Signature-V4: Include content-length for signature calculation. (#2643)

This is to be compatible with clients which includes content-length for signature calculation
(and hence deviating from AWS Signature-v4 spec)

cmd/utils.go

@@ -21,6 +21,7 @@ import (
 	"encoding/xml"
 	"errors"
 	"io"
+	"net/http"
 	"os"
 	"os/exec"
 	"strings"
@@ -30,6 +31,18 @@ import (
 	"github.com/pkg/profile"
 )
 
+// make a copy of http.Header
+func cloneHeader(h http.Header) http.Header {
+	h2 := make(http.Header, len(h))
+	for k, vv := range h {
+		vv2 := make([]string, len(vv))
+		copy(vv2, vv)
+		h2[k] = vv2
+
+	}
+	return h2
+}
+
 // xmlDecoder provide decoded value in xml.
 func xmlDecoder(body io.Reader, v interface{}, size int64) error {
 	var lbody io.Reader