Add a generic Walk()'er to list a bucket, optinally prefix (#9026)

This generic Walk() is used by likes of Lifecyle, or
KMS to rotate keys or any other functionality which
relies on this functionality.

cmd/storage-datatypes.go

@@ -19,6 +19,8 @@ package cmd
 import (
 	"os"
 	"time"
+
+	xhttp "github.com/minio/minio/cmd/http"
 )
 
 // VolInfo - represents volume stat information.
@@ -62,3 +64,44 @@ type FileInfo struct {
 
 	Quorum int
 }
+
+// ToObjectInfo converts FileInfo into objectInfo.
+func (entry FileInfo) ToObjectInfo() ObjectInfo {
+	var objInfo ObjectInfo
+	if HasSuffix(entry.Name, SlashSeparator) {
+		objInfo = ObjectInfo{
+			Bucket: entry.Volume,
+			Name:   entry.Name,
+			IsDir:  true,
+		}
+	} else {
+		objInfo = ObjectInfo{
+			IsDir:           false,
+			Bucket:          entry.Volume,
+			Name:            entry.Name,
+			ModTime:         entry.ModTime,
+			Size:            entry.Size,
+			ContentType:     entry.Metadata["content-type"],
+			ContentEncoding: entry.Metadata["content-encoding"],
+		}
+
+		// Extract etag from metadata.
+		objInfo.ETag = extractETag(entry.Metadata)
+
+		// All the parts per object.
+		objInfo.Parts = entry.Parts
+
+		// etag/md5Sum has already been extracted. We need to
+		// remove to avoid it from appearing as part of
+		// response headers. e.g, X-Minio-* or X-Amz-*.
+		objInfo.UserDefined = cleanMetadata(entry.Metadata)
+
+		// Update storage class
+		if sc, ok := entry.Metadata[xhttp.AmzStorageClass]; ok {
+			objInfo.StorageClass = sc
+		} else {
+			objInfo.StorageClass = globalMinioDefaultStorageClass
+		}
+	}
+	return objInfo
+}