[#175] adm: pipeline container iteration

Do not accumulate everything in memory.
Also, CLI should be responsive.

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

cmd/frostfs-adm/internal/modules/morph/container.go

@@ -41,28 +41,28 @@ func getContainerContractHash(cmd *cobra.Command, inv *invoker.Invoker, c Client
 	return ch, nil
 }
 
-func getContainersList(inv *invoker.Invoker, ch util.Uint160) ([][]byte, error) {
+func iterateContainerList(inv *invoker.Invoker, ch util.Uint160, f func([]byte) error) error {
 	sid, r, err := unwrap.SessionIterator(inv.Call(ch, "containersOf", ""))
 	if err != nil {
-		return nil, fmt.Errorf("%w: %v", errInvalidContainerResponse, err)
+		return fmt.Errorf("%w: %v", errInvalidContainerResponse, err)
 	}
 	// Nothing bad, except live session on the server, do not report to the user.
 	defer func() { _ = inv.TerminateSession(sid) }()
 
-	var lst [][]byte
-
 	items, err := inv.TraverseIterator(sid, &r, 0)
 	for err == nil && len(items) != 0 {
 		for j := range items {
 			b, err := items[j].TryBytes()
 			if err != nil {
-				return nil, fmt.Errorf("%w: %v", errInvalidContainerResponse, err)
+				return fmt.Errorf("%w: %v", errInvalidContainerResponse, err)
+			}
+			if err := f(b); err != nil {
+				return err
 			}
-			lst = append(lst, b)
 		}
 		items, err = inv.TraverseIterator(sid, &r, 0)
 	}
-	return lst, err
+	return err
 }
 
 func dumpContainers(cmd *cobra.Command, _ []string) error {
@@ -83,56 +83,81 @@ func dumpContainers(cmd *cobra.Command, _ []string) error {
 		return fmt.Errorf("unable to get contaract hash: %w", err)
 	}
 
-	cids, err := getContainersList(inv, ch)
-	if err != nil {
-		return fmt.Errorf("%w: %v", errInvalidContainerResponse, err)
-	}
-
 	isOK, err := getCIDFilterFunc(cmd)
 	if err != nil {
 		return err
 	}
 
-	var containers []*Container
+	f, err := os.OpenFile(filename, os.O_RDWR|os.O_TRUNC|os.O_CREATE, 0o660)
-	bw := io.NewBufBinWriter()
+	if err != nil {
-	for _, id := range cids {
+		return err
-		if !isOK(id) {
-			continue
 	}
+	defer f.Close()
+
+	_, err = f.Write([]byte{'['})
+	if err != nil {
+		return err
+	}
+
+	written := 0
+	enc := json.NewEncoder(f)
+	bw := io.NewBufBinWriter()
+	iterErr := iterateContainerList(inv, ch, func(id []byte) error {
+		if !isOK(id) {
+			return nil
+		}
+
+		cnt, err := dumpSingleContainer(bw, ch, inv, id)
+		if err != nil {
+			return err
+		}
+
+		// Writing directly to the file is ok, because json.Encoder does no internal buffering.
+		if written != 0 {
+			_, err = f.Write([]byte{','})
+			if err != nil {
+				return err
+			}
+		}
+
+		written++
+		return enc.Encode(cnt)
+	})
+	if iterErr != nil {
+		return iterErr
+	}
+
+	_, err = f.Write([]byte{']'})
+	return err
+}
+
+func dumpSingleContainer(bw *io.BufBinWriter, ch util.Uint160, inv *invoker.Invoker, id []byte) (*Container, error) {
 	bw.Reset()
 	emit.AppCall(bw.BinWriter, ch, "get", callflag.All, id)
 	emit.AppCall(bw.BinWriter, ch, "eACL", callflag.All, id)
 	res, err := inv.Run(bw.Bytes())
 	if err != nil {
-			return fmt.Errorf("can't get container info: %w", err)
+		return nil, fmt.Errorf("can't get container info: %w", err)
 	}
 	if len(res.Stack) != 2 {
-			return fmt.Errorf("%w: expected 2 items on stack", errInvalidContainerResponse)
+		return nil, fmt.Errorf("%w: expected 2 items on stack", errInvalidContainerResponse)
 	}
 
 	cnt := new(Container)
 	err = cnt.FromStackItem(res.Stack[0])
 	if err != nil {
-			return fmt.Errorf("%w: %v", errInvalidContainerResponse, err)
+		return nil, fmt.Errorf("%w: %v", errInvalidContainerResponse, err)
 	}
 
 	ea := new(EACL)
 	err = ea.FromStackItem(res.Stack[1])
 	if err != nil {
-			return fmt.Errorf("%w: %v", errInvalidContainerResponse, err)
+		return nil, fmt.Errorf("%w: %v", errInvalidContainerResponse, err)
 	}
 	if len(ea.Value) != 0 {
 		cnt.EACL = ea
 	}
-
+	return cnt, nil
-		containers = append(containers, cnt)
-	}
-
-	out, err := json.Marshal(containers)
-	if err != nil {
-		return err
-	}
-	return os.WriteFile(filename, out, 0o660)
 }
 
 func listContainers(cmd *cobra.Command, _ []string) error {
@@ -148,20 +173,15 @@ func listContainers(cmd *cobra.Command, _ []string) error {
 		return fmt.Errorf("unable to get contaract hash: %w", err)
 	}
 
-	cids, err := getContainersList(inv, ch)
+	return iterateContainerList(inv, ch, func(id []byte) error {
-	if err != nil {
-		return fmt.Errorf("%w: %v", errInvalidContainerResponse, err)
-	}
-
-	for _, id := range cids {
 		var idCnr cid.ID
 		err = idCnr.Decode(id)
 		if err != nil {
 			return fmt.Errorf("unable to decode container id: %w", err)
 		}
 		cmd.Println(idCnr)
-	}
 		return nil
+	})
 }
 
 func restoreContainers(cmd *cobra.Command, _ []string) error {