Add part of #136

Author: cowtowncoder

release-notes/VERSION

@@ -18,6 +18,8 @@ JSON library.
 
 #86: Allow inclusion of request body for JsonParseException
  (contributed by LokeshN)
+#136: Add `JsonpCharacterEscapes` for easier handling of potential problems
+ with JSONP and rare but technically allowed \u2028 and \u2029 linefeed characters
 #117: Add `JsonParser.Feature.ALLOW_MISSING_VALUES` to support for missing values
  (contributed by LokeshN)
 #253: Add `JsonGenerator. writeEmbeddedObject()` to allow writes of opaque native types
@@ -35,7 +37,6 @@ JSON library.
 #285: Add `JsonParser.getText(Writer)`
  (contributed by LokesN)
 #290: Add `JsonGenerator.canWriteFormattedNumbers()` for introspection
-
 - Add `JsonParser.currentToken()` and `JsonParser.currentTokenId()` as replacements
   for `getCurrentToken()` and `getCurrentTokenId()`, respectively. Existing methods
   will likely be deprecated in 2.9.

src/main/java/com/fasterxml/jackson/core/JsonpCharacterEscapes.java

@@ -0,0 +1,46 @@
+package com.fasterxml.jackson.core;
+
+import com.fasterxml.jackson.core.io.CharacterEscapes;
+import com.fasterxml.jackson.core.io.SerializedString;
+
+/**
+ * Convenience {@link CharacterEscapes} implementation that escapes
+ * Unicode characters `0x2028` and `0x2029` (in addition to characters
+ * escaped otherwise), which are apparently considered linefeeds as
+ * per newer Javascript specifications, and consequently problematic
+ * when using JSONP (see https://en.wikipedia.org/wiki/JSONP).
+ *
+ * @since 2.8
+ */
+public class JsonpCharacterEscapes extends CharacterEscapes
+{
+    private static final long serialVersionUID = 1L;
+
+    private static final int[] asciiEscapes = CharacterEscapes.standardAsciiEscapesForJSON();
+    private static final SerializedString escapeFor2028 = new SerializedString("\\u2028");
+    private static final SerializedString escapeFor2029 = new SerializedString("\\u2029");
+
+    private static final JsonpCharacterEscapes sInstance = new JsonpCharacterEscapes();
+
+    public static JsonpCharacterEscapes instance() {
+        return sInstance;
+    }
+
+    @Override
+    public SerializableString getEscapeSequence(int ch)
+    {
+        switch (ch) {
+        case 0x2028:
+            return escapeFor2028;
+        case 0x2029:
+            return escapeFor2029;
+        default:
+            return null;
+        }
+    }
+
+    @Override
+    public int[] getEscapeCodesForAscii() {
+        return asciiEscapes;
+    }
+}

src/test/java/com/fasterxml/jackson/core/json/TestCustomEscaping.java

@@ -78,7 +78,7 @@ public void testAboveAsciiEscapeWithUTF8Stream() throws Exception
     }
 
     // // // Tests for [JACKSON-106]
-    
+
     public void testEscapeCustomWithReader() throws Exception
     {
         _testEscapeCustom(false); // reader
@@ -88,7 +88,40 @@ public void testEscapeCustomWithUTF8Stream() throws Exception
     {
         _testEscapeCustom(true); // stream (utf-8)
     }
-    
+
+    public void testJsonpEscapes() throws Exception {
+        _testJsonpEscapes(false);
+        _testJsonpEscapes(true);
+    }
+
+    @SuppressWarnings("resource")
+    private void _testJsonpEscapes(boolean useStream) throws Exception
+    {
+        JsonFactory f = new JsonFactory();
+        f.setCharacterEscapes(JsonpCharacterEscapes.instance());
+        ByteArrayOutputStream bytes = new ByteArrayOutputStream();
+        JsonGenerator g;
+
+        // First: output normally; should not add escaping
+        if (useStream) {
+            g = f.createGenerator(bytes, JsonEncoding.UTF8);
+        } else {
+            g = f.createGenerator(new OutputStreamWriter(bytes, "UTF-8"));
+        }
+        final String VALUE_TEMPLATE = "String with JS 'linefeeds': %s and %s...";
+        final String INPUT_VALUE = String.format(VALUE_TEMPLATE, "\u2028", "\u2029");
+
+        g.writeStartArray();
+        g.writeString(INPUT_VALUE);
+        g.writeEndArray();
+        g.close();
+
+        String json = bytes.toString("UTF-8");
+        assertEquals(String.format("[%s]",
+                quote(String.format(VALUE_TEMPLATE, "\\u2028", "\\u2029"))),
+                json);
+    }
+
     /*
     /********************************************************
     /* Secondary test methods