client: Add SessionCreate example

Signed-off-by: Evgenii Baidakov <evgenii@nspcc.io>

client/example_test.go

@@ -1,12 +1,21 @@
 package client_test
 
 import (
+	"context"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
 	"time"
 
+	"github.com/google/uuid"
 	rpcClient "github.com/nspcc-dev/neofs-api-go/v2/rpc/client"
 	"github.com/nspcc-dev/neofs-api-go/v2/rpc/common"
 	"github.com/nspcc-dev/neofs-api-go/v2/rpc/grpc"
 	"github.com/nspcc-dev/neofs-sdk-go/client"
+	cid "github.com/nspcc-dev/neofs-sdk-go/container/id"
+	neofsecdsa "github.com/nspcc-dev/neofs-sdk-go/crypto/ecdsa"
+	"github.com/nspcc-dev/neofs-sdk-go/session"
+	"github.com/nspcc-dev/neofs-sdk-go/user"
 )
 
 func ExampleClient_createInstance() {
@@ -100,3 +109,57 @@ func Example_customService() {
 	// // ...
 	// }
 }
+
+// Session created for the one node, and it will work only for this node. Other nodes don't have info about this session.
+// That is why session can't be created with Pool API.
+func ExampleClient_SessionCreate() {
+	// import "github.com/google/uuid"
+
+	var prmInit client.PrmInit
+	// ...
+	c, _ := client.New(prmInit)
+
+	// Epoch when session will expire.
+	// Note that expiration starts since exp+1 epoch.
+	// For instance, now you have 8 epoch. You set exp=10. The session will be still valid during 10th epoch.
+	// Expiration starts since 11 epoch.
+	var exp uint64
+	var prm client.PrmSessionCreate
+	prm.SetExp(exp)
+
+	// The key is generated to simplify the example, in reality it's likely to come from configuration/wallet.
+	pk, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	signer := user.NewAutoIDSignerRFC6979(*pk)
+
+	res, _ := c.SessionCreate(context.Background(), signer, prm)
+
+	var id uuid.UUID
+	_ = id.UnmarshalBinary(res.ID())
+
+	// Public key for separate private key, which was created inside node for this session.
+	var key neofsecdsa.PublicKey
+	_ = key.Decode(res.PublicKey())
+
+	// Fill session parameters
+	var sessionObject session.Object
+	sessionObject.SetID(id)
+	sessionObject.SetAuthKey(&key)
+	sessionObject.SetExp(exp)
+
+	// Attach verb and container. Session allows to do just one action by time. In this example it is a VerbObjectPut.
+	// If you need Get, Delete, etc you should create another session.
+	sessionObject.ForVerb(session.VerbObjectPut)
+	// Session works only with one container.
+	sessionObject.BindContainer(cid.ID{})
+
+	// Finally, token must be signed by container owner or someone who allowed to do the Verb action. In our example
+	// it is VerbObjectPut.
+	_ = sessionObject.Sign(signer)
+
+	// ...
+
+	// This token will be used in object put operation
+	var prmPut client.PrmObjectPutInit
+	prmPut.WithinSession(sessionObject)
+	// ...
+}