Avoid using fastjson parser pool, move back to jsoniter (#8190)

It looks like from implementation point of view fastjson
parser pool doesn't behave the same way as expected
when dealing many `xl.json` from multiple disks.

The fastjson parser pool usage ends up returning incorrect
xl.json entries for checksums, with references pointing
to older entries. This led to the subtle bug where checksum
info is duplicated from a previous xl.json read of a different
file from different disk.

cmd/fs-v1.go

@@ -30,6 +30,7 @@ import (
 	"sync/atomic"
 	"time"
 
+	jsoniter "github.com/json-iterator/go"
 	"github.com/minio/minio-go/v6/pkg/s3utils"
 	"github.com/minio/minio/cmd/logger"
 	"github.com/minio/minio/pkg/lifecycle"
@@ -38,7 +39,6 @@ import (
 	"github.com/minio/minio/pkg/mimedb"
 	"github.com/minio/minio/pkg/mountinfo"
 	"github.com/minio/minio/pkg/policy"
-	"github.com/valyala/fastjson"
 )
 
 // Default etag is used for pre-existing objects.
@@ -1093,22 +1093,19 @@ func (fs *FSObjects) getObjectETag(ctx context.Context, bucket, entry string, lo
 		return "", toObjectErr(err, bucket, entry)
 	}
 
-	parser := fsParserPool.Get()
-	defer fsParserPool.Put(parser)
-
-	var v *fastjson.Value
-	v, err = parser.ParseBytes(fsMetaBuf)
-	if err != nil {
-		return "", toObjectErr(err, bucket, entry)
+	var fsMeta fsMetaV1
+	var json = jsoniter.ConfigCompatibleWithStandardLibrary
+	if err = json.Unmarshal(fsMetaBuf, &fsMeta); err != nil {
+		return "", err
 	}
 
 	// Check if FS metadata is valid, if not return error.
-	if !isFSMetaValid(parseFSVersion(v)) {
+	if !isFSMetaValid(fsMeta.Version) {
 		logger.LogIf(ctx, errCorruptedFormat)
 		return "", toObjectErr(errCorruptedFormat, bucket, entry)
 	}
 
-	return extractETag(parseFSMetaMap(v)), nil
+	return extractETag(fsMeta.Meta), nil
 }
 
 // ListObjects - list all objects at prefix upto maxKeys., optionally delimited by '/'. Maintains the list pool