Introduce a fast proxy mode to improve HTTP/1.1 performances with backends

Co-authored-by: Romain <rtribotte@users.noreply.github.com>
Co-authored-by: Julien Salleyron <julien.salleyron@gmail.com>

pkg/proxy/smart_builder.go

@@ -0,0 +1,61 @@
+package proxy
+
+import (
+	"crypto/tls"
+	"fmt"
+	"net/http"
+	"net/url"
+	"time"
+
+	"github.com/traefik/traefik/v3/pkg/config/dynamic"
+	"github.com/traefik/traefik/v3/pkg/config/static"
+	"github.com/traefik/traefik/v3/pkg/proxy/fast"
+	"github.com/traefik/traefik/v3/pkg/proxy/httputil"
+	"github.com/traefik/traefik/v3/pkg/server/service"
+)
+
+// TransportManager manages transport used for backend communications.
+type TransportManager interface {
+	Get(name string) (*dynamic.ServersTransport, error)
+	GetRoundTripper(name string) (http.RoundTripper, error)
+	GetTLSConfig(name string) (*tls.Config, error)
+}
+
+// SmartBuilder is a proxy builder which returns a fast proxy or httputil proxy corresponding
+// to the ServersTransport configuration.
+type SmartBuilder struct {
+	fastProxyBuilder *fast.ProxyBuilder
+	proxyBuilder     service.ProxyBuilder
+
+	transportManager httputil.TransportManager
+}
+
+// NewSmartBuilder creates and returns a new SmartBuilder instance.
+func NewSmartBuilder(transportManager TransportManager, proxyBuilder service.ProxyBuilder, fastProxyConfig static.FastProxyConfig) *SmartBuilder {
+	return &SmartBuilder{
+		fastProxyBuilder: fast.NewProxyBuilder(transportManager, fastProxyConfig),
+		proxyBuilder:     proxyBuilder,
+		transportManager: transportManager,
+	}
+}
+
+// Update is the handler called when the dynamic configuration is updated.
+func (b *SmartBuilder) Update(newConfigs map[string]*dynamic.ServersTransport) {
+	b.fastProxyBuilder.Update(newConfigs)
+}
+
+// Build builds an HTTP proxy for the given URL using the ServersTransport with the given name.
+func (b *SmartBuilder) Build(configName string, targetURL *url.URL, shouldObserve, passHostHeader bool, flushInterval time.Duration) (http.Handler, error) {
+	serversTransport, err := b.transportManager.Get(configName)
+	if err != nil {
+		return nil, fmt.Errorf("getting ServersTransport: %w", err)
+	}
+
+	// The fast proxy implementation cannot handle HTTP/2 requests for now.
+	// For the https scheme we cannot guess if the backend communication will use HTTP2,
+	// thus we check if HTTP/2 is disabled to use the fast proxy implementation when this is possible.
+	if targetURL.Scheme == "h2c" || (targetURL.Scheme == "https" && !serversTransport.DisableHTTP2) {
+		return b.proxyBuilder.Build(configName, targetURL, shouldObserve, passHostHeader, flushInterval)
+	}
+	return b.fastProxyBuilder.Build(configName, targetURL, passHostHeader)
+}