lneto/internet/definitions.go

package internet

import (
	"log/slog"
	"math"
	"net"
	"slices"

	"github.com/soypat/lneto"
)

// node is a concrete StackNode as stored in Stacks. Methods are devirtualized for performance benefits, especially on TinyGo.
type node struct {
	// currConnID stores the stack node *connID value on registration.
	currConnID uint64
	// connID is StackNode.ConnectionID() return value.
	connID *uint64
	// cbnode has different definitions in tinygo and normal Go compiled programs
	// for performance and heap control reasons.
	callbacks cbnode
	// remoteAddr will be set on active(outbound) port connections
	// that require an ARP to set the remoteAddr beforehand.
	remoteAddr []byte
	proto      uint16 // StackNode.Protocol()
	lport      uint16 // StackNode.LocalPort()
}

type handlers struct {
	nodes []node
	// encapsIdx stores the index of next node to check for encapsulation.
	encapsIdx int

	context string
	logger
}

func (h *handlers) reset(context string, maxNodes int) {
	h.nodes = slices.Grow(h.nodes[:0], maxNodes)
	h.context = context
}

func (h *handlers) registerByProto(n node) error {
	err := h.prepAdd()
	if err != nil {
		return err
	}
	if h.nodeByProto(n.proto) != nil {
		return lneto.ErrAlreadyRegistered
	}
	h.nodes = append(h.nodes, n)
	return nil
}

func (h *handlers) registerByPortProto(n node) error {
	err := h.prepAdd()
	if err != nil {
		return err
	}
	if h.nodeByPortProto(n.lport, n.proto) != nil {
		return lneto.ErrAlreadyRegistered
	}
	h.nodes = append(h.nodes, n)
	return nil
}

func (h *handlers) prepAdd() error {
	if h.full() {
		h.compact()
		if h.full() {
			return lneto.ErrExhausted
		}
	}
	return nil
}

func (h *handlers) full() bool { return cap(h.nodes) == len(h.nodes) }

func (h *handlers) compact() {
	nilOff := 0
	for i := 0; i < len(h.nodes); i++ {
		if !h.nodes[i].IsInvalid() {
			h.nodes[nilOff] = h.nodes[i]
			nilOff++
		}
	}
	h.nodes = h.nodes[:nilOff]
}

func (h *handlers) tryHandleError(node *node, err error) (discardedGracefully bool) {
	if err != nil && (err == net.ErrClosed || node.IsInvalid()) {
		node.destroy()
		discardedGracefully = true
	}
	return discardedGracefully
}

func (h *handlers) nodeByProto(proto uint16) *node {
	for i := range h.nodes {
		node := &h.nodes[i]
		if node.proto == proto && !node.IsInvalid() {
			return node
		}
	}
	return nil
}

func (h *handlers) nodeByPort(port uint16) *node {
	for i := range h.nodes {
		node := &h.nodes[i]
		if node.lport == port && !node.IsInvalid() {
			return node
		}
	}
	return nil
}

func (h *handlers) nodeByPortProto(port uint16, protocol uint16) *node {
	for i := range h.nodes {
		node := &h.nodes[i]
		if node.lport == port && node.proto == protocol && !node.IsInvalid() {
			return node
		}
	}
	return nil
}

func (h *handlers) demuxByProto(buf []byte, offset int, proto uint16) (*node, error) {
	node := h.nodeByProto(proto)
	if node == nil {
		return nil, lneto.ErrPacketDrop
	}
	err := node.callbacks.Demux(buf, offset)
	if h.tryHandleError(node, err) {
		err = nil
	}

	return node, err
}

func (h *handlers) demuxByPort(buf []byte, offset int, port uint16) (*node, error) {
	node := h.nodeByPort(port)
	if node == nil {
		return nil, lneto.ErrPacketDrop
	}
	err := node.callbacks.Demux(buf, offset)
	if h.tryHandleError(node, err) {
		err = nil
		node = nil // Node is destroyed in tryHandleError and invalidated.
	}
	return node, err
}

func (h *handlers) encapsulateNode(node *node, buf []byte, offsetIP, offsetThisFrame int) (n int, err error) {
	if node.IsInvalid() {
		return 0, nil
	}
	n, err = node.callbacks.Encapsulate(buf, offsetIP, offsetThisFrame)
	if h.tryHandleError(node, err) {
		err = nil  // CLOSE error handled gracefully by deleting node.
		node = nil // Node is destroyed in tryHandleError and invalidated.
	}
	// TODO(soypat): We have fuzz tests in place, maybe we can start returning the error up the chain to catch invalid settings at application level so that users don't have to have logs in place to understand invalid config/buffer size.
	// Encapsulate should only fail with error on programmer errors.
	if n > 0 {
		return n, err
	} else if err != nil {
		// Make sure not to hang on one handler that keeps returning an error.
		h.error("handlers:encapsulate", slog.String("func", "encapsulateAny"), slog.String("ctx", h.context), slog.String("err", err.Error()))
	}
	return 0, nil
}

// encapsulateAny finds a node suitable to write and encapsulates the package.
// If no data is sent it returns the last error encountered.
func (h *handlers) encapsulateAny(buf []byte, offsetIP, offsetThisFrame int) (hn *node, n int, err error) {
	// Round robin approach to encapsulation.
	// TODO(soypat): benchmark impact of round robin. Consider removing fields from handlers to make it more lean and potentially get perf improvements that way.
	i := h.encapsIdx
	for range h.nodes {
		hn := &h.nodes[i]
		n, err = h.encapsulateNode(hn, buf, offsetIP, offsetThisFrame)
		i = incLim(i, len(h.nodes))
		if n > 0 || err != nil {
			h.encapsIdx = i
			return hn, n, err
		}
	}
	return nil, 0, err // Return last written error.
}

var (
	_ = net.ErrClosed
)

func (node *node) IsInvalid() bool {
	return node.callbacks.IsZeroed() || (node.connID != nil && node.currConnID != *node.connID)
}

func checkNodeErr(node *node, err error) (discard bool) {
	return node.IsInvalid() || (err != nil && err == net.ErrClosed)
}

func nodeFromStackNode(s lneto.StackNode, port uint16, protocol uint64, remoteAddr []byte) node {
	if protocol > math.MaxUint16 {
		panic(">16bit protocol number unsupported")
	}
	var currConnID uint64
	connIDPtr := s.ConnectionID()
	if connIDPtr != nil {
		currConnID = *connIDPtr
	}
	return node{
		currConnID: currConnID,
		connID:     connIDPtr,
		callbacks:  makecbnode(s),
		proto:      uint16(protocol),
		lport:      port,
		remoteAddr: remoteAddr, // SHARED MEMORY- used to signal.
	}
}

// destroy removes all references to underlying StackNode. Allows garbage collection of node if possible.
func (n *node) destroy() {
	*n = node{}
}

func incLim(v, max int) int {
	v++
	if v == max {
		v = 0
	}
	return v
}