{"record":{"id":"2e5efa0e733a4e2d","repo":"juicedata/juicefs","slug":"failed-to-read-segment-s-length-v","errorCode":null,"errorMessage":"failed to read segment %s length: %v","messagePattern":"failed to read segment (.+?) length: (.+?)","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"pkg/meta/backup.go","lineNumber":359,"sourceCode":"\n\tif n, err := w.Write(data); err != nil || n != len(data) {\n\t\treturn 0, fmt.Errorf(\"failed to write segment data %s: err %w, write len %d, expect len %d\", s, err, n, len(data))\n\t}\n\n\treturn binary.Size(s.typ) + binary.Size(s.len) + len(data), nil\n}\n\nfunc (s *BakSegment) Unmarshal(r io.Reader) error {\n\tif err := binary.Read(r, binary.BigEndian, &s.typ); err != nil {\n\t\treturn fmt.Errorf(\"failed to read segment type: %v\", err)\n\t}\n\n\tif s.typ == BakEOS {\n\t\treturn errBakEOF\n\t}\n\n\tif err := binary.Read(r, binary.BigEndian, &s.len); err != nil {\n\t\treturn fmt.Errorf(\"failed to read segment %s length: %v\", s, err)\n\t}\n\tdata := make([]byte, s.len)\n\tn, err := r.Read(data)\n\tif err != nil && n != int(s.len) {\n\t\treturn fmt.Errorf(\"failed to read segment value: err %v, read len %d, expect len %d\", err, n, s.len)\n\t}\n\n\tmsg, err := getMessageFromType(int(s.typ))\n\tif err != nil {\n\t\treturn fmt.Errorf(\"failed to create message by type %d: %w\", s.typ, err)\n\t}\n\tif err = proto.Unmarshal(data, msg); err != nil {\n\t\treturn fmt.Errorf(\"failed to unmarshal segment msg %d: %w\", s.typ, err)\n\t}\n\ts.val = msg\n\treturn nil\n}\n","sourceCodeStart":341,"sourceCodeEnd":377,"githubUrl":"https://github.com/juicedata/juicefs/blob/c9a67b23e8e08ec23ec331aa6f1675e2319e921c/pkg/meta/backup.go#L341-L377","documentation":"After reading the segment type, BakSegment.Unmarshal reads the 8-byte big-endian segment length with binary.Read. This error is thrown when that read fails, typically io.EOF/io.ErrUnexpectedEOF — the stream ended between the type byte and the complete length field. It signals a truncated or corrupt backup stream, since a valid segment always carries a full 8-byte length after its type.","triggerScenarios":"Calling ReadFooter on a stream truncated right after a segment type byte; a corrupted backup file with a partial final segment; an underlying read I/O error (device error, closed handle).","commonSituations":"Backup interrupted mid-write leaving a partial trailing segment; copying/truncating a backup file; reading a backup from a flaky network mount.","solutions":["Regenerate the metadata backup — the file is truncated and cannot be safely parsed","Check for free-space or write errors that caused the original backup to be cut short","Verify the backup file's integrity (size/checksum) against its source","Ensure the storage holding the backup is healthy before re-reading"],"exampleFix":null,"handlingStrategy":"validation","validationCode":"fi, err := os.Stat(backupPath)\nif err != nil || fi.Size() < minFooterHeaderBytes { return fmt.Errorf(\"backup too small/truncated: %s\", backupPath) }","typeGuard":null,"tryCatchPattern":"if err := seg.Unmarshal(r); err != nil {\n    if strings.Contains(err.Error(), \"failed to read segment\") || errors.Is(err, io.ErrUnexpectedEOF) {\n        return fmt.Errorf(\"corrupt/truncated backup segment header: %w\", err)\n    }\n    return err\n}","preventionTips":["Regenerate backups that were written by an interrupted process","Transfer backup files with checksum verification","Keep sufficient free space so backup writes complete"],"tags":["io","read-failed","eof","truncated-data","backup"],"backgroundTag":"file-read-failed","analyzedSha":"c9a67b23e8e08ec23ec331aa6f1675e2319e921c","analyzedAt":"2026-09-06T17:55:48.476Z","contentChangedAt":"2026-09-06T17:55:48.476Z","schemaVersion":2},"datasetVersion":"2026-09-14T00:17:10.932Z"}