进入crypto / ssh包，stdoutpipe（）io.Reader的缓冲区限制是多少

Question

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.

Answer 1

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.