[#233] services/object: Implement new Get algorithm

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/services/object/get/container.go

@@ -0,0 +1,54 @@
+package getsvc
+
+import (
+	"context"
+
+	"go.uber.org/zap"
+)
+
+func (exec *execCtx) executeOnContainer() {
+	if exec.isLocal() {
+		exec.log.Debug("return result directly")
+		return
+	}
+
+	exec.log.Debug("trying to execute in container...")
+
+	traverser, ok := exec.generateTraverser(exec.address())
+	if !ok {
+		return
+	}
+
+	ctx, cancel := context.WithCancel(exec.context())
+	defer cancel()
+
+	exec.status = statusUndefined
+
+loop:
+	for {
+		addrs := traverser.Next()
+		if len(addrs) == 0 {
+			exec.log.Debug("no more nodes, abort placement iteration")
+			break
+		}
+
+		for i := range addrs {
+			select {
+			case <-ctx.Done():
+				exec.log.Debug("interrupt placement iteration by context",
+					zap.String("error", ctx.Err().Error()),
+				)
+				break loop
+			default:
+			}
+
+			// TODO: consider parallel execution
+			// TODO: consider optimization: if status == SPLIT we can continue until
+			//  we reach the best result - split info with linking object ID.
+			if exec.processNode(ctx, addrs[i]) {
+				exec.log.Debug("completing the operation")
+				break loop
+			}
+		}
+	}
+}