initial v1.0-beta commit

fsd/packet.go

@@ -0,0 +1,219 @@
+package fsd
+
+import "bytes"
+
+type PacketType int
+
+const (
+	PacketTypeUnknown PacketType = iota
+	PacketTypeTextMessage
+	PacketTypePilotPosition
+	PacketTypePilotPositionFast
+	PacketTypePilotPositionSlow
+	PacketTypePilotPositionStopped
+	PacketTypeATCPosition
+	PacketTypeDeleteATC
+	PacketTypeDeletePilot
+	PacketTypeClientQuery
+	PacketTypeClientQueryResponse
+	PacketTypeProController
+	PacketTypeSquawkbox
+	PacketTypeMetarRequest
+	PacketTypeKillRequest
+	PacketTypeAuthChallenge
+	PacketTypeHandoffRequest
+	PacketTypeHandoffAccept
+	PacketTypeFlightPlan
+	PacketTypeFlightPlanAmendment
+)
+
+// sourceCallsignFieldIndex returns the index of the field containing the source callsign
+func sourceCallsignFieldIndex(packetType PacketType) (index int) {
+	switch packetType {
+	case PacketTypePilotPosition:
+		return 1
+	default:
+		return 0
+	}
+}
+
+// getPacketType parses the packet type given a packet
+func getPacketType(packet []byte) PacketType {
+	switch packet[0] {
+	case '^':
+		return PacketTypePilotPositionFast
+	case '@':
+		return PacketTypePilotPosition
+	case '%':
+		return PacketTypeATCPosition
+	case '#':
+		switch string(packet[:3]) {
+		case "#DA":
+			return PacketTypeDeleteATC
+		case "#DP":
+			return PacketTypeDeletePilot
+		case "#TM":
+			return PacketTypeTextMessage
+		case "#SL":
+			return PacketTypePilotPositionSlow
+		case "#ST":
+			return PacketTypePilotPositionStopped
+		case "#PC":
+			return PacketTypeProController
+		case "#SB":
+			return PacketTypeSquawkbox
+		default:
+			return PacketTypeUnknown
+		}
+	case '$':
+		switch string(packet[:3]) {
+		case "$CQ":
+			return PacketTypeClientQuery
+		case "$CR":
+			return PacketTypeClientQueryResponse
+		case "$AX":
+			return PacketTypeMetarRequest
+		case "$!!":
+			return PacketTypeKillRequest
+		case "$ZC":
+			return PacketTypeAuthChallenge
+		case "$HO":
+			return PacketTypeHandoffRequest
+		case "$HA":
+			return PacketTypeHandoffAccept
+		case "$FP":
+			return PacketTypeFlightPlan
+		case "$AM":
+			return PacketTypeFlightPlanAmendment
+		default:
+			return PacketTypeUnknown
+		}
+	default:
+		return PacketTypeUnknown
+	}
+}
+
+func getPacketPrefix(packetType PacketType) string {
+	switch packetType {
+	case PacketTypePilotPositionFast:
+		return "^"
+	case PacketTypePilotPosition:
+		return "@"
+	case PacketTypeATCPosition:
+		return "%"
+	case PacketTypeDeleteATC:
+		return "#DA"
+	case PacketTypeDeletePilot:
+		return "#DP"
+	case PacketTypeTextMessage:
+		return "#TM"
+	case PacketTypePilotPositionSlow:
+		return "#SL"
+	case PacketTypePilotPositionStopped:
+		return "#ST"
+	case PacketTypeProController:
+		return "#PC"
+	case PacketTypeSquawkbox:
+		return "#SB"
+	case PacketTypeClientQuery:
+		return "$CQ"
+	case PacketTypeClientQueryResponse:
+		return "$CR"
+	case PacketTypeMetarRequest:
+		return "$AX"
+	case PacketTypeKillRequest:
+		return "$!!"
+	case PacketTypeAuthChallenge:
+		return "$ZC"
+	case PacketTypeHandoffRequest:
+		return "$HO"
+	case PacketTypeHandoffAccept:
+		return "$HA"
+	case PacketTypeFlightPlan:
+		return "$FP"
+	case PacketTypeFlightPlanAmendment:
+		return "$AM"
+	default:
+		return ""
+	}
+}
+
+func minFields(packetType PacketType) int {
+	switch packetType {
+	case PacketTypePilotPosition:
+		return 9
+	case PacketTypePilotPositionFast, PacketTypePilotPositionSlow, PacketTypePilotPositionStopped:
+		return 7
+	case PacketTypeATCPosition:
+		return 7
+	case PacketTypeDeleteATC, PacketTypeDeletePilot:
+		return 2
+	case PacketTypeTextMessage:
+		return 3
+	case PacketTypeProController:
+		return 4
+	case PacketTypeSquawkbox:
+		return 3
+	case PacketTypeClientQuery:
+		return 3
+	case PacketTypeClientQueryResponse:
+		return 3
+	case PacketTypeMetarRequest:
+		return 4
+	case PacketTypeKillRequest:
+		return 3
+	case PacketTypeAuthChallenge:
+		return 3
+	case PacketTypeHandoffRequest, PacketTypeHandoffAccept:
+		return 3
+	case PacketTypeFlightPlan:
+		return 17
+	case PacketTypeFlightPlanAmendment:
+		return 18
+	default:
+		return -1
+	}
+}
+
+type handlerFunc func(client *Client, packet []byte)
+
+func getSourceCallsign(packet []byte, packetType PacketType) []byte {
+	callsign, _ := bytes.CutPrefix(
+		getField(packet, sourceCallsignFieldIndex(packetType)),
+		[]byte(getPacketPrefix(packetType)),
+	)
+	return callsign
+}
+
+func verifySourceCallsign(packet []byte, packetType PacketType, callsign string) bool {
+	sourceCallsign := getSourceCallsign(packet, packetType)
+	return string(sourceCallsign) == callsign
+}
+
+// verifyPacket runs a set of sanity checks against a packet sent by a client and returns the detected packet type
+func verifyPacket(packet []byte, client *Client) (packetType PacketType, ok bool) {
+	numFields := countFields(packet)
+	if len(packet) < 8 || numFields < 3 {
+		client.sendError(SyntaxError, "Packet too short")
+		return
+	}
+
+	packetType = getPacketType(packet)
+	if packetType == PacketTypeUnknown {
+		client.sendError(SyntaxError, "Unknown packet type")
+		return
+	}
+
+	if !verifySourceCallsign(packet, packetType, client.callsign) {
+		client.sendError(SourceInvalidError, "Source invalid")
+		return
+	}
+
+	if numFields < minFields(packetType) {
+		client.sendError(SyntaxError, "Minimum field count requirement not satisfied")
+		return
+	}
+
+	ok = true
+	return
+}