@Override
            public int read() throws IOException {
              SimpleServerRpcConnection.this.rpcServer.channelRead(channel, buf);
              buf.flip();
              int x = buf.get();
              buf.flip();
              return x;
            }
Read off the wire. If there is not enough data to read, update the connection state with what
we have and returns.
@return Returns -1 if failure (and caller will close connection), else zero or more.
hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/SimpleServerRpcConnection.java