Support nil in table / null in array

json.lua

@@ -55,6 +55,9 @@ local function encode_nil(val)
   return "null"
 end
 
+local function encode_string(val)
+  return '"' .. val:gsub('[%z\1-\31\\"]', escape_char) .. '"'
+end
 
 local function encode_table(val, stack)
   local res = {}
@@ -65,44 +68,48 @@ local function encode_table(val, stack)
 
   stack[val] = true
 
-  if rawget(val, 1) ~= nil or next(val) == nil then
-    -- Treat as array -- check keys are valid and it is not sparse
-    local n = 0
+  if next(val) == nil then
+    return '[]'
+  end
+
+  local types = {}
+
+  for k in pairs(val) do
+    types[type(k)] = true
+  end
+
+  if #types > 1 then
+    error("invalid table: mixed or invalid key types")
+  elseif types["number"] then
+    -- Treat as array
+    local max_key = 0
     for k in pairs(val) do
-      if type(k) ~= "number" then
-        error("invalid table: mixed or invalid key types")
+      if k > max_key then
+        max_key = k
       end
-      n = n + 1
-    end
-    if n ~= #val then
-      error("invalid table: sparse array")
     end
-    -- Encode
-    for i, v in ipairs(val) do
-      table.insert(res, encode(v, stack))
+    for i = 1, max_key do
+      if val[i] == nil then
+        table.insert(res, "null")
+      else
+        local v = encode(val[i], stack)
+        table.insert(res, v)
+      end
     end
     stack[val] = nil
     return "[" .. table.concat(res, ",") .. "]"
-
-  else
-    -- Treat as an object
+  elseif types["string"] then
+    -- Treat as object
     for k, v in pairs(val) do
-      if type(k) ~= "string" then
-        error("invalid table: mixed or invalid key types")
-      end
-      table.insert(res, encode(k, stack) .. ":" .. encode(v, stack))
+      table.insert(res, encode_string(k) .. ":" .. encode(v, stack))
     end
     stack[val] = nil
     return "{" .. table.concat(res, ",") .. "}"
+  else
+    error( string.format("invalid table: unsupported key type %s", types[1]) )
   end
 end
 
-
-local function encode_string(val)
-  return '"' .. val:gsub('[%z\1-\31\\"]', escape_char) .. '"'
-end
-
-
 local function encode_number(val)
   -- Check for NaN, -inf and inf
   if val ~= val or val <= -math.huge or val >= math.huge then

test/test.lua

@@ -91,12 +91,37 @@ test("arrays", function()
 end)
 
 
+test("arrays with nil / null", function()
+  local t = {
+    { [1000] = "b" },
+    { nil, 2, 3, 4 },
+    { nil, "test" },
+    { [1] = "a", [3] = "b" },
+  }
+  for i, v in ipairs(t) do
+    assert( equal( v, json.decode( json.encode(v) ) ) )
+  end
+end)
+
+
 test("objects", function()
   local t = { x = 10, y = 20, z = 30 }
   assert( equal( t, json.decode( json.encode(t) ) ) )
 end)
 
 
+test("encode empty", function()
+  local t = {
+    [ '[]' ] = {},
+    [ '""' ] = "",
+  }
+  for k, v in pairs(t) do
+    local res = json.encode(v)
+    assert( equal(res, k), fmt("'%s' did not equal expected %s", res, k) )
+  end
+end)
+
+
 --test("strict decode", function()
 --  local t = {
 --    '{x : 1}',
@@ -203,11 +228,8 @@ end)
 
 test("encode invalid", function()
   local t = {
-    { [1000] = "b" },
     { [ function() end ] = 12 },
-    { nil, 2, 3, 4 },
     { x = 10, [1] = 2 },
-    { [1] = "a", [3] = "b" },
     { x = 10, [4] = 5 },
   }
   for i, v in ipairs(t) do