stellar-stellar/src/session/session_manager.cpp

#include <time.h>
#include <stdlib.h>
#include <assert.h>

#include "macro.h"
#include "tcp_utils.h"
#include "udp_utils.h"
#include "id_generator.h"
#include "session_pool.h"
#include "session_table.h"
#include "session_timer.h"
#include "session_manager.h"
#include "session_transition.h"
#include "evicted_session_filter.h"
#include "duplicated_packet_filter.h"

struct session_manager
{
     struct list_head evicte_queue;
     struct session_pool *sess_pool;
     struct session_timer *sess_timer;
     struct session_table *tcp_sess_table;
     struct session_table *udp_sess_table;

     struct duplicated_packet_filter *dup_pkt_filter;
     struct evicted_session_filter *evicte_sess_filter;

     struct session_manager_stat stat;
     struct session_manager_options opts;
};

#define EVICTE_SESSION_BURST (RX_BURST_MAX)

/******************************************************************************
 * Session Manager Stat
 ******************************************************************************/

#define SESS_MGR_STAT_INC(stat, state, proto)            \
     {                                                   \
          switch ((state))                               \
          {                                              \
          case SESSION_STATE_OPENING:                    \
               (stat)->curr_nr_##proto##_sess_opening++; \
               break;                                    \
          case SESSION_STATE_ACTIVE:                     \
               (stat)->curr_nr_##proto##_sess_active++;  \
               break;                                    \
          case SESSION_STATE_CLOSING:                    \
               (stat)->curr_nr_##proto##_sess_closing++; \
               break;                                    \
          case SESSION_STATE_DISCARD:                    \
               (stat)->curr_nr_##proto##_sess_discard++; \
               break;                                    \
          case SESSION_STATE_CLOSED:                     \
               (stat)->curr_nr_##proto##_sess_closed++;  \
               break;                                    \
          default:                                       \
               break;                                    \
          }                                              \
     }

#define SESS_MGR_STAT_DEC(stat, state, proto)            \
     {                                                   \
          switch ((state))                               \
          {                                              \
          case SESSION_STATE_OPENING:                    \
               (stat)->curr_nr_##proto##_sess_opening--; \
               break;                                    \
          case SESSION_STATE_ACTIVE:                     \
               (stat)->curr_nr_##proto##_sess_active--;  \
               break;                                    \
          case SESSION_STATE_CLOSING:                    \
               (stat)->curr_nr_##proto##_sess_closing--; \
               break;                                    \
          case SESSION_STATE_DISCARD:                    \
               (stat)->curr_nr_##proto##_sess_discard--; \
               break;                                    \
          case SESSION_STATE_CLOSED:                     \
               (stat)->curr_nr_##proto##_sess_closed--;  \
               break;                                    \
          default:                                       \
               break;                                    \
          }                                              \
     }

#define SESS_MGR_STAT_UPDATE(stat, curr, next, proto) \
     {                                                \
          if (curr != next)                           \
          {                                           \
               SESS_MGR_STAT_DEC(stat, curr, proto);  \
               SESS_MGR_STAT_INC(stat, next, proto);  \
          }                                           \
     }

/******************************************************************************
 * Session Manager Options
 ******************************************************************************/

static int check_options(const struct session_manager_options *opts)
{
     if (opts == NULL)
     {
          SESSION_LOG_ERROR("invalid options");
          return -1;
     }

     // max session number
     if (opts->max_tcp_session_num < EVICTE_SESSION_BURST * 2)
     {
          SESSION_LOG_ERROR("invalid max_tcp_session_num: %lu, supported range: [%u, %lu]", opts->max_tcp_session_num, EVICTE_SESSION_BURST * 2, UINT64_MAX);
          return -1;
     }
     if (opts->max_udp_session_num < EVICTE_SESSION_BURST * 2)
     {
          SESSION_LOG_ERROR("invalid max_udp_session_num: %lu, supported range: [%u, %lu]", opts->max_udp_session_num, EVICTE_SESSION_BURST * 2, UINT64_MAX);
          return -1;
     }

     // session overload (skip)

     // TCP timeout
     if (opts->tcp_init_timeout < 1 || opts->tcp_init_timeout > 60000)
     {
          SESSION_LOG_ERROR("invalid tcp_init_timeout: %lu, supported range: [1, 60000]", opts->tcp_init_timeout);
          return -1;
     }
     if (opts->tcp_handshake_timeout < 1 || opts->tcp_handshake_timeout > 60000)
     {
          SESSION_LOG_ERROR("invalid tcp_handshake_timeout: %lu, supported range: [1, 60000]", opts->tcp_handshake_timeout);
          return -1;
     }
     if (opts->tcp_data_timeout < 1 || opts->tcp_data_timeout > 15999999000)
     {
          SESSION_LOG_ERROR("invalid tcp_data_timeout: %lu, supported range: [1, 15999999000]", opts->tcp_data_timeout);
          return -1;
     }
     if (opts->tcp_half_closed_timeout < 1 || opts->tcp_half_closed_timeout > 604800000)
     {
          SESSION_LOG_ERROR("invalid tcp_half_closed_timeout: %lu, supported range: [1, 604800000]", opts->tcp_half_closed_timeout);
          return -1;
     }
     if (opts->tcp_time_wait_timeout < 1 || opts->tcp_time_wait_timeout > 600000)
     {
          SESSION_LOG_ERROR("invalid tcp_time_wait_timeout: %lu, supported range: [1, 600000]", opts->tcp_time_wait_timeout);
          return -1;
     }
     if (opts->tcp_discard_timeout < 1 || opts->tcp_discard_timeout > 15999999000)
     {
          SESSION_LOG_ERROR("invalid tcp_discard_timeout: %lu, supported range: [1, 15999999000]", opts->tcp_discard_timeout);
          return -1;
     }
     if (opts->tcp_unverified_rst_timeout < 1 || opts->tcp_unverified_rst_timeout > 600000)
     {
          SESSION_LOG_ERROR("invalid tcp_unverified_rst_timeout: %lu, supported range: [1, 600000]", opts->tcp_unverified_rst_timeout);
          return -1;
     }
     // UDP timeout
     if (opts->udp_data_timeout < 1 || opts->udp_data_timeout > 15999999000)
     {
          SESSION_LOG_ERROR("invalid udp_data_timeout: %lu, supported range: [1, 15999999000]", opts->udp_data_timeout);
          return -1;
     }

     // duplicate packet filter
     if (opts->duplicated_packet_filter_enable)
     {
          if (opts->duplicated_packet_filter_capacity == 0)
          {
               // UINT32_MAX = 4294967295
               SESSION_LOG_ERROR("invalid duplicated_packet_filter_capacity: %u, supported range: [1, 4294967295]", opts->duplicated_packet_filter_capacity);
               return -1;
          }
          if (opts->duplicated_packet_filter_timeout < 1 || opts->duplicated_packet_filter_timeout > 60000)
          {
               SESSION_LOG_ERROR("invalid duplicated_packet_filter_timeout: %u, supported range: [1, 60000]", opts->duplicated_packet_filter_timeout);
               return -1;
          }
          if (opts->duplicated_packet_filter_error_rate < 0.0 || opts->duplicated_packet_filter_error_rate > 1.0)
          {
               SESSION_LOG_ERROR("invalid duplicated_packet_filter_error_rate: %f, supported range: [0.0, 1.0]", opts->duplicated_packet_filter_error_rate);
               return -1;
          }
     }

     // evicted session filter
     if (opts->evicted_session_filter_enable)
     {
          if (opts->evicted_session_filter_capacity == 0)
          {
               // UINT32_MAX = 4294967295
               SESSION_LOG_ERROR("invalid evicted_session_filter_capacity: %u, supported range: [1, 4294967295]", opts->evicted_session_filter_capacity);
               return -1;
          }
          if (opts->evicted_session_filter_timeout < 1 || opts->evicted_session_filter_timeout > 60000)
          {
               SESSION_LOG_ERROR("invalid evicted_session_filter_timeout: %u, supported range: [1, 60000]", opts->evicted_session_filter_timeout);
               return -1;
          }
          if (opts->evicted_session_filter_error_rate < 0.0 || opts->evicted_session_filter_error_rate > 1.0)
          {
               SESSION_LOG_ERROR("invalid evicted_session_filter_error_rate: %f, supported range: [0.0, 1.0]", opts->evicted_session_filter_error_rate);
               return -1;
          }
     }

     // TCP reassembly
     if (opts->tcp_reassembly_enable)
     {
          if (opts->tcp_reassembly_max_timeout < 1 || opts->tcp_reassembly_max_timeout > 60000)
          {
               SESSION_LOG_ERROR("invalid tcp_reassembly_max_timeout: %u, supported range: [1, 60000]", opts->tcp_reassembly_max_timeout);
               return -1;
          }
          if (opts->tcp_reassembly_max_segments < 2 || opts->tcp_reassembly_max_segments > 512)
          {
               SESSION_LOG_ERROR("invalid tcp_reassembly_max_segments: %u, supported range: [2, 512]", opts->tcp_reassembly_max_segments);
               return -1;
          }
     }

     return 0;
}

/******************************************************************************
 * TCP
 ******************************************************************************/

static void tcp_clean(struct session_manager *mgr, struct session *sess)
{
     struct tcp_reassembly *c2s_ssembler = sess->tcp_halfs[SESSION_DIRECTION_C2S].assembler;
     struct tcp_reassembly *s2c_ssembler = sess->tcp_halfs[SESSION_DIRECTION_S2C].assembler;
     struct tcp_segment *seg;
     if (c2s_ssembler)
     {
          while ((seg = tcp_reassembly_expire(c2s_ssembler, UINT64_MAX)))
          {
               session_inc_stat(sess, SESSION_DIRECTION_C2S, STAT_TCP_SEGS_RELEASED, 1);
               session_inc_stat(sess, SESSION_DIRECTION_C2S, STAT_TCP_PLDS_RELEASED, seg->len);
               mgr->stat.nr_tcp_seg_released++;
               tcp_segment_free(seg);
          }
          tcp_reassembly_free(c2s_ssembler);
     }
     if (s2c_ssembler)
     {
          while ((seg = tcp_reassembly_expire(s2c_ssembler, UINT64_MAX)))
          {
               session_inc_stat(sess, SESSION_DIRECTION_S2C, STAT_TCP_SEGS_RELEASED, 1);
               session_inc_stat(sess, SESSION_DIRECTION_S2C, STAT_TCP_PLDS_RELEASED, seg->len);
               mgr->stat.nr_tcp_seg_released++;
               tcp_segment_free(seg);
          }
          tcp_reassembly_free(s2c_ssembler);
     }
}

static int tcp_init(struct session_manager *mgr, struct session *sess)
{
     if (!mgr->opts.tcp_reassembly_enable)
     {
          return 0;
     }

     sess->tcp_halfs[SESSION_DIRECTION_C2S].assembler = tcp_reassembly_new(mgr->opts.tcp_reassembly_max_timeout, mgr->opts.tcp_reassembly_max_segments);
     sess->tcp_halfs[SESSION_DIRECTION_S2C].assembler = tcp_reassembly_new(mgr->opts.tcp_reassembly_max_timeout, mgr->opts.tcp_reassembly_max_segments);
     if (sess->tcp_halfs[SESSION_DIRECTION_C2S].assembler == NULL || sess->tcp_halfs[SESSION_DIRECTION_S2C].assembler == NULL)
     {
          tcp_clean(mgr, sess);
          return -1;
     }

     SESSION_LOG_DEBUG("session %lu %s new c2s tcp assembler %p, s2c tcp assembler %p",
                       session_get_id(sess), session_get_tuple_str(sess),
                       sess->tcp_halfs[SESSION_DIRECTION_C2S].assembler,
                       sess->tcp_halfs[SESSION_DIRECTION_S2C].assembler);

     return 0;
}

static void tcp_update(struct session_manager *mgr, struct session *sess, enum session_direction dir, const struct packet_layer *tcp_layer, uint64_t now)
{
     struct tcp_segment *seg;
     struct tcphdr *hdr = (struct tcphdr *)tcp_layer->hdr_ptr;
     struct tcp_half *half = &sess->tcp_halfs[dir];
     uint8_t flags = tcp_hdr_get_flags(hdr);
     uint16_t len = tcp_layer->pld_len;

     half->flags |= flags;
     half->seq = tcp_hdr_get_seq(hdr);
     half->ack = tcp_hdr_get_ack(hdr);
     half->len = tcp_layer->pld_len;

     if (!mgr->opts.tcp_reassembly_enable)
     {
          if (len)
          {
               session_inc_stat(sess, dir, STAT_TCP_SEGS_RX, 1);
               session_inc_stat(sess, dir, STAT_TCP_PLDS_RX, len);
               mgr->stat.nr_tcp_seg_received++;

               session_inc_stat(sess, dir, STAT_TCP_SEGS_INORDER, 1);
               session_inc_stat(sess, dir, STAT_TCP_PLDS_INORDER, len);
               mgr->stat.nr_tcp_seg_inorder++;

               half->in_order.data = tcp_layer->pld_ptr;
               half->in_order.len = len;
          }
          return;
     }

     if (unlikely(flags & TH_SYN))
     {
          // len > 0 is SYN with data (TCP Fast Open)
          tcp_reassembly_set_recv_next(half->assembler, len ? half->seq : half->seq + 1);
     }

     seg = tcp_reassembly_expire(half->assembler, now);
     if (seg)
     {
          session_inc_stat(sess, dir, STAT_TCP_SEGS_EXPIRED, 1);
          session_inc_stat(sess, dir, STAT_TCP_PLDS_EXPIRED, seg->len);
          mgr->stat.nr_tcp_seg_expired++;

          session_inc_stat(sess, dir, STAT_TCP_SEGS_RELEASED, 1);
          session_inc_stat(sess, dir, STAT_TCP_PLDS_RELEASED, seg->len);
          mgr->stat.nr_tcp_seg_released++;

          tcp_segment_free(seg);
     }

     if (len)
     {
          session_inc_stat(sess, dir, STAT_TCP_SEGS_RX, 1);
          session_inc_stat(sess, dir, STAT_TCP_PLDS_RX, len);
          mgr->stat.nr_tcp_seg_received++;

          uint32_t rcv_nxt = tcp_reassembly_get_recv_next(half->assembler);
          // in order
          if (half->seq == rcv_nxt)
          {
               session_inc_stat(sess, dir, STAT_TCP_SEGS_INORDER, 1);
               session_inc_stat(sess, dir, STAT_TCP_PLDS_INORDER, len);
               mgr->stat.nr_tcp_seg_inorder++;

               half->in_order.data = tcp_layer->pld_ptr;
               half->in_order.len = len;
               tcp_reassembly_inc_recv_next(half->assembler, len);
          }
          // retransmission
          else if (uint32_before(uint32_add(half->seq, len), rcv_nxt))
          {
               session_inc_stat(sess, dir, STAT_TCP_SEGS_RETRANSMIT, 1);
               session_inc_stat(sess, dir, STAT_TCP_PLDS_RETRANSMIT, len);
               mgr->stat.nr_tcp_seg_retransmit++;
          }
          else if ((seg = tcp_segment_new(half->seq, tcp_layer->pld_ptr, len)))
          {
               switch (tcp_reassembly_push(half->assembler, seg, now))
               {
               case -2:
                    session_inc_stat(sess, dir, STAT_TCP_SEGS_RETRANSMIT, 1);
                    session_inc_stat(sess, dir, STAT_TCP_PLDS_RETRANSMIT, len);
                    mgr->stat.nr_tcp_seg_retransmit++;
                    tcp_segment_free(seg);
               case -1:
                    session_inc_stat(sess, dir, STAT_TCP_SEGS_NOSPACE, 1);
                    session_inc_stat(sess, dir, STAT_TCP_PLDS_NOSPACE, len);
                    mgr->stat.nr_tcp_seg_no_space++;
                    tcp_segment_free(seg);
                    break;
               case 0:
                    session_inc_stat(sess, dir, STAT_TCP_SEGS_BUFFERED, 1);
                    session_inc_stat(sess, dir, STAT_TCP_PLDS_BUFFERED, len);
                    mgr->stat.nr_tcp_seg_buffered++;
                    break;
               case 1:
                    session_inc_stat(sess, dir, STAT_TCP_SEGS_OVERLAP, 1);
                    session_inc_stat(sess, dir, STAT_TCP_PLDS_OVERLAP, len);
                    mgr->stat.nr_tcp_seg_overlap++;

                    session_inc_stat(sess, dir, STAT_TCP_SEGS_BUFFERED, 1);
                    session_inc_stat(sess, dir, STAT_TCP_PLDS_BUFFERED, len);
                    mgr->stat.nr_tcp_seg_buffered++;
                    break;
               default:
                    assert(0);
                    break;
               }
          }
          else
          {
               session_inc_stat(sess, dir, STAT_TCP_SEGS_NOSPACE, 1);
               session_inc_stat(sess, dir, STAT_TCP_PLDS_NOSPACE, len);
               mgr->stat.nr_tcp_seg_no_space++;
          }
     }
}

/******************************************************************************
 * Session Direction
 ******************************************************************************/

static enum session_direction identify_direction_by_port(uint16_t src_port, uint16_t dst_port)
{
     // big port is client
     if (src_port > dst_port)
     {
          return SESSION_DIRECTION_C2S;
     }
     else if (src_port < dst_port)
     {
          return SESSION_DIRECTION_S2C;
     }
     else
     {
          // if port is equal, first packet is C2S
          return SESSION_DIRECTION_C2S;
     }
}

static enum session_direction identify_direction_by_history(const struct session *sess, const struct tuple6 *key)
{
     if (tuple6_cmp(session_get_tuple(sess), key) == 0)
     {
          return session_get_tuple_direction(sess);
     }
     else
     {
          return (session_get_tuple_direction(sess) == SESSION_DIRECTION_C2S ? SESSION_DIRECTION_S2C : SESSION_DIRECTION_C2S);
     }
}

/******************************************************************************
 * Session Filter
 ******************************************************************************/

// on new session
static int tcp_overload_bypass(struct session_manager *mgr, const struct tuple6 *key, uint64_t now)
{
     if (key->ip_proto == IPPROTO_TCP && mgr->stat.curr_nr_tcp_sess_used >= mgr->opts.max_tcp_session_num)
     {
          mgr->stat.nr_tcp_pkts_nospace_bypass++;
          return 1;
     }
     return 0;
}
static int udp_overload_bypass(struct session_manager *mgr, const struct tuple6 *key, uint64_t now)
{
     if (key->ip_proto == IPPROTO_UDP && mgr->stat.curr_nr_udp_sess_used >= mgr->opts.max_udp_session_num)
     {
          mgr->stat.nr_udp_pkts_nospace_bypass++;
          return 1;
     }
     return 0;
}
static int evicted_session_bypass(struct session_manager *mgr, const struct tuple6 *key, uint64_t now)
{
     if (mgr->opts.evicted_session_filter_enable && evicted_session_filter_lookup(mgr->evicte_sess_filter, key, now))
     {
          mgr->stat.nr_udp_pkts_evctd_bypass++;
          return 1;
     }

     return 0;
}
// on update session
static int duplicated_packet_bypass(struct session_manager *mgr, struct session *sess, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     if (mgr->opts.duplicated_packet_filter_enable == 0)
     {
          return 0;
     }

     enum session_direction dir = identify_direction_by_history(sess, key);
     if (session_get_stat(sess, dir, STAT_RAW_PKTS_RX) < 3 || session_has_dup_traffic(sess))
     {
          if (duplicated_packet_filter_lookup(mgr->dup_pkt_filter, pkt, now))
          {
               session_inc_stat(sess, dir, STAT_DUP_PKTS_BYPASS, 1);
               session_inc_stat(sess, dir, STAT_DUP_BYTES_BYPASS, packet_get_len(pkt));
               switch (session_get_type(sess))
               {
               case SESSION_TYPE_TCP:
                    mgr->stat.nr_tcp_pkts_duped_bypass++;
                    break;
               case SESSION_TYPE_UDP:
                    mgr->stat.nr_udp_pkts_duped_bypass++;
                    break;
               default:
                    assert(0);
                    break;
               }
               session_set_dup_traffic(sess);
               return 1;
          }
          else
          {
               duplicated_packet_filter_add(mgr->dup_pkt_filter, pkt, now);
               return 0;
          }
     }

     return 0;
}

/******************************************************************************
 * Session Manager
 ******************************************************************************/

static void session_update(struct session *sess, enum session_state next_state, const struct packet *pkt, const struct tuple6 *key, enum session_direction dir)
{
     struct timespec real;
     clock_gettime(CLOCK_REALTIME, &real); // must be realtime

     if (session_get_state(sess) == SESSION_STATE_INIT)
     {
          session_set_id(sess, id_generator_alloc());
          session_set_tuple(sess, key);
          session_set_tuple_direction(sess, dir);
          tuple6_to_str(key, sess->tuple_str, sizeof(sess->tuple_str));
          session_set_timestamp(sess, SESSION_TIMESTAMP_START, real.tv_sec);
          switch (key->ip_proto)
          {
          case IPPROTO_TCP:
               session_set_type(sess, SESSION_TYPE_TCP);
               break;
          case IPPROTO_UDP:
               session_set_type(sess, SESSION_TYPE_UDP);
               break;
          default:
               assert(0);
               break;
          }
     }

     session_inc_stat(sess, dir, STAT_RAW_PKTS_RX, 1);
     session_inc_stat(sess, dir, STAT_RAW_BYTES_RX, packet_get_len(pkt));

     if (!session_get_1st_packet(sess, dir))
     {
          struct route_ctx ctx = {0};
          struct sid_list list = {0};
          packet_get_route_ctx(pkt, &ctx);
          packet_get_sid_list(pkt, &list);

          session_set_1st_packet(sess, dir, pkt);
          session_set_route_ctx(sess, dir, &ctx);
          session_set_sid_list(sess, dir, &list);
     }

     session_set_current_packet(sess, pkt);
     session_set_current_direction(sess, dir);
     session_set_timestamp(sess, SESSION_TIMESTAMP_LAST, real.tv_sec);
     session_set_state(sess, next_state);
}

static void session_manager_evicte_session(struct session_manager *mgr, struct session *sess, uint64_t now)
{
     if (sess == NULL)
     {
          return;
     }

     // when session add to evicted queue, session lifetime is over
     enum session_state curr_state = session_get_state(sess);
     enum session_state next_state = session_transition_run(curr_state, LRU_EVICT);
     session_transition_log(sess, curr_state, next_state, LRU_EVICT);
     session_set_state(sess, next_state);
     if (!session_get_closing_reason(sess))
     {
          session_set_closing_reason(sess, CLOSING_BY_EVICTED);
     }
     session_timer_del(mgr->sess_timer, sess);
     list_add_tail(&sess->evicte, &mgr->evicte_queue);

     switch (session_get_type(sess))
     {
     case SESSION_TYPE_TCP:
          SESSION_LOG_DEBUG("evicte tcp old session: %lu", session_get_id(sess));
          session_table_del(mgr->tcp_sess_table, sess);
          SESS_MGR_STAT_UPDATE(&mgr->stat, curr_state, next_state, tcp);
          mgr->stat.nr_tcp_sess_evicted++;
          break;
     case SESSION_TYPE_UDP:
          SESSION_LOG_DEBUG("evicte udp old session: %lu", session_get_id(sess));
          session_table_del(mgr->udp_sess_table, sess);
          if (mgr->opts.evicted_session_filter_enable)
          {
               evicted_session_filter_add(mgr->evicte_sess_filter, session_get_tuple(sess), now);
          }
          SESS_MGR_STAT_UPDATE(&mgr->stat, curr_state, next_state, udp);
          mgr->stat.nr_udp_sess_evicted++;
          break;
     default:
          assert(0);
          break;
     }
}

static struct session *session_manager_new_tcp_session(struct session_manager *mgr, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     const struct packet_layer *tcp_layer = packet_get_innermost_layer(pkt, LAYER_TYPE_TCP);
     const struct tcphdr *hdr = (const struct tcphdr *)tcp_layer->hdr_ptr;
     uint8_t flags = tcp_hdr_get_flags(hdr);
     if (!(flags & TH_SYN))
     {
          mgr->stat.nr_tcp_pkts_nosess_bypass++;
          return NULL;
     }

     // tcp table full evict old session
     if (mgr->opts.tcp_overload_evict_old_sess && mgr->stat.curr_nr_tcp_sess_used >= mgr->opts.max_tcp_session_num - EVICTE_SESSION_BURST)
     {
          struct session *evic_sess = session_table_find_lru(mgr->tcp_sess_table);
          session_manager_evicte_session(mgr, evic_sess, now);
     }

     enum session_direction dir = (flags & TH_ACK) ? SESSION_DIRECTION_S2C : SESSION_DIRECTION_C2S;
     struct session *sess = session_pool_pop(mgr->sess_pool);
     if (sess == NULL)
     {
          assert(0);
          return NULL;
     }
     session_init(sess);
     sess->mgr_stat = &mgr->stat;

     enum session_state next_state = session_transition_run(SESSION_STATE_INIT, TCP_SYN);
     session_update(sess, next_state, pkt, key, dir);
     session_transition_log(sess, SESSION_STATE_INIT, next_state, TCP_SYN);

     if (tcp_init(mgr, sess) == -1)
     {
          assert(0);
          session_pool_push(mgr->sess_pool, sess);
          return NULL;
     }
     tcp_update(mgr, sess, dir, tcp_layer, now);

     uint64_t timeout = (flags & TH_ACK) ? mgr->opts.tcp_handshake_timeout : mgr->opts.tcp_init_timeout;
     session_timer_update(mgr->sess_timer, sess, now + timeout);
     session_table_add(mgr->tcp_sess_table, sess);

     if (mgr->opts.duplicated_packet_filter_enable)
     {
          duplicated_packet_filter_add(mgr->dup_pkt_filter, pkt, now);
     }

     SESS_MGR_STAT_INC(&mgr->stat, next_state, tcp);
     mgr->stat.curr_nr_tcp_sess_used++;
     mgr->stat.total_nr_tcp_sess_used++;

     return sess;
}

static struct session *session_manager_new_udp_session(struct session_manager *mgr, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     // udp table full evict old session
     if (mgr->opts.udp_overload_evict_old_sess && mgr->stat.curr_nr_udp_sess_used >= mgr->opts.max_udp_session_num - EVICTE_SESSION_BURST)
     {
          struct session *evic_sess = session_table_find_lru(mgr->udp_sess_table);
          session_manager_evicte_session(mgr, evic_sess, now);
     }

     struct session *sess = session_pool_pop(mgr->sess_pool);
     if (sess == NULL)
     {
          assert(sess);
          return NULL;
     }
     session_init(sess);
     sess->mgr_stat = &mgr->stat;

     enum session_direction dir = identify_direction_by_port(ntohs(key->src_port), ntohs(key->dst_port));
     enum session_state next_state = session_transition_run(SESSION_STATE_INIT, UDP_DATA);
     session_update(sess, next_state, pkt, key, dir);
     session_transition_log(sess, SESSION_STATE_INIT, next_state, UDP_DATA);

     session_timer_update(mgr->sess_timer, sess, now + mgr->opts.udp_data_timeout);
     session_table_add(mgr->udp_sess_table, sess);

     SESS_MGR_STAT_INC(&mgr->stat, next_state, udp);
     mgr->stat.curr_nr_udp_sess_used++;
     mgr->stat.total_nr_udp_sess_used++;

     return sess;
}

static int session_manager_update_tcp_session(struct session_manager *mgr, struct session *sess, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     const struct packet_layer *tcp_layer = packet_get_innermost_layer(pkt, LAYER_TYPE_TCP);
     const struct tcphdr *hdr = (const struct tcphdr *)tcp_layer->hdr_ptr;
     enum session_direction dir = identify_direction_by_history(sess, key);
     uint8_t flags = tcp_hdr_get_flags(hdr);
     int inputs = 0;
     inputs |= (flags & TH_SYN) ? TCP_SYN : NONE;
     inputs |= (flags & TH_FIN) ? TCP_FIN : NONE;
     inputs |= (flags & TH_RST) ? TCP_RST : NONE;
     inputs |= tcp_layer->pld_len ? TCP_DATA : NONE;

     // update state
     enum session_state curr_state = session_get_state(sess);
     enum session_state next_state = session_transition_run(curr_state, inputs);

     // update session
     session_update(sess, next_state, pkt, key, dir);
     session_transition_log(sess, curr_state, next_state, inputs);

     // update tcp
     tcp_update(mgr, sess, dir, tcp_layer, now);

     // set closing reason
     if (next_state == SESSION_STATE_CLOSING && !session_get_closing_reason(sess))
     {
          if (flags & TH_FIN)
          {
               session_set_closing_reason(sess, (dir == SESSION_DIRECTION_C2S ? CLOSING_BY_CLIENT_FIN : CLOSING_BY_SERVER_FIN));
          }
          if (flags & TH_RST)
          {
               session_set_closing_reason(sess, (dir == SESSION_DIRECTION_C2S ? CLOSING_BY_CLIENT_RST : CLOSING_BY_SERVER_RST));
          }
     }

     // update timeout
     struct tcp_half *curr = &sess->tcp_halfs[dir];
     struct tcp_half *peer = &sess->tcp_halfs[(dir == SESSION_DIRECTION_C2S ? SESSION_DIRECTION_S2C : SESSION_DIRECTION_C2S)];
     uint64_t timeout = 0;
     switch (next_state)
     {
     case SESSION_STATE_OPENING:
          if (flags & TH_SYN)
          {
               timeout = (flags & TH_ACK) ? mgr->opts.tcp_handshake_timeout : mgr->opts.tcp_init_timeout;
          }
          else
          {
               timeout = mgr->opts.tcp_data_timeout;
          }
          break;
     case SESSION_STATE_ACTIVE:
          timeout = mgr->opts.tcp_data_timeout;
          break;
     case SESSION_STATE_CLOSING:
          if (flags & TH_FIN)
          {
               timeout = (peer->flags & TH_FIN) ? mgr->opts.tcp_time_wait_timeout : mgr->opts.tcp_half_closed_timeout;
          }
          else if (flags & TH_RST)
          {
               // if fin is received, the expected sequence number should be increased by 1
               uint32_t expected = (peer->flags & TH_FIN) ? peer->ack + 1 : peer->ack;
               timeout = (expected == curr->seq) ? mgr->opts.tcp_time_wait_timeout : mgr->opts.tcp_unverified_rst_timeout;
          }
          else
          {
               timeout = mgr->opts.tcp_data_timeout;
          }
          break;
     case SESSION_STATE_DISCARD:
          timeout = mgr->opts.tcp_discard_timeout;
          break;
     default:
          assert(0);
          break;
     }
     session_timer_update(mgr->sess_timer, sess, now + timeout);

     SESS_MGR_STAT_UPDATE(&mgr->stat, curr_state, next_state, tcp);

     return 0;
}

static int session_manager_update_udp_session(struct session_manager *mgr, struct session *sess, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     enum session_direction dir = identify_direction_by_history(sess, key);
     enum session_state curr_state = session_get_state(sess);
     enum session_state next_state = session_transition_run(curr_state, UDP_DATA);
     session_update(sess, next_state, pkt, key, dir);
     session_transition_log(sess, curr_state, next_state, UDP_DATA);

     if (session_get_state(sess) == SESSION_STATE_DISCARD)
     {
          session_timer_update(mgr->sess_timer, sess, now + mgr->opts.udp_discard_timeout);
     }
     else
     {
          session_timer_update(mgr->sess_timer, sess, now + mgr->opts.udp_data_timeout);
     }

     SESS_MGR_STAT_UPDATE(&mgr->stat, curr_state, next_state, udp);

     return 0;
}

/******************************************************************************
 * Public API
 ******************************************************************************/

struct session_manager *session_manager_new(struct session_manager_options *opts, uint64_t now)
{
     if (check_options(opts) == -1)
     {
          return NULL;
     }

     struct session_manager *mgr = (struct session_manager *)calloc(1, sizeof(struct session_manager));
     if (mgr == NULL)
     {
          return NULL;
     }
     memcpy(&mgr->opts, opts, sizeof(struct session_manager_options));

     mgr->sess_pool = session_pool_new(mgr->opts.max_tcp_session_num + mgr->opts.max_udp_session_num);
     mgr->tcp_sess_table = session_table_new();
     mgr->udp_sess_table = session_table_new();
     mgr->sess_timer = session_timer_new(now);
     if (mgr->sess_pool == NULL || mgr->tcp_sess_table == NULL || mgr->udp_sess_table == NULL || mgr->sess_timer == NULL)
     {
          goto error;
     }
     if (mgr->opts.evicted_session_filter_enable)
     {
          mgr->evicte_sess_filter = evicted_session_filter_new(mgr->opts.evicted_session_filter_capacity,
                                                               mgr->opts.evicted_session_filter_timeout,
                                                               mgr->opts.evicted_session_filter_error_rate, now);
          if (mgr->evicte_sess_filter == NULL)
          {
               goto error;
          }
     }
     if (mgr->opts.duplicated_packet_filter_enable)
     {
          mgr->dup_pkt_filter = duplicated_packet_filter_new(mgr->opts.duplicated_packet_filter_capacity,
                                                             mgr->opts.duplicated_packet_filter_timeout,
                                                             mgr->opts.duplicated_packet_filter_error_rate, now);
          if (mgr->dup_pkt_filter == NULL)
          {
               goto error;
          }
     }

     INIT_LIST_HEAD(&mgr->evicte_queue);
     session_transition_init();

     return mgr;

error:
     session_manager_free(mgr);
     return NULL;
}

void session_manager_free(struct session_manager *mgr)
{
     struct session *sess;
     if (mgr)
     {
          // free all evicted session
          while (!list_empty(&mgr->evicte_queue))
          {
               sess = list_first_entry(&mgr->evicte_queue, struct session, evicte);
               list_del(&sess->evicte);
               session_manager_free_session(mgr, sess);
          }
          // free all udp session
          while (mgr->udp_sess_table && (sess = session_table_find_lru(mgr->udp_sess_table)))
          {
               session_manager_free_session(mgr, sess);
          }
          // free all tcp session
          while (mgr->tcp_sess_table && (sess = session_table_find_lru(mgr->tcp_sess_table)))
          {
               session_manager_free_session(mgr, sess);
          }
          if (mgr->opts.evicted_session_filter_enable)
          {
               evicted_session_filter_free(mgr->evicte_sess_filter);
          }
          if (mgr->opts.duplicated_packet_filter_enable)
          {
               duplicated_packet_filter_free(mgr->dup_pkt_filter);
          }
          session_timer_free(mgr->sess_timer);
          session_table_free(mgr->udp_sess_table);
          session_table_free(mgr->tcp_sess_table);
          session_pool_free(mgr->sess_pool);
          free(mgr);
          mgr = NULL;
     }
}

struct session *session_manager_new_session(struct session_manager *mgr, const struct packet *pkt, uint64_t now)
{
     struct tuple6 key;
     if (packet_get_innermost_tuple6(pkt, &key))
     {
          return NULL;
     }
     switch (key.ip_proto)
     {
     case IPPROTO_TCP:
          if (tcp_overload_bypass(mgr, &key, now))
          {
               return NULL;
          }
          return session_manager_new_tcp_session(mgr, pkt, &key, now);
     case IPPROTO_UDP:
          if (udp_overload_bypass(mgr, &key, now))
          {
               return NULL;
          }
          if (evicted_session_bypass(mgr, &key, now))
          {
               return NULL;
          }
          return session_manager_new_udp_session(mgr, pkt, &key, now);
     default:
          return NULL;
     }
}

void session_manager_free_session(struct session_manager *mgr, struct session *sess)
{
     if (sess)
     {
          SESSION_LOG_DEBUG("session %lu closed (%s)", session_get_id(sess), closing_reason_to_str(session_get_closing_reason(sess)));

          session_timer_del(mgr->sess_timer, sess);
          switch (session_get_type(sess))
          {
          case SESSION_TYPE_TCP:
               tcp_clean(mgr, sess);
               if (session_table_find_sessid(mgr->tcp_sess_table, session_get_id(sess)) == sess)
               {
                    session_table_del(mgr->tcp_sess_table, sess);
               }
               SESS_MGR_STAT_DEC(&mgr->stat, session_get_state(sess), tcp);
               mgr->stat.curr_nr_tcp_sess_used--;
               break;
          case SESSION_TYPE_UDP:
               if (session_table_find_sessid(mgr->udp_sess_table, session_get_id(sess)) == sess)
               {
                    session_table_del(mgr->udp_sess_table, sess);
               }
               SESS_MGR_STAT_DEC(&mgr->stat, session_get_state(sess), udp);
               mgr->stat.curr_nr_udp_sess_used--;
               break;
          default:
               assert(0);
               break;
          }

          session_free_all_ex_data(sess);
          packet_free((struct packet *)session_get_1st_packet(sess, SESSION_DIRECTION_C2S));
          packet_free((struct packet *)session_get_1st_packet(sess, SESSION_DIRECTION_S2C));
          session_set_1st_packet(sess, SESSION_DIRECTION_C2S, NULL);
          session_set_1st_packet(sess, SESSION_DIRECTION_S2C, NULL);
          session_clear_route_ctx(sess, SESSION_DIRECTION_C2S);
          session_clear_route_ctx(sess, SESSION_DIRECTION_S2C);
          session_clear_sid_list(sess, SESSION_DIRECTION_C2S);
          session_clear_sid_list(sess, SESSION_DIRECTION_S2C);
          session_set_current_packet(sess, NULL);
          session_set_current_direction(sess, SESSION_DIRECTION_NONE);
          session_pool_push(mgr->sess_pool, sess);
          sess = NULL;
     }
}

struct session *session_manager_lookup_session(struct session_manager *mgr, const struct packet *pkt)
{
     struct tuple6 key;
     if (packet_get_innermost_tuple6(pkt, &key))
     {
          return NULL;
     }
     switch (key.ip_proto)
     {
     case IPPROTO_UDP:
          return session_table_find_tuple6(mgr->udp_sess_table, &key);
     case IPPROTO_TCP:
          return session_table_find_tuple6(mgr->tcp_sess_table, &key);
     default:
          return NULL;
     }
}

int session_manager_update_session(struct session_manager *mgr, struct session *sess, const struct packet *pkt, uint64_t now)
{
     struct tuple6 key;
     if (packet_get_innermost_tuple6(pkt, &key))
     {
          return -1;
     }
     if (duplicated_packet_bypass(mgr, sess, pkt, &key, now))
     {
          return -1;
     }
     switch (session_get_type(sess))
     {
     case SESSION_TYPE_TCP:
          return session_manager_update_tcp_session(mgr, sess, pkt, &key, now);
     case SESSION_TYPE_UDP:
          return session_manager_update_udp_session(mgr, sess, pkt, &key, now);
     default:
          return -1;
     }
}

struct session *session_manager_get_expired_session(struct session_manager *mgr, uint64_t now)
{
     struct session *sess = session_timer_expire(mgr->sess_timer, now);
     if (sess)
     {
          enum session_state curr_state = session_get_state(sess);
          enum session_state next_state = session_transition_run(curr_state, TIMEOUT);
          session_transition_log(sess, curr_state, next_state, TIMEOUT);
          session_set_state(sess, next_state);

          switch (session_get_type(sess))
          {
          case SESSION_TYPE_TCP:
               SESS_MGR_STAT_UPDATE(&mgr->stat, curr_state, next_state, tcp);
               break;
          case SESSION_TYPE_UDP:
               SESS_MGR_STAT_UPDATE(&mgr->stat, curr_state, next_state, udp);
               break;
          default:
               assert(0);
               break;
          }

          // next state is closed, need to free session
          if (next_state == SESSION_STATE_CLOSED)
          {
               if (!session_get_closing_reason(sess))
               {
                    session_set_closing_reason(sess, CLOSING_BY_TIMEOUT);
               }
               return sess;
          }
          // next state is closing, only update timeout
          else
          {
               switch (session_get_type(sess))
               {
               case SESSION_TYPE_TCP:
                    session_timer_update(mgr->sess_timer, sess, now + mgr->opts.tcp_data_timeout);
                    break;
               case SESSION_TYPE_UDP:
                    session_timer_update(mgr->sess_timer, sess, now + mgr->opts.udp_data_timeout);
                    break;
               default:
                    assert(0);
                    break;
               }
               return NULL;
          }
     }

     return NULL;
}

struct session *session_manager_get_evicted_session(struct session_manager *mgr)
{
     if (list_empty(&mgr->evicte_queue))
     {
          return NULL;
     }
     else
     {
          struct session *sess = list_first_entry(&mgr->evicte_queue, struct session, evicte);
          list_del(&sess->evicte);
          return sess;
     }
}

uint64_t session_manager_get_expire_interval(struct session_manager *mgr)
{
     return session_timer_next_expire_interval(mgr->sess_timer);
}

struct session_manager_stat *session_manager_stat(struct session_manager *mgr)
{
     return &mgr->stat;
}