// readFileMetaData reads thrift.FileMetaData object from r that provides
// read interface to data in parquet format.
//
// Parquet format is described here:
// https://github.com/apache/parquet-format/blob/master/README.md
// Note that the File Metadata is at the END of the file.
//
func readFileMetaData(r io.ReadSeeker) (*thrift.FileMetaData, error) {
_, err := r.Seek(0, os.SEEK_SET)
if err != nil {
return nil, fmt.Errorf("read metadata: error seeking to header: %s", err)
}
buf := make([]byte, magicSize, magicSize)
// read and validate header
_, err = io.ReadFull(r, buf)
if err != nil {
return nil, fmt.Errorf("read metadata: error reading header: %s", err)
}
if !bytes.Equal(buf, parquetMagic) {
return nil, ErrNotParquetFile
}
// read and validate footer
_, err = r.Seek(-magicSize, os.SEEK_END)
if err != nil {
return nil, fmt.Errorf("read metadata: error seeking to footer: %s", err)
}
_, err = io.ReadFull(r, buf)
if err != nil {
return nil, fmt.Errorf("read metadata: error reading footer: %s", err)
}
if !bytes.Equal(buf, parquetMagic) {
return nil, ErrNotParquetFile
}
_, err = r.Seek(-footerSize, os.SEEK_END)
if err != nil {
return nil, fmt.Errorf("read metadata: error seeking to footer length: %s", err)
}
var footerLength int32
err = binary.Read(r, binary.LittleEndian, &footerLength)
if err != nil {
return nil, fmt.Errorf("read metadata: error reading footer length: %s", err)
}
if footerLength <= 0 {
return nil, fmt.Errorf("read metadata: invalid footer length %d", footerLength)
}
// read file metadata
_, err = r.Seek(-footerSize-int64(footerLength), os.SEEK_END)
if err != nil {
return nil, fmt.Errorf("read metadata: error seeking to file: %s", err)
}
var meta thrift.FileMetaData
err = meta.Read(io.LimitReader(r, int64(footerLength)))
if err != nil {
return nil, fmt.Errorf("read metadata: error reading file: %s", err)
}
return &meta, nil
}
