Unit TCP - Ultibo.org

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Description

Ultibo TCP (Transmission Control Protocol) unit

Notes:

Segment handling:

Send adds new segments to the end of the list only accepts ACKs for whole segments.

Recv adds/inserts segments in correct SEQ order accepts overlapping segments only sends ACKs for whole segments.

Send will coalesce small data writes into larger segments if options allow this.

Recv will store the segments exactly as received.

TCP Send and Recv do not use a block buffer as per UDP etc. Instead the data for each Segment is stored in memory (TCP_MAX_MSS) allocated with the Segment. The Free and Used values still track the amount of data in the buffer but this method allows OOB data to be handled correctly.

TCP Sequence numbers are compared using modulo 2^32 arithmetic. The following calculations provide the necessary handling of wraparound etc.

LT = (A - B) < 0

LEQ = (A - B) <= 0

GT = (A - B) > 0

GEQ = (A - B) >= 0

See GlobalSock.pas for actual functions that implement this.

Constants

TCP specific constants TCP_*

Note: Some TCP definitions are in the Protocol or IP modules

`TCP_PROTOCOL_NAME = 'TCP';`

`TCP_TIMER_INTERVAL = 1;`	1ms timer interval for TCP

`MIN_TCP_PACKET = 20;`	Not Counting Adapter and Transport Header
`MAX_TCP_PACKET = 1480;`	Not Counting Adapter and Transport Header

`TCP_DEFAULT_MSS = 536;`	Default Segment Size for TCP (576 - TCP - IP)
`TCP_MAX_MSS = 1460;`	Max Segment Size for TCP (1500 - TCP - IP)

`TCP_MAX_LIFETIME = 120000;`	Max Segment Lifetime (2 minutes)

`TCP_TIMEOUT = 0;`	Wait forever on a TCP Read/Write
`TCP_BUFFER_SIZE = 262144;`	65536; TCP Send/Receive Buffer Sizes
`TCP_WINDOW_SIZE = 64240;`	Sliding Window Receive Size (44 x MSS)
`TCP_INITIAL_WINDOW = 8192;`	Initial Window to advertise in SYN packet

`TCP_TIMEOUT_OFFSET = 10;`	How much time offset to allow from the designated value

`TCP_ADVERT_TIMEOUT = 100;`	Time to wait before sending a window size update after closing the receive window

`TCP_WINDOW_TIMEOUT = 5000;`	Time to wait before probing small/zero Window
`TCP_ACK_TIMEOUT = 200;`	Max Delayed Ack Time

`TCP_CONNECT_COUNT = 3;`	Number of Connect retries (on RST) before Failure
`TCP_RESTART_TIMEOUT = 400;`	Timeout between Connect retries (Milliseconds)

`TCP_RETRY_COUNT = 10;`	Number of Retransmits before Reset

`TCP_RETRY_TIMEOUT:array[1..TCP_RETRY_COUNT] of LongWord = (250,500,1000,2000,4000,8000,15000,30000,60000,120000);`

`TCP_KEEPALIVE_COUNT = 3;`	Number of Failed Keepalives before Reset

`TCP_KEEPALIVE_TIMEOUT:array[1..TCP_KEEPALIVE_COUNT] of LongWord = (600000,60000,60000);`

`TCP_MAX_PORT = 65536;`

`TCP_HEADER_SIZE = 20;`	SizeOf(TTCPHeader) Does Not Allow for Options
`TCP_OPTIONS_SIZE = 40;`	Maximum Allowed Options

`TCP_SEGMENT_SIZE = 68;`	SizeOf(TTCPSegment) Including TSocketTimerItem

TCP socket state TCP_STATE_*

`TCP_STATE_LISTEN = 0;`	listening for connection
`TCP_STATE_SYNSENT = 1;`	SYN sent, active open
`TCP_STATE_SYNREC = 2;`	SYN received, SYNACK sent
`TCP_STATE_ESTAB = 3;`	established
`TCP_STATE_FINWAIT1 = 4;`	sent FIN
`TCP_STATE_FINWAIT2 = 5;`	sent FIN, received FINACK
`TCP_STATE_CLOSWAIT = 6;`	received FIN waiting for close
`TCP_STATE_CLOSING = 7;`	sent FIN, received FIN (waiting for FINACK)
`TCP_STATE_LASTACK = 8;`	FIN received, FINACK + FIN sent
`TCP_STATE_TIMEWAIT = 9;`	dally after sending final FINACK
`TCP_STATE_CLOSED = 10;`	FINACK received

TCP header option TCPOPT_*

`TCPOPT_EOL = 0;`	end-of-option list
`TCPOPT_NOP = 1;`	no-operation
`TCPOPT_MAXSEG = 2;`	maximum segment size
`TCPOPT_WINDOW = 3;`	window scale factor (rfc1072)
`TCPOPT_SACKOK = 4;`	selective ack ok (rfc1072)
`TCPOPT_SACK = 5;`	selective ack (rfc1072)
`TCPOPT_ECHO = 6;`	echo (rfc1072)
`TCPOPT_ECHOREPLY = 7;`	echo (rfc1072)
`TCPOPT_TIMESTAMP = 8;`	timestamps (rfc1323)
`TCPOPT_CC = 11;`	T/TCP CC options (rfc1644)
`TCPOPT_CCNEW = 12;`	T/TCP CC options (rfc1644)
`TCPOPT_CCECHO = 13;`	T/TCP CC options (rfc1644)

TCP header flag TCP_FLAG_*

`TCP_FLAG_FIN = $01;`
`TCP_FLAG_SYN = $02;`
`TCP_FLAG_RST = $04;`
`TCP_FLAG_PUSH = $08;`
`TCP_FLAG_ACK = $10;`
`TCP_FLAG_URG = $20;`
`TCP_FLAG_MASK = $3F;`

Van Jacobson's Algorithm; max std. average and std. deviation
`MAX_VJSA = 80000;`
`MAX_VJSD = 20000;`
`INIT_VJSA = 220;`

TCP port TCP_PORT_*

`TCP_PORT_START = 49152;`	First dynamic port (Previously 1024) As per IANA assignment
`TCP_PORT_STOP = 65534;`	Last dynamic port (Previously 5000) Short of IANA assignment to allow for rollover

Type definitions

TCP header

PTCPHeader = ^TTCPHeader;

TTCPHeader = packed record

Note: Some TCP definitions are in the Protocol or IP modules
Note: 20 Bytes unless TCP Options are added
`SourcePort:Word;`	Network Order
`DestPort:Word;`	Network Order
`Sequence:LongWord;`	First Sequence number in Data
`Acknowledge:LongWord;`	Next Sequence number expected
`HeaderLength:Byte;`	Number of 32 bit words in Header and Options (Bits 4-7 Reserved)
`Flags:Byte;`	Flags for TCP Control (Bits 1-2 Reserved)
`WindowSize:Word;`	Max 65536 (See WindowScale for higher values)
`Checksum:Word;`	As per standard (Header, Options and Data)
`Urgent:Word;`

TCP segment

PTCPSegment = ^TTCPSegment;

TTCPSegment = record

Note: 48 Bytes (Used by TCPSendBuffer/TCPRecvBuffer)
`Size:Word;`	Size of Segment Data (Can be zero)
`Data:Pointer;`	Pointer to Data in Buffer (Can be nil)
`FirstSequence:LongWord;`	Start Sequence of Data
`LastSequence:LongWord;`	End Sequence of Data (including Control bits)(actually the Start Sequence of next Segment)

`Control:Word;`	Control Bits on this segment (SYN/FIN/URG) (Send/Recv)
`Transferred:WordBool;`	Data has been Transferred to/from Buffer (Send/Recv)
`Acknowledged:WordBool;`	Data has been Acknowledged (Send/Recv)
`SelectiveAck:WordBool;`	Data has been Selective Acknowledged (Send/Recv)
`RoundTripTime:Int64;`

`Count:Word;`	Transmit Count (Send)
`Timeout:Int64;`	Transmit (Send)/Acknowledge (Recv) Timeout
`Prev:PTCPSegment;`	Pointer to Prev Segment
`Next:PTCPSegment;`	Pointer to Next Segment

`Item:TSocketTimerItem;`	Socket Timer Item for this Segment

Class definitions

TCP specific classes

Public variables

None defined