Move common parts of the protocol to dedicated file

protocol_common.go

@@ -0,0 +1,66 @@
+package headscale
+
+import (
+	"encoding/json"
+	"net/http"
+	"strconv"
+
+	"github.com/rs/zerolog/log"
+	"tailscale.com/tailcfg"
+)
+
+// KeyHandler provides the Headscale pub key
+// Listens in /key.
+func (h *Headscale) KeyHandler(
+	writer http.ResponseWriter,
+	req *http.Request,
+) {
+	// New Tailscale clients send a 'v' parameter to indicate the CurrentCapabilityVersion
+	clientCapabilityStr := req.URL.Query().Get("v")
+	if clientCapabilityStr != "" {
+		clientCapabilityVersion, err := strconv.Atoi(clientCapabilityStr)
+		if err != nil {
+			writer.Header().Set("Content-Type", "text/plain; charset=utf-8")
+			writer.WriteHeader(http.StatusBadRequest)
+			_, err := writer.Write([]byte("Wrong params"))
+			if err != nil {
+				log.Error().
+					Caller().
+					Err(err).
+					Msg("Failed to write response")
+			}
+
+			return
+		}
+
+		if clientCapabilityVersion >= NoiseCapabilityVersion {
+			// Tailscale has a different key for the TS2021 protocol
+			resp := tailcfg.OverTLSPublicKeyResponse{
+				LegacyPublicKey: h.privateKey.Public(),
+				PublicKey:       h.noisePrivateKey.Public(),
+			}
+			writer.Header().Set("Content-Type", "application/json")
+			writer.WriteHeader(http.StatusOK)
+			err = json.NewEncoder(writer).Encode(resp)
+			if err != nil {
+				log.Error().
+					Caller().
+					Err(err).
+					Msg("Failed to write response")
+			}
+
+			return
+		}
+	}
+
+	// Old clients don't send a 'v' parameter, so we send the legacy public key
+	writer.Header().Set("Content-Type", "text/plain; charset=utf-8")
+	writer.WriteHeader(http.StatusOK)
+	_, err := writer.Write([]byte(MachinePublicKeyStripPrefix(h.privateKey.Public())))
+	if err != nil {
+		log.Error().
+			Caller().
+			Err(err).
+			Msg("Failed to write response")
+	}
+}