TTCPSendBuffer

Return to Unit TCP

Description

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To be documented

Class definitions

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TTCPSendBuffer = class(TSocketBuffer)

constructor Create(ASocket:TTransportSocket);
destructor Destroy; override;
private
FFirst:PTCPSegment;	Pointer to First Segment
FLast:PTCPSegment;	Pointer to Last Segment
function AddSegment(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 Local (ISS)
NextSequence:LongWord;	Next Sequence number to Send (SND.NXT
LastSequence:LongWord;	Last Sequence number in Buffer
LastAcknowledge:LongWord;	Last Acknowledged number from Remote (SND.UNA) Note: LastAcknowledge is the NextSequence that Remote expects to Receive or the first Unacknowledged Sequence number. If LastAcknowledge equals NextSequence all segments have been Acknowledged LastSequence is the last sequence in our buffer to send. If NextSequence equals LastSequence there is no more data to send.
UrgentPointer:LongWord;	(SND.UP)
MaxSeg:Word;	Remote Max Segment Size (Learned from Remote)
WindowSize:LongWord;	Remote Window Size (SND.WND)
WindowScale:Byte;	Remote Window Scale
WindowTimeout:Int64;	Timeout for probing small/zero Window
CongestionWindow:Word;	Slow Start Window Size
SynSequence:LongWord;	Sequence number of our SYN
FinSequence:LongWord;	Sequence number of our FIN
WindowSequence:LongWord;	Sequence number of last Window update (SND.WL1)
WindowAcknowledge:LongWord;	Acknowledge number of last Window update (SND.WL2)
NoPush:Boolean;	Disable Push on final segment
NoSack:Boolean;	Selective Ack not in use
NoNagle:Boolean;	Nagle not in use
VjSa:LongWord;	VJ's alg, standard average
VjSd:LongWord;	VJ's alg, standard deviation
VjLast:LongWord;	VJ's alg, last transmit time
function CheckIdle:Boolean;
function SynAcknowledged:Boolean;
function FinAcknowledged:Boolean;
function TestAcknowledge(AAcknowledge:LongWord):Boolean;
function CheckAcknowledge(AAcknowledge:LongWord):Boolean;
function ValidateAcknowledge(AAcknowledge:LongWord):Boolean;
function WriteData(var ABuffer; ASize,AFlags:Integer):Boolean;
function Finish:Boolean;
function Synchronize:Boolean;
function ReadSegment(var ASequence:LongWord; var AUrgent:Word; var AFlags:Byte; var AData:Pointer; var ASize:Word; AForce:Boolean):Boolean;
function AcknowledgeSegments(ASequence,AAcknowledge:LongWord; AWindow:Word):Boolean;
function TimestampSegment(AOptions:Pointer; var AOffset:Word):Boolean;
function SelectiveAckSegments(AOptions:Pointer; var AOffset:Word; ASize:Byte):Boolean;

Function declarations

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constructor TTCPSendBuffer.Create;

Description: To be documented

Note	None documented

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destructor TTCPSendBuffer.Destroy;

Description: To be documented

Note	None documented

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

Description: Adds a new Segment as the last segment in the list

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

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

Description: Removes the passed Segment from the list

Note	None documented

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procedure TTCPSendBuffer.FlushSegments(All:Boolean);

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

Note	None documented

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procedure TTCPSendBuffer.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

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function TTCPSendBuffer.CheckIdle:Boolean;

Description: Check if all data in the send buffer has been sent and acknowledged

Note	None documented

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function TTCPSendBuffer.SynAcknowledged:Boolean;

Description: Test if a SYN has been sent and if it has been ACKed

Note	None documented

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function TTCPSendBuffer.FinAcknowledged:Boolean;

Description: Test if a FIN has been sent and if it has been ACKed

Note	None documented

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function TTCPSendBuffer.TestAcknowledge(AAcknowledge:LongWord):Boolean;

Description: Tests an Acknowledge for invalidity

Note	If SEG.ACK =< ISS, or SEG.ACK > SND.NXT then the ACK is unacceptable Only ever used when Socket is in SYN_SENT state

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function TTCPSendBuffer.CheckAcknowledge(AAcknowledge:LongWord):Boolean;

Description: Checks an Acknowledge for validity

Note	If SND.UNA =< SEG.ACK =< SND.NXT then the ACK is acceptable Only ever used when Socket is in SYN_REC state

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function TTCPSendBuffer.ValidateAcknowledge(AAcknowledge:LongWord):Boolean;

Description: Checks an Acknowledge for validity

Note	If the ACK acks something not yet sent (SEG.ACK > SND.NXT) then send an ACK Used when Socket is in any of the Synchronized states

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function TTCPSendBuffer.WriteData(var ABuffer; ASize,AFlags:Integer):Boolean;

Description: Used by Send/SendTo to Write data into the buffer ready for Sending

Flags	Flags is for MSG_PEEK and MSG_OOB when applicable
Note	Data that will not fit in the Buffer is simply discarded Send coalescing is handled here by checking Last segment Push flag is set on the last written segment of user data
Socket Timing	Whenever data is written to the buffer a notification is sent to the socket thread to check the socket immediately. This ensures that the segment is sent immediately if acceptable or otherwise will be sent when an acknowledge is received from the remote due to the Nagle algorithm.

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function TTCPSendBuffer.Finish:Boolean;

Description: To be documented

Socket Timing	When the FIN segment is written to the buffer a notification is sent to the socket thread to check the socket immediately. This ensures that the segment will be sent to the remote either immediately or after the Nagle delay.

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function TTCPSendBuffer.Synchronize:Boolean;

Description: To be documented

Socket Timing	When the SYN segment is written to the buffer a notification is sent to the socket thread to check the socket immediately. This ensures that the segment will be sent to the remote immediately.

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function TTCPSendBuffer.ReadSegment(var ASequence:LongWord; var AUrgent:Word; var AFlags:Byte; var AData:Pointer; var ASize:Word; AForce:Boolean):Boolean;

Description: Used by Socket to Read segments to be (re)sent from queue

Note

Nagle Algorithm and Retry Timeouts are handled here

Socket Timing

For each sent segment a notification is scheduled for the socket thread to check the socket in TCP_RETRY_TIMEOUT[Segment.Count] milliseconds. This is to ensure that the segment is retried if not acknowledged by that time. For each sent segment that has a following segment a notification is sent to the socket thread to check the socket immediately. This ensures that all acceptable segments are sent immediately. For each retried segment a notification is also scheduled for the socket thread to check the socket in TCP_RETRY_TIMEOUT[Segment.Count] milliseconds which will be the next retry time if still not acknowledged. If the remote Window is not large enough to send the next segment then a notification is scheduled for the socket thread to check the socket in TCP_WINDOW_TIMEOUT milliseconds to ensure that a window probe is sent at the appropriate time.

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function TTCPSendBuffer.AcknowledgeSegments(ASequence,AAcknowledge:LongWord; AWindow:Word):Boolean;

Description: Used by Socket to Acknowledge segments that have been sent and update the Window

Note	Sequence, Acknowledge and Window are from the received Segment
Socket Timing	For each acknowledged segment a notification is sent to the socket thread to check the socket immediately. This is to ensure that segments waiting to be sent due to the Nagle algorithm are sent on receipt of an acknowledge.

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

Description: Used by Socket to Timestamp (RTT) segments that have been sent

Offset	Offset points to the point to extract the timestamp option

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function TTCPSendBuffer.SelectiveAckSegments(AOptions:Pointer; var AOffset:Word; ASize:Byte):Boolean;

Description: Used by Socket to Selective Ack segments that have been sent

Offset	Offset points to the point to start extracting SACKS
Size	Size includes the Option and Size

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