kolibrios-gitea/kernel/branches/net/network/tcp_input.inc

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;                                                                 ;;
;; Copyright (C) KolibriOS team 2004-2011. All rights reserved.    ;;
;; Distributed under terms of the GNU General Public License       ;;
;;                                                                 ;;
;;  Part of the tcp/ip network stack for KolibriOS                 ;;
;;                                                                 ;;
;;   Written by hidnplayr@kolibrios.org                            ;;
;;                                                                 ;;
;;    Based on the code of 4.4BSD                                  ;;
;;                                                                 ;;
;;          GNU GENERAL PUBLIC LICENSE                             ;;
;;             Version 2, June 1991                                ;;
;;                                                                 ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

$Revision$

;-----------------------------------------------------------------
;
; TCP_input:
;
;  IN:  [esp] = ptr to buffer
;       [esp+4] = buffer size
;       ebx = ptr to device struct
;       ecx = segment size
;       edx = ptr to TCP segment
;
;       esi = ipv4 source address
;       edi = ipv4 dest   address
;
;  OUT: /
;
;-----------------------------------------------------------------
align 4
TCP_input:

       DEBUGF  1,"TCP_input size=%u ", ecx
; Offset must be greater than or equal to the size of the standard TCP header (20) and less than or equal to the TCP length.

	movzx	eax, [edx + TCP_segment.DataOffset]
	and	eax, 0xf0
	shr	al, 2

	DEBUGF	1,"headersize=%u\n", eax

	cmp	eax, 20
	jl	.drop_not_locked

;-------------------------------
; Now, re-calculate the checksum

	push	eax ecx edx
	pushw	[edx + TCP_segment.Checksum]
	mov	[edx + TCP_segment.Checksum], 0
	push	esi edi
	mov	esi, edx
	TCP_checksum (esp), (esp+4)
	pop	esi edi ; yes, swap them (we dont need dest addr)
	pop	cx	; previous checksum
	cmp	cx, dx
	pop	edx ecx esi
	jnz	.drop_not_locked

	DEBUGF	1,"Checksum is correct\n"

	sub	ecx, esi	; update packet size
	jl	.drop_not_locked
	DEBUGF	1,"we got %u bytes of data\n", ecx

;-----------------------------------------------------------------------------------------
; Check if this packet has a timestamp option (We do it here so we can process it quickly)

	cmp	esi, 20 + 12					; Timestamp option is 12 bytes
	jl	.no_timestamp
	je	.is_ok

	cmp	byte [edx + TCP_segment.Data + 12], TCP_OPT_EOL ; end of option list
	jne	.no_timestamp

  .is_ok:
	test	[edx + TCP_segment.Flags], TH_SYN		; SYN flag must not be set
	jnz	.no_timestamp

	cmp	dword [edx + TCP_segment.Data], 0x0101080a	; Timestamp header
	jne	.no_timestamp

	DEBUGF	1,"timestamp ok\n"

	; TODO: Parse the option
	; TODO: Set a Bit in the TCP to tell all options are parsed

  .no_timestamp:

;-------------------------------------------
; Convert Big-endian values to little endian

	ntohd	[edx + TCP_segment.SequenceNumber]
	ntohd	[edx + TCP_segment.AckNumber]

	ntohw	[edx + TCP_segment.Window]
	ntohw	[edx + TCP_segment.UrgentPointer]
	ntohw	[edx + TCP_segment.SourcePort]
	ntohw	[edx + TCP_segment.DestinationPort]

;------------------------------------------------------------
; Next thing to do is find the TCB (thus, the socket pointer)

; IP Packet TCP Destination Port = local Port
; (IP Packet SenderAddress = Remote IP)  OR  (Remote IP = 0)
; (IP Packet TCP Source Port = remote Port)  OR (remote Port = 0)

	mov	ebx, net_sockets

  .socket_loop:
	mov	ebx, [ebx + SOCKET.NextPtr]
	or	ebx, ebx
	jz	.drop_with_reset_not_locked

	cmp	[ebx + SOCKET.Domain], AF_INET4
	jne	.socket_loop

	cmp	[ebx + SOCKET.Protocol], IP_PROTO_TCP
	jne	.socket_loop

	mov	ax, [edx + TCP_segment.DestinationPort]
	cmp	[ebx + TCP_SOCKET.LocalPort], ax
	jne	.socket_loop

	mov	eax, [ebx + IP_SOCKET.RemoteIP]
	cmp	eax, edi			; edi is source ip from packet
	je	@f
	test	eax, eax
	jnz	.socket_loop
       @@:

	mov	ax, [ebx + TCP_SOCKET.RemotePort]
	cmp	[edx + TCP_segment.SourcePort] , ax
	je	.found_socket
	test	ax, ax
	jnz	.socket_loop
  .found_socket:
	DEBUGF	1,"Socket ptr: %x\n", ebx

; ebx now contains the pointer to the socket

;----------------------------
; Check if socket isnt closed

	cmp	[ebx + TCP_SOCKET.t_state], TCB_CLOSED
	je	.drop_not_locked

;----------------
; Lock the socket

	add	ebx, SOCKET.lock
	DEBUGF	1,"lock: %x\n", [ebx]
	call	wait_mutex
	sub	ebx, SOCKET.lock

	DEBUGF	1,"Socket locked\n"

;---------------------------------------
; unscale the window into a 32 bit value

	movzx	eax, [edx + TCP_segment.Window]
	push	ecx
	mov	cl, [ebx + TCP_SOCKET.SND_SCALE]
	shl	eax, cl
	mov	dword [edx + TCP_segment.Window], eax	; word after window is checksum, we dont need checksum anymore
	pop	ecx

;-----------------------------------
; Is this socket a listening socket?

	test	[ebx + SOCKET.options], SO_ACCEPTCON
	jz	.no_listening_socket

	call	SOCKET_fork
	jz	.drop

	push	[edx + TCP_segment.DestinationPort]
	pop	[eax + TCP_SOCKET.LocalPort]

	push	[edx - IPv4_Packet.DataOrOptional + IPv4_Packet.DestinationAddress]	;;; FIXME
	pop	[eax + IP_SOCKET.LocalIP]

	push	[edx - IPv4_Packet.DataOrOptional + IPv4_Packet.SourceAddress]	   ;;; FIXME
	pop	[eax + IP_SOCKET.RemoteIP]

	mov	[eax + TCP_SOCKET.t_state], TCB_LISTEN

	jmp	.not_uni_xfer

  .no_listening_socket:

;-------------------------------------
; Reset idle timer and keepalive timer

	mov	[ebx + TCP_SOCKET.t_idle], 0
	mov	[ebx + TCP_SOCKET.timer_keepalive], TCP_time_keep_interval

;--------------------
; Process TCP options

	cmp	esi, 20 			; esi is headersize
	je	.no_options

	DEBUGF	1,"Segment has options\n"

	cmp	[ebx + TCP_SOCKET.t_state], TCB_LISTEN		; no options when in listen state
	jz	.not_uni_xfer					; also no header prediction

	lea	edi, [edx + TCP_segment.Data]
	lea	eax, [edx + esi]

  .opt_loop:
	cmp	edi, eax
	jge	.no_options

	cmp	byte [edi], TCP_OPT_EOL 	; end of option list?
	jz	.no_options

	cmp	byte [edi], TCP_OPT_NOP 	; nop ?
	jz	.opt_nop

	cmp	byte [edi], TCP_OPT_MAXSEG
	je	.opt_maxseg

	cmp	byte [edi], TCP_OPT_WINDOW
	je	.opt_window

	cmp	byte [edi], TCP_OPT_TIMESTAMP
	je	.opt_timestamp

	jmp	.no_options	; If we reach here, some unknown options were received, skip them all!

  .opt_nop:
	inc	edi
	jmp	.opt_loop

  .opt_maxseg:
	cmp	byte [edi+1], 4
	jne	.no_options		; error occured, ignore all options!

	test	[edx + TCP_segment.Flags], TH_SYN
	jz	@f

	movzx	eax, word[edi+2]
	rol	ax, 8
	DEBUGF	1,"Maxseg: %u\n", ax

	mov	[ebx + TCP_SOCKET.t_maxseg], eax

       @@:
	add	edi, 4
	jmp	.opt_loop


  .opt_window:
	cmp	byte [edi+1], 3
	jne	.no_options

	test	[edx + TCP_segment.Flags], TH_SYN
	jz	@f

	DEBUGF	1,"Got window option\n"

	;;;;;
       @@:
	add	edi, 3
	jmp	.opt_loop


  .opt_timestamp:
	cmp	byte [edi+1], 10
	jne	.no_options

	DEBUGF	1,"Got timestamp option\n"

	;;;;;

	add	edi, 10
	jmp	.opt_loop

  .no_options:






;-----------------------------------------------------------------------
; Time to do some header prediction (Original Principle by Van Jacobson)

; There are two common cases for an uni-directional data transfer.
;
; General rule: the packets has no control flags, is in-sequence,
;   window width didnt change and we're not retransmitting.
;
; Second rules:
;  -  If the length is 0 and the ACK moved forward, we're the sender side of the transfer.
;      In this case we'll free the ACK'ed data and notify higher levels that we have free space in buffer
;
;  -  If the length is not 0 and the ACK didn't move, we're the receiver side of the transfer.
;      If the packets are in order (data queue is empty), add the data to the socket buffer and request a delayed ACK

	cmp	[ebx + TCP_SOCKET.t_state], TCB_ESTABLISHED
	jnz	.not_uni_xfer

	test	[edx + TCP_segment.Flags], TH_SYN + TH_FIN + TH_RST + TH_URG
	jnz	.not_uni_xfer

	test	[edx + TCP_segment.Flags], TH_ACK
	jz	.not_uni_xfer

	mov	eax, [edx + TCP_segment.SequenceNumber]
	cmp	eax, [ebx + TCP_SOCKET.RCV_NXT]
	jne	.not_uni_xfer

	mov	eax, dword [edx + TCP_segment.Window]
	cmp	eax, [ebx + TCP_SOCKET.SND_WND]
	jne	.not_uni_xfer

	mov	eax, [ebx + TCP_SOCKET.SND_NXT]
	cmp	eax, [ebx + TCP_SOCKET.SND_MAX]
	jne	.not_uni_xfer

;---------------------------------------
; check if we are sender in the uni-xfer

; If the following 4 conditions are all true, this segment is a pure ACK.
;
; - The segment contains no data.
	test	ecx, ecx
	jnz	.not_sender

; - The congestion window is greater than or equal to the current send window.
;     This test is true only if the window is fully open, that is, the connection is not in the middle of slow start or congestion avoidance.
	mov	eax, [ebx + TCP_SOCKET.SND_CWND]
	cmp	eax, [ebx + TCP_SOCKET.SND_WND]
	jl	.not_uni_xfer

; - The acknowledgment field in the segment is less than or equal to the maximum sequence number sent.
	mov	eax, [edx + TCP_segment.AckNumber]
	cmp	eax, [ebx + TCP_SOCKET.SND_MAX]
	jg	.not_uni_xfer

; - The acknowledgment field in the segment is greater than the largest unacknowledged sequence number.
	sub	eax, [ebx + TCP_SOCKET.SND_UNA]
	jle	.not_uni_xfer

	DEBUGF	1,"Header prediction: we are sender\n"

;---------------------------------
; Packet is a pure ACK, process it

; Update RTT estimators

;;; TODO

; Delete acknowledged bytes from send buffer
	pusha
	mov	ecx, eax
	lea	eax, [ebx + STREAM_SOCKET.snd]
	call	SOCKET_ring_free
	popa

; update window pointers
	mov	eax, [edx + TCP_segment.AckNumber]
	mov	[ebx + TCP_SOCKET.SND_UNA], eax

; Stop retransmit timer
	mov	[ebx + TCP_SOCKET.timer_ack], 0

; Awaken waiting processes
	mov	[ebx + SOCKET.lock], 0
	mov	eax, ebx
	call	SOCKET_notify_owner

; Generate more output
	call	TCP_output

	jmp	.drop_not_locked

;-------------------------------------------------
; maybe we are the receiver in the uni-xfer then..

  .not_sender:
; - The amount of data in the segment is greater than 0 (data count is in ecx)

; - The acknowledgment field equals the largest unacknowledged sequence number. This means no data is acknowledged by this segment.
	mov	eax, [edx + TCP_segment.AckNumber]
	cmp	eax, [ebx + TCP_SOCKET.SND_UNA]
	jne	.not_uni_xfer

; - The reassembly list of out-of-order segments for the connection is empty (seg_next equals tp).

;;; TODO

	jnz	.not_uni_xfer

; Complete processing of received data

	DEBUGF	1,"header prediction: we are receiver\nreceiving %u bytes of data\n", ecx

	add	[ebx + TCP_SOCKET.RCV_NXT], ecx 	; Update sequence number with number of bytes we have copied

	add	esi, edx
	lea	eax, [ebx + STREAM_SOCKET.rcv]
	call	SOCKET_ring_write			; Add the data to the socket buffer

	mov	eax, ebx
	call	SOCKET_notify_owner

	or	[ebx + TCP_SOCKET.t_flags], TF_DELACK	; Set delayed ack flag

	jmp	.drop






;--------------------------------------------------
; Header prediction failed, do it the slow way

  .not_uni_xfer:

	DEBUGF	1,"Header prediction failed\n"

; Calculate receive window size

;;;; TODO: 444

	cmp	[ebx + TCP_SOCKET.t_state], TCB_LISTEN
	je	.LISTEN

	cmp	[ebx + TCP_SOCKET.t_state], TCB_SYN_SENT
	je	.SYN_SENT

	jmp	.NOT_LISTEN_OR_SYN_SENT



;-------------
; Passive Open

align 4
.LISTEN:

	DEBUGF	1,"TCP state: listen\n"

	test	[edx + TCP_segment.Flags], TH_RST	;;; TODO: kill new socket on error
	jnz	.drop

	test	[edx + TCP_segment.Flags], TH_ACK
	jnz	.drop_with_reset

	test	[edx + TCP_segment.Flags], TH_SYN
	jz	.drop

;;; TODO: check if it's a broadcast or multicast, and drop if so

	add	[TCP_sequence_num], 64000

	push	[edx + TCP_segment.SourcePort]
	pop	[eax + TCP_SOCKET.RemotePort]

	push	[edx + TCP_segment.SequenceNumber]
	pop	[eax + TCP_SOCKET.IRS]

	push	[eax + TCP_SOCKET.ISS]
	pop	[eax + TCP_SOCKET.SND_NXT]

	TCP_sendseqinit eax
	TCP_rcvseqinit eax

	mov	[eax + TCP_SOCKET.t_state], TCB_SYN_RECEIVED
	mov	[eax + TCP_SOCKET.t_flags], TF_ACKNOW
	mov	[eax + TCP_SOCKET.timer_keepalive], TCP_time_keep_interval  ;;;; macro

	add	eax, STREAM_SOCKET.snd
	call	SOCKET_ring_create

	add	eax, STREAM_SOCKET.rcv - STREAM_SOCKET.snd
	call	SOCKET_ring_create

	lea	ebx, [eax - STREAM_SOCKET.rcv]
	mov	[ebx + SOCKET.lock], 0

	jmp	.trim_then_step6








;------------
; Active Open

align 4
.SYN_SENT:

	DEBUGF	1,"TCP state: syn_sent\n"

	test	[edx + TCP_segment.Flags], TH_ACK
	jz	@f

	mov	eax, [edx + TCP_segment.AckNumber]
	cmp	eax, [ebx + TCP_SOCKET.ISS]
	jle	.drop_with_reset

	cmp	eax, [ebx + TCP_SOCKET.SND_MAX]
	jg	.drop_with_reset
       @@:

	test	[edx + TCP_segment.Flags], TH_RST
	jz	@f

	test	[edx + TCP_segment.Flags], TH_ACK
	jz	.drop

	mov	eax, ebx
	mov	ebx, ECONNREFUSED
	call	TCP_drop

	jmp	.drop
       @@:

	test	[edx + TCP_segment.Flags], TH_SYN
	jz	.drop

; at this point, segment seems to be valid

	test	[edx + TCP_segment.Flags], TH_ACK
	jz	.no_syn_ack

; now, process received SYN in response to an active open

	mov	eax, [edx + TCP_segment.AckNumber]
	mov	[ebx + TCP_SOCKET.SND_UNA], eax
	cmp	eax, [ebx + TCP_SOCKET.SND_NXT]
	jle	@f
	mov	[ebx + TCP_SOCKET.SND_NXT], eax
       @@:

  .no_syn_ack:

	mov	[ebx + TCP_SOCKET.timer_retransmission], 0	; disable retransmission

	push	[edx + TCP_segment.SequenceNumber]
	pop	[ebx + TCP_SOCKET.IRS]

	TCP_rcvseqinit ebx

	or	[ebx + TCP_SOCKET.t_flags], TF_ACKNOW

	mov	eax, [ebx + TCP_SOCKET.SND_UNA]
	cmp	eax, [ebx + TCP_SOCKET.ISS]
	jle	.simultaneous_open

	test	[edx + TCP_segment.Flags], TH_ACK
	jz	.simultaneous_open

	DEBUGF	1,"TCP: active open\n"

;;; TODO: update stats

; set socket state to connected

	mov	[ebx + SOCKET.state],1	;;;; FIXME

	mov	[ebx + TCP_SOCKET.t_state], TCB_ESTABLISHED

;;; TODO: check if we should scale the connection (567-572)
;;; TODO: update RTT estimators

	jmp	.trim_then_step6

  .simultaneous_open:

	DEBUGF	1,"TCP: simultaneous open\n"
; We have received a syn but no ACK, so we are having a simultaneous open..
	mov	[ebx + TCP_SOCKET.t_state], TCB_SYN_RECEIVED







;-------------------------------------
; Common processing for receipt of SYN

  .trim_then_step6:

	inc	[edx + TCP_segment.SequenceNumber]

;;; TODO: Drop any received data that follows receive window (590)

	mov	eax, [edx + TCP_segment.SequenceNumber]
	mov	[ebx + TCP_SOCKET.RCV_UP], eax
	dec	eax
	mov	[ebx + TCP_SOCKET.SND_WL1], eax

	jmp	.ack_processed








  .NOT_LISTEN_OR_SYN_SENT:

	DEBUGF	1,"Slow TCP input: not listen or syn_sent state\n"

;--------------------------------------------
; Protection Against Wrapped Sequence Numbers

; First, check if timestamp is present

;;;; TODO 602

; Then, check if at least some bytes of data are within window

;;;; TODO








;----------------------------
; trim any data not in window

; check for duplicate data at beginning of segment

	mov	eax, [ebx + TCP_SOCKET.RCV_NXT]
	sub	eax, [edx + TCP_segment.SequenceNumber]
	jle	.no_duplicate

	DEBUGF	1,"Uh oh.. %x bytes of duplicate data!\n", eax

	test	[edx + TCP_segment.Flags], TH_SYN
	jz	.no_dup_syn

; remove duplicate syn

	and	[edx + TCP_segment.Flags], not (TH_SYN)
	inc	[edx + TCP_segment.SequenceNumber]

	cmp	[edx + TCP_segment.UrgentPointer], 1
	jl	@f

	dec	[edx + TCP_segment.UrgentPointer]

	jmp	.no_dup_syn
       @@:

	and	[edx + TCP_segment.Flags], not (TH_URG)
	dec	eax
	jz	.no_duplicate
  .no_dup_syn:

	DEBUGF	1,"Going to drop %u out of %u bytes\n", eax, ecx

; eax holds number of bytes to drop

; Check for entire duplicate packet

	cmp	eax, ecx
	jge	.duplicate

;;; TODO: apply figure 28.30

; Check for duplicate FIN

	test	[edx + TCP_segment.Flags], TH_FIN
	jz	@f
	inc	ecx
	cmp	eax, ecx
	dec	ecx
	jne	@f

	mov	eax, ecx
	and	[edx + TCP_segment.Flags], not TH_FIN
	or	[ebx + TCP_SOCKET.t_flags], TF_ACKNOW
	jmp	.no_duplicate
       @@:

; Handle the case when a bound socket connects to itself
; Allow packets with a SYN and an ACKto continue with the processing

;-------------------------------------
; Generate duplicate ACK if nescessary

; This code also handles simultaneous half-open or self-connects

	test	eax, eax
	jnz	.drop_after_ack

	cmp	[edx + TCP_segment.Flags], TH_ACK
	jz	.drop_after_ack

  .duplicate:

	DEBUGF	1,"Duplicate received\n"

;----------------------------------------
; Update statistics for duplicate packets

;;; TODO

	jmp	.drop	       ;;; DROP the packet ??

  .no_duplicate:

;-----------------------------------------------
; Remove duplicate data and update urgent offset

	add	[edx + TCP_segment.SequenceNumber], eax

;;; TODO

	sub	[edx + TCP_segment.UrgentPointer], ax
	jg	@f

	and	[edx + TCP_segment.Flags], not (TH_URG)
	mov	[edx + TCP_segment.UrgentPointer], 0
       @@:

;--------------------------------------------------
; Handle data that arrives after process terminates

	cmp	[ebx + SOCKET.PID], 0
	jg	@f

	cmp	[ebx + TCP_SOCKET.t_state], TCB_CLOSE_WAIT
	jle	@f

	test	ecx, ecx
	jz	@f

;;; Close the socket
;;; update stats

	jmp	.drop_with_reset
       @@:

;----------------------------------------
; Remove data beyond right edge of window

	mov	eax, [edx + TCP_segment.SequenceNumber]
	add	eax, ecx
	sub	eax, [ebx + TCP_SOCKET.RCV_NXT]
	sub	ax, [ebx + TCP_SOCKET.RCV_WND]

; eax now holds the number of bytes to drop

	jle	.no_excess_data

;;; TODO: update stats

	cmp	eax, ecx
	jl	.dont_drop_all

;;; TODO 700-736

  .dont_drop_all:

  .no_excess_data:








;-----------------
; Record timestamp

;;; TODO 737-746





;------------------
; Process RST flags

	test	[edx + TCP_segment.Flags], TH_RST
	jz	.rst_skip

	DEBUGF	1,"Got an RST flag"

	mov	eax, [ebx + TCP_SOCKET.t_state]
	shl	eax, 2
	jmp	dword [eax + .rst_sw_list]

  .rst_sw_list:
	dd	.rst_skip	;TCB_CLOSED
	dd	.rst_skip	;TCB_LISTEN
	dd	.rst_skip	;TCB_SYN_SENT
	dd	.econnrefused	;TCB_SYN_RECEIVED
	dd	.econnreset	;TCB_ESTABLISHED
	dd	.econnreset	;TCB_CLOSE_WAIT
	dd	.econnreset	;TCB_FIN_WAIT_1
	dd	.rst_close	;TCB_CLOSING
	dd	.rst_close	;TCB_LAST_ACK
	dd	.econnreset	;TCB_FIN_WAIT_2
	dd	.rst_close	;TCB_TIMED_WAIT

  .econnrefused:

	DEBUGF	1,"Connection refused"

;;; TODO: debug info

	jmp	.close

  .econnreset:

	DEBUGF	1,"Connection reset"

;;; TODO: debug info

  .close:

	DEBUGF	1,"Closing connection"

;;; update stats

  .rst_close:

	DEBUGF	1,"Closing with reset\n"

;;; Close the socket

	jmp	.drop







  .rst_skip:


;--------------------------------------
; handle SYN-full and ACK-less segments

	test	[edx + TCP_segment.Flags], TH_SYN
	jz	@f

	mov	ebx, ECONNRESET
	call	TCP_drop

	jmp	.drop_with_reset

	test	[edx + TCP_segment.Flags], TH_ACK
	jz	.drop
      @@:







;---------------
; ACK processing

	cmp	[ebx + TCP_SOCKET.t_state], TCB_SYN_RECEIVED
	jnz	.no_syn_rcv

	DEBUGF	1,"TCP state = syn received\n"

	;;;;;  801-815

  .no_syn_rcv:

; check for duplicate ACK

	mov	eax, [edx + TCP_segment.AckNumber]
	cmp	eax, [ebx + TCP_SOCKET.SND_UNA]
	jg	.not_dup_ack

	test	ecx, ecx
	jnz	.reset_dupacks

	mov	eax, dword [edx + TCP_segment.Window]
	cmp	eax, [ebx + TCP_SOCKET.SND_WND]
	jne	.reset_dupacks

	DEBUGF	1,"Processing a duplicate ACK..\n"

	cmp	[ebx + TCP_SOCKET.timer_retransmission], 10000 ;;;;
	jg	@f

	mov	eax, [edx + TCP_segment.AckNumber]
	cmp	eax, [ebx + TCP_SOCKET.SND_UNA]
	je	.dup_ack

       @@:
	mov	[ebx + TCP_SOCKET.t_dupacks], 0
	jmp	.not_dup_ack

  .dup_ack:
	inc	[ebx + TCP_SOCKET.t_dupacks]
	cmp	[ebx + TCP_SOCKET.t_dupacks], TCP_re_xmit_thresh
	jne	.no_re_xmit

	push	[ebx + TCP_SOCKET.SND_NXT]		; >>>>

	mov	eax, [ebx + TCP_SOCKET.SND_WND]
	cmp	eax, [ebx + TCP_SOCKET.SND_CWND]
	cmovg	eax, [ebx + TCP_SOCKET.SND_CWND]
	shr	eax, 1
	push	edx
	xor	edx, edx
	div	[ebx + TCP_SOCKET.t_maxseg]
	cmp	eax, 2
	jge	@f
	mov	ax, 2
       @@:
	mul	[ebx + TCP_SOCKET.t_maxseg]
	pop	edx
	mov	[ebx + TCP_SOCKET.SND_SSTHRESH], eax

	mov	[ebx + TCP_SOCKET.timer_retransmission], 0	; turn off retransmission timer
	mov	[ebx + TCP_SOCKET.t_rtt], 0
	mov	eax, [edx + TCP_segment.AckNumber]
	mov	[ebx + TCP_SOCKET.SND_NXT], eax
	mov	eax, [ebx + TCP_SOCKET.t_maxseg]
	mov	[ebx + TCP_SOCKET.SND_CWND], eax

	mov	eax, ebx
	call	TCP_output					; retransmit missing segment

	push	edx
	xor	edx, edx
	mov	eax, [ebx + TCP_SOCKET.t_maxseg]
	mul	[ebx + TCP_SOCKET.t_dupacks]
	pop	edx
	add	eax, [ebx + TCP_SOCKET.SND_SSTHRESH]
	mov	[ebx + TCP_SOCKET.SND_CWND], eax

	pop	eax					; <<<<
	cmp	eax, [ebx + TCP_SOCKET.SND_NXT]
	jl	@f
	mov	[ebx + TCP_SOCKET.SND_NXT], eax
       @@:

	jmp	.drop


  .no_re_xmit:
	jle	.not_dup_ack

	DEBUGF	1,"Increasing congestion window\n"

	mov	eax, [ebx + TCP_SOCKET.t_maxseg]
	add	[ebx + TCP_SOCKET.SND_CWND], eax

	mov	eax, ebx
	call	TCP_output

	jmp	.drop






  .not_dup_ack:

;-------------------------------------------------
; If the congestion window was inflated to account
; for the other side's cached packets, retract it

	mov	eax, [ebx + TCP_SOCKET.SND_SSTHRESH]
	cmp	eax, [ebx + TCP_SOCKET.SND_CWND]
	jg	@f
	cmp	[ebx + TCP_SOCKET.t_dupacks], TCP_re_xmit_thresh
	jle	@f
	mov	[ebx + TCP_SOCKET.SND_CWND], eax
       @@:

	mov	[ebx + TCP_SOCKET.t_dupacks], 0

	mov	eax, [edx + TCP_segment.AckNumber]
	cmp	eax, [ebx + TCP_SOCKET.SND_MAX]
	jle	@f

	;;; TODO: update stats
	jmp	.drop_after_ack

       @@:

	mov	edi, [edx + TCP_segment.AckNumber]
	sub	edi, [ebx + TCP_SOCKET.SND_UNA] 	; now we got the number of acked bytes in esi

	;;; TODO: update stats


	DEBUGF	1,"We have an acceptable ACK of %x bytes\n", esi






;------------------------------------------
; RTT measurements and retransmission timer

	;;;;; 912 - 926

	mov	[ebx + TCP_SOCKET.timer_retransmission], 0

	mov	eax, [ebx + TCP_SOCKET.SND_MAX]
	cmp	eax, [edx + TCP_segment.AckNumber]
	je	.all_outstanding
	mov	[ebx + TCP_SOCKET.timer_retransmission], 120 ;;;; TODO: correct this value (use a macro for it)
  .all_outstanding:







;-------------------------------------------
; Open congestion window in response to ACKs

	mov	esi, [ebx + TCP_SOCKET.SND_CWND]
	mov	eax, [ebx + TCP_SOCKET.t_maxseg]

	cmp	esi, [ebx + TCP_SOCKET.SND_SSTHRESH]
	jle	@f
	push	edx
	push	eax
	mul	eax
	div	esi
	pop	edx
	shr	edx, 3
	add	eax, edx
	pop	edx
       @@:

	add	esi, eax

	push	ecx
	mov	cl, [ebx + TCP_SOCKET.SND_SCALE]
	mov	eax, TCP_max_win
	shl	eax, cl
	pop	ecx

	cmp	esi, eax
	cmovg	esi, eax
	mov	[ebx + TCP_SOCKET.SND_CWND], esi







;------------------------------------------
; Remove acknowledged data from send buffer

	push	ecx edx ebx
	mov	ecx, edi
	lea	eax, [ebx + STREAM_SOCKET.snd]
	call	SOCKET_ring_free
	pop	ebx
	sub	[ebx + TCP_SOCKET.SND_WND], ecx
	pop	edx ecx

; Wake up process waiting on send buffer

	mov	eax, ebx
	call	SOCKET_notify_owner

; Update TCB

	mov	eax, [edx + TCP_segment.AckNumber]
	mov	[ebx + TCP_SOCKET.SND_UNA], eax

	cmp	eax, [ebx + TCP_SOCKET.SND_NXT]
	jl	@f
	mov	[ebx + TCP_SOCKET.SND_NXT], eax
       @@:


	;; TODO: use zero flag as 'ourfinisacked'




; General ACK handling complete
; Now do the state-specific ones

	mov	eax, [ebx + TCP_SOCKET.t_state]
	jmp	dword [eax*4 + .ACK_sw_list]

  .ACK_sw_list:
	dd	.ack_processed	;TCB_CLOSED
	dd	.ack_processed	;TCB_LISTEN
	dd	.ack_processed	;TCB_SYN_SENT
	dd	.ack_processed	;TCB_SYN_RECEIVED
	dd	.ack_processed	;TCB_ESTABLISHED
	dd	.ack_processed	;TCB_CLOSE_WAIT
	dd	.ack_fw1	;TCB_FIN_WAIT_1
	dd	.ack_c		;TCB_CLOSING
	dd	.ack_la 	;TCB_LAST_ACK
	dd	.ack_processed	;TCB_FIN_WAIT_2
	dd	.ack_tw 	;TCB_TIMED_WAIT


  .ack_fw1:
	jz	.ack_processed

	test	[ebx + SOCKET.state], SS_CANTRCVMORE
	jnz	@f
	mov	eax, ebx
	call	SOCKET_is_disconnected
;;;        mov     [ebx + TCP_SOCKET.timer_timed_wait], TCP_time_max_idle
       @@:

	mov	[ebx + TCP_SOCKET.t_state], TCB_FIN_WAIT_2
	jmp	.ack_processed


  .ack_c:
	jz	.ack_processed

	mov	[ebx + TCP_SOCKET.t_state], TCB_TIMED_WAIT
	mov	eax, ebx
	call	TCP_cancel_timers
	mov	[ebx + TCP_SOCKET.timer_timed_wait], 2 * TCP_time_MSL
	mov	eax, ebx
	call	SOCKET_is_disconnected
	jmp	.ack_processed


  .ack_la:
	jz	.ack_processed


	mov	eax, ebx
	call	TCP_close
	jmp	.drop


  .ack_tw:
	mov	[ebx + TCP_SOCKET.timer_timed_wait], 2 * TCP_time_MSL
	jmp	.drop_after_ack







  .reset_dupacks:		; We got a new ACK, reset duplicate ACK counter

	mov	[ebx + TCP_SOCKET.t_dupacks], 0

  .ack_processed:	; (step 6)

	DEBUGF	1,"ACK processed\n"

;----------------------------------------------
; check if we need to update window information

	test	[edx + TCP_segment.Flags], TH_ACK
	jz	.no_window_update

	mov	eax, [ebx + TCP_SOCKET.SND_WL1]
	cmp	eax, [edx + TCP_segment.SequenceNumber]
	jl	.update_window
	jg	@f

	mov	eax, [ebx + TCP_SOCKET.SND_WL2]
	cmp	eax, [edx + TCP_segment.AckNumber]
	jl	.update_window
	jg	.no_window_update
       @@:

	mov	eax, [ebx + TCP_SOCKET.SND_WL2]
	cmp	eax, [edx + TCP_segment.AckNumber]
	jne	.no_window_update

	movzx	eax, [edx + TCP_segment.Window]
	cmp	eax, [ebx + TCP_SOCKET.SND_WND]
	jle	.no_window_update

  .update_window:

	DEBUGF	1,"Updating window\n"

; Keep track of pure window updates

;        test    ecx, ecx
;        jz      @f
;
;        mov     eax, [ebx + TCP_SOCKET.SND_WL2]
;        cmp     eax, [edx + TCP_segment.AckNumber]
;        jne     @f
;
;        ;; mov eax, tiwin
;        cmp     eax, [ebx + TCP_SOCKET.SND_WND]
;        jle     @f
;
;        ;;; update stats
;
;       @@:

	mov	eax, dword [edx + TCP_segment.Window]
	cmp	eax, [ebx + TCP_SOCKET.max_sndwnd]
	jle	@f
	mov	[ebx + TCP_SOCKET.max_sndwnd], eax
       @@:
	mov	[ebx + TCP_SOCKET.SND_WND], eax

	push	[edx + TCP_segment.SequenceNumber]
	pop	[ebx + TCP_SOCKET.SND_WL1]

	push	[edx + TCP_segment.AckNumber]
	pop	[ebx + TCP_SOCKET.SND_WL2]

	;;; needoutput = 1

  .no_window_update:







;-----------------
; process URG flag

	test	[edx + TCP_segment.Flags], TH_URG
	jz	.not_urgent

	cmp	[edx + TCP_segment.UrgentPointer], 0
	jz	.not_urgent

	cmp	[ebx + TCP_SOCKET.t_state], TCB_TIMED_WAIT
	je	.not_urgent

; Ignore bogus urgent offsets

	;;; 1040-1050

	movzx	eax, [edx + TCP_segment.UrgentPointer]
	add	eax, [ebx + STREAM_SOCKET.rcv + RING_BUFFER.size]
	cmp	eax, SOCKET_MAXDATA
	jle	.not_urgent

	mov	[edx + TCP_segment.UrgentPointer], 0
	and	[edx + TCP_segment.Flags], not (TH_URG)
	jmp	.do_data

  .not_urgent:

; processing of received urgent pointer

	;;; TODO (1051-1093)








;--------------------------------
; process the data in the segment

  .do_data:

	DEBUGF	1,"TCP: do data (%u)\n", ecx

	test	[edx + TCP_segment.Flags], TH_FIN
	jnz	.process_fin

	cmp	[ebx + TCP_SOCKET.t_state], TCB_FIN_WAIT_1
	jge	.dont_do_data

	test	ecx, ecx
	jz	.final_processing

	DEBUGF	1,"Processing data in segment\n"

;; TODO: check if data is in sequence !

	movzx	eax, [edx + TCP_segment.DataOffset]		;;; todo: remember this in.. edi ?
	and	eax, 0xf0
	shr	al, 2

	lea	esi, [edx + eax]

	or	[ebx + TCP_SOCKET.t_flags], TF_DELACK
	add	[ebx + TCP_SOCKET.RCV_NXT], ecx

	lea	eax, [ebx + STREAM_SOCKET.rcv]
	call	SOCKET_ring_write

	mov	eax, ebx
	call	SOCKET_notify_owner

	jmp	.final_processing


  .dont_do_data:







;---------------
; FIN processing

  .process_fin:

	DEBUGF	1,"Processing FIN\n"

	mov	eax, [ebx + TCP_SOCKET.t_state]
	shl	eax, 2
	jmp	dword [eax + .FIN_sw_list]

  .FIN_sw_list:
	dd	.no_fin 	;TCB_CLOSED
	dd	.no_fin 	;TCB_LISTEN
	dd	.no_fin 	;TCB_SYN_SENT
	dd	.fin_syn_est	;TCB_SYN_RECEIVED
	dd	.fin_syn_est	;TCB_ESTABLISHED
	dd	.no_fin 	;TCB_CLOSE_WAIT
	dd	.fin_wait1	;TCB_FIN_WAIT_1
	dd	.no_fin 	;TCB_CLOSING
	dd	.no_fin 	;TCB_LAST_ACK
	dd	.fin_wait2	;TCB_FIN_WAIT_2
	dd	.fin_timed	;TCB_TIMED_WAIT



  .fin_syn_est:

	jmp	.final_processing

  .fin_wait1:

	jmp	.final_processing

  .fin_wait2:

	jmp	.final_processing

  .fin_timed:

	jmp	.final_processing

  .no_fin:








;-----------------
; Final processing

  .final_processing:

	DEBUGF	1,"Final processing\n"

	;;; if debug enabled, output packet

	;test    needoutput, needoutput
	;jz      .dumpit

	test	[ebx + TCP_SOCKET.t_flags], TF_ACKNOW
	jz	.dumpit

	DEBUGF	1,"ACK now!\n"

	push	ebx
	mov	eax, ebx
	call	TCP_output
	pop	ebx

  .dumpit:

	mov	[ebx + SOCKET.lock], 0

	call	kernel_free
	add	esp, 4
	ret







;------------------------------------------
; Generate an ACK, droping incoming segment

align 4
.drop_after_ack:

	DEBUGF	1,"Drop after ACK\n"

	test	[edx + TCP_segment.Flags], TH_RST
	jnz	.drop

	and	[ebx + TCP_SOCKET.t_flags], TF_ACKNOW

	mov	[ebx + SOCKET.lock], 0

	push	ebx
	mov	eax, ebx
	call	TCP_output
	pop	ebx

	call	kernel_free
	add	esp, 4
	ret








;-------------------------------------------
; Generate an RST, dropping incoming segment

align 4
.drop_with_reset:

	mov	[ebx + SOCKET.lock], 0

.drop_with_reset_not_locked:

	DEBUGF	1,"Drop with reset\n"

	test	[edx + TCP_segment.Flags], TH_RST
	jnz	.drop

	;;; if its a multicast/broadcast, also drop

	test	[edx + TCP_segment.Flags], TH_ACK
	jnz	.respond_ack

	test	[edx + TCP_segment.Flags], TH_SYN
	jnz	.respond_syn

	call	kernel_free
	add	esp, 4
	ret

  .respond_ack:

	mov	dl, TH_RST

	push	ebx
	call	TCP_respond_segment
	pop	ebx

	jmp	.destroy_new_socket


  .respond_syn:

	mov	dl, TH_RST + TH_ACK

	push	ebx
	call	TCP_respond_socket
	pop	ebx

	jmp	.destroy_new_socket







;-----
; Drop

align 4
.drop:

	mov	[ebx + SOCKET.lock], 0

.drop_not_locked:

	DEBUGF	1,"Dropping packet\n"

	;;;; If debugging options are enabled, output the packet somwhere

  .destroy_new_socket:

	;;;; kill the newly created socket

	call	kernel_free
	add	esp, 4
	ret