public static CharStream fromChannel(ReadableByteChannel channel) throws IOException {
		return fromChannel(channel, StandardCharsets.UTF_8);
	}
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