private int readFromAppBuffer(ByteBuffer dst) {
    appReadBuffer.flip();
    int remaining = Math.min(appReadBuffer.remaining(), dst.remaining());
    if (remaining > 0) {
      int limit = appReadBuffer.limit();
      appReadBuffer.limit(appReadBuffer.position() + remaining);
      dst.put(appReadBuffer);
      appReadBuffer.limit(limit);
    }
    appReadBuffer.compact();
    return remaining;
  }
transfers appReadBuffer contents (decrypted data) into dst bytebuffer
@param dst ByteBuffer
ambry-network/src/main/java/com/github/ambry/network/SSLTransmission.java