[#35] Add snapshot method for morph/netmap client

With snapshot method node can get previous network
maps from previous epoch.

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

pkg/morph/client/netmap/client.go

@@ -34,6 +34,7 @@ type cfg struct {
 	addPeerMethod, // add peer method name for invocation
 	newEpochMethod, // new epoch method name for invocation
 	netMapMethod, // get network map method name
+	snapshotMethod, // get network map snapshot method name
 	updateStateMethod, // update state method name for invocation
 	innerRingListMethod string // IR list method name for invocation
 }
@@ -42,6 +43,7 @@ const (
 	defaultAddPeerMethod       = "addPeer"       // default add peer method name
 	defaultNewEpochMethod      = "newEpoch"      // default new epoch method name
 	defaultNetMapMethod        = "netmap"        // default get network map method name
+	defaultSnapshotMethod      = "snapshot"      // default get network map snapshot method name
 	defaultUpdateStateMethod   = "updateState"   // default update state method name
 	defaultInnerRIngListMethod = "innerRingList" // default IR list method name
 )
@@ -51,6 +53,7 @@ func defaultConfig() *cfg {
 		addPeerMethod:       defaultAddPeerMethod,
 		newEpochMethod:      defaultNewEpochMethod,
 		netMapMethod:        defaultNetMapMethod,
+		snapshotMethod:      defaultSnapshotMethod,
 		updateStateMethod:   defaultUpdateStateMethod,
 		innerRingListMethod: defaultInnerRIngListMethod,
 	}

pkg/morph/client/netmap/netmap.go

@@ -11,6 +11,12 @@ import (
 type GetNetMapArgs struct {
 }
 
+// GetSnapshotArgs groups the arguments
+// of get netmap snapshot test invoke call.
+type GetSnapshotArgs struct {
+	diff uint64
+}
+
 // GetNetMapValues groups the stack parameters
 // returned by get network map test invoke.
 type GetNetMapValues struct {
@@ -19,6 +25,12 @@ type GetNetMapValues struct {
 
 const nodeInfoFixedPrmNumber = 1
 
+// SetDiff sets argument for snapshot method of
+// netmap contract.
+func (g *GetSnapshotArgs) SetDiff(d uint64) {
+	g.diff = d
+}
+
 // Peers return the list of peers from
 // network map in a binary format.
 func (g GetNetMapValues) Peers() [][]byte {
@@ -32,24 +44,53 @@ func (c *Client) NetMap(_ GetNetMapArgs) (*GetNetMapValues, error) {
 		c.netMapMethod,
 	)
 	if err != nil {
-		return nil, errors.Wrapf(err, "could not perform test invocation (%s)", c.netMapMethod)
+		return nil, errors.Wrapf(err,
-	} else if ln := len(prms); ln != 1 {
+			"could not perform test invocation (%s)",
-		return nil, errors.Errorf("unexpected stack item count (%s): %d", c.netMapMethod, ln)
+			c.netMapMethod)
 	}
 
-	prms, err = client.ArrayFromStackItem(prms[0])
+	return peersFromStackItems(prms, c.netMapMethod)
+}
+
+// NetMap performs the test invoke of get snapshot of network map
+// from NeoFS Netmap contract. Contract saves only one previous epoch,
+// so all invokes with diff > 1 return error.
+func (c *Client) Snapshot(a GetSnapshotArgs) (*GetNetMapValues, error) {
+	prms, err := c.client.TestInvoke(
+		c.snapshotMethod,
+		int64(a.diff),
+	)
 	if err != nil {
-		return nil, errors.Wrapf(err, "could not get stack item array from stack item (%s)", c.netMapMethod)
+		return nil, errors.Wrapf(err,
+			"could not perform test invocation (%s)",
+			c.netMapMethod)
+	}
+
+	return peersFromStackItems(prms, c.snapshotMethod)
+}
+
+func peersFromStackItems(stack []stackitem.Item, method string) (*GetNetMapValues, error) {
+	if ln := len(stack); ln != 1 {
+		return nil, errors.Errorf("unexpected stack item count (%s): %d",
+			method, ln)
+	}
+
+	peers, err := client.ArrayFromStackItem(stack[0])
+	if err != nil {
+		return nil, errors.Wrapf(err,
+			"could not get stack item array from stack item (%s)",
+			method)
 	}
 
 	res := &GetNetMapValues{
-		peers: make([][]byte, 0, len(prms)),
+		peers: make([][]byte, 0, len(peers)),
 	}
 
-	for i := range prms {
+	for i := range peers {
-		peer, err := peerInfoFromStackItem(prms[i])
+		peer, err := peerInfoFromStackItem(peers[i])
 		if err != nil {
-			return nil, errors.Wrapf(err, "could not parse stack item (Peer #%d)", i)
+			return nil, errors.Wrapf(err,
+				"could not parse stack item (Peer #%d)", i)
 		}
 
 		res.peers = append(res.peers, peer)