review WebSocket MessageWriter and MessageReader

[lachlan-roberts]

Jetty version
10.0.x

Description
MessageWriter and MessageOutputStream look inefficient and are duplicated in both the jetty API and javax API implementations.

[lachlan-roberts]

It would be good to implement MessageWriter with an OutputStreamWriter delegating to MessageOutputStream. However OutputStreamWriter uses CodingErrorAction.REPLACE and so will replace coding errors with a replacement character. But we really want CodingErrorAction.REPORT to get the coding errors as exceptions.

Invalid UTF-8 should be tested for both MessageReader and MessageWriter.

Example test for MessageWriterTest.

@Test
public void testInvalidUtf8Sequence() throws IOException, InterruptedException
{
    final CharsetEncoder utf8Encoder = UTF_8.newEncoder()
        .onUnmappableCharacter(CodingErrorAction.REPORT)
        .onMalformedInput(CodingErrorAction.REPORT);

    final String invalidUtf8String = "\uD800";
    assertThrows(MalformedInputException.class, () -> utf8Encoder.encode(CharBuffer.wrap(invalidUtf8String.toCharArray())));

    FrameCapture capture = new FrameCapture();
    capture.setOutputBufferSize(1024);

    MessageWriter writer = new MessageWriter(capture, bufferPool);
    writer.write(invalidUtf8String.toCharArray());
    assertThrows(MalformedInputException.class, writer::flush);
}