feat(forwarder): support plugin-based rewriter in HTTP body rewrite rules

Each rewriteBody/rewriteResponseBody/rewriteRequestBody rule can now
optionally reference a named rewriter plugin (HTTP/gRPC backend) via
the rewriter field. When set, body rewriting delegates to the plugin
rather than applying pattern/replacement, while content-type filtering
still applies.

Coincident fixes:
- rewriter/plugin/grpc: return nil when conn is nil (avoid nil-ptr panic)
- rewriter/plugin/http: drain response body in defer to prevent leaks
- config/parsing/rewriter: pass TimeoutOption to gRPC plugin
- config/parsing/service: warn when referenced rewriter is not registered

config/parsing/node/parse.go

@@ -29,6 +29,29 @@ import (
 // metadata-driven options (so_mark, interface, netns, proxy protocol), sets up
 // bypass rules, node filters, HTTP settings, and TLS node settings. The hop
 // parameter is used only for logging context.
+
+func parseBodyRewrites(vs []config.HTTPBodyRewriteConfig, log logger.Logger) []chain.HTTPBodyRewriteSettings {
+	var out []chain.HTTPBodyRewriteSettings
+	for _, v := range vs {
+		pattern, _ := regexp.Compile(v.Match)
+		rw := chain.HTTPBodyRewriteSettings{
+			Type:        v.Type,
+			Pattern:     pattern,
+			Replacement: []byte(v.Replacement),
+		}
+		if v.Rewriter != "" {
+			if !registry.RewriterRegistry().IsRegistered(v.Rewriter) {
+				log.Warnf("rewriter %q not found in registry for rewrite rule", v.Rewriter)
+			}
+			rw.Rewriter = registry.RewriterRegistry().Get(v.Rewriter)
+		}
+		if pattern != nil || rw.Rewriter != nil {
+			out = append(out, rw)
+		}
+	}
+	return out
+}
+
 func ParseNode(hop string, cfg *config.NodeConfig, log logger.Logger) (*chain.Node, error) {
 	if cfg == nil {
 		return nil, nil
@@ -226,33 +249,9 @@ func ParseNode(hop string, cfg *config.NodeConfig, log logger.Logger) (*chain.No
 				})
 			}
 		}
-		for _, v := range cfg.HTTP.RewriteBody {
-			if pattern, _ := regexp.Compile(v.Match); pattern != nil {
-				settings.RewriteResponseBody = append(settings.RewriteResponseBody, chain.HTTPBodyRewriteSettings{
-					Type:        v.Type,
-					Pattern:     pattern,
-					Replacement: []byte(v.Replacement),
-				})
-			}
-		}
-		for _, v := range cfg.HTTP.RewriteResponseBody {
-			if pattern, _ := regexp.Compile(v.Match); pattern != nil {
-				settings.RewriteResponseBody = append(settings.RewriteResponseBody, chain.HTTPBodyRewriteSettings{
-					Type:        v.Type,
-					Pattern:     pattern,
-					Replacement: []byte(v.Replacement),
-				})
-			}
-		}
-		for _, v := range cfg.HTTP.RewriteRequestBody {
-			if pattern, _ := regexp.Compile(v.Match); pattern != nil {
-				settings.RewriteRequestBody = append(settings.RewriteRequestBody, chain.HTTPBodyRewriteSettings{
-					Type:        v.Type,
-					Pattern:     pattern,
-					Replacement: []byte(v.Replacement),
-				})
-			}
-		}
+		settings.RewriteResponseBody = append(settings.RewriteResponseBody, parseBodyRewrites(cfg.HTTP.RewriteBody, log)...)
+		settings.RewriteResponseBody = append(settings.RewriteResponseBody, parseBodyRewrites(cfg.HTTP.RewriteResponseBody, log)...)
+		settings.RewriteRequestBody = append(settings.RewriteRequestBody, parseBodyRewrites(cfg.HTTP.RewriteRequestBody, log)...)
 		opts = append(opts, chain.HTTPNodeOption(settings))
 	}
 

config/parsing/rewriter/parse.go

@@ -39,6 +39,7 @@ func ParseRewriter(cfg *config.RewriterConfig) rewriter.Rewriter {
 				cfg.Name, cfg.Plugin.Addr,
 				plugin.TokenOption(cfg.Plugin.Token),
 				plugin.TLSConfigOption(tlsCfg),
+				plugin.TimeoutOption(cfg.Plugin.Timeout),
 			)
 		}
 	}

config/parsing/service/parse.go

@@ -10,8 +10,8 @@ import (
 	"github.com/go-gost/core/chain"
 	"github.com/go-gost/core/handler"
 	"github.com/go-gost/core/hop"
-	"github.com/go-gost/core/rewriter"
 	"github.com/go-gost/core/listener"
+	"github.com/go-gost/core/rewriter"
 	"github.com/go-gost/core/logger"
 	"github.com/go-gost/core/observer/stats"
 	"github.com/go-gost/core/recorder"
@@ -356,6 +356,9 @@ func ParseService(cfg *config.ServiceConfig) (service.Service, error) {
 
 	var rew rewriter.Rewriter
 	if cfg.Rewriter != "" {
+		if !registry.RewriterRegistry().IsRegistered(cfg.Rewriter) {
+			serviceLogger.Warnf("rewriter %q not found in registry", cfg.Rewriter)
+		}
 		rew = registry.RewriterRegistry().Get(cfg.Rewriter)
 	}