Enabling 0-RTT for QUIC/H3 clients (#387)

* Updated the DoQ and DoH QUIC client to enable 0-RTT based on the guide from: https://quic-go.net/docs/http3/client/#using-0-rtt

* changed doq client to use DialEarly for 0-RTT support

* Added 0-RTT toggle - introduced the Use0RTT option to the configuration

* reverted the doqcliet DialEarly changes as they were not needed and had a bug.
Renamed the 0RTT toggle and updated the documentation.

* catching missconfig of 0-RTT and HTTP/2

cmd/routedns/config.go

@@ -57,6 +57,9 @@ type resolver struct {
 	Socks5Username     string `toml:"socks5-username"`
 	Socks5Password     string `toml:"socks5-password"`
 	Socks5ResolveLocal bool   `toml:"socks5-resolve-local"` // Resolve DNS server address locally (i.e. bootstrap-resolver), not on the SOCK5 proxy
+
+	//QUIC and DoH/3 configuration
+	Use0RTT       bool   `toml:"enable-0rtt"`
 }
 
 // DoH-specific resolver options

cmd/routedns/example-config/doh-quic-client.toml

@@ -1,9 +1,12 @@
 # DNS-over-HTTPS using the QUIC protocol.
+# New connections get initiated with 0-RTT if possible.
+# Use0RTT will overwrite the method to GET. 
 
 [resolvers.cloudflare-doh-quic]
 address = "https://cloudflare-dns.com/dns-query"
 protocol = "doh"
 transport = "quic"
+enable-0rtt = true
 
 [listeners.local-udp]
 address = "127.0.0.1:53"

cmd/routedns/example-config/doq-client.toml

@@ -1,11 +1,13 @@
 # This config starts a UDP and a TCP resolver on the loopback interface for plain DNS.
 # All queries are forwarded to a local DNS-over-QUIC server.
+# New connections get initiated with 0-RTT if possible.
 
 [resolvers.local-doq]
 address = "server.acme.test:8853"
 protocol = "doq"
 ca = "example-config/server.crt"
 bootstrap-address = "127.0.0.1"
+enable-0rtt = true
 
 [listeners.local-udp]
 address = "127.0.0.1:53"

cmd/routedns/resolver.go

@@ -25,6 +25,7 @@ func instantiateResolver(id string, r resolver, resolvers map[string]rdns.Resolv
 			LocalAddr:     net.ParseIP(r.LocalAddr),
 			TLSConfig:     tlsConfig,
 			QueryTimeout:  time.Duration(r.QueryTimeout) * time.Second,
+			Use0RTT:       r.Use0RTT,
 		}
 		resolvers[id], err = rdns.NewDoQClient(id, r.Address, opt)
 		if err != nil {
@@ -81,6 +82,7 @@ func instantiateResolver(id string, r resolver, resolvers map[string]rdns.Resolv
 			LocalAddr:     net.ParseIP(r.LocalAddr),
 			QueryTimeout:  time.Duration(r.QueryTimeout) * time.Second,
 			Dialer:        socks5DialerFromConfig(r),
+			Use0RTT:       r.Use0RTT,
 		}
 		resolvers[id], err = rdns.NewDoHClient(id, r.Address, opt)
 		if err != nil {

doc/configuration.md

@@ -1512,6 +1512,7 @@ Example config files: [well-known.toml](../cmd/routedns/example-config/well-know
 ### DNS-over-HTTPS Resolver
 
 DNS resolvers using the HTTPS protocol are configured with `protocol = "doh"`. By default, DoH uses TCP as transport, but it can also be run over QUIC (UDP) by providing the option `transport = "quic"`. DoH supports two HTTP methods, GET and POST. By default RouteDNS uses the POST method, but can be configured to use GET as well using the option `doh = { method = "GET" }`.
+DoH with QUIC supports 0-RTT. The DoH resolver will try to use 0-RTT connection establishment if `transport = "quic"` and `enable-0rtt = true` are configured. When 0-RTT is enabled, the resolver will disregard the configured method and always use GET instead.
 
 Examples:
 
@@ -1539,6 +1540,7 @@ DoH resolver using QUIC transport.
 address = "https://cloudflare-dns.com/dns-query"
 protocol = "doh"
 transport = "quic"
+enable-0rtt = true
 ```
 
 Example config files: [well-known.toml](../cmd/routedns/example-config/well-known.toml), [simple-doh.toml](../cmd/routedns/example-config/simple-doh.toml), [mutual-tls-doh-client.toml](../cmd/routedns/example-config/mutual-tls-doh-client.toml)
@@ -1564,6 +1566,7 @@ Example config files: [dtls-client.toml](../cmd/routedns/example-config/dtls-cli
 ### DNS-over-QUIC Resolver
 
 Similar to DoT, but uses a QUIC connection as transport as per [RFC9250](https://datatracker.ietf.org/doc/rfc9250/). Configured with `protocol = "doq"`. Note that this is different from DoH over QUIC. See [DNS-over-HTTPS](#DNS-over-HTTPS-Resolver) for how to configure this.
+The DoQ resolver will try to use 0-RTT connection establishment if `enable-0rtt = true` is configured.
 
 Examples:
 
@@ -1573,6 +1576,7 @@ address = "server.acme.test:8853"
 protocol = "doq"
 ca = "example-config/server.crt"
 bootstrap-address = "127.0.0.1"
+enable-0rtt = true
 ```
 
 Example config files: [doq-client.toml](../cmd/routedns/example-config/doq-client.toml)

dohclient.go

@@ -44,6 +44,8 @@ type DoHClientOptions struct {
 
 	// Optional dialer, e.g. proxy
 	Dialer Dialer
+
+	Use0RTT bool
 }
 
 // DoHClient is a DNS-over-HTTP resolver with support fot HTTP/2.
@@ -85,6 +87,9 @@ func NewDoHClient(id, endpoint string, opt DoHClientOptions) (*DoHClient, error)
 	if opt.Method == "" {
 		opt.Method = "POST"
 	}
+	if opt.Use0RTT && opt.Transport == "quic" {
+		opt.Method = "GET"
+	}
 	if opt.Method != "POST" && opt.Method != "GET" {
 		return nil, fmt.Errorf("unsupported method '%s'", opt.Method)
 	}
@@ -181,7 +186,12 @@ func (d *DoHClient) ResolveGET(q *dns.Msg) (*dns.Msg, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), d.opt.QueryTimeout)
 	defer cancel()
 
-	req, err := http.NewRequestWithContext(ctx, "GET", u, nil)
+	method := http.MethodGet
+	if d.opt.Use0RTT && d.opt.Transport == "quic" {
+		method = http3.MethodGet0RTT
+	}
+
+	req, err := http.NewRequestWithContext(ctx, method, u, nil)
 	if err != nil {
 		d.metrics.err.Add("http", 1)
 		return nil, err
@@ -268,6 +278,9 @@ func dohQuicTransport(endpoint string, opt DoHClientOptions) (http.RoundTripper,
 	if err != nil {
 		return nil, err
 	}
+
+	// enable TLS session caching for session resumption and 0-RTT
+	tlsConfig.ClientSessionCache = tls.NewLRUClientSessionCache(100)
 	tlsConfig.ServerName = u.Hostname()
 	lAddr := net.IPv4zero
 	if opt.LocalAddr != nil {

doqclient.go

@@ -42,6 +42,8 @@ type DoQClientOptions struct {
 	TLSConfig *tls.Config
 
 	QueryTimeout time.Duration
+
+	Use0RTT       bool
 }
 
 var _ Resolver = &DoQClient{}
@@ -77,6 +79,11 @@ func NewDoQClient(id, endpoint string, opt DoQClientOptions) (*DoQClient, error)
 	// quic-go requires the ServerName be set explicitly
 	tlsConfig.ServerName = host
 
+	// enable TLS session caching for session resumption and 0-RTT
+	if opt.Use0RTT {
+		tlsConfig.ClientSessionCache = tls.NewLRUClientSessionCache(100)
+	}
+
 	if opt.QueryTimeout == 0 {
 		opt.QueryTimeout = defaultQueryTimeout
 	}