Add admin file inspector (#12635)

Download files from *any* bucket/path as an encrypted zip file.

The key is included in the response but can be separated so zip 
and the key doesn't have to be sent on the same channel.

Requires https://github.com/minio/pkg/pull/6

cmd/erasure-server-pool.go

@@ -147,6 +147,39 @@ func (z *erasureServerPools) GetDisksID(ids ...string) []StorageAPI {
 	return res
 }
 
+// GetRawData will return all files with a given raw path to the callback.
+// Errors are ignored, only errors from the callback are returned.
+// For now only direct file paths are supported.
+func (z *erasureServerPools) GetRawData(ctx context.Context, volume, file string, fn func(r io.Reader, host string, disk string, filename string, size int64, modtime time.Time) error) error {
+	for _, s := range z.serverPools {
+		for _, disks := range s.erasureDisks {
+			for i, disk := range disks {
+				if disk == OfflineDisk {
+					continue
+				}
+				si, err := disk.StatInfoFile(ctx, volume, file)
+				if err != nil {
+					continue
+				}
+				r, err := disk.ReadFileStream(ctx, volume, file, 0, si.Size)
+				if err != nil {
+					continue
+				}
+				defer r.Close()
+				did, err := disk.GetDiskID()
+				if err != nil {
+					did = fmt.Sprintf("disk-%d", i)
+				}
+				err = fn(r, disk.Hostname(), did, pathJoin(volume, file), si.Size, si.ModTime)
+				if err != nil {
+					return err
+				}
+			}
+		}
+	}
+	return nil
+}
+
 func (z *erasureServerPools) SetDriveCounts() []int {
 	setDriveCounts := make([]int, len(z.serverPools))
 	for i := range z.serverPools {