src/lundump.js: Fix reading empty string constants

Closes https://github.com/fengari-lua/fengari-interop/issues/42

2 files changed, 23 insertions, 9 deletions

diff --git a/src/lundump.js b/src/lundump.js
index cf3fafa..2213015 100644
--- a/src/lundump.js
+++ b/src/lundump.js
@@ -108,16 +108,12 @@ class BytecodeParser {
     }
 
     readString() {
-        let size = Math.max(this.readByte() - 1, 0);
-
-        if (size + 1 === 0xFF)
-            size = this.readSize_t() - 1;
-
-        if (size === 0) {
+        let size = this.readByte();
+        if (size === 0xFF)
+            size = this.readSize_t();
+        if (size === 0)
             return null;
-        }
-
-        return luaS_bless(this.L, this.read(size));
+        return luaS_bless(this.L, this.read(size-1));
     }
 
     /* creates a mask with 'n' 1 bits at position 'p' */
diff --git a/test/load.test.js b/test/load.test.js
index 3c03eec..d778155 100644
--- a/test/load.test.js
+++ b/test/load.test.js
@@ -43,6 +43,24 @@ test('load', () => {
 });
 
 
+test('undump empty string', () => {
+    let L = lauxlib.luaL_newstate();
+    if (!L) throw Error("failed to create lua state");
+
+    let luaCode = `
+        assert(load(string.dump(function()
+			local str = ""
+			return #str -- something that inspects the string
+        end)))()
+    `;
+    {
+        lualib.luaL_openlibs(L);
+        expect(lauxlib.luaL_loadstring(L, to_luastring(luaCode))).toBe(lua.LUA_OK);
+        lua.lua_call(L, 0, 0);
+    }
+});
+
+
 test('luaL_loadbuffer', () => {
     let L = lauxlib.luaL_newstate();
     if (!L) throw Error("failed to create lua state");