Escape reserved characters in JSON strings

assembly/JSON.ts

@@ -149,7 +149,20 @@ export namespace JSON {
     }
 
     toString(): string {
-      return "\"" + this._str + "\"";
+      let escaped: i32[] = [];
+      for (let i = 0; i < this._str.length; i++) {
+        const charCode = this._str.charCodeAt(i)
+        const char = this._str.charAt(i)
+        if (
+          charCode == 0x22 || // "    quotation mark  U+0022
+          charCode == 0x5C || // \    reverse solidus U+005C
+          charCode < 0x20 // control characters
+        ) {
+          escaped.push(0x5c); // add a reverse solidus (backslash) to escape reserved chars 
+        }
+        escaped.push(charCode)
+      }
+      return "\"" + String.fromCharCodes(escaped) + "\"";
     }
   }
 

assembly/__tests__/string_escape.spec.ts

@@ -0,0 +1,53 @@
+import { JSON } from '../JSON'
+
+describe('Escaped characters', () => {
+  it('Does not escape characters unneccessarily', () => {
+    const strings = [
+      'sphinx of black quartz, judge my vow',
+      '{}',
+      '[]',
+      '/',
+      '|',
+      '/|||/|||[{]}<>,.',
+      'ஂ ஃ அ ஆ இ ஈ உ ஊ எ ஏ ஐ ஒ ஓ ஔ க ங ச ஜ ஞ ட ண த ந ன ப ம ய ர ற ல ள',
+      'ᄀ ᄁ ᄂ ᄃ ᄄ ᄅ ᄆ ᄇ ᄈ ᄉ ᄊ ᄋ ᄌ ᄍ ᄎ ᄏ ᄐ ᄑ ᄒ ᄓ ᄔ ᄕ ᄖ ᄗ ᄘ ᄙ ᄚ ᄛ ',
+      '℀ ℁ ℂ ℃ ℄ ℅ ℆ ℇ ℈ ℉ ℊ ℋ ℌ ℍ ℎ ℏ ℐ ℑ ℒ ℓ ℔ ℕ № ℗ ℘ ℙ ℚ ℛ ℜ ℝ ℞ ℟ ℠ ℡ ™ ℣ ℤ ℥ Ω ℧ ℨ ℩ K Å ℬ ℭ ℮ ℯ ℰ ℱ Ⅎ ℳ ℴ ℵ ℶ ℷ ℸ ',
+      '☀ ☁ ☂ ☃ ☄ ★ ☆ ☇ ☈ ☉ ☊ ☋ ☌ ☍ ☎ ☏ ☐ ☑ ☒ ☓ ☚ ☛ ☜ ☝ ☞ ☟ ☠ ☡ ☢ ☣ ☤ ☥ ☦ ☧ ☨ ☩ ☪ ☫ ☬ ☭ ☮ ☯ ☰ ☱ ☲ ☳ ☴ ☵ ☶ ☷ ☸ ☹ ☺ ☻ ☼ ☽ ☾ ☿ ♀ ♁ ♂ ♃ ♄ ♅ ♆ ♇ ♈ ♉ ♊ ♋ ♌ ♍ ♎ ♏ ♐ ♑ ♒ ♓',
+    ]
+    strings.forEach((str) => {
+      const jsonStr = new JSON.Str(str)
+      expect(jsonStr.toString()).toBe('"' + str + '"')
+    })
+  })
+  it('Escapes quotes and backslashes', () => {
+    const strings = ['"', '\\', '"\\"', '\\"\\"']
+    strings.forEach((str) => {
+      const jsonStr = new JSON.Str(str)
+      expect(jsonStr.toString()).toBe('"' + escaped(str) + '"')
+    })
+  })
+  it('Escapes control characters', () => {
+    const strings = ['\n', '\r', '\r\n', '\b', '\f', '\t', '\v', '\b\f\t\v\r']
+    strings.forEach((str) => {
+      const jsonStr = new JSON.Str(str)
+      expect(jsonStr.toString()).toBe('"' + escaped(str) + '"')
+    })
+  })
+})
+
+function escaped(str: string): string {
+  const escapedChars: i32[] = []
+  for (let i = 0; i < str.length; i++) {
+    const charCode = str.charCodeAt(i)
+    if (
+      charCode < 0x20 || // control characters
+      charCode == 0x22 || // double quote (")
+      charCode == 0x5c
+    ) {
+      // backslash / reverse solidus (\)
+      escapedChars.push(0x5c)
+    }
+    escapedChars.push(charCode)
+  }
+  return String.fromCharCodes(escapedChars)
+}