config: add rewrite_response_headers option (#1961)

* add lua script to rewrite response headers

* add policy config

* update docs

internal/controlplane/xds_lua_test.go

@@ -0,0 +1,166 @@
+package controlplane
+
+import (
+	"encoding/json"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	lua "github.com/yuin/gopher-lua"
+)
+
+func TestLuaRewriteHeaders(t *testing.T) {
+	L := lua.NewState()
+	defer L.Close()
+
+	bs, err := luaFS.ReadFile("luascripts/rewrite-headers.lua")
+	require.NoError(t, err)
+
+	err = L.DoString(string(bs))
+	require.NoError(t, err)
+
+	headers := map[string]string{
+		"Location": "https://localhost:8080/two/some/uri/",
+	}
+	metadata := map[string]interface{}{
+		"rewrite_response_headers": []interface{}{
+			map[string]interface{}{
+				"header": "Location",
+				"prefix": "https://localhost:8080/two/",
+				"value":  "https://frontend/one/",
+			},
+			map[string]interface{}{
+				"header": "SomeOtherHeader",
+				"prefix": "x",
+				"value":  "y",
+			},
+		},
+	}
+	handle := newLuaResponseHandle(L, headers, metadata)
+
+	err = L.CallByParam(lua.P{
+		Fn:      L.GetGlobal("envoy_on_response"),
+		NRet:    0,
+		Protect: true,
+	}, handle)
+	require.NoError(t, err)
+
+	assert.Equal(t, "https://frontend/one/some/uri/", headers["Location"])
+}
+
+func newLuaResponseHandle(L *lua.LState, headers map[string]string, metadata map[string]interface{}) lua.LValue {
+	typ := L.NewTable()
+	L.SetFuncs(typ, map[string]lua.LGFunction{
+		"headers": func(L *lua.LState) int {
+			L.Push(newLuaHeaders(L, headers))
+			return 1
+		},
+		"metadata": func(L *lua.LState) int {
+			L.Push(newLuaMetadata(L, metadata))
+			return 1
+		},
+	})
+	L.SetField(typ, "__index", typ)
+
+	tbl := L.NewTable()
+	L.SetMetatable(tbl, typ)
+	return tbl
+}
+
+func newLuaHeaders(L *lua.LState, headers map[string]string) lua.LValue {
+	typ := L.NewTable()
+	L.SetFuncs(typ, map[string]lua.LGFunction{
+		"get": func(L *lua.LState) int {
+			_ = L.CheckTable(1)
+			key := L.CheckString(2)
+
+			str, ok := headers[key]
+			if !ok {
+				L.Push(lua.LNil)
+				return 0
+			}
+
+			L.Push(lua.LString(str))
+			return 1
+		},
+		"replace": func(L *lua.LState) int {
+			_ = L.CheckTable(1)
+			key := L.CheckString(2)
+			value := L.CheckString(3)
+
+			headers[key] = value
+
+			return 0
+		},
+	})
+	L.SetField(typ, "__index", typ)
+
+	tbl := L.NewTable()
+	L.SetMetatable(tbl, typ)
+	return tbl
+}
+
+func newLuaMetadata(L *lua.LState, metadata map[string]interface{}) lua.LValue {
+	typ := L.NewTable()
+	L.SetFuncs(typ, map[string]lua.LGFunction{
+		"get": func(L *lua.LState) int {
+			_ = L.CheckTable(1)
+			key := L.CheckString(2)
+
+			obj, ok := metadata[key]
+			if !ok {
+				L.Push(lua.LNil)
+				return 0
+			}
+
+			L.Push(toLua(L, obj))
+			return 1
+		},
+	})
+	L.SetField(typ, "__index", typ)
+
+	tbl := L.NewTable()
+	L.SetMetatable(tbl, typ)
+	return tbl
+}
+
+func toLua(L *lua.LState, obj interface{}) lua.LValue {
+	// send the object through JSON to remove custom types
+	var normalized interface{}
+	bs, err := json.Marshal(obj)
+	if err != nil {
+		panic(err)
+	}
+	err = json.Unmarshal(bs, &normalized)
+	if err != nil {
+		panic(err)
+	}
+
+	if normalized == nil {
+		return lua.LNil
+	}
+
+	switch t := normalized.(type) {
+	case []interface{}:
+		tbl := L.NewTable()
+		for _, v := range t {
+			tbl.Append(toLua(L, v))
+		}
+		return tbl
+	case map[string]interface{}:
+		tbl := L.NewTable()
+		for k, v := range t {
+			L.SetField(tbl, k, toLua(L, v))
+		}
+		return tbl
+	case bool:
+		return lua.LBool(t)
+	case float64:
+		return lua.LNumber(t)
+	case string:
+		return lua.LString(t)
+	default:
+		panic(fmt.Sprintf("%T not supported for toLua", obj))
+	}
+}