feat: add pkg.string.pascalString

pkg/string/pascalString.lua

@@ -0,0 +1,21 @@
+local pack = require("pkg.string.pack")
+
+---Converts `str` into pascal string
+---@param str string
+---@param align? number pad result string with 0 to make result length to be multiple of `align`
+---@param max_length? number max length of result string
+---@return string
+local toPascalString = function(str, align, max_length)
+    if type(max_length) == "number" then
+        str = str:sub(1, max_length - 1)
+    end
+    if type(align) ~= "number" then
+        align = 1
+    end
+
+    local tail_0_num = align - 1 - #str % align
+
+    return pack.u8(#str) .. str .. ("\x00"):rep(tail_0_num)
+end
+
+return toPascalString

pkg/string/pascalString_test.lua

@@ -0,0 +1,56 @@
+local test = require("lib.test").test
+local describe = require("lib.test").describe
+local expect = require("lib.test").expect
+local toPascalString = require("pkg.string.pascalString")
+
+describe("pascalString", function()
+    describe("no align", function()
+        test("empty", function()
+            expect(toPascalString("")):toBe("\x00")
+        end)
+
+        test("non-empty", function()
+            expect(toPascalString("abc")):toBe("\x03abc")
+        end)
+    end)
+
+    describe("2-align", function()
+        test("empty", function()
+            expect(toPascalString("", 2)):toBe("\x00\x00")
+        end)
+
+        test("odd length", function()
+            expect(toPascalString("abc", 2)):toBe("\x03abc")
+        end)
+
+        test("even length", function()
+            expect(toPascalString("abcd", 2)):toBe("\x04abcd\x00")
+        end)
+    end)
+
+    describe("4-align", function()
+        test("empty", function()
+            expect(toPascalString("", 4)):toBe("\x00\x00\x00\x00")
+        end)
+
+        test("length mod 4 = 1", function()
+            expect(toPascalString("a", 4)):toBe("\x01a\x00\x00")
+        end)
+
+        test("length mod 4 = 2", function()
+            expect(toPascalString("ab", 4)):toBe("\x02ab\x00")
+        end)
+
+        test("length mod 4 = 3", function()
+            expect(toPascalString("abc", 4)):toBe("\x03abc")
+        end)
+
+        test("length mod 4 = 0", function()
+            expect(toPascalString("abcd", 4)):toBe("\x04abcd\x00\x00\x00")
+        end)
+    end)
+
+    test("over max length", function()
+        expect(toPascalString("abcdefg", 4, 4)):toBe("\x03abc")
+    end)
+end)

pkg/test.lua

@@ -5,5 +5,6 @@ describe("pkg", function()
         require("pkg.string.split_test")
         require("pkg.string.packBits_test")
         require("pkg.string.pack_test")
+        require("pkg.string.pascalString_test")
     end)
 end)