Difficulty using subprocess

[Brian Adkins]

I'm porting a Ruby application to Racket (will be deployed on Linux, but I'm developing on OSX). It uses the s3270 terminal emulator to access a mainframe. An example in Ruby is:

IO.popen('s3270 L:ssl3270.example.com:2023', 'r+') do |pipe|

  pipe.puts "ascii"

  puts (pipe.gets)

  puts (pipe.gets)

end

That issues the "ascii" command, and then reads & displays 2 lines of output. It seems that Racket's subprocess is a reasonable choice for this, so I tried the following:

(define-values (subp inp outp errp) 

  (subprocess #f #f #f "/usr/local/bin/s3270" "L:ssl3270.example.com:2023"))

(displayln "ascii" outp)

(displayln (read-line inp))

(displayln (read-line inp))

It seems to be connecting to the mainframe because I got a request from Little Snitch to allow the outbound connection. The s3270 emulator behaves similar to telnet, if I invoke the command in a shell, the program will start, then I'll enter ascii and it will display a screenful of lines. I must be misunderstanding subprocess or the associated IO functions. Any suggestions?

Thanks,

Brian

[Philippe Mechaï]

Hi Brian

I think you need to add a call to flush-output after sending data to outp 

Regards

Philippe 

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[Brian Adkins]

That was it - thanks! I guess I was spoiled by Ruby's auto-flushing of "puts".

[Philip McGrath]

You can also use `file-stream-buffer-mode` instead of manually flushing the port: https://docs.racket-lang.org/reference/port-buffers.html#(def._((quote._~23~25kernel)._file-stream-buffer-mode))

-Philip

[Brian Adkins]

Good tip - I think (file-stream-buffer-mode outp 'line) makes sense in this case given it's a terminal emulator.