reverseproxy: do not disable keepalive if proxy protocol is used

modules/caddyhttp/reverseproxy/hosts.go

@@ -285,3 +285,6 @@ type ProxyProtocolInfo struct {
 // tlsH1OnlyVarKey is the key used that indicates the connection will use h1 only for TLS.
 // https://github.com/caddyserver/caddy/issues/7292
 const tlsH1OnlyVarKey = "reverse_proxy.tls_h1_only"
+
+// proxyVarKey is the key used that indicates the proxy server used for a request.
+const proxyVarKey = "reverse_proxy.proxy"

modules/caddyhttp/reverseproxy/httptransport.go

@@ -24,6 +24,7 @@ import (
 	weakrand "math/rand"
 	"net"
 	"net/http"
+	"net/url"
 	"os"
 	"reflect"
 	"slices"
@@ -267,15 +268,15 @@ func (h *HTTPTransport) NewTransport(caddyCtx caddy.Context) (*http.Transport, e
 	}
 
 	dialContext := func(ctx context.Context, network, address string) (net.Conn, error) {
-		// For unix socket upstreams, we need to recover the dial info from
-		// the request's context, because the Host on the request's URL
-		// will have been modified by directing the request, overwriting
-		// the unix socket filename.
-		// Also, we need to avoid overwriting the address at this point
-		// when not necessary, because http.ProxyFromEnvironment may have
-		// modified the address according to the user's env proxy config.
+		// The network is usually tcp, and the address is the host in http.Request.URL.Host
+		// and that's been overwritten in directRequest
+		// However, if proxy is used according to http.ProxyFromEnvironment or proxy providers,
+		// address will be the address of the proxy server.
+
+		// This means we can safely use the address in dialInfo if proxy is not used (the address and network will be same any way)
+		// or if the upstream is unix (because there is no way socks or http proxy can be used for unix address).
 		if dialInfo, ok := GetDialInfo(ctx); ok {
-			if strings.HasPrefix(dialInfo.Network, "unix") {
+			if caddyhttp.GetVar(ctx, proxyVarKey) == nil || strings.HasPrefix(dialInfo.Network, "unix") {
 				network = dialInfo.Network
 				address = dialInfo.Address
 			}
@@ -376,9 +377,19 @@ func (h *HTTPTransport) NewTransport(caddyCtx caddy.Context) (*http.Transport, e
 			return nil, fmt.Errorf("network_proxy module is not `(func(*http.Request) (*url.URL, error))``")
 		}
 	}
+	// we need to keep track if a proxy is used for a request
+	proxyWrapper := func(req *http.Request) (*url.URL, error) {
+		u, err := proxy(req)
+		if u == nil || err != nil {
+			return u, err
+		}
+		// there must be a proxy for this request
+		caddyhttp.SetVar(req.Context(), proxyVarKey, u)
+		return u, nil
+	}
 
 	rt := &http.Transport{
-		Proxy:                  proxy,
+		Proxy:                  proxyWrapper,
 		DialContext:            dialContext,
 		MaxConnsPerHost:        h.MaxConnsPerHost,
 		ResponseHeaderTimeout:  time.Duration(h.ResponseHeaderTimeout),
@@ -457,14 +468,6 @@ func (h *HTTPTransport) NewTransport(caddyCtx caddy.Context) (*http.Transport, e
 		rt.IdleConnTimeout = time.Duration(h.KeepAlive.IdleConnTimeout)
 	}
 
-	// The proxy protocol header can only be sent once right after opening the connection.
-	// So single connection must not be used for multiple requests, which can potentially
-	// come from different clients.
-	if !rt.DisableKeepAlives && h.ProxyProtocol != "" {
-		caddyCtx.Logger().Warn("disabling keepalives, they are incompatible with using PROXY protocol")
-		rt.DisableKeepAlives = true
-	}
-
 	if h.Compression != nil {
 		rt.DisableCompression = !*h.Compression
 	}

modules/caddyhttp/reverseproxy/reverseproxy.go

@@ -1194,7 +1194,7 @@ func (lb LoadBalancing) tryAgain(ctx caddy.Context, start time.Time, retries int
 
 // directRequest modifies only req.URL so that it points to the upstream
 // in the given DialInfo. It must modify ONLY the request URL.
-func (Handler) directRequest(req *http.Request, di DialInfo) {
+func (h *Handler) directRequest(req *http.Request, di DialInfo) {
 	// we need a host, so set the upstream's host address
 	reqHost := di.Address
 
@@ -1205,6 +1205,13 @@ func (Handler) directRequest(req *http.Request, di DialInfo) {
 		reqHost = di.Host
 	}
 
+	// add client address to the host to let transport differentiate requests from different clients
+	if ht, ok := h.Transport.(*HTTPTransport); ok && ht.ProxyProtocol != "" {
+		if proxyProtocolInfo, ok := caddyhttp.GetVar(req.Context(), proxyProtocolInfoVarKey).(ProxyProtocolInfo); ok {
+			reqHost = proxyProtocolInfo.AddrPort.String() + "->" + reqHost
+		}
+	}
+
 	req.URL.Host = reqHost
 }