[#299] pool: Do not use pointers to the resulting values

In previous implementation `pool` package provided access to resulting
values as pointers to them. This caused clients to handle nil
cases even when the field presence in the response is required.

Avoid returning pointers to values in result getters. This also reduces
reference counter load and allows values from `client.Client` to be
forwarded directly without additional assignment.

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

pool/mock_test.go

@@ -65,16 +65,16 @@ func newToken(key ecdsa.PrivateKey) *session.Object {
 	return &tok
 }
 
-func (m *mockClient) balanceGet(context.Context, PrmBalanceGet) (*accounting.Decimal, error) {
+func (m *mockClient) balanceGet(context.Context, PrmBalanceGet) (accounting.Decimal, error) {
-	return nil, nil
+	return accounting.Decimal{}, nil
 }
 
-func (m *mockClient) containerPut(context.Context, PrmContainerPut) (*cid.ID, error) {
+func (m *mockClient) containerPut(context.Context, PrmContainerPut) (cid.ID, error) {
-	return nil, nil
+	return cid.ID{}, nil
 }
 
-func (m *mockClient) containerGet(context.Context, PrmContainerGet) (*container.Container, error) {
+func (m *mockClient) containerGet(context.Context, PrmContainerGet) (container.Container, error) {
-	return nil, nil
+	return container.Container{}, nil
 }
 
 func (m *mockClient) containerList(context.Context, PrmContainerList) ([]cid.ID, error) {
@@ -85,65 +85,69 @@ func (m *mockClient) containerDelete(context.Context, PrmContainerDelete) error
 	return nil
 }
 
-func (m *mockClient) containerEACL(context.Context, PrmContainerEACL) (*eacl.Table, error) {
+func (m *mockClient) containerEACL(context.Context, PrmContainerEACL) (eacl.Table, error) {
-	return nil, nil
+	return eacl.Table{}, nil
 }
 
 func (m *mockClient) containerSetEACL(context.Context, PrmContainerSetEACL) error {
 	return nil
 }
 
-func (m *mockClient) endpointInfo(context.Context, prmEndpointInfo) (*netmap.NodeInfo, error) {
+func (m *mockClient) endpointInfo(context.Context, prmEndpointInfo) (netmap.NodeInfo, error) {
-	if m.errorOnEndpointInfo {
-		return nil, m.handleError(nil, errors.New("error"))
-	}
-
 	var ni netmap.NodeInfo
-	ni.SetNetworkEndpoints(m.addr)
-	return &ni, nil
-}
 
-func (m *mockClient) networkInfo(context.Context, prmNetworkInfo) (*netmap.NetworkInfo, error) {
+	if m.errorOnEndpointInfo {
-	if m.errorOnNetworkInfo {
+		return ni, m.handleError(nil, errors.New("error"))
-		return nil, m.handleError(nil, errors.New("error"))
 	}
 
-	var ni netmap.NetworkInfo
+	ni.SetNetworkEndpoints(m.addr)
-	return &ni, nil
+	return ni, nil
 }
 
-func (m *mockClient) objectPut(context.Context, PrmObjectPut) (*oid.ID, error) {
+func (m *mockClient) networkInfo(context.Context, prmNetworkInfo) (netmap.NetworkInfo, error) {
-	return nil, nil
+	var ni netmap.NetworkInfo
+
+	if m.errorOnNetworkInfo {
+		return ni, m.handleError(nil, errors.New("error"))
+	}
+
+	return ni, nil
+}
+
+func (m *mockClient) objectPut(context.Context, PrmObjectPut) (oid.ID, error) {
+	return oid.ID{}, nil
 }
 
 func (m *mockClient) objectDelete(context.Context, PrmObjectDelete) error {
 	return nil
 }
 
-func (m *mockClient) objectGet(context.Context, PrmObjectGet) (*ResGetObject, error) {
+func (m *mockClient) objectGet(context.Context, PrmObjectGet) (ResGetObject, error) {
+	var res ResGetObject
+
 	if m.stOnGetObject == nil {
-		return &ResGetObject{}, nil
+		return res, nil
 	}
 
 	status := apistatus.ErrFromStatus(m.stOnGetObject)
-	return &ResGetObject{}, m.handleError(status, nil)
+	return res, m.handleError(status, nil)
 }
 
-func (m *mockClient) objectHead(context.Context, PrmObjectHead) (*object.Object, error) {
+func (m *mockClient) objectHead(context.Context, PrmObjectHead) (object.Object, error) {
-	return nil, nil
+	return object.Object{}, nil
 }
 
-func (m *mockClient) objectRange(context.Context, PrmObjectRange) (*ResObjectRange, error) {
+func (m *mockClient) objectRange(context.Context, PrmObjectRange) (ResObjectRange, error) {
-	return nil, nil
+	return ResObjectRange{}, nil
 }
 
-func (m *mockClient) objectSearch(context.Context, PrmObjectSearch) (*ResObjectSearch, error) {
+func (m *mockClient) objectSearch(context.Context, PrmObjectSearch) (ResObjectSearch, error) {
-	return nil, nil
+	return ResObjectSearch{}, nil
 }
 
-func (m *mockClient) sessionCreate(context.Context, prmCreateSession) (*resCreateSession, error) {
+func (m *mockClient) sessionCreate(context.Context, prmCreateSession) (resCreateSession, error) {
 	if m.errorOnCreateSession {
-		return nil, m.handleError(nil, errors.New("error"))
+		return resCreateSession{}, m.handleError(nil, errors.New("error"))
 	}
 
 	tok := newToken(m.key)
@@ -151,7 +155,7 @@ func (m *mockClient) sessionCreate(context.Context, prmCreateSession) (*resCreat
 	var v2tok sessionv2.Token
 	tok.WriteToV2(&v2tok)
 
-	return &resCreateSession{
+	return resCreateSession{
 		id:         v2tok.GetBody().GetID(),
 		sessionKey: v2tok.GetBody().GetSessionKey(),
 	}, nil

pool/pool.go

@@ -37,37 +37,37 @@ import (
 // Others are expected to be for test purposes only.
 type client interface {
 	// see clientWrapper.balanceGet.
-	balanceGet(context.Context, PrmBalanceGet) (*accounting.Decimal, error)
+	balanceGet(context.Context, PrmBalanceGet) (accounting.Decimal, error)
 	// see clientWrapper.containerPut.
-	containerPut(context.Context, PrmContainerPut) (*cid.ID, error)
+	containerPut(context.Context, PrmContainerPut) (cid.ID, error)
 	// see clientWrapper.containerGet.
-	containerGet(context.Context, PrmContainerGet) (*container.Container, error)
+	containerGet(context.Context, PrmContainerGet) (container.Container, error)
 	// see clientWrapper.containerList.
 	containerList(context.Context, PrmContainerList) ([]cid.ID, error)
 	// see clientWrapper.containerDelete.
 	containerDelete(context.Context, PrmContainerDelete) error
 	// see clientWrapper.containerEACL.
-	containerEACL(context.Context, PrmContainerEACL) (*eacl.Table, error)
+	containerEACL(context.Context, PrmContainerEACL) (eacl.Table, error)
 	// see clientWrapper.containerSetEACL.
 	containerSetEACL(context.Context, PrmContainerSetEACL) error
 	// see clientWrapper.endpointInfo.
-	endpointInfo(context.Context, prmEndpointInfo) (*netmap.NodeInfo, error)
+	endpointInfo(context.Context, prmEndpointInfo) (netmap.NodeInfo, error)
 	// see clientWrapper.networkInfo.
-	networkInfo(context.Context, prmNetworkInfo) (*netmap.NetworkInfo, error)
+	networkInfo(context.Context, prmNetworkInfo) (netmap.NetworkInfo, error)
 	// see clientWrapper.objectPut.
-	objectPut(context.Context, PrmObjectPut) (*oid.ID, error)
+	objectPut(context.Context, PrmObjectPut) (oid.ID, error)
 	// see clientWrapper.objectDelete.
 	objectDelete(context.Context, PrmObjectDelete) error
 	// see clientWrapper.objectGet.
-	objectGet(context.Context, PrmObjectGet) (*ResGetObject, error)
+	objectGet(context.Context, PrmObjectGet) (ResGetObject, error)
 	// see clientWrapper.objectHead.
-	objectHead(context.Context, PrmObjectHead) (*object.Object, error)
+	objectHead(context.Context, PrmObjectHead) (object.Object, error)
 	// see clientWrapper.objectRange.
-	objectRange(context.Context, PrmObjectRange) (*ResObjectRange, error)
+	objectRange(context.Context, PrmObjectRange) (ResObjectRange, error)
 	// see clientWrapper.objectSearch.
-	objectSearch(context.Context, PrmObjectSearch) (*ResObjectSearch, error)
+	objectSearch(context.Context, PrmObjectSearch) (ResObjectSearch, error)
 	// see clientWrapper.sessionCreate.
-	sessionCreate(context.Context, prmCreateSession) (*resCreateSession, error)
+	sessionCreate(context.Context, prmCreateSession) (resCreateSession, error)
 
 	clientStatus
 }
@@ -273,8 +273,7 @@ func newWrapper(prm wrapperPrm) (*clientWrapper, error) {
 }
 
 // balanceGet invokes sdkClient.BalanceGet parse response status to error and return result as is.
-// Exactly one return value is non-nil.
+func (c *clientWrapper) balanceGet(ctx context.Context, prm PrmBalanceGet) (accounting.Decimal, error) {
-func (c *clientWrapper) balanceGet(ctx context.Context, prm PrmBalanceGet) (*accounting.Decimal, error) {
 	var cliPrm sdkClient.PrmBalanceGet
 	cliPrm.SetAccount(prm.account)
 
@@ -286,17 +285,15 @@ func (c *clientWrapper) balanceGet(ctx context.Context, prm PrmBalanceGet) (*acc
 		st = res.Status()
 	}
 	if err = c.handleError(st, err); err != nil {
-		return nil, fmt.Errorf("balance get on client: %w", err)
+		return accounting.Decimal{}, fmt.Errorf("balance get on client: %w", err)
 	}
 
-	bal := res.Amount()
+	return res.Amount(), nil
-
-	return &bal, nil
 }
 
 // containerPut invokes sdkClient.ContainerPut parse response status to error and return result as is.
 // It also waits for the container to appear on the network.
-func (c *clientWrapper) containerPut(ctx context.Context, prm PrmContainerPut) (*cid.ID, error) {
+func (c *clientWrapper) containerPut(ctx context.Context, prm PrmContainerPut) (cid.ID, error) {
 	start := time.Now()
 	res, err := c.client.ContainerPut(ctx, prm.prmClient)
 	c.incRequests(time.Since(start), methodContainerPut)
@@ -305,7 +302,7 @@ func (c *clientWrapper) containerPut(ctx context.Context, prm PrmContainerPut) (
 		st = res.Status()
 	}
 	if err = c.handleError(st, err); err != nil {
-		return nil, fmt.Errorf("container put on client: %w", err)
+		return cid.ID{}, fmt.Errorf("container put on client: %w", err)
 	}
 
 	if !prm.waitParamsSet {
@@ -316,15 +313,14 @@ func (c *clientWrapper) containerPut(ctx context.Context, prm PrmContainerPut) (
 
 	err = waitForContainerPresence(ctx, c, idCnr, &prm.waitParams)
 	if err = c.handleError(nil, err); err != nil {
-		return nil, fmt.Errorf("wait container presence on client: %w", err)
+		return cid.ID{}, fmt.Errorf("wait container presence on client: %w", err)
 	}
 
-	return &idCnr, nil
+	return idCnr, nil
 }
 
 // containerGet invokes sdkClient.ContainerGet parse response status to error and return result as is.
-// Exactly one return value is non-nil.
+func (c *clientWrapper) containerGet(ctx context.Context, prm PrmContainerGet) (container.Container, error) {
-func (c *clientWrapper) containerGet(ctx context.Context, prm PrmContainerGet) (*container.Container, error) {
 	var cliPrm sdkClient.PrmContainerGet
 	cliPrm.SetContainer(prm.cnrID)
 
@@ -336,11 +332,10 @@ func (c *clientWrapper) containerGet(ctx context.Context, prm PrmContainerGet) (
 		st = res.Status()
 	}
 	if err = c.handleError(st, err); err != nil {
-		return nil, fmt.Errorf("container get on client: %w", err)
+		return container.Container{}, fmt.Errorf("container get on client: %w", err)
 	}
 
-	cnr := res.Container()
+	return res.Container(), nil
-	return &cnr, nil
 }
 
 // containerList invokes sdkClient.ContainerList parse response status to error and return result as is.
@@ -389,8 +384,7 @@ func (c *clientWrapper) containerDelete(ctx context.Context, prm PrmContainerDel
 }
 
 // containerEACL invokes sdkClient.ContainerEACL parse response status to error and return result as is.
-// Exactly one return value is non-nil.
+func (c *clientWrapper) containerEACL(ctx context.Context, prm PrmContainerEACL) (eacl.Table, error) {
-func (c *clientWrapper) containerEACL(ctx context.Context, prm PrmContainerEACL) (*eacl.Table, error) {
 	var cliPrm sdkClient.PrmContainerEACL
 	cliPrm.SetContainer(prm.cnrID)
 
@@ -402,12 +396,10 @@ func (c *clientWrapper) containerEACL(ctx context.Context, prm PrmContainerEACL)
 		st = res.Status()
 	}
 	if err = c.handleError(st, err); err != nil {
-		return nil, fmt.Errorf("get eacl on client: %w", err)
+		return eacl.Table{}, fmt.Errorf("get eacl on client: %w", err)
 	}
 
-	eACL := res.Table()
+	return res.Table(), nil
-
-	return &eACL, nil
 }
 
 // containerSetEACL invokes sdkClient.ContainerSetEACL parse response status to error.
@@ -449,8 +441,7 @@ func (c *clientWrapper) containerSetEACL(ctx context.Context, prm PrmContainerSe
 }
 
 // endpointInfo invokes sdkClient.EndpointInfo parse response status to error and return result as is.
-// Exactly one return value is non-nil.
+func (c *clientWrapper) endpointInfo(ctx context.Context, _ prmEndpointInfo) (netmap.NodeInfo, error) {
-func (c *clientWrapper) endpointInfo(ctx context.Context, _ prmEndpointInfo) (*netmap.NodeInfo, error) {
 	start := time.Now()
 	res, err := c.client.EndpointInfo(ctx, sdkClient.PrmEndpointInfo{})
 	c.incRequests(time.Since(start), methodEndpointInfo)
@@ -459,17 +450,14 @@ func (c *clientWrapper) endpointInfo(ctx context.Context, _ prmEndpointInfo) (*n
 		st = res.Status()
 	}
 	if err = c.handleError(st, err); err != nil {
-		return nil, fmt.Errorf("endpoint info on client: %w", err)
+		return netmap.NodeInfo{}, fmt.Errorf("endpoint info on client: %w", err)
 	}
 
-	nodeInfo := res.NodeInfo()
+	return res.NodeInfo(), nil
-
-	return &nodeInfo, nil
 }
 
 // networkInfo invokes sdkClient.NetworkInfo parse response status to error and return result as is.
-// Exactly one return value is non-nil.
+func (c *clientWrapper) networkInfo(ctx context.Context, _ prmNetworkInfo) (netmap.NetworkInfo, error) {
-func (c *clientWrapper) networkInfo(ctx context.Context, _ prmNetworkInfo) (*netmap.NetworkInfo, error) {
 	start := time.Now()
 	res, err := c.client.NetworkInfo(ctx, sdkClient.PrmNetworkInfo{})
 	c.incRequests(time.Since(start), methodNetworkInfo)
@@ -478,17 +466,14 @@ func (c *clientWrapper) networkInfo(ctx context.Context, _ prmNetworkInfo) (*net
 		st = res.Status()
 	}
 	if err = c.handleError(st, err); err != nil {
-		return nil, fmt.Errorf("network info on client: %w", err)
+		return netmap.NetworkInfo{}, fmt.Errorf("network info on client: %w", err)
 	}
 
-	netInfo := res.Info()
+	return res.Info(), nil
-
-	return &netInfo, nil
 }
 
 // objectPut writes object to NeoFS.
-// Exactly one return value is non-nil.
+func (c *clientWrapper) objectPut(ctx context.Context, prm PrmObjectPut) (oid.ID, error) {
-func (c *clientWrapper) objectPut(ctx context.Context, prm PrmObjectPut) (*oid.ID, error) {
 	var cliPrm sdkClient.PrmObjectPutInit
 	cliPrm.SetCopiesNumber(prm.copiesNumber)
 
@@ -496,7 +481,7 @@ func (c *clientWrapper) objectPut(ctx context.Context, prm PrmObjectPut) (*oid.I
 	wObj, err := c.client.ObjectPutInit(ctx, cliPrm)
 	c.incRequests(time.Since(start), methodObjectPut)
 	if err = c.handleError(nil, err); err != nil {
-		return nil, fmt.Errorf("init writing on API client: %w", err)
+		return oid.ID{}, fmt.Errorf("init writing on API client: %w", err)
 	}
 
 	if prm.stoken != nil {
@@ -550,7 +535,7 @@ func (c *clientWrapper) objectPut(ctx context.Context, prm PrmObjectPut) (*oid.I
 					break
 				}
 
-				return nil, fmt.Errorf("read payload: %w", c.handleError(nil, err))
+				return oid.ID{}, fmt.Errorf("read payload: %w", c.handleError(nil, err))
 			}
 		}
 	}
@@ -561,12 +546,10 @@ func (c *clientWrapper) objectPut(ctx context.Context, prm PrmObjectPut) (*oid.I
 		st = res.Status()
 	}
 	if err = c.handleError(st, err); err != nil { // here err already carries both status and client errors
-		return nil, fmt.Errorf("client failure: %w", err)
+		return oid.ID{}, fmt.Errorf("client failure: %w", err)
 	}
 
-	id := res.StoredObjectID()
+	return res.StoredObjectID(), nil
-
-	return &id, nil
 }
 
 // objectDelete invokes sdkClient.ObjectDelete parse response status to error.
@@ -601,8 +584,7 @@ func (c *clientWrapper) objectDelete(ctx context.Context, prm PrmObjectDelete) e
 }
 
 // objectGet returns reader for object.
-// Exactly one return value is non-nil.
+func (c *clientWrapper) objectGet(ctx context.Context, prm PrmObjectGet) (ResGetObject, error) {
-func (c *clientWrapper) objectGet(ctx context.Context, prm PrmObjectGet) (*ResGetObject, error) {
 	var cliPrm sdkClient.PrmObjectGet
 	cliPrm.FromContainer(prm.addr.Container())
 	cliPrm.ByID(prm.addr.Object())
@@ -619,7 +601,7 @@ func (c *clientWrapper) objectGet(ctx context.Context, prm PrmObjectGet) (*ResGe
 
 	rObj, err := c.client.ObjectGetInit(ctx, cliPrm)
 	if err = c.handleError(nil, err); err != nil {
-		return nil, fmt.Errorf("init object reading on client: %w", err)
+		return ResGetObject{}, fmt.Errorf("init object reading on client: %w", err)
 	}
 
 	if prm.key != nil {
@@ -636,7 +618,7 @@ func (c *clientWrapper) objectGet(ctx context.Context, prm PrmObjectGet) (*ResGe
 			st = rObjRes.Status()
 		}
 		err = c.handleError(st, err)
-		return nil, fmt.Errorf("read header: %w", err)
+		return res, fmt.Errorf("read header: %w", err)
 	}
 
 	res.Payload = &objectReadCloser{
@@ -646,12 +628,11 @@ func (c *clientWrapper) objectGet(ctx context.Context, prm PrmObjectGet) (*ResGe
 		},
 	}
 
-	return &res, nil
+	return res, nil
 }
 
 // objectHead invokes sdkClient.ObjectHead parse response status to error and return result as is.
-// Exactly one return value is non-nil.
+func (c *clientWrapper) objectHead(ctx context.Context, prm PrmObjectHead) (object.Object, error) {
-func (c *clientWrapper) objectHead(ctx context.Context, prm PrmObjectHead) (*object.Object, error) {
 	var cliPrm sdkClient.PrmObjectHead
 	cliPrm.FromContainer(prm.addr.Container())
 	cliPrm.ByID(prm.addr.Object())
@@ -678,18 +659,17 @@ func (c *clientWrapper) objectHead(ctx context.Context, prm PrmObjectHead) (*obj
 		st = res.Status()
 	}
 	if err = c.handleError(st, err); err != nil {
-		return nil, fmt.Errorf("read object header via client: %w", err)
+		return obj, fmt.Errorf("read object header via client: %w", err)
 	}
 	if !res.ReadHeader(&obj) {
-		return nil, errors.New("missing object header in response")
+		return obj, errors.New("missing object header in response")
 	}
 
-	return &obj, nil
+	return obj, nil
 }
 
 // objectRange returns object range reader.
-// Exactly one return value is non-nil.
+func (c *clientWrapper) objectRange(ctx context.Context, prm PrmObjectRange) (ResObjectRange, error) {
-func (c *clientWrapper) objectRange(ctx context.Context, prm PrmObjectRange) (*ResObjectRange, error) {
 	var cliPrm sdkClient.PrmObjectRange
 	cliPrm.FromContainer(prm.addr.Container())
 	cliPrm.ByID(prm.addr.Object())
@@ -708,13 +688,13 @@ func (c *clientWrapper) objectRange(ctx context.Context, prm PrmObjectRange) (*R
 	res, err := c.client.ObjectRangeInit(ctx, cliPrm)
 	c.incRequests(time.Since(start), methodObjectRange)
 	if err = c.handleError(nil, err); err != nil {
-		return nil, fmt.Errorf("init payload range reading on client: %w", err)
+		return ResObjectRange{}, fmt.Errorf("init payload range reading on client: %w", err)
 	}
 	if prm.key != nil {
 		res.UseKey(*prm.key)
 	}
 
-	return &ResObjectRange{
+	return ResObjectRange{
 		payload: res,
 		elapsedTimeCallback: func(elapsed time.Duration) {
 			c.incRequests(elapsed, methodObjectRange)
@@ -723,8 +703,7 @@ func (c *clientWrapper) objectRange(ctx context.Context, prm PrmObjectRange) (*R
 }
 
 // objectSearch invokes sdkClient.ObjectSearchInit parse response status to error and return result as is.
-// Exactly one return value is non-nil.
+func (c *clientWrapper) objectSearch(ctx context.Context, prm PrmObjectSearch) (ResObjectSearch, error) {
-func (c *clientWrapper) objectSearch(ctx context.Context, prm PrmObjectSearch) (*ResObjectSearch, error) {
 	var cliPrm sdkClient.PrmObjectSearch
 
 	cliPrm.InContainer(prm.cnrID)
@@ -740,18 +719,17 @@ func (c *clientWrapper) objectSearch(ctx context.Context, prm PrmObjectSearch) (
 
 	res, err := c.client.ObjectSearchInit(ctx, cliPrm)
 	if err = c.handleError(nil, err); err != nil {
-		return nil, fmt.Errorf("init object searching on client: %w", err)
+		return ResObjectSearch{}, fmt.Errorf("init object searching on client: %w", err)
 	}
 	if prm.key != nil {
 		res.UseKey(*prm.key)
 	}
 
-	return &ResObjectSearch{r: res}, nil
+	return ResObjectSearch{r: res}, nil
 }
 
 // sessionCreate invokes sdkClient.SessionCreate parse response status to error and return result as is.
-// Exactly one return value is non-nil.
+func (c *clientWrapper) sessionCreate(ctx context.Context, prm prmCreateSession) (resCreateSession, error) {
-func (c *clientWrapper) sessionCreate(ctx context.Context, prm prmCreateSession) (*resCreateSession, error) {
 	var cliPrm sdkClient.PrmSessionCreate
 	cliPrm.SetExp(prm.exp)
 	cliPrm.UseKey(prm.key)
@@ -764,10 +742,10 @@ func (c *clientWrapper) sessionCreate(ctx context.Context, prm prmCreateSession)
 		st = res.Status()
 	}
 	if err = c.handleError(st, err); err != nil {
-		return nil, fmt.Errorf("session creation on client: %w", err)
+		return resCreateSession{}, fmt.Errorf("session creation on client: %w", err)
 	}
 
-	return &resCreateSession{
+	return resCreateSession{
 		id:         res.ID(),
 		sessionKey: res.PublicKey(),
 	}, nil
@@ -1797,7 +1775,9 @@ func (p *Pool) fillAppropriateKey(prm *prmCommon) {
 }
 
 // PutObject writes an object through a remote server using NeoFS API protocol.
-func (p *Pool) PutObject(ctx context.Context, prm PrmObjectPut) (*oid.ID, error) {
+//
+// Main return value MUST NOT be processed on an erroneous return.
+func (p *Pool) PutObject(ctx context.Context, prm PrmObjectPut) (oid.ID, error) {
 	cnr, _ := prm.hdr.ContainerID()
 
 	var prmCtx prmContext
@@ -1812,13 +1792,13 @@ func (p *Pool) PutObject(ctx context.Context, prm PrmObjectPut) (*oid.ID, error)
 	ctxCall.Context = ctx
 
 	if err := p.initCallContext(&ctxCall, prm.prmCommon, prmCtx); err != nil {
-		return nil, fmt.Errorf("init call context: %w", err)
+		return oid.ID{}, fmt.Errorf("init call context: %w", err)
 	}
 
 	if ctxCall.sessionDefault {
 		ctxCall.sessionTarget = prm.UseSession
 		if err := p.openDefaultSession(&ctxCall); err != nil {
-			return nil, fmt.Errorf("open default session: %w", err)
+			return oid.ID{}, fmt.Errorf("open default session: %w", err)
 		}
 	}
 
@@ -1826,7 +1806,7 @@ func (p *Pool) PutObject(ctx context.Context, prm PrmObjectPut) (*oid.ID, error)
 	if err != nil {
 		// removes session token from cache in case of token error
 		p.checkSessionTokenErr(err, ctxCall.endpoint)
-		return nil, fmt.Errorf("init writing on API client: %w", err)
+		return id, fmt.Errorf("init writing on API client: %w", err)
 	}
 
 	return id, nil
@@ -1890,8 +1870,9 @@ type ResGetObject struct {
 }
 
 // GetObject reads object header and initiates reading an object payload through a remote server using NeoFS API protocol.
-// Exactly one return value is non-nil.
+//
-func (p *Pool) GetObject(ctx context.Context, prm PrmObjectGet) (*ResGetObject, error) {
+// Main return value MUST NOT be processed on an erroneous return.
+func (p *Pool) GetObject(ctx context.Context, prm PrmObjectGet) (ResGetObject, error) {
 	var prmCtx prmContext
 	prmCtx.useDefaultSession()
 	prmCtx.useVerb(session.VerbObjectGet)
@@ -1903,12 +1884,13 @@ func (p *Pool) GetObject(ctx context.Context, prm PrmObjectGet) (*ResGetObject,
 	cc.Context = ctx
 	cc.sessionTarget = prm.UseSession
 
+	var res ResGetObject
+
 	err := p.initCallContext(&cc, prm.prmCommon, prmCtx)
 	if err != nil {
-		return nil, err
+		return res, err
 	}
 
-	var res *ResGetObject
 	return res, p.call(&cc, func() error {
 		res, err = cc.client.objectGet(ctx, prm)
 		return err
@@ -1916,8 +1898,9 @@ func (p *Pool) GetObject(ctx context.Context, prm PrmObjectGet) (*ResGetObject,
 }
 
 // HeadObject reads object header through a remote server using NeoFS API protocol.
-// Exactly one return value is non-nil.
+//
-func (p *Pool) HeadObject(ctx context.Context, prm PrmObjectHead) (*object.Object, error) {
+// Main return value MUST NOT be processed on an erroneous return.
+func (p *Pool) HeadObject(ctx context.Context, prm PrmObjectHead) (object.Object, error) {
 	var prmCtx prmContext
 	prmCtx.useDefaultSession()
 	prmCtx.useVerb(session.VerbObjectHead)
@@ -1930,12 +1913,13 @@ func (p *Pool) HeadObject(ctx context.Context, prm PrmObjectHead) (*object.Objec
 	cc.Context = ctx
 	cc.sessionTarget = prm.UseSession
 
+	var obj object.Object
+
 	err := p.initCallContext(&cc, prm.prmCommon, prmCtx)
 	if err != nil {
-		return nil, err
+		return obj, err
 	}
 
-	var obj *object.Object
 	return obj, p.call(&cc, func() error {
 		obj, err = cc.client.objectHead(ctx, prm)
 		return err
@@ -1969,8 +1953,9 @@ func (x *ResObjectRange) Close() error {
 
 // ObjectRange initiates reading an object's payload range through a remote
 // server using NeoFS API protocol.
-// Exactly one return value is non-nil.
+//
-func (p *Pool) ObjectRange(ctx context.Context, prm PrmObjectRange) (*ResObjectRange, error) {
+// Main return value MUST NOT be processed on an erroneous return.
+func (p *Pool) ObjectRange(ctx context.Context, prm PrmObjectRange) (ResObjectRange, error) {
 	var prmCtx prmContext
 	prmCtx.useDefaultSession()
 	prmCtx.useVerb(session.VerbObjectRange)
@@ -1982,13 +1967,13 @@ func (p *Pool) ObjectRange(ctx context.Context, prm PrmObjectRange) (*ResObjectR
 	cc.Context = ctx
 	cc.sessionTarget = prm.UseSession
 
+	var res ResObjectRange
+
 	err := p.initCallContext(&cc, prm.prmCommon, prmCtx)
 	if err != nil {
-		return nil, err
+		return res, err
 	}
 
-	var res *ResObjectRange
-
 	return res, p.call(&cc, func() error {
 		res, err = cc.client.objectRange(ctx, prm)
 		return err
@@ -2034,10 +2019,10 @@ func (x *ResObjectSearch) Close() {
 // SearchObjects initiates object selection through a remote server using NeoFS API protocol.
 //
 // The call only opens the transmission channel, explicit fetching of matched objects
-// is done using the ResObjectSearch. Exactly one return value is non-nil.
+// is done using the ResObjectSearch. Resulting reader must be finally closed.
-// Resulting reader must be finally closed.
+//
-// Exactly one return value is non-nil.
+// Main return value MUST NOT be processed on an erroneous return.
-func (p *Pool) SearchObjects(ctx context.Context, prm PrmObjectSearch) (*ResObjectSearch, error) {
+func (p *Pool) SearchObjects(ctx context.Context, prm PrmObjectSearch) (ResObjectSearch, error) {
 	var prmCtx prmContext
 	prmCtx.useDefaultSession()
 	prmCtx.useVerb(session.VerbObjectSearch)
@@ -2050,13 +2035,13 @@ func (p *Pool) SearchObjects(ctx context.Context, prm PrmObjectSearch) (*ResObje
 	cc.Context = ctx
 	cc.sessionTarget = prm.UseSession
 
+	var res ResObjectSearch
+
 	err := p.initCallContext(&cc, prm.prmCommon, prmCtx)
 	if err != nil {
-		return nil, err
+		return res, err
 	}
 
-	var res *ResObjectSearch
-
 	return res, p.call(&cc, func() error {
 		res, err = cc.client.objectSearch(ctx, prm)
 		return err
@@ -2070,21 +2055,24 @@ func (p *Pool) SearchObjects(ctx context.Context, prm PrmObjectSearch) (*ResObje
 //   waiting timeout: 120s
 //
 // Success can be verified by reading by identifier (see GetContainer).
-func (p *Pool) PutContainer(ctx context.Context, prm PrmContainerPut) (*cid.ID, error) {
+//
+// Main return value MUST NOT be processed on an erroneous return.
+func (p *Pool) PutContainer(ctx context.Context, prm PrmContainerPut) (cid.ID, error) {
 	cp, err := p.connection()
 	if err != nil {
-		return nil, err
+		return cid.ID{}, err
 	}
 
 	return cp.containerPut(ctx, prm)
 }
 
 // GetContainer reads NeoFS container by ID.
-// Exactly one return value is non-nil.
+//
-func (p *Pool) GetContainer(ctx context.Context, prm PrmContainerGet) (*container.Container, error) {
+// Main return value MUST NOT be processed on an erroneous return.
+func (p *Pool) GetContainer(ctx context.Context, prm PrmContainerGet) (container.Container, error) {
 	cp, err := p.connection()
 	if err != nil {
-		return nil, err
+		return container.Container{}, err
 	}
 
 	return cp.containerGet(ctx, prm)
@@ -2117,11 +2105,12 @@ func (p *Pool) DeleteContainer(ctx context.Context, prm PrmContainerDelete) erro
 }
 
 // GetEACL reads eACL table of the NeoFS container.
-// Exactly one return value is non-nil.
+//
-func (p *Pool) GetEACL(ctx context.Context, prm PrmContainerEACL) (*eacl.Table, error) {
+// Main return value MUST NOT be processed on an erroneous return.
+func (p *Pool) GetEACL(ctx context.Context, prm PrmContainerEACL) (eacl.Table, error) {
 	cp, err := p.connection()
 	if err != nil {
-		return nil, err
+		return eacl.Table{}, err
 	}
 
 	return cp.containerEACL(ctx, prm)
@@ -2144,11 +2133,12 @@ func (p *Pool) SetEACL(ctx context.Context, prm PrmContainerSetEACL) error {
 }
 
 // Balance requests current balance of the NeoFS account.
-// Exactly one return value is non-nil.
+//
-func (p *Pool) Balance(ctx context.Context, prm PrmBalanceGet) (*accounting.Decimal, error) {
+// Main return value MUST NOT be processed on an erroneous return.
+func (p *Pool) Balance(ctx context.Context, prm PrmBalanceGet) (accounting.Decimal, error) {
 	cp, err := p.connection()
 	if err != nil {
-		return nil, err
+		return accounting.Decimal{}, err
 	}
 
 	return cp.balanceGet(ctx, prm)
@@ -2196,7 +2186,7 @@ func waitForEACLPresence(ctx context.Context, cli client, cnrID *cid.ID, table *
 	return waitFor(ctx, waitParams, func(ctx context.Context) bool {
 		eaclTable, err := cli.containerEACL(ctx, prm)
 		if err == nil {
-			return eacl.EqualTables(*table, *eaclTable)
+			return eacl.EqualTables(*table, eaclTable)
 		}
 		return false
 	})
@@ -2239,11 +2229,12 @@ func waitFor(ctx context.Context, params *WaitParams, condition func(context.Con
 }
 
 // NetworkInfo requests information about the NeoFS network of which the remote server is a part.
-// Exactly one return value is non-nil.
+//
-func (p *Pool) NetworkInfo(ctx context.Context) (*netmap.NetworkInfo, error) {
+// Main return value MUST NOT be processed on an erroneous return.
+func (p *Pool) NetworkInfo(ctx context.Context) (netmap.NetworkInfo, error) {
 	cp, err := p.connection()
 	if err != nil {
-		return nil, err
+		return netmap.NetworkInfo{}, err
 	}
 
 	return cp.networkInfo(ctx, prmNetworkInfo{})
@@ -2269,11 +2260,7 @@ func SyncContainerWithNetwork(ctx context.Context, cnr *container.Container, p *
 		return fmt.Errorf("network info: %w", err)
 	}
 
-	if ni == nil {
+	container.ApplyNetworkConfig(cnr, ni)
-		return errors.New("empty network info")
-	}
-
-	container.ApplyNetworkConfig(cnr, *ni)
 
 	return nil
 }

pool/sampler_test.go

@@ -48,12 +48,12 @@ type clientMock struct {
 	err  error
 }
 
-func (c *clientMock) endpointInfo(context.Context, prmEndpointInfo) (*netmap.NodeInfo, error) {
+func (c *clientMock) endpointInfo(context.Context, prmEndpointInfo) (netmap.NodeInfo, error) {
-	return nil, nil
+	return netmap.NodeInfo{}, nil
 }
 
-func (c *clientMock) networkInfo(context.Context, prmNetworkInfo) (*netmap.NetworkInfo, error) {
+func (c *clientMock) networkInfo(context.Context, prmNetworkInfo) (netmap.NetworkInfo, error) {
-	return nil, nil
+	return netmap.NetworkInfo{}, nil
 }
 
 func newNetmapMock(name string, needErr bool) *clientMock {