ipn/{ipnlocal,localapi}, control/controlclient: add SetDNS localapi

Updates #1235

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/local.go

@@ -2577,6 +2577,42 @@ func (b *LocalBackend) FileTargets() ([]*apitype.FileTarget, error) {
 	return ret, nil
 }
 
+// SetDNS adds a DNS record for the given domain name & TXT record
+// value.
+//
+// It's meant for use with dns-01 ACME (LetsEncrypt) challenges.
+//
+// This is the low-level interface. Other layers will provide more
+// friendly options to get HTTPS certs.
+func (b *LocalBackend) SetDNS(ctx context.Context, name, value string) error {
+	req := &tailcfg.SetDNSRequest{
+		Version: 1,
+		Type:    "TXT",
+		Name:    name,
+		Value:   value,
+	}
+
+	b.mu.Lock()
+	cc := b.cc
+	if prefs := b.prefs; prefs != nil {
+		req.NodeKey = tailcfg.NodeKey(prefs.Persist.PrivateNodeKey.Public())
+	}
+	b.mu.Unlock()
+	if cc == nil {
+		return errors.New("not connected")
+	}
+	if req.NodeKey.IsZero() {
+		return errors.New("no nodekey")
+	}
+	if name == "" {
+		return errors.New("missing 'name'")
+	}
+	if value == "" {
+		return errors.New("missing 'value'")
+	}
+	return cc.SetDNS(ctx, req)
+}
+
 func (b *LocalBackend) registerIncomingFile(inf *incomingFile, active bool) {
 	b.mu.Lock()
 	defer b.mu.Unlock()

ipn/ipnlocal/state_test.go

@@ -248,6 +248,10 @@ func (cc *mockControl) UpdateEndpoints(localPort uint16, endpoints []tailcfg.End
 	cc.called("UpdateEndpoints")
 }
 
+func (*mockControl) SetDNS(context.Context, *tailcfg.SetDNSRequest) error {
+	panic("unexpected SetDNS call")
+}
+
 // A very precise test of the sequence of function calls generated by
 // ipnlocal.Local into its controlclient instance, and the events it
 // produces upstream into the UI.

ipn/localapi/localapi.go

@@ -100,6 +100,8 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		h.serveBugReport(w, r)
 	case "/localapi/v0/file-targets":
 		h.serveFileTargets(w, r)
+	case "/localapi/v0/set-dns":
+		h.serveSetDNS(w, r)
 	case "/":
 		io.WriteString(w, "tailscaled\n")
 	default:
@@ -382,6 +384,25 @@ func (h *Handler) serveFilePut(w http.ResponseWriter, r *http.Request) {
 	rp.ServeHTTP(w, outReq)
 }
 
+func (h *Handler) serveSetDNS(w http.ResponseWriter, r *http.Request) {
+	if !h.PermitWrite {
+		http.Error(w, "access denied", http.StatusForbidden)
+		return
+	}
+	if r.Method != "POST" {
+		http.Error(w, "want POST", 400)
+		return
+	}
+	ctx := r.Context()
+	err := h.b.SetDNS(ctx, r.FormValue("name"), r.FormValue("value"))
+	if err != nil {
+		writeErrorJSON(w, err)
+		return
+	}
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(struct{}{})
+}
+
 var dialPeerTransportOnce struct {
 	sync.Once
 	v *http.Transport