Refactor s3select to support parquet. (#7023)

Also handle pretty formatted JSON documents.

pkg/s3select/parquet/args.go

@@ -0,0 +1,42 @@
+/*
+ * 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 parquet
+
+import "encoding/xml"
+
+// ReaderArgs - represents elements inside <InputSerialization><Parquet/> in request XML.
+type ReaderArgs struct {
+	unmarshaled bool
+}
+
+// IsEmpty - returns whether reader args is empty or not.
+func (args *ReaderArgs) IsEmpty() bool {
+	return !args.unmarshaled
+}
+
+// UnmarshalXML - decodes XML data.
+func (args *ReaderArgs) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
+	// Make subtype to avoid recursive UnmarshalXML().
+	type subReaderArgs ReaderArgs
+	parsedArgs := subReaderArgs{}
+	if err := d.DecodeElement(&parsedArgs, &start); err != nil {
+		return err
+	}
+
+	args.unmarshaled = true
+	return nil
+}