feat: 提供Member的遍历方法，提供从sessionId获取session的方法。

group.go

@@ -51,24 +51,48 @@ func (c *Group) Member(uid int64) (*session.Session, error) {
 	return nil, ErrMemberNotFound
 }
 
-// Members returns all members in current group
-func (c *Group) Members() map[int64]*session.Session {
+// MemberBySID returns specified sId's session
+func (c *Group) MemberBySID(id int64) (*session.Session, error) {
 	c.mu.RLock()
 	defer c.mu.RUnlock()
 
-	return c.sessions
+	for sId, s := range c.sessions {
+		if sId == id {
+			return s, nil
+		}
+	}
+
+	return nil, ErrMemberNotFound
+}
+
+func (c *Group) Members() []*session.Session {
+	var resp []*session.Session
+	c.PeekMembers(func(_ int64, s *session.Session) bool {
+		resp = append(resp, s)
+		return true
+	})
+	return resp
 }
 
-// MemberIDs returns all member's UID in current group
-func (c *Group) MemberIDs() []int64 {
+// PeekMembers returns all members in current group
+func (c *Group) PeekMembers(fn func(sId int64, s *session.Session) bool) {
 	c.mu.RLock()
 	defer c.mu.RUnlock()
 
-	var members []int64
-	for _, s := range c.sessions {
-		members = append(members, s.UID())
+	for sId, s := range c.sessions {
+		if !fn(sId, s) {
+			break
+		}
 	}
+}
 
+// MemberUIDs returns all member's UID in current group
+func (c *Group) MemberUIDs() []int64 {
+	var members []int64
+	c.PeekMembers(func(_ int64, s *session.Session) bool {
+		members = append(members, s.UID())
+		return false
+	})
 	return members
 }