f.opt.FailHard {
+					return nil, err
+				}
+				badEntry[mainRemote] = true
+			}
 		case fs.Directory:
 			isSubdir[entry.Remote()] = true
 			wrapDir := fs.NewDirCopy(ctx, entry)
@@ -784,6 +790,13 @@ func (f *Fs) processEntries(ctx context.Context, origEntries fs.DirEntries, dirP
 // but opening even a small file can be slow on some backends.
 //
 func (f *Fs) NewObject(ctx context.Context, remote string) (fs.Object, error) {
+	return f.scanObject(ctx, remote, false)
+}
+
+// scanObject is like NewObject with optional quick scan mode.
+// The quick mode avoids directory requests other than `List`,
+// ignores non-chunked objects and skips chunk size checks.
+func (f *Fs) scanObject(ctx context.Context, remote string, quickScan bool) (fs.Object, error) {
 	if err := f.forbidChunk(false, remote); err != nil {
 		return nil, errors.Wrap(err, "can't access")
 	}
@@ -844,8 +857,15 @@ func (f *Fs) NewObject(ctx context.Context, remote string) (fs.Object, error) {
 			continue // bypass regexp to save cpu
 		}
 		mainRemote, chunkNo, ctrlType, xactID := f.parseChunkName(entryRemote)
-		if mainRemote == "" || mainRemote != remote || ctrlType != "" || xactID != "" {
-			continue // skip non-conforming, temporary and control chunks
+		if mainRemote == "" || mainRemote != remote {
+			continue // skip non-conforming chunks
+		}
+		if ctrlType != "" || xactID != "" {
+			if f.useMeta {
+				// temporary/control chunk calls for lazy metadata read
+				o.unsure = true
+			}
+			continue
 		}
 		//fs.Debugf(f, "%q belongs to %q as chunk %d", entryRemote, mainRemote, chunkNo)
 		if err := o.addChunk(entry, chunkNo); err != nil {
@@ -855,7 +875,7 @@ func (f *Fs) NewObject(ctx context.Context, remote string) (fs.Object, error) {
 
 	if o.main == nil && (o.chunks == nil || len(o.chunks) == 0) {
 		// Scanning hasn't found data chunks with conforming names.
-		if f.useMeta {
+		if f.useMeta || quickScan {
 			// Metadata is required but absent and there are no chunks.
 			return nil, fs.ErrorObjectNotFound
 		}
@@ -878,8 +898,10 @@ func (f *Fs) NewObject(ctx context.Context, remote string) (fs.Object, error) {
 	// file without metadata. Validate it and update the total data size.
 	// As an optimization, skip metadata reading here - we will call
 	// readMetadata lazily when needed (reading can be expensive).
-	if err := o.validate(); err != nil {
-		return nil, err
+	if !quickScan {
+		if err := o.validate(); err != nil {
+			return nil, err
+		}
 	}
 	return o, nil
 }
@@ -888,13 +910,24 @@ func (o *Object) readMetadata(ctx context.Context) error {
 	if o.isFull {
 		return nil
 	}
-	if !o.isComposite() || !o.f.useMeta {
+	if !o.f.useMeta || (!o.isComposite() && !o.unsure) {
 		o.isFull = true
 		return nil
 	}
 
 	// validate metadata
 	metaObject := o.main
+	if metaObject.Size() > maxMetadataSize {
+		if o.unsure {
+			// this is not metadata but a foreign object
+			o.unsure = false
+			o.chunks = nil  // make isComposite return false
+			o.isFull = true // cache results
+			return nil
+		}
+		return ErrMetaTooBig
+	}
+
 	reader, err := metaObject.Open(ctx)
 	if err != nil {
 		return err
@@ -907,8 +940,22 @@ func (o *Object) readMetadata(ctx context.Context) error {
 
 	switch o.f.opt.MetaFormat {
 	case "simplejson":
-		metaInfo, err := unmarshalSimpleJSON(ctx, metaObject, metadata, true)
-		if err != nil {
+		metaInfo, madeByChunker, err := unmarshalSimpleJSON(ctx, metaObject, metadata)
+		if o.unsure {
+			o.unsure = false
+			if !madeByChunker {
+				// this is not metadata but a foreign object
+				o.chunks = nil  // make isComposite return false
+				o.isFull = true // cache results
+				return nil
+			}
+		}
+		switch err {
+		case nil:
+			// fall thru
+		case ErrMetaTooBig, ErrMetaUnknown:
+			return err // return these errors unwrapped for unit tests
+		default:
 			return errors.Wrap(err, "invalid metadata")
 		}
 		if o.size != metaInfo.Size() || len(o.chunks) != metaInfo.nChunks {
@@ -923,7 +970,27 @@ func (o *Object) readMetadata(ctx context.Context) error {
 }
 
 // put implements Put, PutStream, PutUnchecked, Update
-func (f *Fs) put(ctx context.Context, in io.Reader, src fs.ObjectInfo, remote string, options []fs.OpenOption, basePut putFn) (obj fs.Object, err error) {
+func (f *Fs) put(
+	ctx context.Context, in io.Reader, src fs.ObjectInfo, remote string, options []fs.OpenOption,
+	basePut putFn, action string, target fs.Object) (obj fs.Object, err error) {
+
+	if err := f.forbidChunk(src, remote); err != nil {
+		return nil, errors.Wrap(err, action+" refused")
+	}
+	if target == nil {
+		// Get target object with a quick directory scan
+		if obj, err := f.scanObject(ctx, remote, true); err == nil {
+			target = obj
+		}
+	}
+	if target != nil {
+		obj := target.(*Object)
+		if err := obj.readMetadata(ctx); err == ErrMetaUnknown {
+			// refuse to update a file of unsupported format
+			return nil, errors.Wrap(err, "refusing to "+action)
+		}
+	}
+
 	c := f.newChunkingReader(src)
 	wrapIn := c.wrapStream(ctx, in, src)
 
@@ -1013,8 +1080,8 @@ func (f *Fs) put(ctx context.Context, in io.Reader, src fs.ObjectInfo, remote st
 	// Check for input that looks like valid metadata
 	needMeta := len(c.chunks) > 1
 	if c.readCount <= maxMetadataSize && len(c.chunks) == 1 {
-		_, err := unmarshalSimpleJSON(ctx, c.chunks[0], c.smallHead, false)
-		needMeta = err == nil
+		_, madeByChunker, _ := unmarshalSimpleJSON(ctx, c.chunks[0], c.smallHead)
+		needMeta = madeByChunker
 	}
 
 	// Finalize small object as non-chunked.
@@ -1273,29 +1340,16 @@ func (f *Fs) removeOldChunks(ctx context.Context, remote string) {
 // will return the object and the error, otherwise will return
 // nil and the error
 func (f *Fs) Put(ctx context.Context, in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) (fs.Object, error) {
-	if err := f.forbidChunk(src, src.Remote()); err != nil {
-		return nil, errors.Wrap(err, "refusing to put")
-	}
-	return f.put(ctx, in, src, src.Remote(), options, f.base.Put)
+	return f.put(ctx, in, src, src.Remote(), options, f.base.Put, "put", nil)
 }
 
 // PutStream uploads to the remote path with the modTime given of indeterminate size
 func (f *Fs) PutStream(ctx context.Context, in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) (fs.Object, error) {
-	if err := f.forbidChunk(src, src.Remote()); err != nil {
-		return nil, errors.Wrap(err, "refusing to upload")
-	}
-	return f.put(ctx, in, src, src.Remote(), options, f.base.Features().PutStream)
+	return f.put(ctx, in, src, src.Remote(), options, f.base.Features().PutStream, "upload", nil)
 }
 
 // Update in to the object with the modTime given of the given size
 func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) error {
-	if err := o.f.forbidChunk(o, o.Remote()); err != nil {
-		return errors.Wrap(err, "update refused")
-	}
-	if err := o.readMetadata(ctx); err != nil {
-		// refuse to update a file of unsupported format
-		return errors.Wrap(err, "refusing to update")
-	}
 	basePut := o.f.base.Put
 	if src.Size() < 0 {
 		basePut = o.f.base.Features().PutStream
@@ -1303,7 +1357,7 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 			return errors.New("wrapped file system does not support streaming uploads")
 		}
 	}
-	oNew, err := o.f.put(ctx, in, src, o.Remote(), options, basePut)
+	oNew, err := o.f.put(ctx, in, src, o.Remote(), options, basePut, "update", o)
 	if err == nil {
 		*o = *oNew.(*Object)
 	}
@@ -1417,7 +1471,7 @@ func (o *Object) Remove(ctx context.Context) (err error) {
 		// to corrupt file in hard mode. Hence, refuse to Remove, too.
 		return errors.Wrap(err, "refuse to corrupt")
 	}
-	if err := o.readMetadata(ctx); err != nil {
+	if err := o.readMetadata(ctx); err == ErrMetaUnknown {
 		// Proceed but warn user that unexpected things can happen.
 		fs.Errorf(o, "Removing a file with unsupported metadata: %v", err)
 	}
@@ -1445,6 +1499,11 @@ func (f *Fs) copyOrMove(ctx context.Context, o *Object, remote string, do copyMo
 	if err := f.forbidChunk(o, remote); err != nil {
 		return nil, errors.Wrapf(err, "can't %s", opName)
 	}
+	if err := o.readMetadata(ctx); err != nil {
+		// Refuse to copy/move composite files with invalid or future
+		// metadata format which might involve unsupported chunk types.
+		return nil, errors.Wrapf(err, "can't %s this file", opName)
+	}
 	if !o.isComposite() {
 		fs.Debugf(o, "%s non-chunked object...", opName)
 		oResult, err := do(ctx, o.mainChunk(), remote) // chain operation to a single wrapped chunk
@@ -1453,11 +1512,6 @@ func (f *Fs) copyOrMove(ctx context.Context, o *Object, remote string, do copyMo
 		}
 		return f.newObject("", oResult, nil), nil
 	}
-	if err := o.readMetadata(ctx); err != nil {
-		// Refuse to copy/move composite files with invalid or future
-		// metadata format which might involve unsupported chunk types.
-		return nil, errors.Wrapf(err, "can't %s this file", opName)
-	}
 
 	fs.Debugf(o, "%s %d data chunks...", opName, len(o.chunks))
 	mainRemote := o.remote
@@ -1548,6 +1602,10 @@ func (f *Fs) okForServerSide(ctx context.Context, src fs.Object, opName string)
 		return
 	}
 
+	if obj.unsure {
+		// ensure object is composite if need to re-read metadata
+		_ = obj.readMetadata(ctx)
+	}
 	requireMetaHash := obj.isComposite() && f.opt.MetaFormat == "simplejson"
 	if !requireMetaHash && !f.hashAll {
 		ok = true // hash is not required for metadata
@@ -1741,6 +1799,7 @@ type Object struct {
 	chunks []fs.Object // active data chunks if file is composite, or wrapped file as a single chunk if meta format is 'none'
 	size   int64       // cached total size of chunks in a composite file or -1 for non-chunked files
 	isFull bool        // true if metadata has been read
+	unsure bool        // true if need to read metadata to detect object type
 	md5    string
 	sha1   string
 	f      *Fs
@@ -1891,15 +1950,16 @@ func (o *Object) SetModTime(ctx context.Context, mtime time.Time) error {
 // on the level of wrapped remote but chunker is unaware of that.
 //
 func (o *Object) Hash(ctx context.Context, hashType hash.Type) (string, error) {
+	if err := o.readMetadata(ctx); err != nil {
+		return "", err // valid metadata is required to get hash, abort
+	}
 	if !o.isComposite() {
 		// First, chain to the wrapped non-chunked file if possible.
 		if value, err := o.mainChunk().Hash(ctx, hashType); err == nil && value != "" {
 			return value, nil
 		}
 	}
-	if err := o.readMetadata(ctx); err != nil {
-		return "", err // valid metadata is required to get hash, abort
-	}
+
 	// Try hash from metadata if the file is composite or if wrapped remote fails.
 	switch hashType {
 	case hash.MD5:
@@ -1924,13 +1984,13 @@ func (o *Object) UnWrap() fs.Object {
 
 // Open opens the file for read.  Call Close() on the returned io.ReadCloser
 func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (rc io.ReadCloser, err error) {
-	if !o.isComposite() {
-		return o.mainChunk().Open(ctx, options...) // chain to wrapped non-chunked file
-	}
 	if err := o.readMetadata(ctx); err != nil {
 		// refuse to open unsupported format
 		return nil, errors.Wrap(err, "can't open")
 	}
+	if !o.isComposite() {
+		return o.mainChunk().Open(ctx, options...) // chain to wrapped non-chunked file
+	}
 
 	var openOptions []fs.OpenOption
 	var offset, limit int64 = 0, -1
@@ -2203,57 +2263,57 @@ func marshalSimpleJSON(ctx context.Context, size int64, nChunks int, md5, sha1 s
 // handled by current implementation.
 // The version check below will then explicitly ask user to upgrade rclone.
 //
-func unmarshalSimpleJSON(ctx context.Context, metaObject fs.Object, data []byte, strictChecks bool) (info *ObjectInfo, err error) {
+func unmarshalSimpleJSON(ctx context.Context, metaObject fs.Object, data []byte) (info *ObjectInfo, madeByChunker bool, err error) {
 	// Be strict about JSON format
 	// to reduce possibility that a random small file resembles metadata.
 	if data != nil && len(data) > maxMetadataSize {
-		return nil, errors.New("too big")
+		return nil, false, ErrMetaTooBig
 	}
 	if data == nil || len(data) < 2 || data[0] != '{' || data[len(data)-1] != '}' {
-		return nil, errors.New("invalid json")
+		return nil, false, errors.New("invalid json")
 	}
 	var metadata metaSimpleJSON
 	err = json.Unmarshal(data, &metadata)
 	if err != nil {
-		return nil, err
+		return nil, false, err
 	}
 	// Basic fields are strictly required
 	// to reduce possibility that a random small file resembles metadata.
 	if metadata.Version == nil || metadata.Size == nil || metadata.ChunkNum == nil {
-		return nil, errors.New("missing required field")
+		return nil, false, errors.New("missing required field")
 	}
 	// Perform strict checks, avoid corruption of future metadata formats.
 	if *metadata.Version < 1 {
-		return nil, errors.New("wrong version")
+		return nil, false, errors.New("wrong version")
 	}
 	if *metadata.Size < 0 {
-		return nil, errors.New("negative file size")
+		return nil, false, errors.New("negative file size")
 	}
 	if *metadata.ChunkNum < 0 {
-		return nil, errors.New("negative number of chunks")
+		return nil, false, errors.New("negative number of chunks")
 	}
 	if *metadata.ChunkNum > maxSafeChunkNumber {
-		return nil, ErrChunkOverflow
+		return nil, true, ErrChunkOverflow // produced by incompatible version of rclone
 	}
 	if metadata.MD5 != "" {
 		_, err = hex.DecodeString(metadata.MD5)
 		if len(metadata.MD5) != 32 || err != nil {
-			return nil, errors.New("wrong md5 hash")
+			return nil, false, errors.New("wrong md5 hash")
 		}
 	}
 	if metadata.SHA1 != "" {
 		_, err = hex.DecodeString(metadata.SHA1)
 		if len(metadata.SHA1) != 40 || err != nil {
-			return nil, errors.New("wrong sha1 hash")
+			return nil, false, errors.New("wrong sha1 hash")
 		}
 	}
 	// ChunkNum is allowed to be 0 in future versions
 	if *metadata.ChunkNum < 1 && *metadata.Version <= metadataVersion {
-		return nil, errors.New("wrong number of chunks")
+		return nil, false, errors.New("wrong number of chunks")
 	}
 	// Non-strict mode also accepts future metadata versions
-	if *metadata.Version > metadataVersion && strictChecks {
-		return nil, fmt.Errorf("version %d is not supported, please upgrade rclone", metadata.Version)
+	if *metadata.Version > metadataVersion {
+		return nil, true, ErrMetaUnknown // produced by incompatible version of rclone
 	}
 
 	var nilFs *Fs // nil object triggers appropriate type method
@@ -2261,7 +2321,7 @@ func unmarshalSimpleJSON(ctx context.Context, metaObject fs.Object, data []byte,
 	info.nChunks = *metadata.ChunkNum
 	info.md5 = metadata.MD5
 	info.sha1 = metadata.SHA1
-	return info, nil
+	return info, true, nil
 }
 
 func silentlyRemove(ctx context.Context, o fs.Object) {