caddyhttp: Enable HTTP/3 by default

caddyconfig/httpcaddyfile/serveroptions.go

@@ -39,8 +39,7 @@ type serverOptions struct {
 	WriteTimeout         caddy.Duration
 	IdleTimeout          caddy.Duration
 	MaxHeaderBytes       int
-	AllowH2C             bool
-	ExperimentalHTTP3    bool
+	Protocols            []string
 	StrictSNIHost        *bool
 	ShouldLogCredentials bool
 }
@@ -141,22 +140,51 @@ func unmarshalCaddyfileServerOptions(d *caddyfile.Dispenser) (any, error) {
 				}
 				serverOpts.ShouldLogCredentials = true
 
+			case "protocols":
+				protos := d.RemainingArgs()
+				for _, proto := range protos {
+					if proto != "h1" && proto != "h2" && proto != "h2c" && proto != "h3" {
+						return nil, d.Errf("unknown protocol '%s': expected h1, h2, h2c, or h3", proto)
+					}
+					if sliceContains(serverOpts.Protocols, proto) {
+						return nil, d.Errf("protocol %s specified more than once", proto)
+					}
+					serverOpts.Protocols = append(serverOpts.Protocols, proto)
+				}
+				if d.NextBlock(0) {
+					return nil, d.ArgErr()
+				}
+
+			case "strict_sni_host":
+				if d.NextArg() && d.Val() != "insecure_off" && d.Val() != "on" {
+					return nil, d.Errf("strict_sni_host only supports 'on' or 'insecure_off', got '%s'", d.Val())
+				}
+				boolVal := true
+				if d.Val() == "insecure_off" {
+					boolVal = false
+				}
+				serverOpts.StrictSNIHost = &boolVal
+
+			// TODO: DEPRECATED. (August 2022)
 			case "protocol":
+				caddy.Log().Named("caddyfile").Warn("DEPRECATED: protocol sub-option will be removed soon")
+
 				for nesting := d.Nesting(); d.NextBlock(nesting); {
 					switch d.Val() {
 					case "allow_h2c":
-						if d.NextArg() {
-							return nil, d.ArgErr()
-						}
-						serverOpts.AllowH2C = true
+						caddy.Log().Named("caddyfile").Warn("DEPRECATED: allow_h2c will be removed soon; use protocols option instead")
 
-					case "experimental_http3":
 						if d.NextArg() {
 							return nil, d.ArgErr()
 						}
-						serverOpts.ExperimentalHTTP3 = true
+						if sliceContains(serverOpts.Protocols, "h2c") {
+							return nil, d.Errf("protocol h2c already specified")
+						}
+						serverOpts.Protocols = append(serverOpts.Protocols, "h2c")
 
 					case "strict_sni_host":
+						caddy.Log().Named("caddyfile").Warn("DEPRECATED: protocol > strict_sni_host in this position will be removed soon; move up to the servers block instead")
+
 						if d.NextArg() && d.Val() != "insecure_off" && d.Val() != "on" {
 							return nil, d.Errf("strict_sni_host only supports 'on' or 'insecure_off', got '%s'", d.Val())
 						}
@@ -185,17 +213,6 @@ func applyServerOptions(
 	options map[string]any,
 	warnings *[]caddyconfig.Warning,
 ) error {
-	// If experimental HTTP/3 is enabled, enable it on each server.
-	// We already know there won't be a conflict with serverOptions because
-	// we validated earlier that "experimental_http3" cannot be set at the same
-	// time as "servers"
-	if enableH3, ok := options["experimental_http3"].(bool); ok && enableH3 {
-		*warnings = append(*warnings, caddyconfig.Warning{Message: "the 'experimental_http3' global option is deprecated, please use the 'servers > protocol > experimental_http3' option instead"})
-		for _, srv := range servers {
-			srv.ExperimentalHTTP3 = true
-		}
-	}
-
 	serverOpts, ok := options["servers"].([]serverOptions)
 	if !ok {
 		return nil
@@ -229,8 +246,7 @@ func applyServerOptions(
 		server.WriteTimeout = opts.WriteTimeout
 		server.IdleTimeout = opts.IdleTimeout
 		server.MaxHeaderBytes = opts.MaxHeaderBytes
-		server.AllowH2C = opts.AllowH2C
-		server.ExperimentalHTTP3 = opts.ExperimentalHTTP3
+		server.Protocols = opts.Protocols
 		server.StrictSNIHost = opts.StrictSNIHost
 		if opts.ShouldLogCredentials {
 			if server.Logs == nil {

caddytest/integration/caddyfile_adapt/global_server_options_single.txt

@@ -12,11 +12,8 @@
 		}
 		max_header_size 100MB
 		log_credentials
-		protocol {
-			allow_h2c
-			experimental_http3
-			strict_sni_host
-		}
+		strict_sni_host
+		protocols h1 h2 h2c h3
 	}
 }
 
@@ -61,8 +58,12 @@ foo.com {
 					"logs": {
 						"should_log_credentials": true
 					},
-					"experimental_http3": true,
-					"allow_h2c": true
+					"protocols": [
+						"h1",
+						"h2",
+						"h2c",
+						"h3"
+					]
 				}
 			}
 		}

listeners.go

@@ -88,11 +88,26 @@ func ListenPacket(network, addr string) (net.PacketConn, error) {
 // ListenQUIC returns a quic.EarlyListener suitable for use in a Caddy module.
 // Note that the context passed to Accept is currently ignored, so using
 // a context other than context.Background is meaningless.
-func ListenQUIC(addr string, tlsConf *tls.Config) (quic.EarlyListener, error) {
+func ListenQUIC(addr string, tlsConf *tls.Config, activeRequests *int64) (quic.EarlyListener, error) {
 	lnKey := listenerKey("udp", addr)
 
 	sharedEl, _, err := listenerPool.LoadOrNew(lnKey, func() (Destructor, error) {
-		el, err := quic.ListenAddrEarly(addr, http3.ConfigureTLSConfig(tlsConf), &quic.Config{})
+		el, err := quic.ListenAddrEarly(addr, http3.ConfigureTLSConfig(tlsConf), &quic.Config{
+			AcceptToken: func(clientAddr net.Addr, token *quic.Token) bool {
+				var highLoad bool
+				if activeRequests != nil {
+					highLoad = atomic.LoadInt64(activeRequests) > 1000 // TODO: make tunable?
+				}
+				if !highLoad {
+					return true
+				}
+				if token == nil {
+					return false
+				}
+				// TODO: validate the token (can we just use quic.defaultAcceptToken? - it also does the nil check btw...)
+				return true
+			},
+		})
 		if err != nil {
 			return nil, err
 		}

modules/caddyhttp/app.go

@@ -25,7 +25,6 @@ import (
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/modules/caddytls"
-	"github.com/lucas-clemente/quic-go/http3"
 	"go.uber.org/zap"
 	"golang.org/x/net/http2"
 	"golang.org/x/net/http2/h2c"
@@ -185,6 +184,17 @@ func (app *App) Provision(ctx caddy.Context) error {
 			srv.accessLogger = app.logger.Named("log.access")
 		}
 
+		// the Go standard library does not let us serve only HTTP/2 using
+		// http.Server; we would probably need to write our own server
+		if !srv.protocol("h1") && (srv.protocol("h2") || srv.protocol("h2c")) {
+			return fmt.Errorf("server %s: cannot enable HTTP/2 or H2C without enabling HTTP/1.1; add h1 to protocols or remove h2/h2c", srvName)
+		}
+
+		// if no protocols configured explicitly, enable all except h2c
+		if len(srv.Protocols) == 0 {
+			srv.Protocols = []string{"h1", "h2", "h3"}
+		}
+
 		// if not explicitly configured by the user, disallow TLS
 		// client auth bypass (domain fronting) which could
 		// otherwise be exploited by sending an unprotected SNI
@@ -196,8 +206,7 @@ func (app *App) Provision(ctx caddy.Context) error {
 		// based on hostname
 		if srv.StrictSNIHost == nil && srv.hasTLSClientAuth() {
 			app.logger.Warn("enabling strict SNI-Host enforcement because TLS client auth is configured",
-				zap.String("server_id", srvName),
-			)
+				zap.String("server_id", srvName))
 			trueBool := true
 			srv.StrictSNIHost = &trueBool
 		}
@@ -206,8 +215,7 @@ func (app *App) Provision(ctx caddy.Context) error {
 		for i := range srv.Listen {
 			lnOut, err := repl.ReplaceOrErr(srv.Listen[i], true, true)
 			if err != nil {
-				return fmt.Errorf("server %s, listener %d: %v",
-					srvName, i, err)
+				return fmt.Errorf("server %s, listener %d: %v", srvName, i, err)
 			}
 			srv.Listen[i] = lnOut
 		}
@@ -324,10 +332,34 @@ func (app *App) Start() error {
 			Handler:           srv,
 			ErrorLog:          serverLogger,
 		}
+
+		// disable HTTP/2, which we enabled by default during provisioning
+		if !srv.protocol("h2") {
+			srv.server.TLSNextProto = make(map[string]func(*http.Server, *tls.Conn, http.Handler))
+			for _, cp := range srv.TLSConnPolicies {
+				// the TLSConfig was already provisioned, so... manually remove it
+				for i, np := range cp.TLSConfig.NextProtos {
+					if np == "h2" {
+						cp.TLSConfig.NextProtos = append(cp.TLSConfig.NextProtos[:i], cp.TLSConfig.NextProtos[i+1:]...)
+						break
+					}
+				}
+				// remove it from the parent connection policy too, just to keep things tidy
+				for i, alpn := range cp.ALPN {
+					if alpn == "h2" {
+						cp.ALPN = append(cp.ALPN[:i], cp.ALPN[i+1:]...)
+						break
+					}
+				}
+			}
+		}
+
+		// this TLS config is used by the std lib to choose the actual TLS config for connections
+		// by looking through the connection policies to find the first one that matches
 		tlsCfg := srv.TLSConnPolicies.TLSConfig(app.ctx)
 
-		// enable h2c if configured
-		if srv.AllowH2C {
+		// enable H2C if configured
+		if srv.protocol("h2c") {
 			h2server := &http2.Server{
 				IdleTimeout: time.Duration(srv.IdleTimeout),
 			}
@@ -362,27 +394,15 @@ 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 TLS listener
+					// create TLS listener - this enables and terminates TLS
 					ln = tls.NewListener(ln, tlsCfg)
 
-					// TODO: HTTP/3 support is experimental for now
-					if srv.ExperimentalHTTP3 {
-						if srv.h3server == nil {
-							srv.h3server = &http3.Server{
-								Handler:        srv,
-								TLSConfig:      tlsCfg,
-								MaxHeaderBytes: srv.MaxHeaderBytes,
-							}
+					// enable HTTP/3 if configured
+					if srv.protocol("h3") {
+						app.logger.Info("enabling HTTP/3 listener", zap.String("addr", hostport))
+						if err := srv.serveHTTP3(hostport, tlsCfg); err != nil {
+							return err
 						}
-
-						app.logger.Info("enabling experimental HTTP/3 listener", zap.String("addr", hostport))
-						h3ln, err := caddy.ListenQUIC(hostport, tlsCfg)
-						if err != nil {
-							return fmt.Errorf("getting HTTP/3 QUIC listener: %v", err)
-						}
-
-						//nolint:errcheck
-						go srv.h3server.ServeListener(h3ln)
 					}
 				}
 
@@ -402,16 +422,22 @@ func (app *App) Start() error {
 
 				app.logger.Debug("starting server loop",
 					zap.String("address", ln.Addr().String()),
-					zap.Bool("http3", srv.ExperimentalHTTP3),
 					zap.Bool("tls", useTLS),
-				)
+					zap.Bool("http3", srv.h3server != nil))
 
 				srv.listeners = append(srv.listeners, ln)
 
-				//nolint:errcheck
-				go srv.server.Serve(ln)
+				// enable HTTP/1 if configured
+				if srv.protocol("h1") {
+					//nolint:errcheck
+					go srv.server.Serve(ln)
+				}
 			}
 		}
+
+		srv.logger.Info("server running",
+			zap.String("name", srvName),
+			zap.Strings("protocols", srv.Protocols))
 	}
 
 	// finish automatic HTTPS by finally beginning