connect reverse_proxy transport to global node config

allow specifying a node name when configuring the tailscale transport,
which is used to lookup config values from the global tailscale app.

Also rename to just "Transport" and do some cleanup and simplification.

Signed-off-by: Will Norris <will@tailscale.com>

Author: willnorris

module.go

@@ -21,7 +21,6 @@ import (
 func init() {
 	caddy.RegisterNetwork("tailscale", getPlainListener)
 	caddy.RegisterNetwork("tailscale+tls", getTLSListener)
-	caddy.RegisterModule(&TailscaleCaddyTransport{})
 }
 
 func getPlainListener(c context.Context, _ string, addr string, _ net.ListenConfig) (any, error) {
@@ -211,8 +210,8 @@ func (t *tsnetServerListener) Close() error {
 		return err
 	}
 
-	// Decrement usage count of server for this hostname.
-	// If usage reaches zero, then the server is actually shutdown.
+	// Decrement usage count of this node.
+	// If usage reaches zero, then the node is actually shutdown.
 	_, err := nodes.Delete(t.name)
 	return err
 }

transport.go

@@ -1,66 +1,77 @@
 package tscaddy
 
-// transport.go contains the TailscaleCaddyTransport module.
+// transport.go contains the Transport module.
 
 import (
-	"fmt"
 	"net/http"
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
-	"go.uber.org/zap"
 )
 
-// TailscaleCaddyTransport is a caddy transport that uses a tailscale node to make requests.
-type TailscaleCaddyTransport struct {
-	logger *zap.Logger
-	node   *tailscaleNode
+func init() {
+	caddy.RegisterModule(&Transport{})
 }
 
-func (t *TailscaleCaddyTransport) CaddyModule() caddy.ModuleInfo {
-	return caddy.ModuleInfo{
-		ID: "http.reverse_proxy.transport.tailscale",
-		New: func() caddy.Module {
-			return new(TailscaleCaddyTransport)
-		},
-	}
-}
+// Transport is a caddy transport that uses a tailscale node to make requests.
+type Transport struct {
+	Name string `json:"name,omitempty"`
 
-func (t *TailscaleCaddyTransport) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
-	return nil
+	node *tailscaleNode
 }
 
-func (t *TailscaleCaddyTransport) Provision(ctx caddy.Context) error {
-	t.logger = ctx.Logger()
-
-	// TODO(will): allow users to specify a node name used to lookup that node's config in TSApp.
-	s, err := getNode(ctx, "caddy-tsnet-client")
-	if err != nil {
-		return err
+func (t *Transport) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		ID:  "http.reverse_proxy.transport.tailscale",
+		New: func() caddy.Module { return new(Transport) },
 	}
+}
 
-	s.Ephemeral = true
-	s.Logf = func(format string, args ...any) {
-		t.logger.Debug(fmt.Sprintf(format, args))
-	}
+// UnmarshalCaddyfile populates a Transport config from a caddyfile.
+//
+// We only support a single token identifying the name of a node in the TSApp config.
+// For example:
+//
+//	reverse_proxy {
+//	  transport tailscale my-node
+//	}
+//
+// If a node name is not specified, a default name is used.
+func (t *Transport) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
+	const defaultNodeName = "caddy-proxy"
 
-	if err := s.Start(); err != nil {
-		return err
+	d.Next() // skip transport name
+	if d.NextArg() {
+		t.Name = d.Val()
+	} else {
+		t.Name = defaultNodeName
 	}
-	t.node = s
 
 	return nil
 }
 
-func (t *TailscaleCaddyTransport) RoundTrip(request *http.Request) (*http.Response, error) {
-	if request.URL.Scheme == "" {
-		request.URL.Scheme = "http"
+func (t *Transport) Provision(ctx caddy.Context) error {
+	var err error
+	t.node, err = getNode(ctx, t.Name)
+	return err
+}
+
+func (t *Transport) Cleanup() error {
+	// Decrement usage count of this node.
+	_, err := nodes.Delete(t.Name)
+	return err
+}
+
+func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
+	if req.URL.Scheme == "" {
+		req.URL.Scheme = "http"
 	}
-	return t.node.HTTPClient().Transport.RoundTrip(request)
+	return t.node.HTTPClient().Transport.RoundTrip(req)
 }
 
 var (
-	_ http.RoundTripper     = (*TailscaleCaddyTransport)(nil)
-	_ caddy.Provisioner     = (*TailscaleCaddyTransport)(nil)
-	_ caddyfile.Unmarshaler = (*TailscaleCaddyTransport)(nil)
+	_ http.RoundTripper     = (*Transport)(nil)
+	_ caddy.Provisioner     = (*Transport)(nil)
+	_ caddy.CleanerUpper    = (*Transport)(nil)
+	_ caddyfile.Unmarshaler = (*Transport)(nil)
 )