[#369] Move playback source files

Move git.frostfs.info/TrueCloudLab/frostfs-s3-gw/cmd/frostfs-s3-playback/request package to git.frostfs.info/TrueCloudLab/frostfs-s3-gw/playback.
Move playback.yaml example config to root config folder.

Signed-off-by: Nikita Zinkevich <n.zinkevich@yadro.com>

playback/multipart.go

@@ -1,4 +1,4 @@
-package request
+package playback
 
 import (
 	"context"

playback/request.go

@@ -1,4 +1,4 @@
-package request
+package playback
 
 import (
 	"context"

playback/request_test.go

@@ -1,4 +1,4 @@
-package request
+package playback
 
 import (
 	"strings"

playback/utils/utils.go

@@ -0,0 +1,43 @@
+package utils
+
+import (
+	"bytes"
+	"encoding/base64"
+	"encoding/xml"
+	"errors"
+	"io"
+)
+
+const BodyRecognizeLimit int64 = 128
+
+func DetectXML(reader io.Reader) (bool, []byte, error) {
+	checkBuf := bytes.NewBuffer(nil)
+	token, err := xml.NewDecoder(io.TeeReader(io.LimitReader(reader, BodyRecognizeLimit), checkBuf)).RawToken()
+	if err != nil {
+		var xmlErr *xml.SyntaxError
+		if errors.Is(err, io.EOF) || errors.As(err, &xmlErr) {
+			return false, checkBuf.Bytes(), nil
+		}
+		return false, checkBuf.Bytes(), err
+	}
+
+	switch token.(type) {
+	case xml.StartElement, xml.ProcInst:
+		return true, checkBuf.Bytes(), nil
+	}
+	return false, checkBuf.Bytes(), nil
+}
+
+func ChooseWriter(isXML bool, body *bytes.Buffer) io.Writer {
+	if !isXML {
+		return base64.NewEncoder(base64.StdEncoding, body)
+	}
+	return body
+}
+
+func ChooseReader(isXml bool, bodyReader io.Reader) io.Reader {
+	if !isXml {
+		return base64.NewDecoder(base64.StdEncoding, bodyReader)
+	}
+	return bodyReader
+}