[Lua] Avoid infinite loop when creating empty string (#6614)

* [Lua] Avoid infinite loop when creating empty string

* [Lua] Check empty string output

2 files changed, 20 insertions, 1 deletions

diff --git a/lua/flatbuffers/binaryarray.lua b/lua/flatbuffers/binaryarray.lua
index 3d16c36e..4d723753 100644
--- a/lua/flatbuffers/binaryarray.lua
+++ b/lua/flatbuffers/binaryarray.lua
@@ -50,7 +50,10 @@ function mt:Slice(startPos, endPos)
         -- updated the startPos based on the size of the
         -- value
         while startPos < endPos do
-            local v = d[startPos] or '/0'
+            local v = d[startPos]
+            if not v or v == "" then
+                v = '/0'
+            end
             table.insert(b, v)
             startPos = startPos + #v
         end
diff --git a/tests/luatest.lua b/tests/luatest.lua
index 7380d7d2..26b0a98d 100644
--- a/tests/luatest.lua
+++ b/tests/luatest.lua
@@ -222,6 +222,18 @@ local function testCanonicalData()
     checkReadBuffer(wireData)  
 end    
     
+local function testCreateEmptyString()
+    local b = flatbuffers.Builder(0)
+    local str = b:CreateString("")
+    monster.Start(b)
+    monster.AddName(b, str)
+    b:Finish(monster.End(b))
+    local s = b:Output()
+    local data = flatbuffers.binaryArray.New(s)
+    local mon = monster.GetRootAsMonster(data, 0)
+    assert(mon:Name() == "")
+end
+
 local function benchmarkMakeMonster(count, reuseBuilder)
     local fbb = reuseBuilder and flatbuffers.Builder(0)
     local length = #(generateMonster(false, fbb))
@@ -286,6 +298,10 @@ local tests =
         d = "Tests Canonical flatbuffer file included in repo"       
     },
     {
+        f = testCreateEmptyString,
+        d = "Avoid infinite loop when creating empty string"
+    },
+    {
         f = getRootAs_canAcceptString,
         d = "Tests that GetRootAs<type>() generated methods accept strings"
     },