caddy/modules/caddyhttp/app.go

// Copyright 2015 Matthew Holt and The Caddy Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package caddyhttp

import (
	"context"
	"crypto/tls"
	"fmt"
	"maps"
	"net"
	"net/http"
	"strconv"
	"sync"
	"time"

	"go.uber.org/zap"
	"golang.org/x/net/http2"
	"golang.org/x/net/http2/h2c"

	"github.com/caddyserver/caddy/v2"
	"github.com/caddyserver/caddy/v2/modules/caddyevents"
	"github.com/caddyserver/caddy/v2/modules/caddytls"
)

func init() {
	caddy.RegisterModule(App{})
}

// App is a robust, production-ready HTTP server.
//
// HTTPS is enabled by default if host matchers with qualifying names are used
// in any of routes; certificates are automatically provisioned and renewed.
// Additionally, automatic HTTPS will also enable HTTPS for servers that listen
// only on the HTTPS port but which do not have any TLS connection policies
// defined by adding a good, default TLS connection policy.
//
// In HTTP routes, additional placeholders are available (replace any `*`):
//
// Placeholder | Description
// ------------|---------------
// `{http.request.body}` | The request body (⚠️ inefficient; use only for debugging)
// `{http.request.cookie.*}` | HTTP request cookie
// `{http.request.duration}` | Time up to now spent handling the request (after decoding headers from client)
// `{http.request.duration_ms}` | Same as 'duration', but in milliseconds.
// `{http.request.uuid}` | The request unique identifier
// `{http.request.header.*}` | Specific request header field
// `{http.request.host}` | The host part of the request's Host header
// `{http.request.host.labels.*}` | Request host labels (0-based from right); e.g. for foo.example.com: 0=com, 1=example, 2=foo
// `{http.request.hostport}` | The host and port from the request's Host header
// `{http.request.method}` | The request method
// `{http.request.orig_method}` | The request's original method
// `{http.request.orig_uri}` | The request's original URI
// `{http.request.orig_uri.path}` | The request's original path
// `{http.request.orig_uri.path.*}` | Parts of the original path, split by `/` (0-based from left)
// `{http.request.orig_uri.path.dir}` | The request's original directory
// `{http.request.orig_uri.path.file}` | The request's original filename
// `{http.request.orig_uri.query}` | The request's original query string (without `?`)
// `{http.request.port}` | The port part of the request's Host header
// `{http.request.proto}` | The protocol of the request
// `{http.request.local.host}` | The host (IP) part of the local address the connection arrived on
// `{http.request.local.port}` | The port part of the local address the connection arrived on
// `{http.request.local}` | The local address the connection arrived on
// `{http.request.remote.host}` | The host (IP) part of the remote client's address
// `{http.request.remote.port}` | The port part of the remote client's address
// `{http.request.remote}` | The address of the remote client
// `{http.request.scheme}` | The request scheme, typically `http` or `https`
// `{http.request.tls.version}` | The TLS version name
// `{http.request.tls.cipher_suite}` | The TLS cipher suite
// `{http.request.tls.resumed}` | The TLS connection resumed a previous connection
// `{http.request.tls.proto}` | The negotiated next protocol
// `{http.request.tls.proto_mutual}` | The negotiated next protocol was advertised by the server
// `{http.request.tls.server_name}` | The server name requested by the client, if any
// `{http.request.tls.client.fingerprint}` | The SHA256 checksum of the client certificate
// `{http.request.tls.client.public_key}` | The public key of the client certificate.
// `{http.request.tls.client.public_key_sha256}` | The SHA256 checksum of the client's public key.
// `{http.request.tls.client.certificate_pem}` | The PEM-encoded value of the certificate.
// `{http.request.tls.client.certificate_der_base64}` | The base64-encoded value of the certificate.
// `{http.request.tls.client.issuer}` | The issuer DN of the client certificate
// `{http.request.tls.client.serial}` | The serial number of the client certificate
// `{http.request.tls.client.subject}` | The subject DN of the client certificate
// `{http.request.tls.client.san.dns_names.*}` | SAN DNS names(index optional)
// `{http.request.tls.client.san.emails.*}` | SAN email addresses (index optional)
// `{http.request.tls.client.san.ips.*}` | SAN IP addresses (index optional)
// `{http.request.tls.client.san.uris.*}` | SAN URIs (index optional)
// `{http.request.uri}` | The full request URI
// `{http.request.uri.path}` | The path component of the request URI
// `{http.request.uri.path.*}` | Parts of the path, split by `/` (0-based from left)
// `{http.request.uri.path.dir}` | The directory, excluding leaf filename
// `{http.request.uri.path.file}` | The filename of the path, excluding directory
// `{http.request.uri.query}` | The query string (without `?`)
// `{http.request.uri.query.*}` | Individual query string value
// `{http.response.header.*}` | Specific response header field
// `{http.vars.*}` | Custom variables in the HTTP handler chain
// `{http.shutting_down}` | True if the HTTP app is shutting down
// `{http.time_until_shutdown}` | Time until HTTP server shutdown, if scheduled
type App struct {
	// HTTPPort specifies the port to use for HTTP (as opposed to HTTPS),
	// which is used when setting up HTTP->HTTPS redirects or ACME HTTP
	// challenge solvers. Default: 80.
	HTTPPort int `json:"http_port,omitempty"`

	// HTTPSPort specifies the port to use for HTTPS, which is used when
	// solving the ACME TLS-ALPN challenges, or whenever HTTPS is needed
	// but no specific port number is given. Default: 443.
	HTTPSPort int `json:"https_port,omitempty"`

	// GracePeriod is how long to wait for active connections when shutting
	// down the servers. During the grace period, no new connections are
	// accepted, idle connections are closed, and active connections will
	// be given the full length of time to become idle and close.
	// Once the grace period is over, connections will be forcefully closed.
	// If zero, the grace period is eternal. Default: 0.
	GracePeriod caddy.Duration `json:"grace_period,omitempty"`

	// ShutdownDelay is how long to wait before initiating the grace
	// period. When this app is stopping (e.g. during a config reload or
	// process exit), all servers will be shut down. Normally this immediately
	// initiates the grace period. However, if this delay is configured, servers
	// will not be shut down until the delay is over. During this time, servers
	// continue to function normally and allow new connections. At the end, the
	// grace period will begin. This can be useful to allow downstream load
	// balancers time to move this instance out of the rotation without hiccups.
	//
	// When shutdown has been scheduled, placeholders {http.shutting_down} (bool)
	// and {http.time_until_shutdown} (duration) may be useful for health checks.
	ShutdownDelay caddy.Duration `json:"shutdown_delay,omitempty"`

	// Servers is the list of servers, keyed by arbitrary names chosen
	// at your discretion for your own convenience; the keys do not
	// affect functionality.
	Servers map[string]*Server `json:"servers,omitempty"`

	ctx    caddy.Context
	logger *zap.Logger
	tlsApp *caddytls.TLS

	// used temporarily between phases 1 and 2 of auto HTTPS
	allCertDomains []string
}

// CaddyModule returns the Caddy module information.
func (App) CaddyModule() caddy.ModuleInfo {
	return caddy.ModuleInfo{
		ID:  "http",
		New: func() caddy.Module { return new(App) },
	}
}

// Provision sets up the app.
func (app *App) Provision(ctx caddy.Context) error {
	// store some references
	tlsAppIface, err := ctx.App("tls")
	if err != nil {
		return fmt.Errorf("getting tls app: %v", err)
	}
	app.tlsApp = tlsAppIface.(*caddytls.TLS)
	app.ctx = ctx
	app.logger = ctx.Logger()

	eventsAppIface, err := ctx.App("events")
	if err != nil {
		return fmt.Errorf("getting events app: %v", err)
	}

	repl := caddy.NewReplacer()

	// this provisions the matchers for each route,
	// and prepares auto HTTP->HTTPS redirects, and
	// is required before we provision each server
	err = app.automaticHTTPSPhase1(ctx, repl)
	if err != nil {
		return err
	}

	// prepare each server
	oldContext := ctx.Context
	for srvName, srv := range app.Servers {
		ctx.Context = context.WithValue(oldContext, ServerCtxKey, srv)
		srv.name = srvName
		srv.tlsApp = app.tlsApp
		srv.events = eventsAppIface.(*caddyevents.App)
		srv.ctx = ctx
		srv.logger = app.logger.Named("log")
		srv.errorLogger = app.logger.Named("log.error")
		srv.shutdownAtMu = new(sync.RWMutex)

		// only enable access logs if configured
		if srv.Logs != nil {
			srv.accessLogger = app.logger.Named("log.access")
			if srv.Logs.Trace {
				srv.traceLogger = app.logger.Named("log.trace")
			}
		}

		// if no protocols configured explicitly, enable all except h2c
		if len(srv.Protocols) == 0 {
			srv.Protocols = []string{"h1", "h2", "h3"}
		}

		srvProtocolsUnique := map[string]struct{}{}
		for _, srvProtocol := range srv.Protocols {
			srvProtocolsUnique[srvProtocol] = struct{}{}
		}
		_, h1ok := srvProtocolsUnique["h1"]
		_, h2ok := srvProtocolsUnique["h2"]
		_, h2cok := srvProtocolsUnique["h2c"]

		// 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 !h1ok && (h2ok || h2cok) {
			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 srv.ListenProtocols != nil {
			if len(srv.ListenProtocols) != len(srv.Listen) {
				return fmt.Errorf("server %s: listener protocols count does not match address count: %d != %d",
					srvName, len(srv.ListenProtocols), len(srv.Listen))
			}

			for i, lnProtocols := range srv.ListenProtocols {
				if lnProtocols != nil {
					// populate empty listen protocols with server protocols
					lnProtocolsDefault := false
					var lnProtocolsInclude []string
					srvProtocolsInclude := maps.Clone(srvProtocolsUnique)

					// keep existing listener protocols unless they are empty
					for _, lnProtocol := range lnProtocols {
						if lnProtocol == "" {
							lnProtocolsDefault = true
						} else {
							lnProtocolsInclude = append(lnProtocolsInclude, lnProtocol)
							delete(srvProtocolsInclude, lnProtocol)
						}
					}

					// append server protocols to listener protocols if any listener protocols were empty
					if lnProtocolsDefault {
						for _, srvProtocol := range srv.Protocols {
							if _, ok := srvProtocolsInclude[srvProtocol]; ok {
								lnProtocolsInclude = append(lnProtocolsInclude, srvProtocol)
							}
						}
					}

					lnProtocolsIncludeUnique := map[string]struct{}{}
					for _, lnProtocol := range lnProtocolsInclude {
						lnProtocolsIncludeUnique[lnProtocol] = struct{}{}
					}
					_, h1ok := lnProtocolsIncludeUnique["h1"]
					_, h2ok := lnProtocolsIncludeUnique["h2"]
					_, h2cok := lnProtocolsIncludeUnique["h2c"]

					// check if any listener protocols contain h2 or h2c without h1
					if !h1ok && (h2ok || h2cok) {
						return fmt.Errorf("server %s, listener %d: cannot enable HTTP/2 or H2C without enabling HTTP/1.1; add h1 to protocols or remove h2/h2c", srvName, i)
					}

					srv.ListenProtocols[i] = lnProtocolsInclude
				}
			}
		}

		// if not explicitly configured by the user, disallow TLS
		// client auth bypass (domain fronting) which could
		// otherwise be exploited by sending an unprotected SNI
		// value during a TLS handshake, then putting a protected
		// domain in the Host header after establishing connection;
		// this is a safe default, but we allow users to override
		// it for example in the case of running a proxy where
		// domain fronting is desired and access is not restricted
		// 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))
			trueBool := true
			srv.StrictSNIHost = &trueBool
		}

		// set up the trusted proxies source
		for srv.TrustedProxiesRaw != nil {
			val, err := ctx.LoadModule(srv, "TrustedProxiesRaw")
			if err != nil {
				return fmt.Errorf("loading trusted proxies modules: %v", err)
			}
			srv.trustedProxies = val.(IPRangeSource)
		}

		// set the default client IP header to read from
		if srv.ClientIPHeaders == nil {
			srv.ClientIPHeaders = []string{"X-Forwarded-For"}
		}

		// process each listener address
		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)
			}
			srv.Listen[i] = lnOut
		}

		// set up each listener modifier
		if srv.ListenerWrappersRaw != nil {
			vals, err := ctx.LoadModule(srv, "ListenerWrappersRaw")
			if err != nil {
				return fmt.Errorf("loading listener wrapper modules: %v", err)
			}
			var hasTLSPlaceholder bool
			for i, val := range vals.([]any) {
				if _, ok := val.(*tlsPlaceholderWrapper); ok {
					if i == 0 {
						// putting the tls placeholder wrapper first is nonsensical because
						// that is the default, implicit setting: without it, all wrappers
						// will go after the TLS listener anyway
						return fmt.Errorf("it is unnecessary to specify the TLS listener wrapper in the first position because that is the default")
					}
					if hasTLSPlaceholder {
						return fmt.Errorf("TLS listener wrapper can only be specified once")
					}
					hasTLSPlaceholder = true
				}
				srv.listenerWrappers = append(srv.listenerWrappers, val.(caddy.ListenerWrapper))
			}
			// if any wrappers were configured but the TLS placeholder wrapper is
			// absent, prepend it so all defined wrappers come after the TLS
			// handshake; this simplifies logic when starting the server, since we
			// can simply assume the TLS placeholder will always be there
			if !hasTLSPlaceholder && len(srv.listenerWrappers) > 0 {
				srv.listenerWrappers = append([]caddy.ListenerWrapper{new(tlsPlaceholderWrapper)}, srv.listenerWrappers...)
			}
		}

		// pre-compile the primary handler chain, and be sure to wrap it in our
		// route handler so that important security checks are done, etc.
		primaryRoute := emptyHandler
		if srv.Routes != nil {
			err := srv.Routes.ProvisionHandlers(ctx, srv.Metrics)
			if err != nil {
				return fmt.Errorf("server %s: setting up route handlers: %v", srvName, err)
			}
			primaryRoute = srv.Routes.Compile(emptyHandler)
		}
		srv.primaryHandlerChain = srv.wrapPrimaryRoute(primaryRoute)

		// pre-compile the error handler chain
		if srv.Errors != nil {
			err := srv.Errors.Routes.Provision(ctx)
			if err != nil {
				return fmt.Errorf("server %s: setting up error handling routes: %v", srvName, err)
			}
			srv.errorHandlerChain = srv.Errors.Routes.Compile(errorEmptyHandler)
		}

		// provision the named routes (they get compiled at runtime)
		for name, route := range srv.NamedRoutes {
			err := route.Provision(ctx, srv.Metrics)
			if err != nil {
				return fmt.Errorf("server %s: setting up named route '%s' handlers: %v", name, srvName, err)
			}
		}

		// prepare the TLS connection policies
		err = srv.TLSConnPolicies.Provision(ctx)
		if err != nil {
			return fmt.Errorf("server %s: setting up TLS connection policies: %v", srvName, err)
		}

		// if there is no idle timeout, set a sane default; users have complained
		// before that aggressive CDNs leave connections open until the server
		// closes them, so if we don't close them it leads to resource exhaustion
		if srv.IdleTimeout == 0 {
			srv.IdleTimeout = defaultIdleTimeout
		}
	}
	ctx.Context = oldContext
	return nil
}

// Validate ensures the app's configuration is valid.
func (app *App) Validate() error {
	lnAddrs := make(map[string]string)

	for srvName, srv := range app.Servers {
		// each server must use distinct listener addresses
		for _, addr := range srv.Listen {
			listenAddr, err := caddy.ParseNetworkAddress(addr)
			if err != nil {
				return fmt.Errorf("invalid listener address '%s': %v", addr, err)
			}
			// check that every address in the port range is unique to this server;
			// we do not use <= here because PortRangeSize() adds 1 to EndPort for us
			for i := uint(0); i < listenAddr.PortRangeSize(); i++ {
				addr := caddy.JoinNetworkAddress(listenAddr.Network, listenAddr.Host, strconv.FormatUint(uint64(listenAddr.StartPort+i), 10))
				if sn, ok := lnAddrs[addr]; ok {
					return fmt.Errorf("server %s: listener address repeated: %s (already claimed by server '%s')", srvName, addr, sn)
				}
				lnAddrs[addr] = srvName
			}
		}

		// logger names must not have ports
		if srv.Logs != nil {
			for host := range srv.Logs.LoggerNames {
				if _, _, err := net.SplitHostPort(host); err == nil {
					return fmt.Errorf("server %s: logger name must not have a port: %s", srvName, host)
				}
			}
		}
	}
	return nil
}

// Start runs the app. It finishes automatic HTTPS if enabled,
// including management of certificates.
func (app *App) Start() error {
	// get a logger compatible with http.Server
	serverLogger, err := zap.NewStdLogAt(app.logger.Named("stdlib"), zap.DebugLevel)
	if err != nil {
		return fmt.Errorf("failed to set up server logger: %v", err)
	}

	for srvName, srv := range app.Servers {
		srv.server = &http.Server{
			ReadTimeout:       time.Duration(srv.ReadTimeout),
			ReadHeaderTimeout: time.Duration(srv.ReadHeaderTimeout),
			WriteTimeout:      time.Duration(srv.WriteTimeout),
			IdleTimeout:       time.Duration(srv.IdleTimeout),
			MaxHeaderBytes:    srv.MaxHeaderBytes,
			Handler:           srv,
			ErrorLog:          serverLogger,
			ConnContext: func(ctx context.Context, c net.Conn) context.Context {
				return context.WithValue(ctx, ConnCtxKey, c)
			},
		}
		h2server := new(http2.Server)

		// 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
					}
				}
			}
		} else {
			//nolint:errcheck
			http2.ConfigureServer(srv.server, h2server)
		}

		// 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)
		srv.configureServer(srv.server)

		// enable H2C if configured
		if srv.protocol("h2c") {
			srv.server.Handler = h2c.NewHandler(srv, h2server)
		}

		for lnIndex, lnAddr := range srv.Listen {
			listenAddr, err := caddy.ParseNetworkAddress(lnAddr)
			if err != nil {
				return fmt.Errorf("%s: parsing listen address '%s': %v", srvName, lnAddr, err)
			}

			srv.addresses = append(srv.addresses, listenAddr)

			protocols := srv.Protocols
			if srv.ListenProtocols != nil && srv.ListenProtocols[lnIndex] != nil {
				protocols = srv.ListenProtocols[lnIndex]
			}

			protocolsUnique := map[string]struct{}{}
			for _, protocol := range protocols {
				protocolsUnique[protocol] = struct{}{}
			}
			_, h1ok := protocolsUnique["h1"]
			_, h2ok := protocolsUnique["h2"]
			_, h2cok := protocolsUnique["h2c"]
			_, h3ok := protocolsUnique["h3"]

			for portOffset := uint(0); portOffset < listenAddr.PortRangeSize(); portOffset++ {
				hostport := listenAddr.JoinHostPort(portOffset)

				// 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()

				// enable HTTP/3 if configured
				if h3ok && useTLS {
					app.logger.Info("enabling HTTP/3 listener", zap.String("addr", hostport))
					if err := srv.serveHTTP3(listenAddr.At(portOffset), tlsCfg); err != nil {
						return err
					}
				}

				if h3ok && !useTLS {
					// Can only serve h3 with TLS enabled
					app.logger.Warn("HTTP/3 skipped because it requires TLS",
						zap.String("network", listenAddr.Network),
						zap.String("addr", hostport))
				}

				if h1ok || h2ok && useTLS || h2cok {
					// create the listener for this socket
					lnAny, err := listenAddr.Listen(app.ctx, portOffset, net.ListenConfig{KeepAlive: time.Duration(srv.KeepAliveInterval)})
					if err != nil {
						return fmt.Errorf("listening on %s: %v", listenAddr.At(portOffset), err)
					}
					ln, ok := lnAny.(net.Listener)
					if !ok {
						return fmt.Errorf("network '%s' cannot handle HTTP/1 or HTTP/2 connections", listenAddr.Network)
					}

					// wrap listener before TLS (up to the TLS placeholder wrapper)
					var lnWrapperIdx int
					for i, lnWrapper := range srv.listenerWrappers {
						if _, ok := lnWrapper.(*tlsPlaceholderWrapper); ok {
							lnWrapperIdx = i + 1 // mark the next wrapper's spot
							break
						}
						ln = lnWrapper.WrapListener(ln)
					}

					if useTLS {
						// create TLS listener - this enables and terminates TLS
						ln = tls.NewListener(ln, tlsCfg)
					}

					// finish wrapping listener where we left off before TLS
					for i := lnWrapperIdx; i < len(srv.listenerWrappers); i++ {
						ln = srv.listenerWrappers[i].WrapListener(ln)
					}

					// handle http2 if use tls listener wrapper
					if h2ok {
						http2lnWrapper := &http2Listener{
							Listener: ln,
							server:   srv.server,
							h2server: h2server,
						}
						srv.h2listeners = append(srv.h2listeners, http2lnWrapper)
						ln = http2lnWrapper
					}

					// if binding to port 0, the OS chooses a port for us;
					// but the user won't know the port unless we print it
					if !listenAddr.IsUnixNetwork() && !listenAddr.IsFdNetwork() && listenAddr.StartPort == 0 && listenAddr.EndPort == 0 {
						app.logger.Info("port 0 listener",
							zap.String("input_address", lnAddr),
							zap.String("actual_address", ln.Addr().String()))
					}

					app.logger.Debug("starting server loop",
						zap.String("address", ln.Addr().String()),
						zap.Bool("tls", useTLS),
						zap.Bool("http3", srv.h3server != nil))

					srv.listeners = append(srv.listeners, ln)

					// enable HTTP/1 if configured
					if h1ok {
						//nolint:errcheck
						go srv.server.Serve(ln)
					}
				}

				if h2ok && !useTLS {
					// Can only serve h2 with TLS enabled
					app.logger.Warn("HTTP/2 skipped because it requires TLS",
						zap.String("network", listenAddr.Network),
						zap.String("addr", hostport))
				}
			}
		}

		srv.logger.Info("server running",
			zap.String("name", srvName),
			zap.Strings("protocols", srv.Protocols))
	}

	// finish automatic HTTPS by finally beginning
	// certificate management
	err = app.automaticHTTPSPhase2()
	if err != nil {
		return fmt.Errorf("finalizing automatic HTTPS: %v", err)
	}

	return nil
}

// Stop gracefully shuts down the HTTP server.
func (app *App) Stop() error {
	ctx := context.Background()

	// see if any listeners in our config will be closing or if they are continuing
	// through a reload; because if any are closing, we will enforce shutdown delay
	var delay bool
	scheduledTime := time.Now().Add(time.Duration(app.ShutdownDelay))
	if app.ShutdownDelay > 0 {
		for _, server := range app.Servers {
			for _, na := range server.addresses {
				for _, addr := range na.Expand() {
					if caddy.ListenerUsage(addr.Network, addr.JoinHostPort(0)) < 2 {
						app.logger.Debug("listener closing and shutdown delay is configured", zap.String("address", addr.String()))
						server.shutdownAtMu.Lock()
						server.shutdownAt = scheduledTime
						server.shutdownAtMu.Unlock()
						delay = true
					} else {
						app.logger.Debug("shutdown delay configured but listener will remain open", zap.String("address", addr.String()))
					}
				}
			}
		}
	}

	// honor scheduled/delayed shutdown time
	if delay {
		app.logger.Info("shutdown scheduled",
			zap.Duration("delay_duration", time.Duration(app.ShutdownDelay)),
			zap.Time("time", scheduledTime))
		time.Sleep(time.Duration(app.ShutdownDelay))
	}

	// enforce grace period if configured
	if app.GracePeriod > 0 {
		var cancel context.CancelFunc
		ctx, cancel = context.WithTimeout(ctx, time.Duration(app.GracePeriod))
		defer cancel()
		app.logger.Info("servers shutting down; grace period initiated", zap.Duration("duration", time.Duration(app.GracePeriod)))
	} else {
		app.logger.Info("servers shutting down with eternal grace period")
	}

	// goroutines aren't guaranteed to be scheduled right away,
	// so we'll use one WaitGroup to wait for all the goroutines
	// to start their server shutdowns, and another to wait for
	// them to finish; we'll always block for them to start so
	// that when we return the caller can be confident* that the
	// old servers are no longer accepting new connections
	// (* the scheduler might still pause them right before
	// calling Shutdown(), but it's unlikely)
	var startedShutdown, finishedShutdown sync.WaitGroup

	// these will run in goroutines
	stopServer := func(server *Server) {
		defer finishedShutdown.Done()
		startedShutdown.Done()

		if err := server.server.Shutdown(ctx); err != nil {
			app.logger.Error("server shutdown",
				zap.Error(err),
				zap.Strings("addresses", server.Listen))
		}
	}
	stopH3Server := func(server *Server) {
		defer finishedShutdown.Done()
		startedShutdown.Done()

		if server.h3server == nil {
			return
		}

		// First close h3server then close listeners unlike stdlib for several reasons:
		// 1, udp has only a single socket, once closed, no more data can be read and
		// written. In contrast, closing tcp listeners won't affect established connections.
		// This have something to do with graceful shutdown when upstream implements it.
		// 2, h3server will only close listeners it's registered (quic listeners). Closing
		// listener first and these listeners maybe unregistered thus won't be closed. caddy
		// distinguishes quic-listener and underlying datagram sockets.

		// TODO: CloseGracefully, once implemented upstream (see https://github.com/quic-go/quic-go/issues/2103)
		if err := server.h3server.Close(); err != nil {
			app.logger.Error("HTTP/3 server shutdown",
				zap.Error(err),
				zap.Strings("addresses", server.Listen))
		}
	}
	stopH2Listener := func(server *Server) {
		defer finishedShutdown.Done()
		startedShutdown.Done()

		for i, s := range server.h2listeners {
			if err := s.Shutdown(ctx); err != nil {
				app.logger.Error("http2 listener shutdown",
					zap.Error(err),
					zap.Int("index", i))
			}
		}
	}

	for _, server := range app.Servers {
		startedShutdown.Add(3)
		finishedShutdown.Add(3)
		go stopServer(server)
		go stopH3Server(server)
		go stopH2Listener(server)
	}

	// block until all the goroutines have been run by the scheduler;
	// this means that they have likely called Shutdown() by now
	startedShutdown.Wait()

	// if the process is exiting, we need to block here and wait
	// for the grace periods to complete, otherwise the process will
	// terminate before the servers are finished shutting down; but
	// we don't really need to wait for the grace period to finish
	// if the process isn't exiting (but note that frequent config
	// reloads with long grace periods for a sustained length of time
	// may deplete resources)
	if caddy.Exiting() {
		finishedShutdown.Wait()
	}

	// run stop callbacks now that the server shutdowns are complete
	for name, s := range app.Servers {
		for _, stopHook := range s.onStopFuncs {
			if err := stopHook(ctx); err != nil {
				app.logger.Error("server stop hook", zap.String("server", name), zap.Error(err))
			}
		}
	}

	return nil
}

func (app *App) httpPort() int {
	if app.HTTPPort == 0 {
		return DefaultHTTPPort
	}
	return app.HTTPPort
}

func (app *App) httpsPort() int {
	if app.HTTPSPort == 0 {
		return DefaultHTTPSPort
	}
	return app.HTTPSPort
}

// defaultIdleTimeout is the default HTTP server timeout
// for closing idle connections; useful to avoid resource
// exhaustion behind hungry CDNs, for example (we've had
// several complaints without this).
const defaultIdleTimeout = caddy.Duration(5 * time.Minute)

// Interface guards
var (
	_ caddy.App         = (*App)(nil)
	_ caddy.Provisioner = (*App)(nil)
	_ caddy.Validator   = (*App)(nil)
)