Compiling KasmVNC on NixOS

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nix

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Published

May 2, 2023

This is a living document, for the time being. Rather than a complete blogpost, this is a tracker of my progress, as well as a quick reference I can come back to.

What is this?

Kasmweb is a software to create remote desktops, that exist within docker containers, and allow users to access them, all from a browser based GUI.

Kasmvnc is the VNC server part of kasm web, a custom fork of previous existing features, enhanced with more performance, and most importantly, a web native setup. Incompatible with existing VNC protocols, the only way to access Kasmvnc is through the http/https serive it offers, the web based VNC ui.

KasmVNC is an amazing piece of software, but development for it is not truly, fully public. This is present in their build system. Their build system is a series of bash scripts, that call docker containers, which call more bash scripts, to finally compile the software, and package it, all in one.

As part of the scripts they have to compile kasm, lots of static linking happens. They do this because not all distros package the most updated, performant versions of the libraries that kasmvnc uses.

But Nixos, the distro I want to package KasmVNC for, does. In addition to that, it is completely incompatible with the hacked together build system that kasm uses. In order to package KasmVNC for Nixos, I must reverse engineer their build system, and bit by bit, port it to NixOS.

Nixos Build System

How the nixos build system works. I will do later, but here I will document, step by step, how nixos builds a package.

KasmVNC’s Build System

Reverse engineering KasmVNC’s build system.

The below is what I neeed for the compiliation commands to work. I don’t know where Kasm runs these commands, or similar equivalents, this is just what I’ve figured out.

Perhaps I need to only run make in the KasmVNC/unix directory?


git clone https://github.com/TigerVNC/tigervnc

cd tigervnc

git clone https://github.com/kasmtech/KasmVNC

cd KasmVNC

cp ..vncserver .vncserver # this sets up build environment. I will still need to check if every single one of these things are necessary, but this works for now

The build script can be found here

But from this build script, I don’t think all of it is necessary. Below, I will extract what commands are actually needed, from all the fluff, cruft, and hacks.


cmake -D CMAKE_BUILD_TYPE=RelWithDebInfo . -DBUILD_VIEWER:BOOL=OFF \
  -DENABLE_GNUTLS:BOOL=OFF

make

Builds end up in KasmVNC/unix/

Except the preliminary builds don’t work. They error:

~/vscode/tigervnc/KasmVNC/unix master ?1 ❯ ./vncserver 

Can't locate List/MoreUtils.pm in @INC (you may need to install the List::MoreUtils module) (@INC contains: /usr/lib/perl5/5.36/site_perl /usr/share/perl5/site_perl /usr/lib/perl5/5.36/vendor_perl /usr/share/perl5/vendor_perl /usr/lib/perl5/5.36/core_perl /usr/share/perl5/core_perl) at ./vncserver line 38.
BEGIN failed--compilation aborted at ./vncserver line 38.

The above is probably because a perl library is missing. After attempting to install the missing library using pacman -S perl-list-moreutils I get a different error.


~/vscode/tigervnc/KasmVNC/unix master ?1 ❯ ./vncserver 

Can't locate KasmVNC/CliOption.pm in @INC (you may need to install the KasmVNC::CliOption module) (@INC contains: /usr/lib/perl5/5.36/site_perl /usr/share/perl5/site_perl /usr/lib/perl5/5.36/vendor_perl /usr/share/perl5/vendor_perl /usr/lib/perl5/5.36/core_perl /usr/share/perl5/core_perl) at ./vncserver line 42.
BEGIN failed--compilation aborted at ./vncserver line 42.

Obviously, this won’t work. I must figure out why KasmVNC pacakges perl packages, where it puts them by default, and how to package them for Nix.

Alright, the vncserver command appears to be in the git repo, and rather than being a binary, it is a perl wrapper script to start an xvnc server. from the script:

use KasmVNC::CliOption;
use KasmVNC::ConfigKey;
use KasmVNC::PatternValidator;
use KasmVNC::EnumValidator;
use KasmVNC::Config;
use KasmVNC::Users;
use KasmVNC::TextOption;
use KasmVNC::TextUI;
use KasmVNC::Utils;
use KasmVNC::Logger;

These perl modules/libraries can be found in KasmVNC/unix/KasmVNC

So that is what is necessary for the vncserver script to run. But is this script really necessary? Based on the names of the perl libraries, this script might not be adding any core functionalities to kasmvnc, only things like additional command line options, or loggers.

I need to find where this script runs kasmvnc, and also where the actual kasmvnc binary is.

I think their fork of xvnc is located in KasmVNC/unix/xserver/hw/vnc/xvnc.c.

But I get compilation errors:


[nix-shell:~/vscode/tigervnc/KasmVNC]$ make 
[  3%] Built target os
[ 13%] Built target rdr
[ 30%] Built target network
[ 31%] Built target Xregion
[ 78%] Built target rfb
[ 80%] Built target tx
[ 81%] Built target unixcommon
[ 81%] Linking CXX executable vncconfig
/nix/store/178vvank67pg2ckr5ic5gmdkm3ri72f3-binutils-2.39/bin/ld: cannot find -lturbojpeg: No such file or directory
collect2: error: ld returned 1 exit status
make[2]: *** [unix/vncconfig/CMakeFiles/vncconfig.dir/build.make:157: unix/vncconfig/vncconfig] Error 1
make[1]: *** [CMakeFiles/Makefile2:610: unix/vncconfig/CMakeFiles/vncconfig.dir/all] Error 2
make: *** [Makefile:136: all] Error 2

I don’t know why this happens. For those who don’t know, make pretty much calls a set of scripts, called Makefiles. I will need to find where in these scripts, the error commands are run.

Weirdly, I can’t reproduce outside of the build script:


~/vscode/tigervnc/KasmVNC master ?1 ❯ ld -lsdsakdfj
ld: cannot find -lsdsakdfj: No such file or directory
~/vscode/tigervnc/KasmVNC master ?1 ❯ ld -lturbojpeg
ld: warning: cannot find entry symbol _start; not setting start address
~/vscode/tigervnc/KasmVNC master ?2 ❯ ld -ljpeg     
ld: warning: cannot find entry symbol _start; not setting start address
~/vscode/tigervnc/KasmVNC master ?2 ❯ ld -ljpeg-turbo
ld: cannot find -ljpeg-turbo: No such file or directory
~/vscode/tigervnc/KasmVNC master ?1 ❯

I suspect the make scripts have some hacks that change working directory, or otherwise hide my installation of libjpeg.

When commenting out the part of the KasmVNC/Cmakelists.txt file that appears to be related to libjpeg, the error when I run make changes.

[ 95%] Building CXX object unix/vncconfig/CMakeFiles/vncconfig.dir/vncconfig.cxx.o
/home/moonpie/vscode/tigervnc/KasmVNC/vncviewer/Surface.cxx:23:10: fatal error: FL/Fl_RGB_Image.H: No such file or directory
   23 | #include <FL/Fl_RGB_Image.H>
      |          ^~~~~~~~~~~~~~~~~~~
compilation terminated.
make[2]: *** [tests/CMakeFiles/fbperf.dir/build.make:104: tests/CMakeFiles/fbperf.dir/__/vncviewer/Surface.cxx.o] Error 1
make[2]: *** Waiting for unfinished jobs....
/home/moonpie/vscode/tigervnc/KasmVNC/vncviewer/Surface_X11.cxx:26:10: fatal error: FL/Fl_RGB_Image.H: No such file or directory
   26 | #include <FL/Fl_RGB_Image.H>
      |          ^~~~~~~~~~~~~~~~~~~
compilation terminated.
make[2]: *** [tests/CMakeFiles/fbperf.dir/build.make:118: tests/CMakeFiles/fbperf.dir/__/vncviewer/Surface_X11.cxx.o] Error 1
/home/moonpie/vscode/tigervnc/KasmVNC/vncviewer/PlatformPixelBuffer.cxx:31:10: fatal error: FL/Fl.H: No such file or directory
   31 | #include <FL/Fl.H>
      |          ^~~~~~~~~

This is probably missing libraries.

After installing fltk (pacman -S fltk), this error goes away, and I get a new, even harder to comprehend error.


[ 97%] Building CXX object tests/CMakeFiles/decperf.dir/decperf.cxx.o
/home/moonpie/vscode/tigervnc/KasmVNC/vncviewer/PlatformPixelBuffer.cxx: In constructor ‘PlatformPixelBuffer::PlatformPixelBuffer(int, int)’:
/home/moonpie/vscode/tigervnc/KasmVNC/vncviewer/PlatformPixelBuffer.cxx:64:29: error: ‘uint8_t’ was not declared in this scope
   64 |   setBuffer(width, height, (uint8_t*)xim->data,
      |                             ^~~~~~~
/home/moonpie/vscode/tigervnc/KasmVNC/vncviewer/PlatformPixelBuffer.cxx:38:1: note: ‘uint8_t’ is defined in header ‘<cstdint>’; did you forget to ‘#include <cstdint>’?
   37 | #include "PlatformPixelBuffer.h"
  +++ |+#include <cstdint>
   38 | 
/home/moonpie/vscode/tigervnc/KasmVNC/vncviewer/PlatformPixelBuffer.cxx:64:37: error: expected primary-expression before ‘)’ token
   64 |   setBuffer(width, height, (uint8_t*)xim->data,
      |                                     ^

I suspect I have the wrong version of the tigervnc source code/libraries. I will need to investigate where Kasm’s build system downloads these vncviewer libraries from.

After editing the errored file, to include the library:

Within KasmVNC/vncviewer/PlatformPixelBuffer.cxx:


#include <cstdint>

I get a different error.


[ 94%] Building CXX object tests/CMakeFiles/fbperf.dir/__/vncviewer/PlatformPixelBuffer.cxx.o
/home/moonpie/vscode/tigervnc/KasmVNC/vncviewer/PlatformPixelBuffer.cxx: In constructor ‘PlatformPixelBuffer::PlatformPixelBuffer(int, int)’:
/home/moonpie/vscode/tigervnc/KasmVNC/vncviewer/PlatformPixelBuffer.cxx:66:3: error: ‘setBuffer’ was not declared in this scope; did you mean ‘setbuffer’?
   66 |   setBuffer(width, height, (uint8_t*)xim->dtion.

I think it’s likely that I have the wrong version of tigervnc or something. I will try to see how Kasm’s build scripts set this up.

Okay, I will attempt to create a visual graph, documenting each step of KasmVNC’s build system, to build an ubuntu package. I will have hyperlinks to each of the scripts/dockerfiles, or other pieces of the github repo. Currently still working on figuring out how to use Graphviz.

Note about dependencies install

For some reason they use multiple build phases for the same step of installing packages. In addition to that, they don’t clean the apt cache between build stages.

Note about webp and libjpeg-turbo

They make and install — in the build dockerfile. I will end up skipping this step, as nix packages these, but why do they do that?

I will expand on this, and organize it further. But based on these beginnings, kasmvnc appears to be a perl script that either starts a sepreate webserver or serves a webserver (if there is a perl native way to do this?), which appears to be based on novnc, while it also starts the vnc server, which is based on tigervnc.

However, I am still confused about one thing: Where does it download the vnc server source code.

The easy way

After I packaged quarto, I realized that I can actually package the kasmvnc binary using nix. I have decided to do this for now.

Here is first attempt for this. Now, kasmvnc’s packaging system is weird, in that they do not offer a binary tarball for their packages. So, I have decided to convert their alpine package into something I can use, because based on a cursory look into all the packages, it seems to be the easiest to package for Nix/Nixos.

First try!

{
    stdenv,
    lib,
    fetchurl,
    makeWrapper,
} :

stdenv.mkDerivation rec {
  pname = "kasmvnc";
  version = "1.1.0";
  src = fetchurl {
    url = "https://github.com/kasmtech/KasmVNC/releases/download/v${version}/kasmvnc.alpine_317_x86_64.tgz";
    sha256 = "sha256-j/3PUwBd8XygBKYfFdAwN15cwxDPf3vbEwbLy1laxSU=";
  };

  nativeBuildInputs = [
  ];

  patches = [
  ];

  postPatch = ''
  '';

  dontStrip = true;

  preFixup = ''
  '';

  installPhase = ''
      runHook preInstall

      mkdir -p $out/bin $out/share $out/man $out/etc $out/lib

      echo here
      ls
      ls local/bin

      mv local/etc/* $out/etc
      mv local/share/* $out/share
      mv local/man/* $out/man
      mv local/lib/* $out/lib
      mv local/bin/* $out/bin

      runHook preInstall
  '';

  meta = with lib; {
    description = "Kasmvnc";
    longDescription = ''
        Long description here
    '';
    homepage = "";
    changelog = "https://github.com/kasmtech/KasmVNC/releases/tag/v${version}";
    license = licenses.gpl2Plus;
    maintainers = with maintainers; [ moonpiedumplings ];
    platforms = [ "x86_64-linux" ];
    sourceProvenance = with sourceTypes; [ binaryNativeCode binaryBytecode ];
  };
}

This is my first attempt at a derivation. I’ve converted this one from the quarto derivation I built, which is also on my blog.

I’m installing it using a simple shell.nix, that uses the nix callPackage function to build the kasmvnc nix package, and make it available in my current shell.

let
    pkgs = import <nixpkgs> {};
    kasmvnc = pkgs.callPackage ./kasmvnctest.nix {};
in
    pkgs.mkShell {
        packages = [ kasmvnc ];
    }

To run kasmvnc, I run the vncserver command.

However, I get an error.