Move common parts of the protocol to dedicated file

protocol_common_utils.go

@@ -0,0 +1,47 @@
+package headscale
+
+import (
+	"encoding/binary"
+	"encoding/json"
+
+	"github.com/klauspost/compress/zstd"
+	"github.com/rs/zerolog/log"
+	"tailscale.com/tailcfg"
+	"tailscale.com/types/key"
+)
+
+func (h *Headscale) getMapKeepAliveResponse(
+	machineKey key.MachinePublic,
+	mapRequest tailcfg.MapRequest,
+) ([]byte, error) {
+	mapResponse := tailcfg.MapResponse{
+		KeepAlive: true,
+	}
+	var respBody []byte
+	var err error
+	if mapRequest.Compress == ZstdCompression {
+		src, err := json.Marshal(mapResponse)
+		if err != nil {
+			log.Error().
+				Caller().
+				Str("func", "getMapKeepAliveResponse").
+				Err(err).
+				Msg("Failed to marshal keepalive response for the client")
+
+			return nil, err
+		}
+		encoder, _ := zstd.NewWriter(nil)
+		srcCompressed := encoder.EncodeAll(src, nil)
+		respBody = h.privateKey.SealTo(machineKey, srcCompressed)
+	} else {
+		respBody, err = encode(mapResponse, &machineKey, h.privateKey)
+		if err != nil {
+			return nil, err
+		}
+	}
+	data := make([]byte, reservedResponseHeaderSize)
+	binary.LittleEndian.PutUint32(data, uint32(len(respBody)))
+	data = append(data, respBody...)
+
+	return data, nil
+}