reverse_proxy: use interfaces to modify the behaviors of the transports (#7353)

modules/caddyhttp/reverseproxy/caddyfile.go

@@ -888,8 +888,11 @@ func (h *Handler) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 			if commonScheme == "http" && te.TLSEnabled() {
 				return d.Errf("upstream address scheme is HTTP but transport is configured for HTTP+TLS (HTTPS)")
 			}
-			if te, ok := transport.(*HTTPTransport); ok && commonScheme == "h2c" {
-				te.Versions = []string{"h2c", "2"}
+			if h2ct, ok := transport.(H2CTransport); ok && commonScheme == "h2c" {
+				err := h2ct.EnableH2C()
+				if err != nil {
+					return err
+				}
 			}
 		} else if commonScheme == "https" {
 			return d.Errf("upstreams are configured for HTTPS but transport module does not support TLS: %T", transport)

modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go

@@ -112,6 +112,20 @@ func (t *Transport) Provision(ctx caddy.Context) error {
 	return nil
 }
 
+// DefaultBufferSizes enables request buffering for fastcgi if not configured.
+// This is because most fastcgi servers are php-fpm that require the content length to be set to read the body, golang
+// std has fastcgi implementation that doesn't need this value to process the body, but we can safely assume that's
+// not used.
+// http3 requests have a negative content length for GET and HEAD requests, if that header is not sent.
+// see: https://github.com/caddyserver/caddy/issues/6678#issuecomment-2472224182
+// Though it appears even if CONTENT_LENGTH is invalid, php-fpm can handle just fine if the body is empty (no Stdin records sent).
+// php-fpm will hang if there is any data in the body though, https://github.com/caddyserver/caddy/issues/5420#issuecomment-2415943516
+
+// TODO: better default buffering for fastcgi requests without content length, in theory a value of 1 should be enough, make it bigger anyway
+func (t Transport) DefaultBufferSizes() (int64, int64) {
+	return 4096, 0
+}
+
 // RoundTrip implements http.RoundTripper.
 func (t Transport) RoundTrip(r *http.Request) (*http.Response, error) {
 	server := r.Context().Value(caddyhttp.ServerCtxKey).(*caddyhttp.Server)
@@ -427,6 +441,7 @@ var headerNameReplacer = strings.NewReplacer(" ", "_", "-", "_")
 var (
 	_ zapcore.ObjectMarshaler = (*loggableEnv)(nil)
 
-	_ caddy.Provisioner = (*Transport)(nil)
-	_ http.RoundTripper = (*Transport)(nil)
+	_ caddy.Provisioner              = (*Transport)(nil)
+	_ http.RoundTripper              = (*Transport)(nil)
+	_ reverseproxy.BufferedTransport = (*Transport)(nil)
 )

modules/caddyhttp/reverseproxy/healthchecks.go

@@ -23,7 +23,6 @@ import (
 	"net/url"
 	"regexp"
 	"runtime/debug"
-	"slices"
 	"strconv"
 	"strings"
 	"time"
@@ -405,14 +404,9 @@ func (h *Handler) doActiveHealthCheck(dialInfo DialInfo, hostAddr string, networ
 		u.Host = net.JoinHostPort(host, port)
 	}
 
-	// this is kind of a hacky way to know if we should use HTTPS, but whatever
-	if tt, ok := h.Transport.(TLSTransport); ok && tt.TLSEnabled() {
-		u.Scheme = "https"
-
-		// if the port is in the except list, flip back to HTTP
-		if ht, ok := h.Transport.(*HTTPTransport); ok && slices.Contains(ht.TLS.ExceptPorts, port) {
-			u.Scheme = "http"
-		}
+	// override health check schemes if applicable
+	if hcsot, ok := h.Transport.(HealthCheckSchemeOverriderTransport); ok {
+		hcsot.OverrideHealthCheckScheme(u, port)
 	}
 
 	// if we have a provisioned uri, use that, otherwise use

modules/caddyhttp/reverseproxy/httptransport.go

@@ -564,6 +564,26 @@ func (h *HTTPTransport) EnableTLS(base *TLSConfig) error {
 	return nil
 }
 
+// EnableH2C enables H2C (HTTP/2 over Cleartext) on the transport.
+func (h *HTTPTransport) EnableH2C() error {
+	h.Versions = []string{"h2c", "2"}
+	return nil
+}
+
+// OverrideHealthCheckScheme overrides the scheme of the given URL
+// used for health checks.
+func (h HTTPTransport) OverrideHealthCheckScheme(base *url.URL, port string) {
+	// if tls is enabled and the port isn't in the except list, use HTTPs
+	if h.TLSEnabled() && !slices.Contains(h.TLS.ExceptPorts, port) {
+		base.Scheme = "https"
+	}
+}
+
+// ProxyProtocolEnabled returns true if proxy protocol is enabled.
+func (h HTTPTransport) ProxyProtocolEnabled() bool {
+	return h.ProxyProtocol != ""
+}
+
 // Cleanup implements caddy.CleanerUpper and closes any idle connections.
 func (h HTTPTransport) Cleanup() error {
 	if h.Transport == nil {
@@ -820,8 +840,11 @@ func decodeBase64DERCert(certStr string) (*x509.Certificate, error) {
 
 // Interface guards
 var (
-	_ caddy.Provisioner  = (*HTTPTransport)(nil)
-	_ http.RoundTripper  = (*HTTPTransport)(nil)
-	_ caddy.CleanerUpper = (*HTTPTransport)(nil)
-	_ TLSTransport       = (*HTTPTransport)(nil)
+	_ caddy.Provisioner                   = (*HTTPTransport)(nil)
+	_ http.RoundTripper                   = (*HTTPTransport)(nil)
+	_ caddy.CleanerUpper                  = (*HTTPTransport)(nil)
+	_ TLSTransport                        = (*HTTPTransport)(nil)
+	_ H2CTransport                        = (*HTTPTransport)(nil)
+	_ HealthCheckSchemeOverriderTransport = (*HTTPTransport)(nil)
+	_ ProxyProtocolTransport              = (*HTTPTransport)(nil)
 )

modules/caddyhttp/reverseproxy/reverseproxy.go

@@ -243,18 +243,16 @@ func (h *Handler) Provision(ctx caddy.Context) error {
 			return fmt.Errorf("loading transport: %v", err)
 		}
 		h.Transport = mod.(http.RoundTripper)
-		// enable request buffering for fastcgi if not configured
-		// This is because most fastcgi servers are php-fpm that require the content length to be set to read the body, golang
-		// std has fastcgi implementation that doesn't need this value to process the body, but we can safely assume that's
-		// not used.
-		// http3 requests have a negative content length for GET and HEAD requests, if that header is not sent.
-		// see: https://github.com/caddyserver/caddy/issues/6678#issuecomment-2472224182
-		// Though it appears even if CONTENT_LENGTH is invalid, php-fpm can handle just fine if the body is empty (no Stdin records sent).
-		// php-fpm will hang if there is any data in the body though, https://github.com/caddyserver/caddy/issues/5420#issuecomment-2415943516
 
-		// TODO: better default buffering for fastcgi requests without content length, in theory a value of 1 should be enough, make it bigger anyway
-		if module, ok := h.Transport.(caddy.Module); ok && module.CaddyModule().ID.Name() == "fastcgi" && h.RequestBuffers == 0 {
-			h.RequestBuffers = 4096
+		// set default buffer sizes if applicable
+		if bt, ok := h.Transport.(BufferedTransport); ok {
+			reqBuffers, respBuffers := bt.DefaultBufferSizes()
+			if h.RequestBuffers == 0 {
+				h.RequestBuffers = reqBuffers
+			}
+			if h.ResponseBuffers == 0 {
+				h.ResponseBuffers = respBuffers
+			}
 		}
 	}
 	if h.LoadBalancing != nil && h.LoadBalancing.SelectionPolicyRaw != nil {
@@ -1210,7 +1208,7 @@ func (h *Handler) directRequest(req *http.Request, di DialInfo) {
 	}
 
 	// add client address to the host to let transport differentiate requests from different clients
-	if ht, ok := h.Transport.(*HTTPTransport); ok && ht.ProxyProtocol != "" {
+	if ppt, ok := h.Transport.(ProxyProtocolTransport); ok && ppt.ProxyProtocolEnabled() {
 		if proxyProtocolInfo, ok := caddyhttp.GetVar(req.Context(), proxyProtocolInfoVarKey).(ProxyProtocolInfo); ok {
 			reqHost = proxyProtocolInfo.AddrPort.String() + "->" + reqHost
 		}
@@ -1501,6 +1499,32 @@ type TLSTransport interface {
 	EnableTLS(base *TLSConfig) error
 }
 
+// H2CTransport is implemented by transports
+// that are capable of using h2c.
+type H2CTransport interface {
+	EnableH2C() error
+}
+
+// ProxyProtocolTransport is implemented by transports
+// that are capable of using proxy protocol.
+type ProxyProtocolTransport interface {
+	ProxyProtocolEnabled() bool
+}
+
+// HealthCheckSchemeOverriderTransport is implemented by transports
+// that can override the scheme used for health checks.
+type HealthCheckSchemeOverriderTransport interface {
+	OverrideHealthCheckScheme(base *url.URL, port string)
+}
+
+// BufferedTransport is implemented by transports
+// that needs to buffer requests and/or responses.
+type BufferedTransport interface {
+	// DefaultBufferSizes returns the default buffer sizes
+	// for requests and responses, respectively if buffering isn't enabled.
+	DefaultBufferSizes() (int64, int64)
+}
+
 // roundtripSucceededError is an error type that is returned if the
 // roundtrip succeeded, but an error occurred after-the-fact.
 type roundtripSucceededError struct{ error }