;-----------------------------------------------------------------
;
; TCP_output
;
; IN:  eax = socket pointer
;
; OUT: /
;
;-----------------------------------------------------------------
align 4
TCP_output:

	DEBUGF 1,"TCP_output, socket: %x\n", eax


; We'll detect the length of the data to be transmitted, and flags to be used
; If there is some data, or any critical controls to send (SYN / RST), then transmit
; Otherwise, investigate further

	mov	ebx, [eax + TCP_SOCKET.SND_MAX]
	cmp	ebx, [eax + TCP_SOCKET.SND_UNA]
	jne	.not_idle

	mov	ebx, [eax + TCP_SOCKET.t_idle]
	cmp	ebx, [eax + TCP_SOCKET.t_rxtcur]
	jle	.not_idle

; We have been idle for a while and no ACKS are expected to clock out any data we send..
; Slow start to get ack "clock" running again.

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

  .not_idle:
  .again:
	mov	ebx, [eax + TCP_SOCKET.SND_NXT] 	; calculate offset
	sub	ebx, [eax + TCP_SOCKET.SND_UNA] 	;

	mov	ecx, [eax + TCP_SOCKET.SND_WND] 	; determine window
	cmp	ecx, [eax + TCP_SOCKET.SND_CWND]	;
	jl	@f					;
	mov	ecx, [eax + TCP_SOCKET.SND_CWND]	;
       @@:						;

	call	TCP_outflags	; in dl

; If in persist timeout with window of 0, send 1 byte.
; Otherwise, if window is small but nonzero, and timer expired,
; we will send what we can and go to transmit state

	test	[eax + TCP_SOCKET.t_force], -1
	jz	.no_persist_timeout

	test	ecx, ecx
	jnz	.no_zero_window

	cmp	ebx, [eax + STREAM_SOCKET.snd + RING_BUFFER.size]
	jge	@f

	and	dl, not (TH_FIN)	  ; clear the FIN flag    ??? how can it be set before?

       @@:
	inc	ecx
	jmp	.no_persist_timeout

  .no_zero_window:

	mov	[eax + TCP_SOCKET.timer_persist], 0
	mov	[eax + TCP_SOCKET.t_rxtshift], 0

  .no_persist_timeout:

;;;106

	mov	esi, [eax + STREAM_SOCKET.snd + RING_BUFFER.size]
	cmp	esi, ecx
	jl	@f
	mov	esi, ecx
       @@:
	sub	esi, ebx

	cmp	esi, -1
	jne	.not_minus_one

; If FIN has been set, but not ACKed, and we havent been called to retransmit,
; len (esi) will be -1
; Otherwise, window shrank after we sent into it.
; If window shrank to 0, cancel pending retransmit and pull SND_NXT back to (closed) window
; We will enter persist state below.
; If window didn't close completely, just wait for an ACK

	xor	esi, esi

	test	ecx, ecx
	jnz	@f

	mov	[eax + TCP_SOCKET.timer_retransmission], 0   ; cancel retransmit

	push	[eax + TCP_SOCKET.SND_UNA]
	pop	[eax + TCP_SOCKET.SND_NXT]
       @@:

  .not_minus_one:

;;; 124

	cmp	esi, [eax + TCP_SOCKET.t_maxseg]
	jle	@f

	mov	esi, [eax + TCP_SOCKET.t_maxseg]
	;sendalot = 1

       @@:

;;; 128

	mov	edi, [eax + TCP_SOCKET.SND_NXT]
	add	edi, esi	; len
	sub	edi, [eax + TCP_SOCKET.SND_UNA]
	add	edi, [eax + STREAM_SOCKET.snd + RING_BUFFER.size]
	cmp	edi, 0
	jle	@f

	and	dl, not (TH_FIN)	  ; clear the FIN flag

       @@:


; set ecx to space available in receive buffer
; From now on, ecx will be the window we advertise to the other end

	mov	ecx, SOCKET_MAXDATA
	sub	ecx, [eax + STREAM_SOCKET.rcv + RING_BUFFER.size]

;------------------------------
; Sender silly window avoidance

	cmp	ecx, [eax + TCP_SOCKET.t_maxseg]
	je	.send

;;; TODO: 144-145

	test	[eax + TCP_SOCKET.t_force], -1
	jnz	.send

	mov	ebx, [eax + TCP_SOCKET.max_sndwnd]
	shr	ebx, 1
	cmp	ecx, ebx
	jge	.send

	mov	ebx, [eax + TCP_SOCKET.SND_NXT]
	cmp	ebx, [eax + TCP_SOCKET.SND_MAX]
	jl	.send

;----------------------------------------
; Check if a window update should be sent

	test	ecx, ecx	; window
	jz	.no_window

;;; TODO 154-172

  .no_window:

;--------------------------
; Should a segment be sent?

	test	[eax + TCP_SOCKET.t_flags], TF_ACKNOW
	jnz	.send

	test	dl, TH_SYN + TH_RST
	jnz	.send

	mov	ebx, [eax + TCP_SOCKET.SND_UP]
	cmp	ebx, [eax + TCP_SOCKET.SND_UNA]
	jg	.send

	test	dl, TH_FIN
	jz	.enter_persist

	test	[eax + TCP_SOCKET.t_flags], TF_SENTFIN
	jnz	.send

	mov	ebx, [eax + TCP_SOCKET.SND_NXT]
	cmp	ebx, [eax + TCP_SOCKET.SND_UNA]
	je	.send

;--------------------
; Enter persist state

  .enter_persist:

	DEBUGF	1,"Entering persist state\n"

;--------------------------------------
; No reason to send a segment, just ret

	DEBUGF	1,"No reason to send a segment\n"

	mov	[ebx + SOCKET.lock], 0

	ret


;-----------------------------------------------
;
; Send a segment
;
; eax = socket pointer
;  dl = flags
;
;-----------------------------------------------

  .send:

	DEBUGF	1,"Preparing to send a segment\n"

	mov	edi, TCP_segment.Data	; edi will contain headersize

	sub	esp, 8			; create some space on stack
	push	eax			; save this too..

;------------------------------------
; Send options with first SYN segment

	test	dl, TH_SYN
	jz	.no_options

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

	test	[eax + TCP_SOCKET.t_flags], TF_NOOPT
	jnz	.no_options

	mov	ecx, 1460
	or	ecx, TCP_OPT_MAXSEG shl 24 + 4 shl 16
	bswap	ecx
	push	ecx
	add	di, 4

	test	[eax + TCP_SOCKET.t_flags], TF_REQ_SCALE
	jz	.no_syn

	test	dl, TH_ACK
	jnz	.scale_opt

	test	[eax + TCP_SOCKET.t_flags], TF_RCVD_SCALE
	jz	.no_syn

  .scale_opt:
	movzx	ecx, byte [eax + TCP_SOCKET.request_r_scale]
	or	ecx, TCP_OPT_WINDOW shl 24 + 4 shl 16 + TCP_OPT_NOP shl 8
	bswap	ecx
	pushd	ecx
	add	di, 4

  .no_syn:

;------------------------------------
; Make the timestamp option if needed

	test	[eax + TCP_SOCKET.t_flags], TF_REQ_TSTMP
	jz	.no_timestamp

	test	dl, TH_RST
	jnz	.no_timestamp

	test	dl, TH_ACK
	jz	.timestamp

	test	[eax + TCP_SOCKET.t_flags], TF_RCVD_TSTMP
	jz	.no_timestamp

  .timestamp:
	mov	esi, [timer_ticks]
	bswap	esi
	push	esi
	pushw	0
	pushd	TCP_OPT_TIMESTAMP + 10 shl 8 + TCP_OPT_NOP shl 16 + TCP_OPT_NOP shl 24
	add	di, 10

  .no_timestamp:
	;; TODO: check if we dont exceed the max segment size

  .no_options:
	; eax = socket ptr
	; edx = flags
	; ecx = data size
	; edi = header size
	; esi = snd ring buff ptr

	mov	ecx, [eax + STREAM_SOCKET.snd + RING_BUFFER.size]
	cmp	ecx, [eax + TCP_SOCKET.t_maxseg]			;;; right?
	jle	@f
	mov	ecx, [eax + TCP_SOCKET.t_maxseg]
       @@:
	add	ecx, edi	; total TCP segment size

; Start by pushing all TCP header values in reverse order on stack
; (essentially, creating the tcp header!)

	pushw	0	;        .UrgentPointer          dw ?
	pushw	0	;        .Checksum               dw ?
	pushw	0x00a0	;        .Window                 dw ?    ;;;;;;;
	shl	edi, 2	;        .DataOffset             db ?  only 4 left-most bits
	shl	dx, 8
	or	dx, di	;        .Flags                  db ?
	pushw	dx
	shr	edi, 2	;        .DataOffset             db ? ;;;;

	push	[eax + TCP_SOCKET.RCV_NXT]	;        .AckNumber              dd ?
	ntohd	[esp]

	push	[eax + TCP_SOCKET.SND_NXT]	;        .SequenceNumber         dd ?
	ntohd	[esp]

	push	[eax + TCP_SOCKET.RemotePort]	;        .DestinationPort        dw ?
	ntohw	[esp]

	push	[eax + TCP_SOCKET.LocalPort]	;        .SourcePort             dw ?
	ntohw	[esp]

	push	edi		; header size

; Create the IP packet
	mov	ebx, [eax + IP_SOCKET.LocalIP]	; source ip
	mov	eax, [eax + IP_SOCKET.RemoteIP] ; dest ip
	mov	di, IP_PROTO_TCP shl 8 + 128
	call	IPv4_output
	jz	.fail

;-----------------------------------------
; Move TCP header from stack to TCP packet

	push	ecx
	mov	ecx, [esp+4]
	lea	esi, [esp+4+4]
	shr	ecx, 2
	rep	movsd
	pop	ecx		; full TCP packet size

	pop	esi		; headersize
	add	esp, esi

	mov	[esp + 4], eax		; packet ptr
	mov	[esp + 4+4], edx	; packet size

	mov	edx, edi		; begin of data
	sub	edx, esi		; begin of packet (edi = begin of data)
	push	ecx
	sub	ecx, esi		; data size

;--------------
; Copy the data

; eax = ptr to ring struct
; ecx = buffer size
; edi = ptr to buffer

;        test    ecx, ecx
	mov	eax, [esp+4]		  ; socket ptr
	add	[eax + TCP_SOCKET.SND_NXT], ecx
	add	eax, STREAM_SOCKET.snd
	push	edx
	call	SOCKET_ring_read
	pop	esi
	pop	ecx
	pop	eax

	test	[esi + TCP_segment.Flags], TH_SYN + TH_FIN
	jz	@f
	inc	[eax + TCP_SOCKET.SND_NXT]
	;;; TODO: update sentfin flag
       @@:

	mov	edx, [eax + TCP_SOCKET.SND_NXT]
	cmp	edx, [eax + TCP_SOCKET.SND_MAX]
	jle	@f
	mov	[eax + TCP_SOCKET.SND_MAX], edx

	;;;; TODO: time transmission (420)
       @@:

	;;; TODO: set retransmission timer

;--------------------
; Create the checksum

	DEBUGF	1,"checksum: ptr=%x size=%u\n", esi, ecx

	TCP_checksum (eax + IP_SOCKET.LocalIP), (eax + IP_SOCKET.RemoteIP)
	mov	[esi+TCP_segment.Checksum], dx

;----------------
; Send the packet

	DEBUGF	1,"Sending TCP Packet to device %x\n", ebx
	call	[ebx + NET_DEVICE.transmit]
	ret


  .fail:
	pop	ecx
	add	esp, ecx
	add	esp, 4+8
	DEBUGF 1,"TCP_output: failed\n"
	ret