[erlang-questions] Issues with stdin on ports

Robert Raschke rtrlists@REDACTED
Mon Jul 29 11:12:31 CEST 2013

Hi Anthony,

In the past, I've tended to use the port mechanism to simply kick off a C
node, which then allows you to have full control over whatever
communications needs you have.

This obviously only works if you are interfacing with a technology that
will allow you to create C node and use the EI libs in some way. Not sure
if that is the case from what you wrote.

On Jul 29, 2013 8:04 AM, "Anthony Grimes" <i@REDACTED> wrote:

>  Howdy folks.
> I unfortunately have not been able to use Erlang for most of what I've
> been doing lately because of a long standing issue with Erlang ports
> that I'd like to start a discussion about here.
> As far as I am aware, ports are generally the only option for creating
> and communicating with external processes in Erlang. They seem to have
> at least one particular fatal flaw which prevents them from being very
> useful to me, and that is that there is no way to close stdin (and send
> EOF) and then also read from the process's stdout. For example, I cannot
> use a port to start the 'cat' program which listens on stdin for data
> and waits for EOF and then echos that data back to you. I can do the
> first part, which is send it data on stdin, but the only way for me to
> close it is to call port_close and close the entire process.
> This issue prevents Erlang users from doing any even slightly more than
> trivial communication with external processes without having some kind
> of middleman program that handles the creation of the actual process you
> need to talk to and looks for a specific byte sequence to indicate 'EOF'.
> I could totally be wrong, but it seems like we need something other than
> just port_close. Something like
> http://www.erlang.org/doc/man/**gen_tcp.html#shutdown-2<http://www.erlang.org/doc/man/gen_tcp.html#shutdown-2>
>  which lets you say
> "Hey, I want to close the stdin of this process but still read from its
> stdout." or something similar. I could be totally off track on what a
> good solution would be.
> So I'm wondering if people are aware of this problem, and I'd like to
> make sure that people think it is an actual problem that should be
> fixed. I'm also curious what people think a good solution to the problem
> would be. I'm not sure I have the time/particular skill set to fix it
> given that the port code is some pretty obscure (to me) C code, but
> starting conversation seems like a good way to begin.
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