Azure gateway complete multipart ETag (#7500)

Compute md5 for azure multipart upload that matches s3 behavior
Reuse complete multipart md5 function in azure gateway

cmd/gateway-common.go

@@ -17,6 +17,7 @@
 package cmd
 
 import (
+	"context"
 	"net/http"
 	"os"
 	"strings"
@@ -349,6 +350,11 @@ func ErrorRespToObjectError(err error, params ...string) error {
 	return err
 }
 
+// ComputeCompleteMultipartMD5 calculates MD5 ETag for complete multipart responses
+func ComputeCompleteMultipartMD5(parts []CompletePart) (string, error) {
+	return getCompleteMultipartMD5(context.Background(), parts)
+}
+
 // parse gateway sse env variable
 func parseGatewaySSE(s string) (gatewaySSE, error) {
 	l := strings.Split(s, ";")

cmd/gateway/azure/gateway-azure.go

@@ -37,6 +37,7 @@ import (
 	humanize "github.com/dustin/go-humanize"
 	"github.com/minio/cli"
 	miniogopolicy "github.com/minio/minio-go/pkg/policy"
+	"github.com/minio/minio/cmd"
 	"github.com/minio/minio/cmd/logger"
 	"github.com/minio/minio/pkg/auth"
 	"github.com/minio/minio/pkg/policy"
@@ -1202,11 +1203,14 @@ func (a *azureObjects) CompleteMultipartUpload(ctx context.Context, bucket, obje
 	if err != nil {
 		return objInfo, azureToObjectError(err, bucket, object)
 	}
-	if len(metadata.Metadata) > 0 {
 	objBlob.Metadata, objBlob.Properties, err = s3MetaToAzureProperties(ctx, metadata.Metadata)
 	if err != nil {
 		return objInfo, azureToObjectError(err, bucket, object)
 	}
+	objBlob.Metadata["md5sum"], err = cmd.ComputeCompleteMultipartMD5(uploadedParts)
+	if err != nil {
+		return objInfo, err
+	}
 	err = objBlob.SetProperties(nil)
 	if err != nil {
 		return objInfo, azureToObjectError(err, bucket, object)
@@ -1215,7 +1219,6 @@ func (a *azureObjects) CompleteMultipartUpload(ctx context.Context, bucket, obje
 	if err != nil {
 		return objInfo, azureToObjectError(err, bucket, object)
 	}
-	}
 	var partNumberMarker int
 	for {
 		lpi, err := a.ListObjectParts(ctx, bucket, object, uploadID, partNumberMarker, maxPartsCount, minio.ObjectOptions{})