fix: isWellFormed

lib/serializer.js

@@ -1,5 +1,8 @@
 'use strict'
 
+// eslint-disable-next-line
+const ASCII_ESCAPE = /[\u0000-\u001f\u0022\u005c]/
+
 module.exports = class Serializer {
   constructor (options) {
     switch (options && options.rounding) {
@@ -89,9 +92,16 @@ module.exports = class Serializer {
 
   asString (str) {
     const len = str.length
+
     if (len === 0) {
       return '""'
-    } else if (len < 42) {
+    }
+
+    if (!str.isWellFormed()) {
+      return JSON.stringify(str)
+    }
+
+    if (len < 42) {
       // magically escape strings for json
       // relying on their charCodeAt
       // everything below 32 needs JSON.stringify()
@@ -110,13 +120,13 @@ module.exports = class Serializer {
           last === -1 && (last = 0)
           result += str.slice(last, i) + '\\'
           last = i
-        } else if (point < 32 || (point >= 0xD800 && point <= 0xDFFF)) {
+        } else if (point < 32) {
           // The current character is non-printable characters or a surrogate.
           return JSON.stringify(str)
         }
       }
       return (last === -1 && ('"' + str + '"')) || ('"' + result + str.slice(last) + '"')
-    } else if (len < 5000 && str.isWellFormed()) {
+    } else if (len < 5000 && ASCII_ESCAPE.test(str) === false) {
       // Only use the regular expression for shorter input. The overhead is otherwise too much.
       return '"' + str + '"'
     } else {

test/string.test.js

@@ -34,6 +34,21 @@ test('serialize short string', (t) => {
   t.assert.equal(JSON.parse(output), input)
 })
 
+test('serialize medium string', (t) => {
+  t.plan(2)
+
+  const schema = {
+    type: 'string'
+  }
+
+  const input = new Array(150).fill('\x00').join('')
+  const stringify = build(schema)
+  const output = stringify(input)
+
+  t.assert.equal(output, `"${new Array(150).fill('\\u0000').join('')}"`)
+  t.assert.equal(JSON.parse(output), input)
+})
+
 test('serialize long string', (t) => {
   t.plan(2)