doumindang2416
2019-02-10 03:27
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进入crypto / ssh包,stdoutpipe()io.Reader的缓冲区限制是多少

I'm writing a utility to execute commands on remote servers with the crypto/ssh package. I'm currently reading from the session.stdoutpipe() io.Reader in to a bytes.Buffer which I can format and print out after the session is complete.

The documentation states:

StdoutPipe func() (io.Reader, error) StdoutPipe returns a pipe that will be connected to the remote command's standard output when the command starts. There is a fixed amount of buffering that is shared between stdout and stderr streams. If the StdoutPipe reader is not serviced fast enough it may eventually cause the remote command to block.

I haven't had any issues so far with my testing, but it got me curious to know what is the fixed amount. I've successfully streamed text up to 6.5mb without reading the pipe Reader until the command has finished.

Does anyone know what the fixed amount is, or when the command will start to block? I can't find it in the source.

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我正在编写一个实用程序,以使用crypto / ssh软件包在远程服务器上执行命令。 我目前正在从session.stdoutpipe()io.Reader中读取一个bytes.Buffer,我可以在会话完成后对其进行格式化和打印。

文档说明:

StdoutPipe func()(io.Reader,错误) StdoutPipe返回一个管道,该管道将 命令启动时将其连接到远程命令的标准输出。 在stdout和stderr流之间共享固定数量的缓冲。 如果StdoutPipe阅读器的维修速度不够快,则最终可能导致远程命令被阻止。

到目前为止,我的测试没有任何问题,但是 我很想知道固定金额是多少。 在命令完成之前,我已经成功读取了6.5mb的文本,而没有读取Pipe Reader。

有人知道固定金额是多少,或者什么时候该命令将开始阻塞? 我在源代码中找不到它。

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  • douliexu5623 2019-02-10 12:34
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    It is not in the Go source because it's OS dependent.

    Applications should not rely on a particular capacity: an application should be designed so that a reading process consumes data as soon as it is available, so that a writing process does not remain blocked.

    For example, on Linux:

    $ man pipe
    
    PIPE(2)                    Linux Programmer's Manual                   PIPE(2)
    
    NAME
           pipe, pipe2 - create pipe
    
    Pipe capacity
    
           A pipe has a limited capacity.  If the pipe is full, then a write(2)
           will block or fail, depending on whether the O_NONBLOCK flag is set
           (see below).  Different implementations have different limits for the
           pipe capacity.  Applications should not rely on a particular
           capacity: an application should be designed so that a reading process
           consumes data as soon as it is available, so that a writing process
           does not remain blocked.
    
           In Linux versions before 2.6.11, the capacity of a pipe was the same
           as the system page size (e.g., 4096 bytes on i386).  Since Linux
           2.6.11, the pipe capacity is 16 pages (i.e., 65,536 bytes in a system
           with a page size of 4096 bytes).  Since Linux 2.6.35, the default
           pipe capacity is 16 pages, but the capacity can be queried and set
           using the fcntl(2) F_GETPIPE_SZ and F_SETPIPE_SZ operations.  See
           fcntl(2) for more information.
    
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