net: Add TCP protocol

Currently file transfers are done using tftp or NFS both
over udp. This requires a request to be sent from client
(u-boot) to the boot server.

The current standard is TCP with selective acknowledgment.

Signed-off-by: Duncan Hare <DH@Synoia.com>
Signed-off-by: Duncan Hare <DuncanCHare@yahoo.com>
Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Cc: Christian Gmeiner <christian.gmeiner@gmail.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>

4 files changed, 767 insertions, 0 deletions

diff --git a/net/Kconfig b/net/Kconfig
index 52e261884d..cb600fe5eb 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -174,6 +174,22 @@ config BOOTP_MAX_ROOT_PATH_LEN
 	help
 	  Select maximal length of option 17 root path.
 
+config PROT_TCP
+	bool "TCP stack"
+	help
+	  Enable a generic tcp framework that allows defining a custom
+	  handler for tcp protocol.
+
+config PROT_TCP_SACK
+	bool "TCP SACK support"
+	depends on PROT_TCP
+	help
+	  TCP protocol with SACK. SACK means selective acknowledgements.
+	  By turning this option on TCP will learn what segments are already
+	  received. So that it improves TCP's retransmission efficiency.
+	  This option should be turn on if you want to achieve the fastest
+	  file transfer possible.
+
 endif   # if NET
 
 config SYS_RX_ETH_BUFFER
diff --git a/net/Makefile b/net/Makefile
index 6c812502d3..d131d1cb1a 100644
--- a/net/Makefile
+++ b/net/Makefile
@@ -30,6 +30,7 @@ obj-$(CONFIG_CMD_TFTPBOOT) += tftp.o
 obj-$(CONFIG_UDP_FUNCTION_FASTBOOT)  += fastboot.o
 obj-$(CONFIG_CMD_WOL)  += wol.o
 obj-$(CONFIG_PROT_UDP) += udp.o
+obj-$(CONFIG_PROT_TCP) += tcp.o
 
 # Disable this warning as it is triggered by:
 # sprintf(buf, index ? "foo%d" : "foo", index)
diff --git a/net/net.c b/net/net.c
index 6f0a48361c..9cb2aab09d 100644
--- a/net/net.c
+++ b/net/net.c
@@ -117,6 +117,7 @@
 #if defined(CONFIG_CMD_WOL)
 #include "wol.h"
 #endif
+#include <net/tcp.h>
 
 /** BOOTP EXTENTIONS **/
 
@@ -387,6 +388,8 @@ int net_init(void)
 
 		/* Only need to setup buffer pointers once. */
 		first_call = 0;
+		if (IS_ENABLED(CONFIG_PROT_TCP))
+			tcp_set_tcp_state(TCP_CLOSED);
 	}
 
 	return net_init_loop();
@@ -833,6 +836,16 @@ int net_send_udp_packet(uchar *ether, struct in_addr dest, int dport, int sport,
 				  IPPROTO_UDP, 0, 0, 0);
 }
 
+#if defined(CONFIG_PROT_TCP)
+int net_send_tcp_packet(int payload_len, int dport, int sport, u8 action,
+			u32 tcp_seq_num, u32 tcp_ack_num)
+{
+	return net_send_ip_packet(net_server_ethaddr, net_server_ip, dport,
+				  sport, payload_len, IPPROTO_TCP, action,
+				  tcp_seq_num, tcp_ack_num);
+}
+#endif
+
 int net_send_ip_packet(uchar *ether, struct in_addr dest, int dport, int sport,
 		       int payload_len, int proto, u8 action, u32 tcp_seq_num,
 		       u32 tcp_ack_num)
@@ -864,6 +877,14 @@ int net_send_ip_packet(uchar *ether, struct in_addr dest, int dport, int sport,
 				   payload_len);
 		pkt_hdr_size = eth_hdr_size + IP_UDP_HDR_SIZE;
 		break;
+#if defined(CONFIG_PROT_TCP)
+	case IPPROTO_TCP:
+		pkt_hdr_size = eth_hdr_size
+			+ tcp_set_tcp_header(pkt + eth_hdr_size, dport, sport,
+					     payload_len, action, tcp_seq_num,
+					     tcp_ack_num);
+		break;
+#endif
 	default:
 		return -EINVAL;
 	}
@@ -1289,6 +1310,15 @@ void net_process_received_packet(uchar *in_packet, int len)
 		if (ip->ip_p == IPPROTO_ICMP) {
 			receive_icmp(ip, len, src_ip, et);
 			return;
+#if defined(CONFIG_PROT_TCP)
+		} else if (ip->ip_p == IPPROTO_TCP) {
+			debug_cond(DEBUG_DEV_PKT,
+				   "TCP PH (to=%pI4, from=%pI4, len=%d)\n",
+				   &dst_ip, &src_ip, len);
+
+			rxhand_tcp_f((union tcp_build_pkt *)ip, len);
+			return;
+#endif
 		} else if (ip->ip_p != IPPROTO_UDP) {	/* Only UDP packets */
 			return;
 		}
diff --git a/net/tcp.c b/net/tcp.c
new file mode 100644
index 0000000000..8d338c72e8
--- /dev/null
+++ b/net/tcp.c
@@ -0,0 +1,720 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2017 Duncan Hare, all rights reserved.
+ */
+
+/*
+ * General Desription:
+ *
+ * TCP support for the wget command, for fast file downloading.
+ *
+ * HTTP/TCP Receiver:
+ *
+ *      Prerequisites:  - own ethernet address
+ *                      - own IP address
+ *                      - Server IP address
+ *                      - Server with TCP
+ *                      - TCP application (eg wget)
+ *      Next Step       HTTPS?
+ */
+#include <common.h>
+#include <command.h>
+#include <console.h>
+#include <env_internal.h>
+#include <errno.h>
+#include <net.h>
+#include <net/tcp.h>
+
+/*
+ * TCP sliding window  control used by us to request re-TX
+ */
+static struct tcp_sack_v tcp_lost;
+
+/* TCP option timestamp */
+static u32 loc_timestamp;
+static u32 rmt_timestamp;
+
+static u32 tcp_seq_init;
+static u32 tcp_ack_edge;
+static u32 tcp_seq_max;
+
+static int tcp_activity_count;
+
+/*
+ * Search for TCP_SACK and review the comments before the code section
+ * TCP_SACK is the number of packets at the front of the stream
+ */
+
+enum pkt_state {PKT, NOPKT};
+struct sack_r {
+	struct sack_edges se;
+	enum pkt_state st;
+};
+
+static struct sack_r edge_a[TCP_SACK];
+static unsigned int sack_idx;
+static unsigned int prev_len;
+
+/*
+ * TCP lengths are stored as a rounded up number of 32 bit words.
+ * Add 3 to length round up, rounded, then divided into the
+ * length in 32 bit words.
+ */
+#define LEN_B_TO_DW(x) ((x) >> 2)
+#define ROUND_TCPHDR_LEN(x) (LEN_B_TO_DW((x) + 3))
+#define SHIFT_TO_TCPHDRLEN_FIELD(x) ((x) << 4)
+#define GET_TCP_HDR_LEN_IN_BYTES(x) ((x) >> 2)
+
+/* TCP connection state */
+static enum tcp_state current_tcp_state;
+
+/* Current TCP RX packet handler */
+static rxhand_tcp *tcp_packet_handler;
+
+/**
+ * tcp_get_tcp_state() - get current TCP state
+ *
+ * Return: Current TCP state
+ */
+enum tcp_state tcp_get_tcp_state(void)
+{
+	return current_tcp_state;
+}
+
+/**
+ * tcp_set_tcp_state() - set current TCP state
+ * @new_state: new TCP state
+ */
+void tcp_set_tcp_state(enum tcp_state new_state)
+{
+	current_tcp_state = new_state;
+}
+
+static void dummy_handler(uchar *pkt, unsigned int dport,
+			  struct in_addr sip, unsigned int sport,
+			  unsigned int len)
+{
+}
+
+/**
+ * tcp_set_tcp_handler() - set a handler to receive data
+ * @f: handler
+ */
+void tcp_set_tcp_handler(rxhand_tcp *f)
+{
+	debug_cond(DEBUG_INT_STATE, "--- net_loop TCP handler set (%p)\n", f);
+	if (!f)
+		tcp_packet_handler = dummy_handler;
+	else
+		tcp_packet_handler = f;
+}
+
+/**
+ * tcp_set_pseudo_header() - set TCP pseudo header
+ * @pkt: the packet
+ * @src: source IP address
+ * @dest: destinaion IP address
+ * @tcp_len: tcp length
+ * @pkt_len: packet length
+ *
+ * Return: the checksum of the packet
+ */
+u16 tcp_set_pseudo_header(uchar *pkt, struct in_addr src, struct in_addr dest,
+			  int tcp_len, int pkt_len)
+{
+	union tcp_build_pkt *b = (union tcp_build_pkt *)pkt;
+	int checksum_len;
+
+	/*
+	 * Pseudo header
+	 *
+	 * Zero the byte after the last byte so that the header checksum
+	 * will always work.
+	 */
+	pkt[pkt_len] = 0;
+
+	net_copy_ip((void *)&b->ph.p_src, &src);
+	net_copy_ip((void *)&b->ph.p_dst, &dest);
+	b->ph.rsvd = 0;
+	b->ph.p	= IPPROTO_TCP;
+	b->ph.len = htons(tcp_len);
+	checksum_len = tcp_len + PSEUDO_HDR_SIZE;
+
+	debug_cond(DEBUG_DEV_PKT,
+		   "TCP Pesudo  Header  (to=%pI4, from=%pI4, Len=%d)\n",
+		   &b->ph.p_dst, &b->ph.p_src, checksum_len);
+
+	return compute_ip_checksum(pkt + PSEUDO_PAD_SIZE, checksum_len);
+}
+
+/**
+ * net_set_ack_options() - set TCP options in acknowledge packets
+ * @b: the packet
+ *
+ * Return: TCP header length
+ */
+int net_set_ack_options(union tcp_build_pkt *b)
+{
+	b->sack.hdr.tcp_hlen = SHIFT_TO_TCPHDRLEN_FIELD(LEN_B_TO_DW(TCP_HDR_SIZE));
+
+	b->sack.t_opt.kind = TCP_O_TS;
+	b->sack.t_opt.len = TCP_OPT_LEN_A;
+	b->sack.t_opt.t_snd = htons(loc_timestamp);
+	b->sack.t_opt.t_rcv = rmt_timestamp;
+	b->sack.sack_v.kind = TCP_1_NOP;
+	b->sack.sack_v.len = 0;
+
+	if (IS_ENABLED(CONFIG_PROT_TCP_SACK)) {
+		if (tcp_lost.len > TCP_OPT_LEN_2) {
+			debug_cond(DEBUG_DEV_PKT, "TCP ack opt lost.len %x\n",
+				   tcp_lost.len);
+			b->sack.sack_v.len = tcp_lost.len;
+			b->sack.sack_v.kind = TCP_V_SACK;
+			b->sack.sack_v.hill[0].l = htonl(tcp_lost.hill[0].l);
+			b->sack.sack_v.hill[0].r = htonl(tcp_lost.hill[0].r);
+
+			/*
+			 * These SACK structures are initialized with NOPs to
+			 * provide TCP header alignment padding. There are 4
+			 * SACK structures used for both header padding and
+			 * internally.
+			 */
+			b->sack.sack_v.hill[1].l = htonl(tcp_lost.hill[1].l);
+			b->sack.sack_v.hill[1].r = htonl(tcp_lost.hill[1].r);
+			b->sack.sack_v.hill[2].l = htonl(tcp_lost.hill[2].l);
+			b->sack.sack_v.hill[2].r = htonl(tcp_lost.hill[2].r);
+			b->sack.sack_v.hill[3].l = TCP_O_NOP;
+			b->sack.sack_v.hill[3].r = TCP_O_NOP;
+		}
+
+		b->sack.hdr.tcp_hlen = SHIFT_TO_TCPHDRLEN_FIELD(ROUND_TCPHDR_LEN(TCP_HDR_SIZE +
+										 TCP_TSOPT_SIZE +
+										 tcp_lost.len));
+	} else {
+		b->sack.sack_v.kind = 0;
+		b->sack.hdr.tcp_hlen = SHIFT_TO_TCPHDRLEN_FIELD(ROUND_TCPHDR_LEN(TCP_HDR_SIZE +
+										 TCP_TSOPT_SIZE));
+	}
+
+	/*
+	 * This returns the actual rounded up length of the
+	 * TCP header to add to the total packet length
+	 */
+
+	return GET_TCP_HDR_LEN_IN_BYTES(b->sack.hdr.tcp_hlen);
+}
+
+/**
+ * net_set_ack_options() - set TCP options in SYN packets
+ * @b: the packet
+ */
+void net_set_syn_options(union tcp_build_pkt *b)
+{
+	if (IS_ENABLED(CONFIG_PROT_TCP_SACK))
+		tcp_lost.len = 0;
+
+	b->ip.hdr.tcp_hlen = 0xa0;
+
+	b->ip.mss.kind = TCP_O_MSS;
+	b->ip.mss.len = TCP_OPT_LEN_4;
+	b->ip.mss.mss = htons(TCP_MSS);
+	b->ip.scale.kind = TCP_O_SCL;
+	b->ip.scale.scale = TCP_SCALE;
+	b->ip.scale.len = TCP_OPT_LEN_3;
+	if (IS_ENABLED(CONFIG_PROT_TCP_SACK)) {
+		b->ip.sack_p.kind = TCP_P_SACK;
+		b->ip.sack_p.len = TCP_OPT_LEN_2;
+	} else {
+		b->ip.sack_p.kind = TCP_1_NOP;
+		b->ip.sack_p.len = TCP_1_NOP;
+	}
+	b->ip.t_opt.kind = TCP_O_TS;
+	b->ip.t_opt.len = TCP_OPT_LEN_A;
+	loc_timestamp = get_ticks();
+	rmt_timestamp = 0;
+	b->ip.t_opt.t_snd = 0;
+	b->ip.t_opt.t_rcv = 0;
+	b->ip.end = TCP_O_END;
+}
+
+int tcp_set_tcp_header(uchar *pkt, int dport, int sport, int payload_len,
+		       u8 action, u32 tcp_seq_num, u32 tcp_ack_num)
+{
+	union tcp_build_pkt *b = (union tcp_build_pkt *)pkt;
+	int pkt_hdr_len;
+	int pkt_len;
+	int tcp_len;
+
+	/*
+	 * Header: 5 32 bit words. 4 bits TCP header Length,
+	 *         4 bits reserved options
+	 */
+	b->ip.hdr.tcp_flags = action;
+	pkt_hdr_len = IP_TCP_HDR_SIZE;
+	b->ip.hdr.tcp_hlen = SHIFT_TO_TCPHDRLEN_FIELD(LEN_B_TO_DW(TCP_HDR_SIZE));
+
+	switch (action) {
+	case TCP_SYN:
+		debug_cond(DEBUG_DEV_PKT,
+			   "TCP Hdr:SYN (%pI4, %pI4, sq=%d, ak=%d)\n",
+			   &net_server_ip, &net_ip,
+			   tcp_seq_num, tcp_ack_num);
+		tcp_activity_count = 0;
+		net_set_syn_options(b);
+		tcp_seq_num = 0;
+		tcp_ack_num = 0;
+		pkt_hdr_len = IP_TCP_O_SIZE;
+		if (current_tcp_state == TCP_SYN_SENT) {  /* Too many SYNs */
+			action = TCP_FIN;
+			current_tcp_state = TCP_FIN_WAIT_1;
+		} else {
+			current_tcp_state = TCP_SYN_SENT;
+		}
+		break;
+	case TCP_ACK:
+		pkt_hdr_len = IP_HDR_SIZE + net_set_ack_options(b);
+		b->ip.hdr.tcp_flags = action;
+		debug_cond(DEBUG_DEV_PKT,
+			   "TCP Hdr:ACK (%pI4, %pI4, s=%d, a=%d, A=%x)\n",
+			   &net_server_ip, &net_ip, tcp_seq_num, tcp_ack_num,
+			   action);
+		break;
+	case TCP_FIN:
+		debug_cond(DEBUG_DEV_PKT,
+			   "TCP Hdr:FIN  (%pI4, %pI4, s=%d, a=%d)\n",
+			   &net_server_ip, &net_ip, tcp_seq_num, tcp_ack_num);
+		payload_len = 0;
+		pkt_hdr_len = IP_TCP_HDR_SIZE;
+		current_tcp_state = TCP_FIN_WAIT_1;
+		break;
+
+	/* Notify connection closing */
+
+	case (TCP_FIN | TCP_ACK):
+	case (TCP_FIN | TCP_ACK | TCP_PUSH):
+		if (current_tcp_state == TCP_CLOSE_WAIT)
+			current_tcp_state = TCP_CLOSING;
+
+		tcp_ack_edge++;
+		debug_cond(DEBUG_DEV_PKT,
+			   "TCP Hdr:FIN ACK PSH(%pI4, %pI4, s=%d, a=%d, A=%x)\n",
+			   &net_server_ip, &net_ip,
+			   tcp_seq_num, tcp_ack_edge, action);
+		fallthrough;
+	default:
+		pkt_hdr_len = IP_HDR_SIZE + net_set_ack_options(b);
+		b->ip.hdr.tcp_flags = action | TCP_PUSH | TCP_ACK;
+		debug_cond(DEBUG_DEV_PKT,
+			   "TCP Hdr:dft  (%pI4, %pI4, s=%d, a=%d, A=%x)\n",
+			   &net_server_ip, &net_ip,
+			   tcp_seq_num, tcp_ack_num, action);
+	}
+
+	pkt_len	= pkt_hdr_len + payload_len;
+	tcp_len	= pkt_len - IP_HDR_SIZE;
+
+	/* TCP Header */
+	b->ip.hdr.tcp_ack = htonl(tcp_ack_edge);
+	b->ip.hdr.tcp_src = htons(sport);
+	b->ip.hdr.tcp_dst = htons(dport);
+	b->ip.hdr.tcp_seq = htonl(tcp_seq_num);
+	tcp_seq_num = tcp_seq_num + payload_len;
+
+	/*
+	 * TCP window size - TCP header variable tcp_win.
+	 * Change tcp_win only if you have an understanding of network
+	 * overrun, congestion, TCP segment sizes, TCP windows, TCP scale,
+	 * queuing theory  and packet buffering. If there are too few buffers,
+	 * there will be data loss, recovery may work or the sending TCP,
+	 * the server, could abort the stream transmission.
+	 * MSS is governed by maximum Ethernet frame length.
+	 * The number of buffers is governed by the desire to have a queue of
+	 * full buffers to be processed at the destination to maximize
+	 * throughput. Temporary memory use for the boot phase on modern
+	 * SOCs is may not be considered a constraint to buffer space, if
+	 * it is, then the u-boot tftp or nfs kernel netboot should be
+	 * considered.
+	 */
+	b->ip.hdr.tcp_win = htons(PKTBUFSRX * TCP_MSS >> TCP_SCALE);
+
+	b->ip.hdr.tcp_xsum = 0;
+	b->ip.hdr.tcp_ugr = 0;
+
+	b->ip.hdr.tcp_xsum = tcp_set_pseudo_header(pkt, net_ip, net_server_ip,
+						   tcp_len, pkt_len);
+
+	net_set_ip_header((uchar *)&b->ip, net_server_ip, net_ip,
+			  pkt_len, IPPROTO_TCP);
+
+	return pkt_hdr_len;
+}
+
+/**
+ * tcp_hole() - Selective Acknowledgment (Essential for fast stream transfer)
+ * @tcp_seq_num: TCP sequence start number
+ * @len: the length of sequence numbers
+ * @tcp_seq_max: maximum of sequence numbers
+ */
+void tcp_hole(u32 tcp_seq_num, u32 len, u32 tcp_seq_max)
+{
+	u32 idx_sack, sack_in;
+	u32 sack_end = TCP_SACK - 1;
+	u32 hill = 0;
+	enum pkt_state expect = PKT;
+	u32 seq = tcp_seq_num - tcp_seq_init;
+	u32 hol_l = tcp_ack_edge - tcp_seq_init;
+	u32 hol_r = 0;
+
+	/* Place new seq number in correct place in receive array */
+	if (prev_len == 0)
+		prev_len = len;
+
+	idx_sack = sack_idx + ((tcp_seq_num - tcp_ack_edge) / prev_len);
+	if (idx_sack < TCP_SACK) {
+		edge_a[idx_sack].se.l = tcp_seq_num;
+		edge_a[idx_sack].se.r = tcp_seq_num + len;
+		edge_a[idx_sack].st = PKT;
+
+		/*
+		 * The fin (last) packet is not the same length as data
+		 * packets, and if it's length is recorded and used for
+		 *  array index calculation, calculation breaks.
+		 */
+		if (prev_len < len)
+			prev_len = len;
+	}
+
+	debug_cond(DEBUG_DEV_PKT,
+		   "TCP 1 seq %d, edg %d, len %d, sack_idx %d, sack_end %d\n",
+		    seq, hol_l, len, sack_idx, sack_end);
+
+	/* Right edge of contiguous stream, is the left edge of first hill */
+	hol_l = tcp_seq_num - tcp_seq_init;
+	hol_r = hol_l + len;
+
+	if (IS_ENABLED(CONFIG_PROT_TCP_SACK))
+		tcp_lost.len = TCP_OPT_LEN_2;
+
+	debug_cond(DEBUG_DEV_PKT,
+		   "TCP 1 in %d, seq %d, pkt_l %d, pkt_r %d, sack_idx %d, sack_end %d\n",
+		   idx_sack, seq, hol_l, hol_r, sack_idx, sack_end);
+
+	for (sack_in = sack_idx; sack_in < sack_end && hill < TCP_SACK_HILLS;
+	     sack_in++)  {
+		switch (expect) {
+		case NOPKT:
+			switch (edge_a[sack_in].st) {
+			case NOPKT:
+				debug_cond(DEBUG_INT_STATE, "N");
+				break;
+			case PKT:
+				debug_cond(DEBUG_INT_STATE, "n");
+				if (IS_ENABLED(CONFIG_PROT_TCP_SACK)) {
+					tcp_lost.hill[hill].l =
+						edge_a[sack_in].se.l;
+					tcp_lost.hill[hill].r =
+						edge_a[sack_in].se.r;
+				}
+				expect = PKT;
+				break;
+			}
+			break;
+		case PKT:
+			switch (edge_a[sack_in].st) {
+			case NOPKT:
+				debug_cond(DEBUG_INT_STATE, "p");
+				if (sack_in > sack_idx &&
+				    hill < TCP_SACK_HILLS) {
+					hill++;
+					if (IS_ENABLED(CONFIG_PROT_TCP_SACK))
+						tcp_lost.len += TCP_OPT_LEN_8;
+				}
+				expect = NOPKT;
+				break;
+			case PKT:
+				debug_cond(DEBUG_INT_STATE, "P");
+
+				if (tcp_ack_edge == edge_a[sack_in].se.l) {
+					tcp_ack_edge = edge_a[sack_in].se.r;
+					edge_a[sack_in].st = NOPKT;
+					sack_idx++;
+				} else {
+					if (IS_ENABLED(CONFIG_PROT_TCP_SACK) &&
+					    hill < TCP_SACK_HILLS)
+						tcp_lost.hill[hill].r =
+							edge_a[sack_in].se.r;
+				if (IS_ENABLED(CONFIG_PROT_TCP_SACK) &&
+				    sack_in == sack_end - 1)
+					tcp_lost.hill[hill].r =
+						edge_a[sack_in].se.r;
+				}
+				break;
+			}
+			break;
+		}
+	}
+	debug_cond(DEBUG_INT_STATE, "\n");
+	if (!IS_ENABLED(CONFIG_PROT_TCP_SACK) || tcp_lost.len <= TCP_OPT_LEN_2)
+		sack_idx = 0;
+}
+
+/**
+ * tcp_parse_options() - parsing TCP options
+ * @o: pointer to the option field.
+ * @o_len: length of the option field.
+ */
+void tcp_parse_options(uchar *o, int o_len)
+{
+	struct tcp_t_opt  *tsopt;
+	uchar *p = o;
+
+	/*
+	 * NOPs are options with a zero length, and thus are special.
+	 * All other options have length fields.
+	 */
+	for (p = o; p < (o + o_len); p = p + p[1]) {
+		if (!p[1])
+			return; /* Finished processing options */
+
+		switch (p[0]) {
+		case TCP_O_END:
+			return;
+		case TCP_O_MSS:
+		case TCP_O_SCL:
+		case TCP_P_SACK:
+		case TCP_V_SACK:
+			break;
+		case TCP_O_TS:
+			tsopt = (struct tcp_t_opt *)p;
+			rmt_timestamp = tsopt->t_snd;
+			return;
+		}
+
+		/* Process optional NOPs */
+		if (p[0] == TCP_O_NOP)
+			p++;
+	}
+}
+
+static u8 tcp_state_machine(u8 tcp_flags, u32 *tcp_seq_num, int payload_len)
+{
+	u8 tcp_fin = tcp_flags & TCP_FIN;
+	u8 tcp_syn = tcp_flags & TCP_SYN;
+	u8 tcp_rst = tcp_flags & TCP_RST;
+	u8 tcp_push = tcp_flags & TCP_PUSH;
+	u8 tcp_ack = tcp_flags & TCP_ACK;
+	u8 action = TCP_DATA;
+	int i;
+
+	/*
+	 * tcp_flags are examined to determine TX action in a given state
+	 * tcp_push is interpreted to mean "inform the app"
+	 * urg, ece, cer and nonce flags are not supported.
+	 *
+	 * exe and crw are use to signal and confirm knowledge of congestion.
+	 * This TCP only sends a file request and acks. If it generates
+	 * congestion, the network is broken.
+	 */
+	debug_cond(DEBUG_INT_STATE, "TCP STATE ENTRY %x\n", action);
+	if (tcp_rst) {
+		action = TCP_DATA;
+		current_tcp_state = TCP_CLOSED;
+		net_set_state(NETLOOP_FAIL);
+		debug_cond(DEBUG_INT_STATE, "TCP Reset %x\n", tcp_flags);
+		return TCP_RST;
+	}
+
+	switch  (current_tcp_state) {
+	case TCP_CLOSED:
+		debug_cond(DEBUG_INT_STATE, "TCP CLOSED %x\n", tcp_flags);
+		if (tcp_ack)
+			action = TCP_DATA;
+		else if (tcp_syn)
+			action = TCP_RST;
+		else if (tcp_fin)
+			action = TCP_DATA;
+		break;
+	case TCP_SYN_SENT:
+		debug_cond(DEBUG_INT_STATE, "TCP_SYN_SENT %x, %d\n",
+			   tcp_flags, *tcp_seq_num);
+		if (tcp_fin) {
+			action = action | TCP_PUSH;
+			current_tcp_state = TCP_CLOSE_WAIT;
+		}
+		if (tcp_syn) {
+			action = action | TCP_ACK | TCP_PUSH;
+			if (tcp_ack) {
+				tcp_seq_init = *tcp_seq_num;
+				*tcp_seq_num = *tcp_seq_num + 1;
+				tcp_seq_max = *tcp_seq_num;
+				tcp_ack_edge = *tcp_seq_num;
+				sack_idx = 0;
+				edge_a[sack_idx].se.l = *tcp_seq_num;
+				edge_a[sack_idx].se.r = *tcp_seq_num;
+				prev_len = 0;
+				current_tcp_state = TCP_ESTABLISHED;
+				for (i = 0; i < TCP_SACK; i++)
+					edge_a[i].st = NOPKT;
+			}
+		} else if (tcp_ack) {
+			action = TCP_DATA;
+		}
+
+		break;
+	case TCP_ESTABLISHED:
+		debug_cond(DEBUG_INT_STATE, "TCP_ESTABLISHED %x\n", tcp_flags);
+		if (*tcp_seq_num > tcp_seq_max)
+			tcp_seq_max = *tcp_seq_num;
+		if (payload_len > 0) {
+			tcp_hole(*tcp_seq_num, payload_len, tcp_seq_max);
+			tcp_fin = TCP_DATA;  /* cause standalone FIN */
+		}
+
+		if ((tcp_fin) &&
+		    (!IS_ENABLED(CONFIG_PROT_TCP_SACK) ||
+		     tcp_lost.len <= TCP_OPT_LEN_2)) {
+			action = action | TCP_FIN | TCP_PUSH | TCP_ACK;
+			current_tcp_state = TCP_CLOSE_WAIT;
+		} else if (tcp_ack) {
+			action = TCP_DATA;
+		}
+
+		if (tcp_syn)
+			action = TCP_ACK + TCP_RST;
+		else if (tcp_push)
+			action = action | TCP_PUSH;
+		break;
+	case TCP_CLOSE_WAIT:
+		debug_cond(DEBUG_INT_STATE, "TCP_CLOSE_WAIT (%x)\n", tcp_flags);
+		action = TCP_DATA;
+		break;
+	case TCP_FIN_WAIT_2:
+		debug_cond(DEBUG_INT_STATE, "TCP_FIN_WAIT_2 (%x)\n", tcp_flags);
+		if (tcp_ack) {
+			action = TCP_PUSH | TCP_ACK;
+			current_tcp_state = TCP_CLOSED;
+			puts("\n");
+		} else if (tcp_syn) {
+			action = TCP_DATA;
+		} else if (tcp_fin) {
+			action = TCP_DATA;
+		}
+		break;
+	case TCP_FIN_WAIT_1:
+		debug_cond(DEBUG_INT_STATE, "TCP_FIN_WAIT_1 (%x)\n", tcp_flags);
+		if (tcp_fin) {
+			action = TCP_ACK | TCP_FIN;
+			current_tcp_state = TCP_FIN_WAIT_2;
+		}
+		if (tcp_syn)
+			action = TCP_RST;
+		if (tcp_ack) {
+			current_tcp_state = TCP_CLOSED;
+			tcp_seq_num = tcp_seq_num + 1;
+		}
+		break;
+	case TCP_CLOSING:
+		debug_cond(DEBUG_INT_STATE, "TCP_CLOSING (%x)\n", tcp_flags);
+		if (tcp_ack) {
+			action = TCP_PUSH;
+			current_tcp_state = TCP_CLOSED;
+			puts("\n");
+		} else if (tcp_syn) {
+			action = TCP_RST;
+		} else if (tcp_fin) {
+			action = TCP_DATA;
+		}
+		break;
+	}
+	return action;
+}
+
+/**
+ * rxhand_tcp_f() - process receiving data and call data handler.
+ * @b: the packet
+ * @pkt_len: the length of packet.
+ */
+void rxhand_tcp_f(union tcp_build_pkt *b, unsigned int pkt_len)
+{
+	int tcp_len = pkt_len - IP_HDR_SIZE;
+	u16 tcp_rx_xsum = b->ip.hdr.ip_sum;
+	u8  tcp_action = TCP_DATA;
+	u32 tcp_seq_num, tcp_ack_num;
+	struct in_addr action_and_state;
+	int tcp_hdr_len, payload_len;
+
+	/* Verify IP header */
+	debug_cond(DEBUG_DEV_PKT,
+		   "TCP RX in RX Sum (to=%pI4, from=%pI4, len=%d)\n",
+		   &b->ip.hdr.ip_src, &b->ip.hdr.ip_dst, pkt_len);
+
+	b->ip.hdr.ip_src = net_server_ip;
+	b->ip.hdr.ip_dst = net_ip;
+	b->ip.hdr.ip_sum = 0;
+	if (tcp_rx_xsum != compute_ip_checksum(b, IP_HDR_SIZE)) {
+		debug_cond(DEBUG_DEV_PKT,
+			   "TCP RX IP xSum Error (%pI4, =%pI4, len=%d)\n",
+			   &net_ip, &net_server_ip, pkt_len);
+		return;
+	}
+
+	/* Build pseudo header and verify TCP header */
+	tcp_rx_xsum = b->ip.hdr.tcp_xsum;
+	b->ip.hdr.tcp_xsum = 0;
+	if (tcp_rx_xsum != tcp_set_pseudo_header((uchar *)b, b->ip.hdr.ip_src,
+						 b->ip.hdr.ip_dst, tcp_len,
+						 pkt_len)) {
+		debug_cond(DEBUG_DEV_PKT,
+			   "TCP RX TCP xSum Error (%pI4, %pI4, len=%d)\n",
+			   &net_ip, &net_server_ip, tcp_len);
+		return;
+	}
+
+	tcp_hdr_len = GET_TCP_HDR_LEN_IN_BYTES(b->ip.hdr.tcp_hlen);
+	payload_len = tcp_len - tcp_hdr_len;
+
+	if (tcp_hdr_len > TCP_HDR_SIZE)
+		tcp_parse_options((uchar *)b + IP_TCP_HDR_SIZE,
+				  tcp_hdr_len - TCP_HDR_SIZE);
+	/*
+	 * Incoming sequence and ack numbers are server's view of the numbers.
+	 * The app must swap the numbers when responding.
+	 */
+	tcp_seq_num = ntohl(b->ip.hdr.tcp_seq);
+	tcp_ack_num = ntohl(b->ip.hdr.tcp_ack);
+
+	/* Packets are not ordered. Send to app as received. */
+	tcp_action = tcp_state_machine(b->ip.hdr.tcp_flags,
+				       &tcp_seq_num, payload_len);
+
+	tcp_activity_count++;
+	if (tcp_activity_count > TCP_ACTIVITY) {
+		puts("| ");
+		tcp_activity_count = 0;
+	}
+
+	if ((tcp_action & TCP_PUSH) || payload_len > 0) {
+		debug_cond(DEBUG_DEV_PKT,
+			   "TCP Notify (action=%x, Seq=%d,Ack=%d,Pay%d)\n",
+			   tcp_action, tcp_seq_num, tcp_ack_num, payload_len);
+
+		action_and_state.s_addr = tcp_action;
+		(*tcp_packet_handler) ((uchar *)b + pkt_len - payload_len,
+				       tcp_seq_num, action_and_state,
+				       tcp_ack_num, payload_len);
+
+	} else if (tcp_action != TCP_DATA) {
+		debug_cond(DEBUG_DEV_PKT,
+			   "TCP Action (action=%x,Seq=%d,Ack=%d,Pay=%d)\n",
+			   tcp_action, tcp_seq_num, tcp_ack_num, payload_len);
+
+		/*
+		 * Warning: Incoming Ack & Seq sequence numbers are transposed
+		 * here to outgoing Seq & Ack sequence numbers
+		 */
+		net_send_tcp_packet(0, ntohs(b->ip.hdr.tcp_src),
+				    ntohs(b->ip.hdr.tcp_dst),
+				    (tcp_action & (~TCP_PUSH)),
+				    tcp_seq_num, tcp_ack_num);
+	}
+}