code: @Test public void sourceFromInputStream() throws Exception {
    InputStream in=new ByteArrayInputStream(("a" + repeat('b',Segment.SIZE * 2) + "c").getBytes(UTF_8));
    Source source=Okio.source(in);
    OkBuffer sink=new OkBuffer();
    assertEquals(3,source.read(sink,3));
    assertEquals("abb",sink.readUtf8(3));
    assertEquals(Segment.SIZE,source.read(sink,20000));
    assertEquals(repeat('b',Segment.SIZE),sink.readUtf8(sink.size()));
    assertEquals(Segment.SIZE - 1,source.read(sink,20000));
    assertEquals(repeat('b',Segment.SIZE - 2) + "c",sink.readUtf8(sink.size()));
    assertEquals(-1,source.read(sink,1));
  }
  