HELP-58644 Add RequireNew session option (#13)

* HELP-58644 Add RequireNew option

* HELP-58644 Update field comment

* HELP-58644 Clarify RequireNew usage

* HELP-58644 Mark single-checkout servers as dirty

mongo/client.go

@@ -408,6 +408,9 @@ func (c *Client) StartSession(opts ...*options.SessionOptions) (Session, error)
 	if sopts.Snapshot != nil {
 		coreOpts.Snapshot = sopts.Snapshot
 	}
+	if sopts.RequireNew != nil {
+		coreOpts.RequireNew = sopts.RequireNew
+	}
 
 	sess, err := session.NewClientSession(c.sessionPool, c.id, coreOpts)
 	if err != nil {

mongo/options/sessionoptions.go

@@ -48,6 +48,11 @@ type SessionOptions struct {
 	// be set to true if CausalConsistency is set to true. Transactions and write operations are not allowed on
 	// snapshot sessions and will error. The default value is false.
 	Snapshot *bool
+
+	// RequireNew ensures that starting a session with a client creates a new
+	// server session rather than checking one out from the pool. Since this
+	// avoids pooling, closing the server session is up to the caller.
+	RequireNew *bool
 }
 
 // Session creates a new SessionOptions instance.
@@ -96,6 +101,12 @@ func (s *SessionOptions) SetSnapshot(b bool) *SessionOptions {
 	return s
 }
 
+// SetRequireNew sets the value for the RequireNew field.
+func (s *SessionOptions) SetRequireNew(b bool) *SessionOptions {
+	s.RequireNew = &b
+	return s
+}
+
 // MergeSessionOptions combines the given SessionOptions instances into a single SessionOptions in a last-one-wins
 // fashion.
 //
@@ -125,6 +136,9 @@ func MergeSessionOptions(opts ...*SessionOptions) *SessionOptions {
 		if opt.Snapshot != nil {
 			s.Snapshot = opt.Snapshot
 		}
+		if opt.RequireNew != nil {
+			s.RequireNew = opt.RequireNew
+		}
 	}
 	if s.CausalConsistency == nil && (s.Snapshot == nil || !*s.Snapshot) {
 		s.CausalConsistency = &DefaultCausalConsistency

x/mongo/driver/session/client_session.go

@@ -133,6 +133,7 @@ type Client struct {
 	RecoveryToken    bson.Raw
 	PinnedConnection LoadBalancedTransactionConnection
 	SnapshotTime     *primitive.Timestamp
+	RequireNew       bool
 }
 
 func getClusterTime(clusterTime bson.Raw) (uint32, uint32) {
@@ -207,6 +208,9 @@ func NewClientSession(pool *Pool, clientID uuid.UUID, opts ...*ClientOptions) (*
 	if mergedOpts.Snapshot != nil {
 		c.Snapshot = *mergedOpts.Snapshot
 	}
+	if mergedOpts.RequireNew != nil {
+		c.RequireNew = *mergedOpts.RequireNew
+	}
 
 	// For explicit sessions, the default for causalConsistency is true, unless Snapshot is
 	// enabled, then it's false. Set the default and then allow any explicit causalConsistency
@@ -230,7 +234,17 @@ func NewClientSession(pool *Pool, clientID uuid.UUID, opts ...*ClientOptions) (*
 // SetServer will check out a session from the client session pool.
 func (c *Client) SetServer() error {
 	var err error
-	c.Server, err = c.pool.GetSession()
+	if c.RequireNew {
+		c.Server, err = newServerSession()
+
+		// Mark the server as dirty so that it won't be returned to the pool.
+		if c.Server != nil {
+			c.Server.MarkDirty()
+		}
+	} else {
+		c.Server, err = c.pool.GetSession()
+	}
+
 	return err
 }
 

x/mongo/driver/session/options.go

@@ -22,6 +22,7 @@ type ClientOptions struct {
 	DefaultReadPreference *readpref.ReadPref
 	DefaultMaxCommitTime  *time.Duration
 	Snapshot              *bool
+	RequireNew            *bool
 }
 
 // TransactionOptions represents all possible options for starting a transaction in a session.
@@ -56,6 +57,9 @@ func mergeClientOptions(opts ...*ClientOptions) *ClientOptions {
 		if opt.Snapshot != nil {
 			c.Snapshot = opt.Snapshot
 		}
+		if opt.RequireNew != nil {
+			c.RequireNew = opt.RequireNew
+		}
 	}
 
 	return c