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Subject: Re: When does read block?

Re: When does read block?

From: Peter Stuge <peter_at_stuge.se>
Date: Thu, 10 May 2012 11:47:40 +0200

Seth Willits wrote:
> So when exactly does channel_read block? I'm trying to determine
> exactly if when I should call read(). i.e., if I'm executing an
> arbitrary command from the user, if it's going to block because
> there is no output, I don't want to call it.

If you need to process multiple fds for events then look at some of
the examples which demostrate how to do this correctly, e.g.
direct_tcpip.c or tcpip-forward.c.

> channel = libssh2_channel_open_session(session);
> libssh2_channel_set_blocking(channel, 1);
> libssh2_channel_exec(channel, "touch 'test.tmp'");
> libssh2_channel_eof(channel); // 0
> libssh2_channel_read(channel, buffer, bufferSize); // 0, no blocking

It does block, but it returns when the remote side reports EOF. Exec
sleep 10s instead of touch for comparison.

> libssh2_channel_eof(channel); // 1
> libssh2_channel_read(channel, buffer, bufferSize); // 0, no blocking

Since the channel is now EOF, nothing can be read anymore.

//Peter
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Received on 2012-05-10

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