Export env to JS scripts

README.md

@@ -385,6 +385,10 @@ Following builtin functions are addionally available within JS scripts:
 * `print(val)` - print arbitrary values *val* into dumbproxy log for debugging purposes.
 * `readFile(path: string): string` - read file from *path* and return its content as a string.
 
+Following objects are additionally available in global scope of JS scripts:
+
+* `env` - readonly object containing all environment variables.
+
 ## Supported upstream proxy schemes
 
 Supported proxy schemes are:

access/jsfilter.go

@@ -37,11 +37,11 @@ func NewJSFilter(filename string, instances int, logger *clog.CondLogger, next F
 		vm := goja.New()
 		err = jsext.AddPrinter(vm, logger)
 		if err != nil {
-			return nil, errors.New("can't add print function to runtime")
+			return nil, fmt.Errorf("can't add print function to runtime: %w", err)
 		}
-		err = jsext.AddFileReader(vm)
+		err = jsext.ConfigureRuntime(vm)
 		if err != nil {
-			return nil, errors.New("can't add file reader function to runtime")
+			return nil, fmt.Errorf("can't configure runtime: %w", err)
 		}
 		vm.SetFieldNameMapper(goja.TagFieldNameMapper("json", true))
 		_, err = vm.RunString(string(script))

dialer/jsrouter.go

@@ -35,11 +35,11 @@ func NewJSRouter(filename string, instances int, factory func(string) (Dialer, e
 		vm := goja.New()
 		err := jsext.AddPrinter(vm, logger)
 		if err != nil {
-			return nil, errors.New("can't add print function to runtime")
+			return nil, fmt.Errorf("can't add print function to runtime: %w", err)
 		}
-		err = jsext.AddFileReader(vm)
+		err = jsext.ConfigureRuntime(vm)
 		if err != nil {
-			return nil, errors.New("can't add file reader function to runtime")
+			return nil, fmt.Errorf("can't configure runtime runtime: %w", err)
 		}
 		vm.SetFieldNameMapper(goja.TagFieldNameMapper("json", true))
 		_, err = vm.RunString(string(script))

jsext/env.go

@@ -0,0 +1,74 @@
+package jsext
+
+import (
+	"os"
+	"slices"
+	"strings"
+	"sync"
+
+	"github.com/dop251/goja"
+)
+
+var (
+	createEnvObjectOnce sync.Once
+	envObject           *goja.Object
+)
+
+type readonlyEnvObject struct {
+	m map[string]goja.String
+	k []string
+}
+
+func (o *readonlyEnvObject) Get(key string) goja.Value {
+	v, ok := o.m[key]
+	if ok {
+		return v
+	}
+	return goja.Undefined()
+}
+
+func (o *readonlyEnvObject) Set(_ string, _ goja.Value) bool {
+	return false
+}
+
+func (o *readonlyEnvObject) Has(key string) bool {
+	_, ok := o.m[key]
+	return ok
+}
+
+func (o *readonlyEnvObject) Delete(key string) bool {
+	return false
+}
+
+func (o *readonlyEnvObject) Keys() []string {
+	return o.k
+}
+
+func createEnvObject() *goja.Object {
+	env := os.Environ()
+	m := make(map[string]goja.String, len(env))
+	k := make([]string, 0, len(env))
+	for _, pair := range env {
+		key, value, _ := strings.Cut(pair, "=")
+		sb := new(goja.StringBuilder)
+		sb.WriteUTF8String(value)
+		m[key] = sb.String()
+		k = append(k, key)
+	}
+	slices.Sort(k)
+	return goja.NewSharedDynamicObject(&readonlyEnvObject{
+		m: m,
+		k: k,
+	})
+}
+
+func GetEnvSharedDynamicObject() *goja.Object {
+	createEnvObjectOnce.Do(func() {
+		envObject = createEnvObject()
+	})
+	return envObject
+}
+
+func ExportEnv(vm *goja.Runtime) error {
+	return vm.Set("env", GetEnvSharedDynamicObject())
+}

jsext/jsext.go

@@ -0,0 +1,13 @@
+package jsext
+
+import "github.com/dop251/goja"
+
+func ConfigureRuntime(vm *goja.Runtime) error {
+	if err := AddFileReader(vm); err != nil {
+		return err
+	}
+	if err := ExportEnv(vm); err != nil {
+		return err
+	}
+	return nil
+}