Unit TCP

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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

TTCPProtocolTransport = class(TProtocolTransport)
TTCPProtocol = class(TNetworkProtocol)
TTCPSocket = class(TProtocolSocket)
TTCPState = class(TProtocolState)
TTCPOptions = class(TProtocolOptions)
TTCPSendBuffer = class(TSocketBuffer)
TTCPRecvBuffer = class(TSocketBuffer)


Public variables

None defined

Function declarations


Initialization functions 

procedure TCPInit;
Description: To be documented
Note None documented


TCP functions 

function CheckTCP(AFamily:Word; ABuffer:Pointer):Boolean;
Description: Verify that the packet is a valid TCP packet
Buffer The complete packet including Transport header 


function GetTCPHeaderOffset(AFamily:Word; ABuffer:Pointer):Word;
Description: To be documented
Buffer The complete packet including Transport header 


function GetTCPHeaderLength(AFamily:Word; ABuffer:Pointer):Word;
Description: To be documented
Buffer The complete packet including Transport header 


function GetTCPOptionsLength(AFamily:Word; ABuffer:Pointer):Word;
Description: To be documented
Buffer The complete packet including Transport header 


function GetTCPDataOffset(AFamily:Word; ABuffer:Pointer):Word;
Description: To be documented
Buffer The complete packet including Transport header 


function GetTCPDataLength(AFamily:Word; ABuffer:Pointer):Word;
Description: To be documented
Buffer The complete packet including Transport header 


function ChecksumTCPRecv(AFamily:Word; APseudo:PIPPseudo; ABuffer:Pointer; AOffset,ALength:Word):Word;
Description: Validate the Checksum of TCP Pseudo, Header and Data on Receive
Note None documented 


function ChecksumTCPSend(AFamily:Word; APseudo:PIPPseudo; AHeader:PTCPHeader; AOptions,AData:Pointer; AOptionsLength,ADataLength:Word):Word;
Description: Checksum the TCP Pseudo, Header, Options and Data on Send
Note None documented


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