TTCPRecvBuffer

Return to Unit TCP

Description

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To be documented

Class definitions

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TTCPRecvBuffer = class(TSocketBuffer)

constructor Create(ASocket:TTransportSocket);
destructor Destroy; override;
private
FUrgent:LongWord;	Number of OOB bytes readable from Buffer
FAvailable:LongWord;	Number of bytes readable from Buffer
FFirst:PTCPSegment;	Pointer to First Segment
FLast:PTCPSegment;	Pointer to Last Segment
function DelayOverride(ASegment:PTCPSegment):Boolean;
function GetSegment(ASequence:LongWord; ALength:Word):PTCPSegment;
function GetPrevious(ASequence:LongWord; ALength:Word):PTCPSegment;
function GetOverlapped(ASequence:LongWord; ALength:Word):PTCPSegment;
function AddSegment(APrev:PTCPSegment; ASequence:LongWord; AFlags:Byte; ASize:Word):PTCPSegment;
function RemoveSegment(ASegment:PTCPSegment):Boolean;
procedure FlushSegments(All:Boolean);
protected
procedure SetSize(ASize:LongWord); override;
public
StartSequence:LongWord;	Initial Sequence number of Remote (IRS)
NextSequence:LongWord;	Next Sequence number to Receive (RCV.NXT)
LastSequence:LongWord;	Last Sequence number in Buffer (Including Unacknowledged data)
LastAcknowledge:LongWord;	Last Acknowledged number to Remote Note: NextSequence is the next byte we expect to Receive from Remote. LastAcknowledge will be the first Unacknowledged Seqeunce number of the Remote. LastSequence is the last sequence we have received from the Remote. If NextSequence equals LastSequence and LastAcknowledge equals NextSequence all segments have been Acknowledged.
UrgentPointer:LongWord;	(RCV.UP)
MaxSeg:Word;	Local Max Segment Size
WindowSize:LongWord;	Local Window Size (RCV.WND)
WindowScale:Byte;	Local Window Scale
LastWindow:LongWord;	Last Window value sent to Remote
SynSequence:LongWord;	Sequence number of remote SYN
FinSequence:LongWord;	Sequence number of remote FIN
NoSack:Boolean;	Selective Ack not in use
function CheckIdle:Boolean;
function GetUrgent:LongWord;
function GetAvailable:LongWord;
function SynReceived:Boolean;
function FinReceived:Boolean;
function CheckSequence(ASequence:LongWord; ASize:Word):Boolean;
function ReadData(var ABuffer; var ASize:Integer; AFlags:Integer):Boolean;
function WriteSegment(ASequence:LongWord; AUrgent:Word; AFlags:Byte; AData:Pointer; ASize:Word):Boolean;
function AcknowledgeSegments(var AAcknowledge:LongWord; var AWindow:Word; AForce:Boolean):Boolean;
function TimestampSegment(AOptions:Pointer; var AOffset:Word):Boolean;
function SelectiveAckSegments(AOptions:Pointer; var AOffset:Word):Boolean;

Function declarations

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constructor TTCPRecvBuffer.Create;

Description: To be documented

Note	None documented

destructor TTCPRecvBuffer.Destroy;

Description: To be documented

Note	None documented

function TTCPRecvBuffer.DelayOverride(ASegment:PTCPSegment):Boolean;

Description: Checks if this segment can override delayed ack because it has an in sequence segment following it

Note	Delayed ack must send an ack at least every two segments

function TTCPRecvBuffer.GetSegment(ASequence:LongWord; ALength:Word):PTCPSegment;

Description: Returns the first Segment that contains ALL of the passed Sequence

Sequence	Sequence is the start sequence
Length	Length includes the control bits

function TTCPRecvBuffer.GetPrevious(ASequence:LongWord; ALength:Word):PTCPSegment;

Description: Finds the first Segment that is AFTER the passed Sequence and returns the previous Segment

Sequence	Sequence is the start sequence
Length	Length includes the control bits
Note	If no Segment is after the passed Sequence returns the last Segment

function TTCPRecvBuffer.GetOverlapped(ASequence:LongWord; ALength:Word):PTCPSegment;

Description: Returns the first Segment that overlaps ANY of the passed Sequence

Sequence	Sequence is the start sequence
Length	Length includes the control bits

function TTCPRecvBuffer.AddSegment(APrev:PTCPSegment; ASequence:LongWord; AFlags:Byte; ASize:Word):PTCPSegment;

Description: Adds a new Segment after the previous segment or first in the list

Prev	Prev is the Previous segment
Sequence	Sequence is the start sequence
Size	Size can be zero Size should not include the SYN and FIN sequence

function TTCPRecvBuffer.RemoveSegment(ASegment:PTCPSegment):Boolean;

Description: Removes the passed Segment from the list

Note	None documented

procedure TTCPRecvBuffer.FlushSegments(All:Boolean);

Description: Removes Read Segments from the buffer (or All)

Note	None documented

procedure TTCPRecvBuffer.SetSize(ASize:LongWord);

Description: To be documented

Size	Size cannot be set smaller than the default or existing
Note	For TCP setting the size does not clear existing segments

function TTCPRecvBuffer.CheckIdle:Boolean;

Description: Check if all data in the recv buffer has been acknowledged

Note	None documented

function TTCPRecvBuffer.GetUrgent:LongWord;

Description: To be documented

Note	None documented

function TTCPRecvBuffer.GetAvailable:LongWord;

Description: To be documented

Note	None documented

function TTCPRecvBuffer.SynReceived:Boolean;

Description: Checks if a SYN has been received from the Remote

Note	None documented

function TTCPRecvBuffer.FinReceived:Boolean;

Description: Checks if a FIN has been received from the Remote

Note	None documented

function TTCPRecvBuffer.CheckSequence(ASequence:LongWord; ASize:Word):Boolean;

Description: Checks a Sequence for validity

Note	None documented

function TTCPRecvBuffer.ReadData(var ABuffer; var ASize:Integer; AFlags:Integer):Boolean;

Description: Used by Recv/RecvFrom to Read data from the buffer that has been Received

Size	Passed Size contains size of Buffer and should return the size of Datagram
Flags	Flags is for MSG_PEEK and MSG_OOB when applicable

function TTCPRecvBuffer.WriteSegment(ASequence:LongWord; AUrgent:Word; AFlags:Byte; AData:Pointer; ASize:Word):Boolean;

Description: Used by Socket to Write segments that are received into the queue

Socket Timing	For each received segment a notification is scheduled for the socket thread to check the socket in TCP_ACK_TIMEOUT milliseconds. This is the maximum to before the received segment must be acknowledged, but it may be acknowledged earlier if a segment is sent or if there are earlier received segments to be acknowledged as well.

function TTCPRecvBuffer.AcknowledgeSegments(var AAcknowledge:LongWord; var AWindow:Word; AForce:Boolean):Boolean;

Description: Used by Socket to Acknowledge segments that are received into the queue

Note	Delayed Ack is handled here by checking Timeout and following segments
Socket Timing	No notifications are sent to or scheduled for the socket thread when checking for received segments to acknowledge. This is because WriteSegment will have scheduled a notification for TCP_ACK_TIMEOUT milliseconds after each segment was received which will ensure they are acknowledged in time.

function TTCPRecvBuffer.TimestampSegment(AOptions:Pointer; var AOffset:Word):Boolean;

Description: Used by Socket to Timestamp (RTT) segments that are received into the queue

Offset	Offset points to the point to insert the timestamp option

function TTCPRecvBuffer.SelectiveAckSegments(AOptions:Pointer; var AOffset:Word):Boolean;

Description: To be documented

Note	None documented

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