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soypat
78 lines
3.4 KiB
Go
78 lines
3.4 KiB
Go
package tcp
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import "log/slog"
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// ControlBlock is a partial Transmission Control Block (TCB) implementation as
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// per RFC 9293 in section 3.3.1. In contrast with the description in RFC9293,
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// this implementation is limited to receiving only sequential segments.
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// This means buffer management is left up entirely to the user of the ControlBlock.
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// Use ControlBlock as the building block that solves Sequence Number calculation
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// and validation in a full TCP implementation.
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//
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// A ControlBlock's internal state is modified by the available "System Calls" as defined in
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// RFC9293, such as Close, Listen/Open, Send, and Receive.
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// Sent and received data is represented with the [Segment] struct type.
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type ControlBlock struct {
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// # Send Sequence Space
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//
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// 'Send' sequence numbers correspond to local data being sent.
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//
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// 1 2 3 4
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// ----------|----------|----------|----------
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// SND.UNA SND.NXT SND.UNA
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// +SND.WND
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// 1. old sequence numbers which have been acknowledged
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// 2. sequence numbers of unacknowledged data
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// 3. sequence numbers allowed for new data transmission
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// 4. future sequence numbers which are not yet allowed
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snd sendSpace
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// # Receive Sequence Space
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//
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// 'Receive' sequence numbers correspond to remote data being received.
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//
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// 1 2 3
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// ----------|----------|----------
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// RCV.NXT RCV.NXT
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// +RCV.WND
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// 1 - old sequence numbers which have been acknowledged
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// 2 - sequence numbers allowed for new reception
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// 3 - future sequence numbers which are not yet allowed
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rcv recvSpace
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// When FlagRST is set in pending flags rstPtr will contain the sequence number of the RST segment to make it "believable" (See RFC9293)
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rstPtr Value
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// pending is the queue of pending flags to be sent in the next 2 segments.
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// On a call to Send the queue is advanced and flags set in the segment are unset.
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// The second position of the queue is used for FIN segments.
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pending [2]Flags
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state State
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challengeAck bool
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log *slog.Logger
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}
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// sendSpace contains Send Sequence Space data. Its sequence numbers correspond to local data.
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type sendSpace struct {
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ISS Value // initial send sequence number, defined locally on connection start
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UNA Value // send unacknowledged. Seqs equal to UNA and above have NOT been acked by remote. Corresponds to local data.
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NXT Value // send next. This seq and up to UNA+WND-1 are allowed to be sent. Corresponds to local data.
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WND Size // send window defined by remote. Permitted number of local unacked octets in flight.
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// WL1 Value // segment sequence number used for last window update
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// WL2 Value // segment acknowledgment number used for last window update
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}
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// inFlight returns amount of unacked bytes sent out.
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func (snd *sendSpace) inFlight() Size {
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return Sizeof(snd.UNA, snd.NXT)
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}
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// maxSend returns maximum segment datalength receivable by remote peer.
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func (snd *sendSpace) maxSend() Size {
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return snd.WND - snd.inFlight()
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}
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// recvSpace contains Receive Sequence Space data. Its sequence numbers correspond to remote data.
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type recvSpace struct {
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IRS Value // initial receive sequence number, defined by remote in SYN segment received.
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NXT Value // receive next. seqs before this have been acked. this seq and up to NXT+WND-1 are allowed to be sent. Corresponds to remote data.
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WND Size // receive window defined by local. Permitted number of remote unacked octets in flight.
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}
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