does handin-server really need racket/gui/base?

[Wayne Harris]

I tried the handin-server on a Windows computer and it worked just

fine.  Now I'm trying it on a headless UNIX system and, upon first run,

I got:

$ racket -l handin-server

Unable to init server: Could not connect: Connection refused

Gtk initialization failed for display ":0"

  context...:

   "/usr/share/racket/pkgs/gui-lib/mred/private/wx/gtk/queue.rkt": [running body]

   temp37_0

   for-loop

   run-module-instance!125

   for-loop

   [repeats 1 more time]

   run-module-instance!125

   for-loop

   [repeats 1 more time]

   run-module-instance!125

   do-dynamic-require5

   "/usr/share/racket/pkgs/gui-lib/mred/private/wx/platform.rkt": [running body]

   temp37_0

   for-loop

   run-module-instance!125

   for-loop

   ...

Then taking a peek at

  ~/.racket/7.2/pkgs/handin/handin-server/main.rkt

I saw

  (require ...

         ;; workaround for a confusing problem: without this, the gui

         ;; gets initialized in a handler (since checks use it, and

         ;; they're being required dynamically), and further handlers

         ;; will fail with "queue-callback: eventspace is shutdown",

         ;; requiring it here makes it avoids killing the eventspace

         racket/gui/base)

Just to see what happens, I commented out the racket/gui/base

requirement and the server ran, but the comment says there'll be a

confusing problem.

$ racket -l handin-server

[-|2019-08-17T01:52:22] *** embedded web server started

[-|2019-08-17T01:52:22] Cleaning up all submission directories

[-|2019-08-17T01:52:22] *** handin server started on port 7979

Why does the server need anything GUI-related?  How do you run this

server in production?

[John Clements]

I’m not looking at the code here, but I believe the issue here is that the handin-server receives user code in a serialized-could-contain-images-format that can’t be decoded properly without importing the gui libraries.

It seems not implausible to me that you could special-case all-text submissions to build a handin-server that doesn’t require the gui pieces.

BUT,

I’m here to tell you that I also run the handin server on a headless UNIX system (currently Debian 9) with no problems.

Specifically, I use tigervnc to create an x session, then connect to it remotely (using a local vnc client) and start the handin server with an active X connection.

Let me know if you need more clues on this setup; there are a whole bunch of things that can go wrong.

John

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[Wayne Harris]

On Monday, August 19, 2019 10:40 PM, John Clements <clem...@brinckerhoff.org> wrote:

> I’m not looking at the code here, but I believe the issue here is that the handin-server receives user code in a serialized-could-contain-images-format that can’t be decoded properly without importing the gui libraries.

That makes sense.

> It seems not implausible to me that you could special-case all-text submissions to build a handin-server that doesn’t require the gui pieces.

That'd be an interesting addition to handin-server. I'd love to contribute that, but I need to see if I can understand enough to make it. Thanks for the idea!

> BUT,
>
> I’m here to tell you that I also run the handin server on a headless UNIX system (currently Debian 9) with no problems.
>
> Specifically, I use tigervnc to create an x session, then connect to it remotely (using a local vnc client) and start the handin server with an active X connection.
>
> Let me know if you need more clues on this setup; there are a whole bunch of things that can go wrong.

Thanks a lot! I did make it: I installed Xming on my Windows system and used PuTTY's X11-configuration. The server ran fine! (Now I'm free to study how to implement a checker!) Thanks for your help!