/** * Connects to another host. The function given as the "connected" * argument will be called when the connection has been established. * * @param pcb the tcp_pcb used to establish the connection * @param ipaddr the remote ip address to connect to * @param port the remote tcp port to connect to * @param connected callback function to call when connected (or on error) * @return ERR_VAL if invalid arguments are given * ERR_OK if connect request has been sent * other err_t values if connect request couldn't be sent */ err_t tcp_connect(struct tcp_pcb *pcb, struct ip_addr *ipaddr, u16_t port, err_t (* connected)(void *arg, struct tcp_pcb *tpcb, err_t err)) { err_t ret; u32_t iss; LWIP_ERROR("tcp_connect: can only connected from state CLOSED", pcb->state == CLOSED, return ERR_ISCONN); LWIP_DEBUGF(TCP_DEBUG, ("tcp_connect to port %"U16_F"\n", port)); /* 远端IP地址有效,则记录到TCP控制块中 */ if (ipaddr != NULL) { pcb->remote_ip = *ipaddr; } else { return ERR_VAL; } /* 记录远端PORT */ pcb->remote_port = port; /* 如果本地端口未绑定,则绑定一个短暂端口 */ if (pcb->local_port == 0) { pcb->local_port = tcp_new_port(); } /* 获取初始序号 */ iss = tcp_next_iss(); /* 设置接收窗口下一个接收的序号 */ pcb->rcv_nxt = 0; /* 设置发送窗口各个字段 */ pcb->snd_nxt = iss; pcb->lastack = iss - 1; pcb->snd_lbb = iss - 1; /* 设置接收窗口各个字段 */ pcb->rcv_wnd = TCP_WND; pcb->rcv_ann_wnd = TCP_WND; pcb->rcv_ann_right_edge = pcb->rcv_nxt; pcb->snd_wnd = TCP_WND; /* As initial send MSS, we use TCP_MSS but limit it to 536. The send MSS is updated when an MSS option is received. */ /* 设置MSS */ pcb->mss = (TCP_MSS > 536) ? 536 : TCP_MSS; #if TCP_CALCULATE_EFF_SEND_MSS pcb->mss = tcp_eff_send_mss(pcb->mss, ipaddr); #endif /* TCP_CALCULATE_EFF_SEND_MSS */ /* 初始化阻塞窗口 */ pcb->cwnd = 1; pcb->ssthresh = pcb->mss * 10; /* TCP控制块状态设为SYN_SENT */ pcb->state = SYN_SENT; #if LWIP_CALLBACK_API /* 设置回调函数 */ pcb->connected = connected; #endif /* LWIP_CALLBACK_API */ /* 把TCP控制块从tcp_bound_pcbs链表移除 */ TCP_RMV(&tcp_bound_pcbs, pcb); /* 把TCP控制块插入tcp_active_pcbs链表 */ TCP_REG(&tcp_active_pcbs, pcb); snmp_inc_tcpactiveopens(); /* 构造TCP报文,长度为0,SYN置1,并包含MSS选项字段 */ ret = tcp_enqueue(pcb, NULL, 0, TCP_SYN, 0, TF_SEG_OPTS_MSS #if LWIP_TCP_TIMESTAMPS | TF_SEG_OPTS_TS #endif ); if (ret == ERR_OK) { /* 发送构造的TCP报文 */ tcp_output(pcb); } return ret; }
/** * Called by tcp_input() when a segment arrives for a listening * connection (from tcp_input()). * * @param pcb the tcp_pcb_listen for which a segment arrived * @return ERR_OK if the segment was processed * another err_t on error * * @note the return value is not (yet?) used in tcp_input() * @note the segment which arrived is saved in global variables, therefore only the pcb * involved is passed as a parameter to this function */ static err_t tcp_listen_input(struct tcp_pcb_listen *pcb) { struct tcp_pcb *npcb; u32_t optdata; /* In the LISTEN state, we check for incoming SYN segments, creates a new PCB, and responds with a SYN|ACK. */ if (flags & TCP_ACK) { /* For incoming segments with the ACK flag set, respond with a RST. */ LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_listen_input: ACK in LISTEN, sending reset\n")); tcp_rst(ackno + 1, seqno + tcplen, &(iphdr->dest), &(iphdr->src), tcphdr->dest, tcphdr->src); } else if (flags & TCP_SYN) { LWIP_DEBUGF(TCP_DEBUG, ("TCP connection request %"U16_F" -> %"U16_F".\n", tcphdr->src, tcphdr->dest)); #if TCP_LISTEN_BACKLOG if (pcb->accepts_pending >= pcb->backlog) { return ERR_ABRT; } #endif /* TCP_LISTEN_BACKLOG */ npcb = tcp_alloc(pcb->prio); /* If a new PCB could not be created (probably due to lack of memory), we don't do anything, but rely on the sender will retransmit the SYN at a time when we have more memory available. */ if (npcb == NULL) { LWIP_DEBUGF(TCP_DEBUG, ("tcp_listen_input: could not allocate PCB\n")); TCP_STATS_INC(tcp.memerr); return ERR_MEM; } #if TCP_LISTEN_BACKLOG pcb->accepts_pending++; #endif /* TCP_LISTEN_BACKLOG */ /* Set up the new PCB. */ ip_addr_set(&(npcb->local_ip), &(iphdr->dest)); npcb->local_port = pcb->local_port; ip_addr_set(&(npcb->remote_ip), &(iphdr->src)); npcb->remote_port = tcphdr->src; npcb->state = SYN_RCVD; npcb->rcv_nxt = seqno + 1; npcb->snd_wnd = tcphdr->wnd; npcb->ssthresh = npcb->snd_wnd; npcb->snd_wl1 = seqno - 1;/* initialise to seqno-1 to force window update */ npcb->callback_arg = pcb->callback_arg; #if LWIP_CALLBACK_API npcb->accept = pcb->accept; #endif /* LWIP_CALLBACK_API */ /* inherit socket options */ npcb->so_options = pcb->so_options & (SOF_DEBUG|SOF_DONTROUTE|SOF_KEEPALIVE|SOF_OOBINLINE|SOF_LINGER); /* Register the new PCB so that we can begin receiving segments for it. */ TCP_REG(&tcp_active_pcbs, npcb); /* Parse any options in the SYN. */ tcp_parseopt(npcb); #if TCP_CALCULATE_EFF_SEND_MSS npcb->mss = tcp_eff_send_mss(npcb->mss, &(npcb->remote_ip)); #endif /* TCP_CALCULATE_EFF_SEND_MSS */ snmp_inc_tcppassiveopens(); /* Build an MSS option. */ optdata = TCP_BUILD_MSS_OPTION(); /* Send a SYN|ACK together with the MSS option. */ tcp_enqueue(npcb, NULL, 0, TCP_SYN | TCP_ACK, 0, (u8_t *)&optdata, 4); return tcp_output(npcb); } return ERR_OK; }
/** * Implements the TCP state machine. Called by tcp_input. In some * states tcp_receive() is called to receive data. The tcp_seg * argument will be freed by the caller (tcp_input()) unless the * recv_data pointer in the pcb is set. * * @param pcb the tcp_pcb for which a segment arrived * * @note the segment which arrived is saved in global variables, therefore only the pcb * involved is passed as a parameter to this function */ static err_t tcp_process(struct tcp_pcb *pcb) { struct tcp_seg *rseg; u8_t acceptable = 0; err_t err; u8_t accepted_inseq; err = ERR_OK; /* Process incoming RST segments. */ if (flags & TCP_RST) { /* First, determine if the reset is acceptable. */ if (pcb->state == SYN_SENT) { if (ackno == pcb->snd_nxt) { acceptable = 1; } } else { if (TCP_SEQ_BETWEEN(seqno, pcb->rcv_nxt, pcb->rcv_nxt+pcb->rcv_ann_wnd)) { acceptable = 1; } } if (acceptable) { LWIP_DEBUGF(TCP_INPUT_DEBUG, ("tcp_process: Connection RESET\n")); LWIP_ASSERT("tcp_input: pcb->state != CLOSED", pcb->state != CLOSED); recv_flags = TF_RESET; pcb->flags &= ~TF_ACK_DELAY; return ERR_RST; } else { LWIP_DEBUGF(TCP_INPUT_DEBUG, ("tcp_process: unacceptable reset seqno %"U32_F" rcv_nxt %"U32_F"\n", seqno, pcb->rcv_nxt)); LWIP_DEBUGF(TCP_DEBUG, ("tcp_process: unacceptable reset seqno %"U32_F" rcv_nxt %"U32_F"\n", seqno, pcb->rcv_nxt)); return ERR_OK; } } /* Update the PCB (in)activity timer. */ pcb->tmr = tcp_ticks; pcb->keep_cnt_sent = 0; /* Do different things depending on the TCP state. */ switch (pcb->state) { case SYN_SENT: LWIP_DEBUGF(TCP_INPUT_DEBUG, ("SYN-SENT: ackno %"U32_F" pcb->snd_nxt %"U32_F" unacked %"U32_F"\n", ackno, pcb->snd_nxt, ntohl(pcb->unacked->tcphdr->seqno))); /* received SYN ACK with expected sequence number? */ if ((flags & TCP_ACK) && (flags & TCP_SYN) && ackno == ntohl(pcb->unacked->tcphdr->seqno) + 1) { pcb->snd_buf++; pcb->rcv_nxt = seqno + 1; pcb->lastack = ackno; pcb->snd_wnd = tcphdr->wnd; pcb->snd_wl1 = seqno - 1; /* initialise to seqno - 1 to force window update */ pcb->state = ESTABLISHED; /* Parse any options in the SYNACK before using pcb->mss since that * can be changed by the received options! */ tcp_parseopt(pcb); #if TCP_CALCULATE_EFF_SEND_MSS pcb->mss = tcp_eff_send_mss(pcb->mss, &(pcb->remote_ip)); #endif /* TCP_CALCULATE_EFF_SEND_MSS */ /* Set ssthresh again after changing pcb->mss (already set in tcp_connect * but for the default value of pcb->mss) */ pcb->ssthresh = pcb->mss * 10; pcb->cwnd = ((pcb->cwnd == 1) ? (pcb->mss * 2) : pcb->mss); LWIP_ASSERT("pcb->snd_queuelen > 0", (pcb->snd_queuelen > 0)); --pcb->snd_queuelen; LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_process: SYN-SENT --queuelen %"U16_F"\n", (u16_t)pcb->snd_queuelen)); rseg = pcb->unacked; pcb->unacked = rseg->next; /* If there's nothing left to acknowledge, stop the retransmit timer, otherwise reset it to start again */ if(pcb->unacked == NULL) pcb->rtime = -1; else { pcb->rtime = 0; pcb->nrtx = 0; } tcp_seg_free(rseg); /* Call the user specified function to call when sucessfully * connected. */ TCP_EVENT_CONNECTED(pcb, ERR_OK, err); tcp_ack_now(pcb); } /* received ACK? possibly a half-open connection */ else if (flags & TCP_ACK) { /* send a RST to bring the other side in a non-synchronized state. */ tcp_rst(ackno, seqno + tcplen, &(iphdr->dest), &(iphdr->src), tcphdr->dest, tcphdr->src); } break; case SYN_RCVD: if (flags & TCP_ACK && !(flags & TCP_RST)) { /* expected ACK number? */ if (TCP_SEQ_BETWEEN(ackno, pcb->lastack+1, pcb->snd_nxt)) { u16_t old_cwnd; pcb->state = ESTABLISHED; LWIP_DEBUGF(TCP_DEBUG, ("TCP connection established %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest)); #if LWIP_CALLBACK_API LWIP_ASSERT("pcb->accept != NULL", pcb->accept != NULL); #endif /* Call the accept function. */ TCP_EVENT_ACCEPT(pcb, ERR_OK, err); if (err != ERR_OK) { /* If the accept function returns with an error, we abort * the connection. */ tcp_abort(pcb); return ERR_ABRT; } old_cwnd = pcb->cwnd; /* If there was any data contained within this ACK, * we'd better pass it on to the application as well. */ accepted_inseq = tcp_receive(pcb); pcb->cwnd = ((old_cwnd == 1) ? (pcb->mss * 2) : pcb->mss); if ((flags & TCP_FIN) && accepted_inseq) { tcp_ack_now(pcb); pcb->state = CLOSE_WAIT; } } /* incorrect ACK number */ else { /* send RST */ tcp_rst(ackno, seqno + tcplen, &(iphdr->dest), &(iphdr->src), tcphdr->dest, tcphdr->src); } } break; case CLOSE_WAIT: /* FALLTHROUGH */ case ESTABLISHED: accepted_inseq = tcp_receive(pcb); if ((flags & TCP_FIN) && accepted_inseq) { /* passive close */ tcp_ack_now(pcb); pcb->state = CLOSE_WAIT; } break; case FIN_WAIT_1: tcp_receive(pcb); if (flags & TCP_FIN) { if (flags & TCP_ACK && ackno == pcb->snd_nxt) { LWIP_DEBUGF(TCP_DEBUG, ("TCP connection closed %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest)); tcp_ack_now(pcb); tcp_pcb_purge(pcb); TCP_RMV(&tcp_active_pcbs, pcb); pcb->state = TIME_WAIT; TCP_REG(&tcp_tw_pcbs, pcb); } else { tcp_ack_now(pcb); pcb->state = CLOSING; } } else if (flags & TCP_ACK && ackno == pcb->snd_nxt) { pcb->state = FIN_WAIT_2; } break; case FIN_WAIT_2: tcp_receive(pcb); if (flags & TCP_FIN) { LWIP_DEBUGF(TCP_DEBUG, ("TCP connection closed %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest)); tcp_ack_now(pcb); tcp_pcb_purge(pcb); TCP_RMV(&tcp_active_pcbs, pcb); pcb->state = TIME_WAIT; TCP_REG(&tcp_tw_pcbs, pcb); } break; case CLOSING: tcp_receive(pcb); if (flags & TCP_ACK && ackno == pcb->snd_nxt) { LWIP_DEBUGF(TCP_DEBUG, ("TCP connection closed %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest)); tcp_ack_now(pcb); tcp_pcb_purge(pcb); TCP_RMV(&tcp_active_pcbs, pcb); pcb->state = TIME_WAIT; TCP_REG(&tcp_tw_pcbs, pcb); } break; case LAST_ACK: tcp_receive(pcb); if (flags & TCP_ACK && ackno == pcb->snd_nxt) { LWIP_DEBUGF(TCP_DEBUG, ("TCP connection closed %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest)); /* bugfix #21699: don't set pcb->state to CLOSED here or we risk leaking segments */ recv_flags = TF_CLOSED; } break; default: break; } return ERR_OK; }
/** * Connects to another host. The function given as the "connected" * argument will be called when the connection has been established. * * @param pcb the tcp_pcb used to establish the connection * @param ipaddr the remote ip address to connect to * @param port the remote tcp port to connect to * @param connected callback function to call when connected (or on error) * @return ERR_VAL if invalid arguments are given * ERR_OK if connect request has been sent * other err_t values if connect request couldn't be sent */ err_t tcp_connect(struct tcp_pcb *pcb, ip_addr_t *ipaddr, u16_t port, tcp_connected_fn connected) { err_t ret; u32_t iss; u16_t old_local_port; LWIP_ERROR("tcp_connect: can only connect from state CLOSED", pcb->state == CLOSED, return ERR_ISCONN); LWIP_DEBUGF(TCP_DEBUG, ("tcp_connect to port %"U16_F"\n", port)); if (ipaddr != NULL) { pcb->remote_ip = *ipaddr; } else { return ERR_VAL; } pcb->remote_port = port; /* check if we have a route to the remote host */ if (ip_addr_isany(&(pcb->local_ip))) { /* no local IP address set, yet. */ struct netif *netif = ip_route(&(pcb->remote_ip)); if (netif == NULL) { /* Don't even try to send a SYN packet if we have no route since that will fail. */ return ERR_RTE; } /* Use the netif's IP address as local address. */ ip_addr_copy(pcb->local_ip, netif->ip_addr); } old_local_port = pcb->local_port; if (pcb->local_port == 0) { pcb->local_port = tcp_new_port(); } #if SO_REUSE if ((pcb->so_options & SOF_REUSEADDR) != 0) { /* Since SOF_REUSEADDR allows reusing a local address, we have to make sure now that the 5-tuple is unique. */ struct tcp_pcb *cpcb; int i; /* Don't check listen- and bound-PCBs, check active- and TIME-WAIT PCBs. */ for (i = 2; i < NUM_TCP_PCB_LISTS; i++) { for(cpcb = *tcp_pcb_lists[i]; cpcb != NULL; cpcb = cpcb->next) { if ((cpcb->local_port == pcb->local_port) && (cpcb->remote_port == port) && ip_addr_cmp(&cpcb->local_ip, &pcb->local_ip) && ip_addr_cmp(&cpcb->remote_ip, ipaddr)) { /* linux returns EISCONN here, but ERR_USE should be OK for us */ return ERR_USE; } } } } #endif /* SO_REUSE */ iss = tcp_next_iss(); pcb->rcv_nxt = 0; pcb->snd_nxt = iss; pcb->lastack = iss - 1; pcb->snd_lbb = iss - 1; pcb->rcv_wnd = TCP_WND; pcb->rcv_ann_wnd = TCP_WND; pcb->rcv_ann_right_edge = pcb->rcv_nxt; pcb->snd_wnd = TCP_WND; /* As initial send MSS, we use TCP_MSS but limit it to 536. The send MSS is updated when an MSS option is received. */ pcb->mss = (TCP_MSS > 536) ? 536 : TCP_MSS; #if TCP_CALCULATE_EFF_SEND_MSS pcb->mss = tcp_eff_send_mss(pcb->mss, ipaddr); #endif /* TCP_CALCULATE_EFF_SEND_MSS */ pcb->cwnd = 1; pcb->ssthresh = pcb->mss * 10; #if LWIP_CALLBACK_API pcb->connected = connected; #else /* LWIP_CALLBACK_API */ LWIP_UNUSED_ARG(connected); #endif /* LWIP_CALLBACK_API */ /* Send a SYN together with the MSS option. */ ret = tcp_enqueue_flags(pcb, TCP_SYN); if (ret == ERR_OK) { /* SYN segment was enqueued, changed the pcbs state now */ pcb->state = SYN_SENT; if (old_local_port != 0) { TCP_RMV(&tcp_bound_pcbs, pcb); } TCP_REG(&tcp_active_pcbs, pcb); snmp_inc_tcpactiveopens(); tcp_output(pcb); } return ret; }