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reader.go
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/
reader.go
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/*
* Minio Cloud Storage, (C) 2018 Minio, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package parquet
import (
"encoding/binary"
"encoding/json"
"io"
"git.apache.org/thrift.git/lib/go/thrift"
"github.com/minio/minio-go/v7/pkg/set"
"github.com/minio/minio/pkg/s3select/internal/parquet-go/gen-go/parquet"
)
// GetReaderFunc - function type returning io.ReadCloser for requested offset/length.
type GetReaderFunc func(offset, length int64) (io.ReadCloser, error)
func footerSize(getReaderFunc GetReaderFunc) (size int64, err error) {
rc, err := getReaderFunc(-8, 4)
if err != nil {
return 0, err
}
defer rc.Close()
buf := make([]byte, 4)
if _, err = io.ReadFull(rc, buf); err != nil {
return 0, err
}
size = int64(binary.LittleEndian.Uint32(buf))
return size, nil
}
func fileMetadata(getReaderFunc GetReaderFunc) (*parquet.FileMetaData, error) {
size, err := footerSize(getReaderFunc)
if err != nil {
return nil, err
}
rc, err := getReaderFunc(-(8 + size), size)
if err != nil {
return nil, err
}
defer rc.Close()
fileMeta := parquet.NewFileMetaData()
pf := thrift.NewTCompactProtocolFactory()
protocol := pf.GetProtocol(thrift.NewStreamTransportR(rc))
err = fileMeta.Read(protocol)
if err != nil {
return nil, err
}
return fileMeta, nil
}
// Value - denotes column value
type Value struct {
Value interface{}
Type parquet.Type
}
// MarshalJSON - encodes to JSON data
func (value Value) MarshalJSON() (data []byte, err error) {
return json.Marshal(value.Value)
}
// Reader - denotes parquet file.
type Reader struct {
getReaderFunc GetReaderFunc
schemaElements []*parquet.SchemaElement
rowGroups []*parquet.RowGroup
rowGroupIndex int
nameList []string
columnNames set.StringSet
columns map[string]*column
rowIndex int64
}
// NewReader - creates new parquet reader. Reader calls getReaderFunc to get required data range for given columnNames. If columnNames is empty, all columns are used.
func NewReader(getReaderFunc GetReaderFunc, columnNames set.StringSet) (*Reader, error) {
fileMeta, err := fileMetadata(getReaderFunc)
if err != nil {
return nil, err
}
nameList := []string{}
schemaElements := fileMeta.GetSchema()
for _, element := range schemaElements {
nameList = append(nameList, element.Name)
}
return &Reader{
getReaderFunc: getReaderFunc,
rowGroups: fileMeta.GetRowGroups(),
schemaElements: schemaElements,
nameList: nameList,
columnNames: columnNames,
}, nil
}
// Read - reads single record.
func (reader *Reader) Read() (record *Record, err error) {
if reader.rowGroupIndex >= len(reader.rowGroups) {
return nil, io.EOF
}
if reader.columns == nil {
reader.columns, err = getColumns(
reader.rowGroups[reader.rowGroupIndex],
reader.columnNames,
reader.schemaElements,
reader.getReaderFunc,
)
if err != nil {
return nil, err
}
reader.rowIndex = 0
}
if reader.rowIndex >= reader.rowGroups[reader.rowGroupIndex].GetNumRows() {
reader.rowGroupIndex++
reader.Close()
return reader.Read()
}
record = newRecord(reader.nameList)
for name := range reader.columns {
value, valueType := reader.columns[name].read()
record.set(name, Value{value, valueType})
}
reader.rowIndex++
return record, nil
}
// Close - closes underneath readers.
func (reader *Reader) Close() (err error) {
for _, column := range reader.columns {
column.close()
}
reader.columns = nil
reader.rowIndex = 0
return nil
}