caddyhttp: Move HTTP redirect listener to an optional module

caddytest/integration/caddyfile_adapt/global_server_options_single.txt

@@ -1,6 +1,7 @@
 {
 	servers {
 		listener_wrappers {
+			http_redirect
 			tls
 		}
 		timeouts {
@@ -32,6 +33,9 @@ foo.com {
 						":443"
 					],
 					"listener_wrappers": [
+						{
+							"wrapper": "http_redirect"
+						},
 						{
 							"wrapper": "tls"
 						}

modules/caddyhttp/app.go

@@ -343,11 +343,6 @@ func (app *App) Start() error {
 				// enable TLS if there is a policy and if this is not the HTTP port
 				useTLS := len(srv.TLSConnPolicies) > 0 && int(listenAddr.StartPort+portOffset) != app.httpPort()
 				if useTLS {
-					// create HTTP redirect wrapper, which detects if
-					// the request had HTTP bytes on the HTTPS port, and
-					// triggers a redirect if so.
-					ln = &httpRedirectListener{Listener: ln}
-
 					// create TLS listener
 					tlsCfg := srv.TLSConnPolicies.TLSConfig(app.ctx)
 					ln = tls.NewListener(ln, tlsCfg)

modules/caddyhttp/httpredirectlistener.go

@@ -20,8 +20,45 @@ import (
 	"net"
 	"net/http"
 	"sync"
+
+	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
 )
 
+func init() {
+	caddy.RegisterModule(HTTPRedirectListenerWrapper{})
+}
+
+// HTTPRedirectListenerWrapper provides HTTP->HTTPS redirects for
+// connections that come on the TLS port as an HTTP request,
+// by detecting using the first few bytes that it's not a TLS
+// handshake, but instead an HTTP request.
+//
+// This is especially useful when using a non-standard HTTPS port.
+// A user may simply type the address in their browser without the
+// https:// scheme, which would cause the browser to attempt the
+// connection over HTTP, but this would cause a "Client sent an
+// HTTP request to an HTTPS server" error response.
+//
+// This listener wrapper must be placed BEFORE the "tls" listener
+// wrapper, for it to work properly.
+type HTTPRedirectListenerWrapper struct{}
+
+func (HTTPRedirectListenerWrapper) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		ID:  "caddy.listeners.http_redirect",
+		New: func() caddy.Module { return new(HTTPRedirectListenerWrapper) },
+	}
+}
+
+func (h *HTTPRedirectListenerWrapper) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
+	return nil
+}
+
+func (h *HTTPRedirectListenerWrapper) WrapListener(l net.Listener) net.Listener {
+	return &httpRedirectListener{l}
+}
+
 // httpRedirectListener is listener that checks the first few bytes
 // of the request when the server is intended to accept HTTPS requests,
 // to respond to an HTTP request with a redirect.
@@ -112,3 +149,8 @@ func firstBytesLookLikeHTTP(hdr []byte) bool {
 	}
 	return false
 }
+
+var (
+	_ caddy.ListenerWrapper = (*HTTPRedirectListenerWrapper)(nil)
+	_ caddyfile.Unmarshaler = (*HTTPRedirectListenerWrapper)(nil)
+)