Repository: traefik/traefik
File: pkg/plugins/middlewarewasm.go (Go)

Code before:
		middlewareName: middlewareName,
		config:         reflect.ValueOf(config),
		builder:        b,
	}, nil
}

func (b wasmMiddlewareBuilder) newHandler(ctx context.Context, next http.Handler, cfg reflect.Value, middlewareName string) (http.Handler, error) {
	h, applyCtx, err := b.buildMiddleware(ctx, next, cfg, middlewareName)
	if err != nil {
		return nil, err
	}

	return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
		h.ServeHTTP(rw, req.WithContext(applyCtx(req.Context())))
	}), nil
}

func (b *wasmMiddlewareBuilder) buildMiddleware(ctx context.Context, next http.Handler, cfg reflect.Value, middlewareName string) (http.Handler, func(ctx context.Context) context.Context, error) {
	code, err := os.ReadFile(b.path)
	if err != nil {
		return nil, nil, fmt.Errorf("loading Wasm binary: %w", err)
	}

	runtime := host.NewRuntime(wazero.NewRuntimeWithConfig(ctx, wazero.NewRuntimeConfig().WithCompilationCache(b.cache)))

	mod, err := runtime.CompileModule(ctx, code)
	if err != nil {
		return nil, nil, err
	}

	applyCtx, err := Instantiate(ctx, runtime, mod, b.settings)
	if err != nil {
		return nil, nil, err
	}

	logger := middlewares.GetLogger(ctx, middlewareName, "wasm")

	config := wazero.NewModuleConfig().WithSysWalltime()
	for _, env := range b.settings.Envs {
		config.WithEnv(env, os.Getenv(env))
	}

	if len(b.settings.Mounts) > 0 {
		fsConfig := wazero.NewFSConfig()
		for _, mount := range b.settings.Mounts {
			withDir := fsConfig.WithDirMount
			prefix, readOnly := strings.CutSuffix(mount, ":ro")
			if readOnly {
				withDir = fsConfig.WithReadOnlyDirMount
			}
			parts := strings.Split(prefix, ":")

Review comment (performance):
```suggestion
	rt := host.NewRuntime(wazero.NewRuntimeWithConfig(ctx, wazero.NewRuntimeConfig().WithCompilationCache(b.cache)))
	mod, err := rt.CompileModule(ctx, code)
```

Code after:
		middlewareName: middlewareName,
		config:         reflect.ValueOf(config),
		builder:        b,
	}, nil
}

func (b wasmMiddlewareBuilder) newHandler(ctx context.Context, next http.Handler, cfg reflect.Value, middlewareName string) (http.Handler, error) {
	h, applyCtx, err := b.buildMiddleware(ctx, next, cfg, middlewareName)
	if err != nil {
		return nil, fmt.Errorf("building Wasm middleware: %w", err)
	}

	return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
		h.ServeHTTP(rw, req.WithContext(applyCtx(req.Context())))
	}), nil
}

func (b *wasmMiddlewareBuilder) buildMiddleware(ctx context.Context, next http.Handler, cfg reflect.Value, middlewareName string) (http.Handler, func(ctx context.Context) context.Context, error) {
	code, err := os.ReadFile(b.path)
	if err != nil {
		return nil, nil, fmt.Errorf("loading binary: %w", err)
	}

	rt := host.NewRuntime(wazero.NewRuntimeWithConfig(ctx, wazero.NewRuntimeConfig().WithCompilationCache(b.cache)))

	guestModule, err := rt.CompileModule(ctx, code)
	if err != nil {
		return nil, nil, fmt.Errorf("compiling guest module: %w", err)
	}

	applyCtx, err := InstantiateHost(ctx, rt, guestModule, b.settings)
	if err != nil {
		return nil, nil, fmt.Errorf("instantiating host module: %w", err)
	}

	logger := middlewares.GetLogger(ctx, middlewareName, "wasm")

	config := wazero.NewModuleConfig().WithSysWalltime()
	for _, env := range b.settings.Envs {
		config.WithEnv(env, os.Getenv(env))
	}

	if len(b.settings.Mounts) > 0 {
		fsConfig := wazero.NewFSConfig()
		for _, mount := range b.settings.Mounts {
			withDir := fsConfig.WithDirMount
			prefix, readOnly := strings.CutSuffix(mount, ":ro")
			if readOnly {
				withDir = fsConfig.WithReadOnlyDirMount
			}
			parts := strings.Split(prefix, ":")