Sbappend adds the data at the end of send buffer and tcp_output sends the segment onto the interface.

sbappend在发送缓冲区的末尾添加数据，并且tcp _ out put将该段发送到接口。

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In a similar fashion, you can read data segments off segment by segment from an abstract buffer with the following function.

采用类似的方式，您可以使用以下函数，逐段地从抽象缓冲区读取数据段。

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