public static CodePointCharStream fromChannel(
		ReadableByteChannel channel,
		int bufferSize,
		CodingErrorAction decodingErrorAction,
		String sourceName)
		throws IOException
	{
		return fromChannel(channel, StandardCharsets.UTF_8, bufferSize, decodingErrorAction, sourceName, -1);
	}
Creates a {@link CharStream} given an opened {@link ReadableByteChannel}
containing UTF-8 bytes.

Reads the entire contents of the {@code channel} into
the result before returning, then closes the {@code channel}.
runtime/Java/src/org/antlr/v4/runtime/CharStreams.java