1 files changed, 298 insertions, 0 deletions
diff --git a/pkg/ipstack/ipstack.go b/pkg/ipstack/ipstack.go
new file mode 100644
index 0000000..770fd17
--- /dev/null
+++ b/pkg/ipstack/ipstack.go
@@ -0,0 +1,298 @@
+package ipstack
+
+import (
+	"fmt"
+	ipv4header "github.com/brown-csci1680/iptcp-headers"
+	"github.com/google/netstack/tcpip/header"
+	"github.com/pkg/errors"
+	"../../pkg/lnxconfig"
+	"log"
+	"net"
+	"net/netip"
+	"os"
+)
+
+const (
+	MAX_IP_PACKET_SIZE = 1400
+)
+
+type Interface struct {
+	Name           string
+	AssignedIP     netip.Addr
+	AssignedPrefix netip.Prefix
+
+	UDPAddr netip.AddrPort
+	State bool
+	neighbors map[netip.AddrPort]netip.AddrPort
+}
+
+// type Host struct {
+// 	Interface Interface
+// 	Neighbors []Neighbor
+// }
+
+// type Router struct {
+// 	Interfaces []Interface
+// 	Neighbors []Neighbor
+// 	RIPNeighbors []Neighbor
+// }
+
+
+type Neighbor struct{
+	DestAddr netip.Addr
+	UDPAddr  netip.AddrPort
+
+	InterfaceName string
+}
+
+type RIPMessage struct {
+	command uint8_t;
+	numEntries uint8_t;
+	entries []RIPEntry;
+}
+
+type RIPEntry struct {
+	addr netip.Addr;
+	cost uint16_t;
+	mask netip.Prefix;
+}
+
+myInterfaces := make([]Interface);
+myNeighbors :=  make(map[string]Neighbor)
+myRIPNeighbors := make(map[string]Neighbor)
+protocolHandlers := make(map[uint16]HandlerFunc)
+// routingTable := make(map[Address]Routing)
+
+func Initialize(config IpConfig) (error) {
+	if len(os.Args) != 2 {
+		fmt.Printf("Usage:  %s <configFile>\n", os.Args[0])
+		os.Exit(1)
+	}
+	fileName := os.Args[1]
+
+	// Parse the file
+	lnxConfig, err := lnxconfig.ParseConfig(fileName)
+	if err != nil {
+		panic(err)
+	}
+
+	// populate routing table??? 
+	for _, iface := range lnxConfig.Interfaces {
+		myInterfaces = append(myInterfaces, Interface{iface.Name, iface.AssignedIP, iface.AssignedPrefix, iface.UDPAddr, 0})
+	}
+
+	for _, neighbor := range lnxConfig.Neighbors {
+		myNeighbors[neighbor.DestAddr.String()] = Neighbor{neighbor.DestAddr, neighbor.UDPAddr, neighbor.InterfaceName}
+	}
+
+	// add RIP neighbors
+	for _, neighbor := range lnxConfig.RipNeighbors {
+		myRIPNeighbors[neighbor.DestAddr.String()] = Neighbor{neighbor.DestAddr, neighbor.UDPAddr, neighbor.InterfaceName}
+	}
+}
+
+func ListerToInterfaces() {
+	for _, iface := range myInterfaces {
+		go RecvIp(iface)
+	}
+}
+
+func RecvIp(iface Interface) (error) {
+	for {
+		buffer := make([]byte, MAX_IP_PACKET_SIZE)
+		_, sourceAddr, err := iface.udp.ReadFrom(buffer)
+		if err != nil {
+			log.Panicln("Error reading from UDP socket ", err)
+		}
+
+		hdr, err := ipv4header.ParseHeader(buffer)
+
+		if err != nil {
+			fmt.Println("Error parsing header", err)
+			continue
+		}
+
+		headerSize := hdr.Len
+		headerBytes := buffer[:headerSize]
+
+		checksumFromHeader := uint16(hdr.Checksum)
+		computedChecksum := ValidateChecksum(headerBytes, checksumFromHeader)
+
+		var checksumState string
+		if computedChecksum == checksumFromHeader {
+			checksumState = "OK"
+		} else {
+			checksumState = "FAIL"
+			continue
+		}
+		
+		// check ttl
+		ttl := data[8]
+		if ttl == 0 {
+			fmt.Println("TTL is 0")
+			continue
+		}
+
+
+		destAddr := netip.AddrFrom(data[16:20])
+		protocolNum := data[9]
+
+		if destAddr == iface.addr {
+			// send to handler
+			protocolHandlers[protocolNum](data)
+			// message := buffer[headerSize:]
+
+			// fmt.Printf("Received IP packet from %s\nHeader:  %v\nChecksum:  %s\nMessage:  %s\n",
+			// sourceAddr.String(), hdr, checksumState, string(message))
+		} else {
+			// decrement ttl and update checksum
+			data[8] = ttl - 1
+			data[10] = 0
+			data[11] = 0
+			newChecksum := int(ComputeChecksum(data[:headerSize]))
+			data[10] = newChecksum >> 8
+			data[11] = newChecksum & 0xff
+
+			// check neighbors
+			for _, neighbor := range iface.neighbors {
+				if neighbor == destAddr {
+					// send to neighbor
+					// SendIp(destAddr, protocolNum, data)
+				}
+			}
+
+			// check forwarding table
+
+		}
+
+	}
+}
+
+func ValidateChecksum(b []byte, fromHeader uint16) uint16 {
+	checksum := header.Checksum(b, fromHeader)
+
+	return checksum
+}
+
+func SendIp(dst netip.Addr, port uint16, protocolNum uint16, data []byte, iface Interface) (error) {
+	bindLocalAddr, err := net.ResolveUDPAddr("udp4", iface.UDPAddr.String())
+	if err != nil {
+		log.Panicln("Error resolving address:  ", err)
+	}
+
+	addrString := fmt.Sprintf("%s:%s", dst, port)
+	remoteAddr, err := net.ResolveUDPAddr("udp4", addrString)
+	if err != nil {
+		log.Panicln("Error resolving address:  ", err)
+	}
+
+	fmt.Printf("Sending to %s:%d\n",
+		remoteAddr.IP.String(), remoteAddr.Port)
+
+	// Bind on the local UDP port:  this sets the source port
+	// and creates a conn
+	conn, err := net.ListenUDP("udp4", bindLocalAddr)
+	if err != nil {
+		log.Panicln("Dial: ", err)
+	}
+
+	// Start filling in the header
+	message := data[20:]
+	hdr := ipv4header.IPv4Header{
+		Version:  data[0] >> 4,
+		Len:      20, // Header length is always 20 when no IP options
+		TOS:      data[1],
+		TotalLen: ipv4header.HeaderLen + len(message),
+		ID:       data[4],
+		Flags:    data[6] >> 5,
+		FragOff:  data[6] & 0x1f,
+		TTL:      data[8],
+		Protocol: data[9],
+		Checksum: 0, // Should be 0 until checksum is computed
+		Src:      netip.MustParseAddr(iface.addr.String()),
+		Dst:      netip.MustParseAddr(dst.String()),
+		Options:  []byte{},
+	}
+
+	// Assemble the header into a byte array
+	headerBytes, err := hdr.Marshal()
+	if err != nil {
+		log.Fatalln("Error marshalling header:  ", err)
+	}
+
+	// Compute the checksum (see below)
+	// Cast back to an int, which is what the Header structure expects
+	hdr.Checksum = int(ComputeChecksum(headerBytes))
+
+	headerBytes, err = hdr.Marshal()
+	if err != nil {
+		log.Fatalln("Error marshalling header:  ", err)
+	}
+
+	bytesToSend := make([]byte, 0, len(headerBytes)+len(message))
+	bytesToSend = append(bytesToSend, headerBytes...)
+	bytesToSend = append(bytesToSend, []byte(message)...)
+
+	// Send the message to the "link-layer" addr:port on UDP
+	bytesWritten, err := conn.WriteToUDP(bytesToSend, remoteAddr)
+	if err != nil {
+		log.Panicln("Error writing to socket: ", err)
+	}
+	fmt.Printf("Sent %d bytes\n", bytesWritten)
+}
+
+func ComputeChecksum(b []byte) uint16 {
+	checksum := header.Checksum(b, 0)
+	checksumInv := checksum ^ 0xffff
+
+	return checksumInv
+}
+
+func ForwardIP(data []byte) (error) {
+}
+
+type HandlerFunc = func help(*Packet, []interface{}) (error) {
+
+	// do smth with packet
+}
+
+func AddRecvHandler(protocolNum uint8, callbackFunc HandlerFunc) (error) {
+	if protocolHandlers[protocolNum] != nil {
+		fmt.Printf("Warning: Handler for protocol %d already exists", protocolNum)
+	}
+	protocolHandlers[protocolNum] = callbackFunc
+	return nil
+}
+
+func RemoveRecvHandler(protocolNum uint8) (error) {
+	// consider error
+	if protocolHandlers[protocolNum] == nil {
+		return errors.Errorf("No handler for protocol %d", protocolNum)
+	}
+	delete(protocolHandlers, protocolNum)
+	return nil
+}
+
+// func routeRip(data []byte) (error) {
+// 	// deconstruct packet
+// 	newRIPMessage := RIPMessage{}
+// 	newRIPMessage.command = data[0]
+// 	newRIPMessage.numEntries = data[1]
+// 	newRIPMessage.entries = make([]RIPEntry, newRIPMessage.numEntries)
+// }
+
+func PrintNeighbors() {
+	for _, iface := range myNeighbors {
+		fmt.Printf("%s\n", iface.addr.String())
+	}
+}
+
+func PrintInterfaces() {
+	for _, iface := range myInterfaces {
+		fmt.Printf("%s\n", iface.addr.String())
+	}
+}
+func GetNeighbors() ([]netip.Addr) {
+	return myNeighbors
+}
+