frostfs-s3-gw/pkg/s3select/json/reader.go

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/*
* MinIO Cloud Storage, (C) 2019 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 json
import (
"errors"
"io"
"sync"
"github.com/minio/minio/pkg/s3select/sql"
"github.com/bcicen/jstream"
)
// Reader - JSON record reader for S3Select.
type Reader struct {
args *ReaderArgs
decoder *jstream.Decoder
valueCh chan *jstream.MetaValue
readCloser io.ReadCloser
}
// Read - reads single record.
func (r *Reader) Read(dst sql.Record) (sql.Record, error) {
v, ok := <-r.valueCh
if !ok {
if err := r.decoder.Err(); err != nil {
return nil, errJSONParsingError(err)
}
return nil, io.EOF
}
var kvs jstream.KVS
if v.ValueType == jstream.Object {
// This is a JSON object type (that preserves key
// order)
kvs = v.Value.(jstream.KVS)
} else {
// To be AWS S3 compatible Select for JSON needs to
// output non-object JSON as single column value
// i.e. a map with `_1` as key and value as the
// non-object.
kvs = jstream.KVS{jstream.KV{Key: "_1", Value: v.Value}}
}
dstRec, ok := dst.(*Record)
if !ok {
dstRec = &Record{}
}
dstRec.KVS = kvs
dstRec.SelectFormat = sql.SelectFmtJSON
return dstRec, nil
}
// Close - closes underlying reader.
func (r *Reader) Close() error {
// Close the input.
err := r.readCloser.Close()
for range r.valueCh {
// Drain values so we don't leak a goroutine.
// Since we have closed the input, it should fail rather quickly.
}
return err
}
// NewReader - creates new JSON reader using readCloser.
func NewReader(readCloser io.ReadCloser, args *ReaderArgs) *Reader {
readCloser = &syncReadCloser{rc: readCloser}
d := jstream.NewDecoder(readCloser, 0).ObjectAsKVS()
return &Reader{
args: args,
decoder: d,
valueCh: d.Stream(),
readCloser: readCloser,
}
}
// syncReadCloser will wrap a readcloser and make it safe to call Close
// while reads are running.
// All read errors are also postponed until Close is called and
// io.EOF is returned instead.
type syncReadCloser struct {
rc io.ReadCloser
errMu sync.Mutex
err error
}
func (pr *syncReadCloser) Read(p []byte) (n int, err error) {
// This ensures that Close will block until Read has completed.
// This allows another goroutine to close the reader.
pr.errMu.Lock()
defer pr.errMu.Unlock()
if pr.err != nil {
return 0, io.EOF
}
n, pr.err = pr.rc.Read(p)
if pr.err != nil {
// Translate any error into io.EOF, so we don't crash:
// https://github.com/bcicen/jstream/blob/master/scanner.go#L48
return n, io.EOF
}
return n, nil
}
var errClosed = errors.New("read after close")
func (pr *syncReadCloser) Close() error {
pr.errMu.Lock()
defer pr.errMu.Unlock()
if pr.err == errClosed {
return nil
}
if pr.err != nil {
return pr.err
}
pr.err = errClosed
return pr.rc.Close()
}