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/storage-rest-server.go

@@ -1038,6 +1038,23 @@ func logFatalErrs(err error, endpoint Endpoint, exit bool) {
 	}
 }
 
+// StatInfoFile returns file stat info.
+func (s *storageRESTServer) StatInfoFile(w http.ResponseWriter, r *http.Request) {
+	if !s.IsValid(w, r) {
+		return
+	}
+	vars := mux.Vars(r)
+	volume := vars[storageRESTVolume]
+	filePath := vars[storageRESTFilePath]
+	done := keepHTTPResponseAlive(w)
+	si, err := s.storage.StatInfoFile(r.Context(), volume, filePath)
+	done(err)
+	if err != nil {
+		return
+	}
+	msgp.Encode(w, &si)
+}
+
 // registerStorageRPCRouter - register storage rpc router.
 func registerStorageRESTHandlers(router *mux.Router, endpointServerPools EndpointServerPools) {
 	storageDisks := make([][]*xlStorage, len(endpointServerPools))
@@ -1129,6 +1146,8 @@ func registerStorageRESTHandlers(router *mux.Router, endpointServerPools Endpoin
 				Queries(restQueries(storageRESTVolume, storageRESTFilePath)...)
 			subrouter.Methods(http.MethodPost).Path(storageRESTVersionPrefix + storageRESTMethodWalkDir).HandlerFunc(httpTraceHdrs(server.WalkDirHandler)).
 				Queries(restQueries(storageRESTVolume, storageRESTDirPath, storageRESTRecursive)...)
+			subrouter.Methods(http.MethodPost).Path(storageRESTVersionPrefix + storageRESTMethodStatInfoFile).HandlerFunc(httpTraceHdrs(server.StatInfoFile)).
+				Queries(restQueries(storageRESTVolume, storageRESTFilePath)...)
 		}
 	}
 }