feat: new string format "dirty"

README.md

@@ -641,8 +641,26 @@ const stringify = fastJson({
   type: 'object',
   properties: {
     'code': {
-	    type: 'string',
-	    format 'unsafe'
+      type: 'string',
+      format: 'unsafe'
+    }
+  }
+})
+```
+
+<a name="dirty"></a>
+#### Dirty string
+String known to contain non-printable characters or surrogate pairs.
+
+Example:
+```javascript
+const stringify = fastJson({
+  title: 'Example Schema',
+  type: 'object',
+  properties: {
+    'code': {
+      type: 'string',
+      format: 'dirty'
     }
   }
 })

benchmark/bench.js

@@ -55,6 +55,14 @@ const benchmarks = [
     },
     input: 'hello world'
   },
+  {
+    name: 'dirty short string',
+    schema: {
+      type: 'string',
+      format: 'dirty'
+    },
+    input: 'hello\nworld'
+  },
   {
     name: 'short string with double quote',
     schema: {
@@ -92,6 +100,14 @@ const benchmarks = [
     },
     input: longString
   },
+  {
+    name: 'dirty long string',
+    schema: {
+      type: 'string',
+      format: 'dirty'
+    },
+    input: longString + '\n'
+  },
   {
     name: 'number',
     schema: {

index.js

@@ -736,6 +736,8 @@ function buildSingleTypeSerializer (context, location, input) {
         return `json += serializer.asTime(${input})`
       } else if (schema.format === 'unsafe') {
         return `json += serializer.asUnsafeString(${input})`
+      } else if (schema.format === 'dirty') {
+        return `json += serializer.asDirty(${input})`
       } else {
         return `
         if (typeof ${input} !== 'string') {

lib/serializer.js

@@ -129,6 +129,10 @@ module.exports = class Serializer {
     return '"' + str + '"'
   }
 
+  asDirty (str) {
+    return JSON.stringify(str)
+  }
+
   getState () {
     return this._options
   }

test/basic.test.js

@@ -24,6 +24,12 @@ buildTest({
   format: 'unsafe'
 }, 'hello world')
 
+buildTest({
+  title: 'string',
+  type: 'string',
+  format: 'dirty'
+}, 'hello\nworld')
+
 buildTest({
   title: 'basic',
   type: 'object',