feat(rewriter): implement plugin-based Rewriter module with gRPC and HTTP backends

Add the first implementation of core/rewriter.Rewriter as a plugin-only
component following the bypass/admission pattern (single-value, no
RewriterObject). Includes:

- plugin/rewriter/proto/: protobuf definition with Rewrite RPC returning
  transformed data in the reply
- x/rewriter/plugin/: gRPC and HTTP plugin clients
- x/registry/rewriter.go: hot-reload-safe RewriterRegistry with wrapper
- x/config/config.go: RewriterConfig, Config.Rewriters, ServiceConfig.Rewriter
- x/config/parsing/rewriter/parse.go: config parser (plugin backends only)
- core/handler/option.go: Rewriter field + RewriterOption on handler.Options
- x/config/loader/loader.go: rewriter registration during startup
- x/config/parsing/service/parse.go: inject rewriter into handler options

config/config.go

@@ -316,6 +316,11 @@ type RecorderObject struct {
 	Metadata map[string]any `yaml:",omitempty" json:"metadata,omitempty"`
 }
 
+type RewriterConfig struct {
+	Name   string        `json:"name"`
+	Plugin *PluginConfig `yaml:",omitempty" json:"plugin,omitempty"`
+}
+
 type LimiterConfig struct {
 	Name   string        `json:"name"`
 	Limits []string      `yaml:",omitempty" json:"limits,omitempty"`
@@ -487,8 +492,9 @@ type ServiceConfig struct {
 	Logger     string            `yaml:",omitempty" json:"logger,omitempty"`
 	Loggers    []string          `yaml:",omitempty" json:"loggers,omitempty"`
 	Observer   string            `yaml:",omitempty" json:"observer,omitempty"`
-	Recorders  []*RecorderObject `yaml:",omitempty" json:"recorders,omitempty"`
+	Rewriter  string            `yaml:",omitempty" json:"rewriter,omitempty"`
-	Handler    *HandlerConfig    `yaml:",omitempty" json:"handler,omitempty"`
+	Recorders []*RecorderObject `yaml:",omitempty" json:"recorders,omitempty"`
+	Handler   *HandlerConfig    `yaml:",omitempty" json:"handler,omitempty"`
 	Listener   *ListenerConfig   `yaml:",omitempty" json:"listener,omitempty"`
 	Forwarder  *ForwarderConfig  `yaml:",omitempty" json:"forwarder,omitempty"`
 	Metadata   map[string]any    `yaml:",omitempty" json:"metadata,omitempty"`
@@ -637,6 +643,7 @@ type Config struct {
 	Routers    []*RouterConfig    `yaml:",omitempty" json:"routers,omitempty"`
 	SDs        []*SDConfig        `yaml:"sds,omitempty" json:"sds,omitempty"`
 	Recorders  []*RecorderConfig  `yaml:",omitempty" json:"recorders,omitempty"`
+	Rewriters  []*RewriterConfig  `yaml:",omitempty" json:"rewriters,omitempty"`
 	Limiters   []*LimiterConfig   `yaml:",omitempty" json:"limiters,omitempty"`
 	Quotas     []*QuotaConfig     `yaml:",omitempty" json:"quotas,omitempty"`
 	CLimiters  []*LimiterConfig   `yaml:"climiters,omitempty" json:"climiters,omitempty"`

config/loader/loader.go

@@ -22,6 +22,7 @@ import (
 	reg "github.com/go-gost/core/registry"
 	"github.com/go-gost/core/resolver"
 	"github.com/go-gost/core/router"
+	"github.com/go-gost/core/rewriter"
 	"github.com/go-gost/core/sd"
 	"github.com/go-gost/x/config"
 	"github.com/go-gost/x/config/parsing"
@@ -38,6 +39,7 @@ import (
 	quota_parser "github.com/go-gost/x/config/parsing/quota"
 	recorder_parser "github.com/go-gost/x/config/parsing/recorder"
 	resolver_parser "github.com/go-gost/x/config/parsing/resolver"
+	rewriter_parser "github.com/go-gost/x/config/parsing/rewriter"
 	router_parser "github.com/go-gost/x/config/parsing/router"
 	sd_parser "github.com/go-gost/x/config/parsing/sd"
 	service_parser "github.com/go-gost/x/config/parsing/service"
@@ -244,6 +246,16 @@ func register(cfg *config.Config) error {
 		}
 	}
 
+	{
+		var entries []named[rewriter.Rewriter]
+		for _, c := range cfg.Rewriters {
+			entries = append(entries, named[rewriter.Rewriter]{c.Name, rewriter_parser.ParseRewriter(c)})
+		}
+		if err := registerGroup(entries, registry.RewriterRegistry()); err != nil {
+			return err
+		}
+	}
+
 	{
 		var entries []named[traffic.TrafficLimiter]
 		for _, c := range cfg.Limiters {

config/parsing/rewriter/parse.go

@@ -0,0 +1,47 @@
+package rewriter
+
+import (
+	"crypto/tls"
+	"strings"
+
+	"github.com/go-gost/core/rewriter"
+	"github.com/go-gost/x/config"
+	"github.com/go-gost/x/internal/plugin"
+	rewriter_plugin "github.com/go-gost/x/rewriter/plugin"
+)
+
+// ParseRewriter converts a RewriterConfig into a rewriter.Rewriter.
+// It currently supports plugin backends only (HTTP or gRPC).
+// Returns nil when cfg is nil or no backend is configured.
+func ParseRewriter(cfg *config.RewriterConfig) rewriter.Rewriter {
+	if cfg == nil {
+		return nil
+	}
+
+	if cfg.Plugin != nil {
+		var tlsCfg *tls.Config
+		if cfg.Plugin.TLS != nil {
+			tlsCfg = &tls.Config{
+				ServerName:         cfg.Plugin.TLS.ServerName,
+				InsecureSkipVerify: !cfg.Plugin.TLS.Secure,
+			}
+		}
+		switch strings.ToLower(cfg.Plugin.Type) {
+		case "http":
+			return rewriter_plugin.NewHTTPPlugin(
+				cfg.Name, cfg.Plugin.Addr,
+				plugin.TokenOption(cfg.Plugin.Token),
+				plugin.TLSConfigOption(tlsCfg),
+				plugin.TimeoutOption(cfg.Plugin.Timeout),
+			)
+		default:
+			return rewriter_plugin.NewGRPCPlugin(
+				cfg.Name, cfg.Plugin.Addr,
+				plugin.TokenOption(cfg.Plugin.Token),
+				plugin.TLSConfigOption(tlsCfg),
+			)
+		}
+	}
+
+	return nil
+}

config/parsing/service/parse.go

@@ -10,6 +10,7 @@ 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/logger"
 	"github.com/go-gost/core/observer/stats"
@@ -353,6 +354,11 @@ func ParseService(cfg *config.ServiceConfig) (service.Service, error) {
 		})
 	}
 
+	var rew rewriter.Rewriter
+	if cfg.Rewriter != "" {
+		rew = registry.RewriterRegistry().Get(cfg.Rewriter)
+	}
+
 	routerOpts = []chain.RouterOption{
 		chain.RetriesRouterOption(cfg.Handler.Retries),
 		chain.TimeoutRouterOption(dialTimeout),
@@ -382,6 +388,7 @@ func ParseService(cfg *config.ServiceConfig) (service.Service, error) {
 			handler.TrafficLimiterOption(registry.TrafficLimiterRegistry().Get(cfg.Handler.Limiter)),
 			handler.ObserverOption(registry.ObserverRegistry().Get(cfg.Handler.Observer)),
 			handler.RecordersOption(recorders...),
+			handler.RewriterOption(rew),
 			handler.LoggerOption(handlerLogger),
 			handler.ServiceOption(cfg.Name),
 			handler.NetnsOption(netnsIn),

go.mod

@@ -7,11 +7,11 @@ require (
 	github.com/asaskevich/govalidator v0.0.0-20210307081110-f21760c49a8d
 	github.com/gin-contrib/cors v1.7.2
 	github.com/gin-gonic/gin v1.10.1
-	github.com/go-gost/core v0.4.3
+	github.com/go-gost/core v0.5.0
 	github.com/go-gost/go-shadowsocks2 v0.1.3
 	github.com/go-gost/gosocks4 v0.1.0
 	github.com/go-gost/gosocks5 v0.5.0
-	github.com/go-gost/plugin v0.3.0
+	github.com/go-gost/plugin v0.4.0
 	github.com/go-gost/relay v0.6.1
 	github.com/go-gost/tls-dissector v0.2.0
 	github.com/go-redis/redis/v8 v8.11.5

go.sum

@@ -51,16 +51,16 @@ github.com/gin-contrib/sse v0.1.0 h1:Y/yl/+YNO8GZSjAhjMsSuLt29uWRFHdHYUb5lYOV9qE
 github.com/gin-contrib/sse v0.1.0/go.mod h1:RHrZQHXnP2xjPF+u1gW/2HnVO7nvIa9PG3Gm+fLHvGI=
 github.com/gin-gonic/gin v1.10.1 h1:T0ujvqyCSqRopADpgPgiTT63DUQVSfojyME59Ei63pQ=
 github.com/gin-gonic/gin v1.10.1/go.mod h1:4PMNQiOhvDRa013RKVbsiNwoyezlm2rm0uX/T7kzp5Y=
-github.com/go-gost/core v0.4.3 h1:9VEHRzuSq/MVdDZYrp/TtVG0+0r6NVGUQDXsJozrvJs=
+github.com/go-gost/core v0.5.0 h1:3SkPojjqw2Av9l5OSyRVlBpRvWhaXgU5BWMXB9aR4SM=
-github.com/go-gost/core v0.4.3/go.mod h1:WGI43jOka7FAsSAwi/fSMaqxdR+E339ycb4NBGlFr6A=
+github.com/go-gost/core v0.5.0/go.mod h1:WGI43jOka7FAsSAwi/fSMaqxdR+E339ycb4NBGlFr6A=
 github.com/go-gost/go-shadowsocks2 v0.1.3 h1:6CUZLp+mTWXnKP2aK8/Z9ZP+ERMX9gSbywmPu4kGX/A=
 github.com/go-gost/go-shadowsocks2 v0.1.3/go.mod h1:866zFNNI3He6Wef1M/IvAjTal74WhcfKfBgRpTlkKys=
 github.com/go-gost/gosocks4 v0.1.0 h1:eAzev6qw4fzkFQKC9uCHLVNnnPdHyqCggbnfNN80Pmk=
 github.com/go-gost/gosocks4 v0.1.0/go.mod h1:hzVjwijJuZR1pp3GqpTj+AKcSGrx68RlWTrQMFMYBP0=
 github.com/go-gost/gosocks5 v0.5.0 h1:YE37l1MJwde8diIQdynStqogMotG5enoTdborhA5yic=
 github.com/go-gost/gosocks5 v0.5.0/go.mod h1:1G6I7HP7VFVxveGkoK8mnprnJqSqJjdcASKsdUn4Pp4=
-github.com/go-gost/plugin v0.3.0 h1:pmll8nNd9PX92BWMB5+b2y2SEkBAWJLxD2ANfX+WHuw=
+github.com/go-gost/plugin v0.4.0 h1:M7MR5PL7QAFCrdWfcXVX+5iLNTVIZlhl8FfdV/K8dZY=
-github.com/go-gost/plugin v0.3.0/go.mod h1:oN23l+yGDCIP9G3KnDl/I/0zVGOobZUDCB2Z5yYYXts=
+github.com/go-gost/plugin v0.4.0/go.mod h1:oN23l+yGDCIP9G3KnDl/I/0zVGOobZUDCB2Z5yYYXts=
 github.com/go-gost/relay v0.6.1 h1:7SqnHFbY8x/DzvjpK03a5zcVH9+TbJAcnW/RT6s1ecc=
 github.com/go-gost/relay v0.6.1/go.mod h1:Dku0f5sfjOClrZFiDmQUrYYJ4uof7rnkCUBfsl0PSAI=
 github.com/go-gost/tls-dissector v0.2.0 h1:9tE6WOzzpurATTBWn60DU4R8gibpGNY8/qVcc1SicVg=

registry/registry.go

@@ -21,6 +21,7 @@ import (
 	reg "github.com/go-gost/core/registry"
 	"github.com/go-gost/core/resolver"
 	"github.com/go-gost/core/router"
+	"github.com/go-gost/core/rewriter"
 	"github.com/go-gost/core/sd"
 	"github.com/go-gost/core/service"
 	"github.com/go-gost/x/limiter/quota"
@@ -46,6 +47,7 @@ var (
 	resolverReg  reg.Registry[resolver.Resolver]   = new(resolverRegistry)
 	hostsReg     reg.Registry[hosts.HostMapper]    = new(hostsRegistry)
 	recorderReg  reg.Registry[recorder.Recorder]   = new(recorderRegistry)
+	rewriterReg  reg.Registry[rewriter.Rewriter]   = new(rewriterRegistry)
 
 	trafficLimiterReg reg.Registry[traffic.TrafficLimiter] = new(trafficLimiterRegistry)
 	connLimiterReg    reg.Registry[conn.ConnLimiter]       = new(connLimiterRegistry)
@@ -187,6 +189,11 @@ func RecorderRegistry() reg.Registry[recorder.Recorder] {
 	return recorderReg
 }
 
+// RewriterRegistry returns the global registry of rewriter instances.
+func RewriterRegistry() reg.Registry[rewriter.Rewriter] {
+	return rewriterReg
+}
+
 // TrafficLimiterRegistry returns the global registry of traffic limiter instances.
 func TrafficLimiterRegistry() reg.Registry[traffic.TrafficLimiter] {
 	return trafficLimiterReg

registry/rewriter.go

@@ -0,0 +1,43 @@
+package registry
+
+import (
+	"context"
+
+	"github.com/go-gost/core/rewriter"
+)
+
+// rewriterRegistry implements a hot-reload-safe registry for rewriter.Rewriter.
+type rewriterRegistry struct {
+	registry[rewriter.Rewriter]
+}
+
+// Register stores a Rewriter under the given name.
+func (r *rewriterRegistry) Register(name string, v rewriter.Rewriter) error {
+	return r.registry.Register(name, v)
+}
+
+// Get returns a wrapper that delegates to the currently registered Rewriter.
+// Returns nil if name is empty.
+func (r *rewriterRegistry) Get(name string) rewriter.Rewriter {
+	if name != "" {
+		return &rewriterWrapper{name: name, r: r}
+	}
+	return nil
+}
+
+func (r *rewriterRegistry) get(name string) rewriter.Rewriter {
+	return r.registry.Get(name)
+}
+
+type rewriterWrapper struct {
+	name string
+	r    *rewriterRegistry
+}
+
+func (w *rewriterWrapper) Rewrite(ctx context.Context, b []byte, opts ...rewriter.RewriteOption) ([]byte, error) {
+	v := w.r.get(w.name)
+	if v == nil {
+		return b, nil
+	}
+	return v.Rewrite(ctx, b, opts...)
+}

rewriter/plugin/grpc.go

@@ -0,0 +1,89 @@
+package rewriter
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+
+	"github.com/go-gost/core/logger"
+	"github.com/go-gost/core/rewriter"
+	"github.com/go-gost/plugin/rewriter/proto"
+	"github.com/go-gost/x/internal/plugin"
+	"google.golang.org/grpc"
+)
+
+type grpcPlugin struct {
+	conn   grpc.ClientConnInterface
+	client proto.RewriterClient
+	log    logger.Logger
+}
+
+// NewGRPCPlugin creates a Rewriter plugin based on gRPC.
+func NewGRPCPlugin(name string, addr string, opts ...plugin.Option) rewriter.Rewriter {
+	var options plugin.Options
+	for _, opt := range opts {
+		opt(&options)
+	}
+
+	log := logger.Default().WithFields(map[string]any{
+		"kind":     "rewriter",
+		"rewriter": name,
+	})
+	conn, err := plugin.NewGRPCConn(addr, &options)
+	if err != nil {
+		log.Error(err)
+	}
+
+	p := &grpcPlugin{
+		conn: conn,
+		log:  log,
+	}
+	if conn != nil {
+		p.client = proto.NewRewriterClient(conn)
+	}
+	return p
+}
+
+func (p *grpcPlugin) Rewrite(ctx context.Context, b []byte, opts ...rewriter.RewriteOption) ([]byte, error) {
+	if p.client == nil {
+		return b, nil
+	}
+
+	var options rewriter.RewriteOptions
+	for _, opt := range opts {
+		opt(&options)
+	}
+
+	md, err := json.Marshal(options.Metadata)
+	if err != nil {
+		return b, err
+	}
+
+	reply, err := p.client.Rewrite(ctx,
+		&proto.RewriteRequest{
+			Data:     b,
+			Metadata: md,
+		})
+	if err != nil {
+		p.log.Error(err)
+		return b, err
+	}
+	if reply == nil || !reply.Ok {
+		return b, nil
+	}
+	if reply.Data != nil {
+		return reply.Data, nil
+	}
+	return b, nil
+}
+
+func (p *grpcPlugin) Close() error {
+	if p.conn == nil {
+		return nil
+	}
+
+	if closer, ok := p.conn.(io.Closer); ok {
+		return closer.Close()
+	}
+	return nil
+}

rewriter/plugin/http.go

@@ -0,0 +1,104 @@
+package rewriter
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"net/http"
+
+	"github.com/go-gost/core/logger"
+	"github.com/go-gost/core/rewriter"
+	"github.com/go-gost/x/internal/plugin"
+)
+
+type httpPluginRequest struct {
+	Data     []byte `json:"data"`
+	Metadata []byte `json:"metadata"`
+}
+
+type httpPluginResponse struct {
+	OK   bool   `json:"ok"`
+	Data []byte `json:"data"`
+}
+
+type httpPlugin struct {
+	url    string
+	client *http.Client
+	header http.Header
+	log    logger.Logger
+}
+
+// NewHTTPPlugin creates a Rewriter plugin based on HTTP.
+func NewHTTPPlugin(name string, url string, opts ...plugin.Option) rewriter.Rewriter {
+	var options plugin.Options
+	for _, opt := range opts {
+		opt(&options)
+	}
+
+	return &httpPlugin{
+		url:    url,
+		client: plugin.NewHTTPClient(&options),
+		header: options.Header,
+		log: logger.Default().WithFields(map[string]any{
+			"kind":     "rewriter",
+			"rewriter": name,
+		}),
+	}
+}
+
+func (p *httpPlugin) Rewrite(ctx context.Context, b []byte, opts ...rewriter.RewriteOption) ([]byte, error) {
+	if p.client == nil {
+		return b, nil
+	}
+
+	var options rewriter.RewriteOptions
+	for _, opt := range opts {
+		opt(&options)
+	}
+
+	md, err := json.Marshal(options.Metadata)
+	if err != nil {
+		return b, err
+	}
+
+	rb := httpPluginRequest{
+		Data:     b,
+		Metadata: md,
+	}
+	v, err := json.Marshal(&rb)
+	if err != nil {
+		return b, err
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, p.url, bytes.NewReader(v))
+	if err != nil {
+		return b, err
+	}
+
+	if p.header != nil {
+		req.Header = p.header.Clone()
+	}
+	req.Header.Set("Content-Type", "application/json")
+	resp, err := p.client.Do(req)
+	if err != nil {
+		return b, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return b, nil
+	}
+
+	res := httpPluginResponse{}
+	if err := json.NewDecoder(resp.Body).Decode(&res); err != nil {
+		return b, err
+	}
+
+	if !res.OK {
+		return b, nil
+	}
+	if res.Data != nil {
+		return res.Data, nil
+	}
+	return b, nil
+}