[#839] service/object: Do not use request forwarding when assembling object

Forwarding mechanism resends original request. During split object chain traversal,
storage node performs multiple `object.Head` requests on each child. If request
forwarding happens, then `object.Head` returns object ID of the original request.
This produces infinite assembly loop.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/services/object/get/assemble.go

@@ -12,7 +12,11 @@ func (exec *execCtx) assemble() {
 		return
 	}
 
-	exec.assembling = true
+	// do not use forwarding during assembly stage
+	// assembly flag is not inherited in produced
+	// `execCtx`, however `commonPrm` does, so it
+	// makes sense to nil it there
+	exec.prm.SetRequestForwarder(nil)
 
 	exec.log.Debug("trying to assemble the object...")
 

pkg/services/object/get/exec.go

@@ -41,12 +41,6 @@ type execCtx struct {
 	head bool
 
 	curProcEpoch uint64
-
-	// true when the processing of the initial request
-	// is turned to assembling stage. When false,
-	// initial request can be forwarded during network
-	// communication.
-	assembling bool
 }
 
 type execOption func(*execCtx)

pkg/services/object/get/util.go

@@ -82,7 +82,7 @@ func (c *clientCacheWrapper) get(addr network.AddressGroup) (getClient, error) {
 }
 
 func (c *clientWrapper) getObject(exec *execCtx, addr network.AddressGroup) (*objectSDK.Object, error) {
-	if !exec.assembling && exec.prm.forwarder != nil {
+	if exec.prm.forwarder != nil {
 		return exec.prm.forwarder(addr, c.client)
 	}