Add JsonFactory.Feature.CHARSET_DETECTION to disable charset detection (default to UTF-8)

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

@@ -122,7 +122,17 @@ public enum Feature
          *
          * @since 2.6
          */
-        USE_THREAD_LOCAL_FOR_BUFFER_RECYCLING(true)
+        USE_THREAD_LOCAL_FOR_BUFFER_RECYCLING(true),
+
+        /**
+         * Feature to control charset detection for byte-based inputs ({@code byte[]}, {@link InputStream}...). When
+         * this feature is enabled (the default), the factory will allow UTF-16 and UTF-32 inputs and try to detect
+         * them, as specified by RFC 4627. When this feature is disabled the factory will assume UTF-8, as specified
+         * by RFC 8259.
+         *
+         * @since 2.15
+         */
+        CHARSET_DETECTION(true),
 
         ;
 

src/main/java/com/fasterxml/jackson/core/json/ByteSourceJsonBootstrapper.java

@@ -253,7 +253,7 @@ public JsonParser constructParser(int parserFeatures, ObjectCodec codec,
             int factoryFeatures) throws IOException
     {
         int prevInputPtr = _inputPtr;
-        JsonEncoding enc = detectEncoding();
+        JsonEncoding enc = JsonFactory.Feature.CHARSET_DETECTION.enabledIn(factoryFeatures) ? detectEncoding() : JsonEncoding.UTF8;
         int bytesProcessed = _inputPtr - prevInputPtr;
 
         if (enc == JsonEncoding.UTF8) {

src/test/java/com/fasterxml/jackson/core/read/SimpleParserTest.java

@@ -1,6 +1,7 @@
 package com.fasterxml.jackson.core.read;
 
 import com.fasterxml.jackson.core.*;
+import com.fasterxml.jackson.core.json.JsonReadFeature;
 import com.fasterxml.jackson.core.testsupport.MockDataInput;
 import com.fasterxml.jackson.core.util.JsonParserDelegate;
 
@@ -703,6 +704,20 @@ private void _testHandlingOfInvalidSpaceFromResource(boolean useStream) throws E
         p.close();
     }
 
+    public void testInvalidUtf8ValidUtf16() throws IOException {
+        JsonFactory factory = new JsonFactoryBuilder()
+                .disable(JsonFactory.Feature.CHARSET_DETECTION)
+                .build();
+        JsonParser parser = factory.createParser(new byte[]{0x22, 0x00, 0x22, 0x5b, 0x22, 0x00});
+        try {
+            //noinspection StatementWithEmptyBody
+            while (parser.nextToken() != null) {}
+            fail("Should have failed");
+        } catch (JsonParseException e) {
+            verifyException(e, "unquoted character");
+        }
+    }
+
     /*
     /**********************************************************
     /* Helper methods