allow removing default WebRTC ICE server with environment variables (#2064)

internal/conf/env/env.go

@@ -150,7 +150,7 @@ func loadEnvInternal(env map[string]string, prefix string, rv reflect.Value) err
 		if rt.Elem() == reflect.TypeOf("") {
 			if ev, ok := env[prefix]; ok {
 				if ev == "" {
-					rv.Set(reflect.ValueOf([]string{}))
+					rv.Set(reflect.MakeSlice(rv.Type(), 0, 0))
 				} else {
 					rv.Set(reflect.ValueOf(strings.Split(ev, ",")))
 				}
@@ -159,19 +159,23 @@ func loadEnvInternal(env map[string]string, prefix string, rv reflect.Value) err
 		}
 
 		if rt.Elem().Kind() == reflect.Struct {
-			for i := 0; ; i++ {
-				itemPrefix := prefix + "_" + strconv.FormatInt(int64(i), 10)
-				if !envHasAtLeastAKeyWithPrefix(env, itemPrefix) {
-					break
-				}
+			if ev, ok := env[prefix]; ok && ev == "" { // special case: empty list
+				rv.Set(reflect.MakeSlice(rv.Type(), 0, 0))
+			} else {
+				for i := 0; ; i++ {
+					itemPrefix := prefix + "_" + strconv.FormatInt(int64(i), 10)
+					if !envHasAtLeastAKeyWithPrefix(env, itemPrefix) {
+						break
+					}
 
-				elem := reflect.New(rt.Elem())
-				err := loadEnvInternal(env, itemPrefix, elem.Elem())
-				if err != nil {
-					return err
-				}
+					elem := reflect.New(rt.Elem())
+					err := loadEnvInternal(env, itemPrefix, elem.Elem())
+					if err != nil {
+						return err
+					}
 
-				rv.Set(reflect.Append(rv, elem.Elem()))
+					rv.Set(reflect.Append(rv, elem.Elem()))
+				}
 			}
 			return nil
 		}

internal/conf/env/env_test.go

@@ -47,15 +47,16 @@ type mySubStruct struct {
 }
 
 type testStruct struct {
-	MyString         string
-	MyInt            int
-	MyFloat          float64
-	MyBool           bool
-	MyDuration       myDuration
-	MyMap            map[string]*mapEntry
-	MySlice          []string
-	MySliceEmpty     []string
-	MySliceSubStruct []mySubStruct
+	MyString              string
+	MyInt                 int
+	MyFloat               float64
+	MyBool                bool
+	MyDuration            myDuration
+	MyMap                 map[string]*mapEntry
+	MySlice               []string
+	MySliceEmpty          []string
+	MySliceSubStruct      []mySubStruct
+	MySliceSubStructEmpty []mySubStruct
 }
 
 func TestLoad(t *testing.T) {
@@ -104,6 +105,9 @@ func TestLoad(t *testing.T) {
 	os.Setenv("MYPREFIX_MYSLICESUBSTRUCT_1_PASSWORD", "pass2")
 	defer os.Unsetenv("MYPREFIX_MYSLICESUBSTRUCT_1_PASSWORD")
 
+	os.Setenv("MYPREFIX_MYSLICESUBSTRUCTEMPTY", "")
+	defer os.Unsetenv("MYPREFIX_MYSLICESUBSTRUCTEMPTY")
+
 	var s testStruct
 	err := Load("MYPREFIX", &s)
 	require.NoError(t, err)
@@ -136,4 +140,6 @@ func TestLoad(t *testing.T) {
 			Password: "pass2",
 		},
 	}, s.MySliceSubStruct)
+
+	require.Equal(t, []mySubStruct{}, s.MySliceSubStructEmpty)
 }