Serialise sparse arrays into JSON (#685)

src/main/resources/data/computercraft/lua/rom/apis/textutils.lua

@@ -381,6 +381,7 @@ local function serializeJSONImpl(t, tTracking, bNBTStyle)
             local sArrayResult = "["
             local nObjectSize = 0
             local nArraySize = 0
+            local largestArrayIndex = 0
             for k, v in pairs(t) do
                 if type(k) == "string" then
                     local sEntry
@@ -395,10 +396,17 @@ local function serializeJSONImpl(t, tTracking, bNBTStyle)
                         sObjectResult = sObjectResult .. "," .. sEntry
                     end
                     nObjectSize = nObjectSize + 1
+                elseif type(k) == "number" and k > largestArrayIndex then --the largest index is kept to avoid losing half the array if there is any single nil in that array
+                    largestArrayIndex = k
                 end
             end
-            for _, v in ipairs(t) do
-                local sEntry = serializeJSONImpl(v, tTracking, bNBTStyle)
+            for k = 1, largestArrayIndex, 1 do --the array is read up to the very last valid array index, ipairs() would stop at the first nil value and we would lose any data after.
+                local sEntry
+                if t[k] == nil then --if the array is nil at index k the value is "null" as to keep the unused indexes in between used ones.
+                    sEntry = "null"
+                else -- if the array index does not point to a nil we serialise it's content.
+                    sEntry = serializeJSONImpl(t[k], tTracking, bNBTStyle)
+                end
                 if nArraySize == 0 then
                     sArrayResult = sArrayResult .. sEntry
                 else

src/test/resources/test-rom/spec/apis/textutils_spec.lua

@@ -70,6 +70,105 @@ describe("The textutils library", function()
             expect.error(textutils.serialiseJSON, nil):eq("bad argument #1 (expected table, string, number or boolean, got nil)")
             expect.error(textutils.serialiseJSON, "", 1):eq("bad argument #2 (expected boolean, got number)")
         end)
+
+        it("serializes empty arrays", function()
+            expect(textutils.serializeJSON(textutils.empty_json_array)):eq("[]")
+        end)
+
+        it("serializes null", function()
+            expect(textutils.serializeJSON(textutils.json_null)):eq("null")
+        end)
+
+        it("serializes strings", function()
+            expect(textutils.serializeJSON('a')):eq('"a"')
+            expect(textutils.serializeJSON('"')):eq('"\\""')
+            expect(textutils.serializeJSON('\\')):eq('"\\\\"')
+            expect(textutils.serializeJSON('/')):eq('"/"')
+            expect(textutils.serializeJSON('\b')):eq('"\\b"')
+            expect(textutils.serializeJSON('\n')):eq('"\\n"')
+            expect(textutils.serializeJSON(string.char(0))):eq('"\\u0000"')
+            expect(textutils.serializeJSON(string.char(0x0A))):eq('"\\n"')
+            expect(textutils.serializeJSON(string.char(0x1D))):eq('"\\u001D"')
+            expect(textutils.serializeJSON(string.char(0x81))):eq('"\\u0081"')
+            expect(textutils.serializeJSON(string.char(0xFF))):eq('"\\u00FF"')
+        end)
+
+        it("serializes arrays until the last index with content", function()
+            expect(textutils.serializeJSON({ 5, "test", nil, nil, 7 })):eq('[5,"test",null,null,7]')
+            expect(textutils.serializeJSON({ 5, "test", nil, nil, textutils.json_null })):eq('[5,"test",null,null,null]')
+            expect(textutils.serializeJSON({ nil, nil, nil, nil, "text" })):eq('[null,null,null,null,"text"]')
+        end)
+    end)
+
+    describe("textutils.unserializeJSON", function()
+        describe("parses", function()
+            it("a list of primitives", function()
+                expect(textutils.unserializeJSON('[1, true, false, "hello"]')):same { 1, true, false, "hello" }
+            end)
+
+            it("null when parse_null is true", function()
+                expect(textutils.unserializeJSON("null", { parse_null = true })):eq(textutils.json_null)
+            end)
+
+            it("null when parse_null is false", function()
+                expect(textutils.unserializeJSON("null", { parse_null = false })):eq(nil)
+            end)
+
+            it("an empty array", function()
+                expect(textutils.unserializeJSON("[]", { parse_null = false })):eq(textutils.empty_json_array)
+            end)
+
+            it("basic objects", function()
+                expect(textutils.unserializeJSON([[{ "a": 1, "b":2 }]])):same { a = 1, b = 2 }
+            end)
+        end)
+
+        describe("parses using NBT-style syntax", function()
+            local function exp(x)
+                local res, err = textutils.unserializeJSON(x, { nbt_style = true })
+                if not res then error(err, 2) end
+                return expect(res)
+            end
+            it("basic objects", function()
+                exp([[{ a: 1, b:2 }]]):same { a = 1, b = 2 }
+            end)
+
+            it("suffixed numbers", function()
+                exp("1b"):eq(1)
+                exp("1.1d"):eq(1.1)
+            end)
+
+            it("strings", function()
+                exp("'123'"):eq("123")
+                exp("\"123\""):eq("123")
+            end)
+
+            it("typed arrays", function()
+                exp("[B; 1, 2, 3]"):same { 1, 2, 3 }
+                exp("[B;]"):same {}
+            end)
+        end)
+
+        describe("passes nst/JSONTestSuite", function()
+            local search_path = "test-rom/data/json-parsing"
+            local skip = dofile(search_path .. "/skip.lua")
+            for _, file in pairs(fs.find(search_path .. "/*.json")) do
+                local name = fs.getName(file):sub(1, -6);
+                (skip[name] and pending or it)(name, function()
+                    local h = io.open(file, "r")
+                    local contents = h:read("*a")
+                    h:close()
+
+                    local res, err = textutils.unserializeJSON(contents)
+                    local kind = fs.getName(file):sub(1, 1)
+                    if kind == "n" then
+                        expect(res):eq(nil)
+                    elseif kind == "y" then
+                        if err ~= nil then fail("Expected test to pass, but failed with " .. err) end
+                    end
+                end)
+            end
+        end)
     end)
 
     describe("textutils.urlEncode", function()